vity; and we might reasonably suppose, that substances of the greatest specific gravity would contain the smallest quantity of water, though still we could by no means determine what quantity they did contain, unless we could lay hold of the element itself.

This seems to be very much the case with elementary fire, if we suppose it to be a fluid per se. We judge of its presence by the degree of expansion which one heated body communicates to another: but this is only similar to the calculation of the quantity of moisture a sponge or any other body contains, by what it communicates to wood when it comes into contact with it; which never could be supposed to carry the least pretensions to accuracy, though we should ascertain it with all imaginable exactness. It is likewise probable that the most dense bodies contain the smallest quantity of fire, as they generally communicate less when heated to an equal temperature than those which are more rare, though we are far from having any perfect knowledge in this respect.

But the greatest difficulty of all will be, on the supposition that heat is a fluid, and an omnipresent one (which it must be, or there would be some places where bodies could not be heated), to answer the question, Why are not all bodies of an equal temperature, excepting only the differences arising from their specific densities, which render some capable of containing a greater quantity than others?—The difficulty will not be lessened, though the omnipresence of the fluid should be given up, if we suppose, as is generally done, that heat has a tendency to diffuse itself equably every way. If it has this tendency, what hinders it from doing so? Why doth not the heat from the burning regions of the torrid zone diffuse itself equally all over the globe, and reduce the earth to one common temperature? This indeed might require time; but the experience of all ages has shown that there is not the least advance towards an equality of temperature. The middle regions of the earth continue as hot, and the polar ones as cold, as we have any reason to believe they were at the creation of the world, or as we have any reason to believe they will be while the world remains. This indeed is one of the many instances of the impropriety of establishing general laws from trifling experiments we are capable of making, and which hold good only on the narrow scales on which we can make them, but are utterly insufficient to solve the phenomena of the great system of nature, and which can be solved only by observing other phenomena of the same system undisturbed by any manoeuvres of our own.

Again, supposing the objection already made could be got over, and satisfactory reasons should be given why an equilibrium of temperature in the earth and its atmosphere should never be obtained, it will by no means be easy to tell what becomes of the heat which is communicated to the earth at certain times of the year. This difficulty, or something similar, Dr Crawford seems to have had in view when treating of the effects of the evolution and absorption of heat. Thus, says he, "the Deity has guarded against sudden vicissitudes of heat and cold upon the surface of the earth."

For if heat were not evolved by the process of congelation, all the waters which were exposed to the influence of the external air, when its temperature was reduced below 32°, would speedily become solid; and, at the moment of congelation, the process of cooling of fire would be as rapid as it was before the air had arrived at its freezing point.

This is manifest from what was formerly observed respecting the congelation of different fluids. It was shown, that if the velocities of the separation of heat were equal, the times of the congelation would be in proportion to the quantities of heat which the fluids gave off from an internal source in the freezing process. Whence it follows, that if no heat were evolved, the congelation would be instantaneous.

In the present state of things, as soon as the atmosphere is cooled below 32°, the waters begin to freeze, and at the same time to evolve heat; in consequence of which, whatever may be the degree of cold in the external air, the freezing mass remains at 32° until the whole is congealed; and as the quantity of heat extricated in the freezing of water is considerable, the process of congelation in large masses is very slow.—That the absorption and extrication of heat in the melting and freezing of bodies has a tendency to retard the progress of these processes, is remarked by Mr Wilkie in his Essay on Latent Heat.—The same doctrine is likewise taught by Dr Black in his lectures.

In the northern and southern regions, therefore, upon the approach of winter, a quantity of elementary fire is extricated from the waters, proportional to the degree of cold that prevails in the atmosphere. Thus, the severity of the frost is mitigated, and its progression retarded; and it would seem that, during this retardation of the cooling process, the various tribes of animals, vegetables which inhabit the circumpolar regions gradually acquire power of resisting its influence.

On the contrary, if, in the melting of ice, a quantity of heat were not absorbed, and rendered insensible that substance, when it was exposed to a medium warmer than 32°, would speedily become fluid, and the process of heating would be as rapid as if no alteration had taken place. If things were thus constituted, the vast masses of ice and snow which are collected in the frigid zones would, upon the approach of summer, suddenly dissolve, and great inundations would annually overflow the regions near to the poles.

But by the operation of the law of the absorption of heat when the ice and snow upon the return of spring have arrived at 32°, they begin to melt, and at the same time to imbibe heat: during this process, a large quantity of elementary fire becomes insensible; in consequence of which the earth is slowly heated, and those gradual changes are produced which are essential to the preservation of the animal and vegetable kingdoms.

We may remark, in the last place, that this law does not only resist sudden changes of temperature, but affords that it likewise contributes to a more equal distribution of the principle of heat throughout the various parts of the earth, in different seasons and climates; and thus the diurnal heats are moderated by the evaporation of the waters on the earth's surface, a portion of the fire derived from the sun being absorbed and extinguished by the vapours at the moment of their ascent. On the approach of night the vapours are again condensed, and falling in the form of dew, communicate to the air and to the earth the fire which they had imbibed during the day.

"It was before shown, that, in the regions near to the poles, when the vernal and summer heats prevail, provision is made for tempering the severity of the winter cold, a quantity of elementary fire, upon the dissolution of the ice and snow, being absorbed by the waters, and deposited, as it were, in a great magazine for the purpose of mitigating the intensity of the cold when the frost returns.

"From the experiments of Hales, Halley, and Watson, it appears, that vast quantities of water are continually converted into vapour by the action of the solar rays upon the portion of the earth's surface which is exposed to the light; and by the celebrated discovery of Dr Black, it is proved, that, in the process of evaporation, much elementary fire is absorbed. It is manifest, that this cause will have a powerful influence in mitigating the intensity of the heat in the torrid zone, and in promoting a more equal diffusion of it through the earth. For a considerable portion of the heat, which is excited by the action of the solar rays upon the earth's surface within the tropics, is absorbed by the aqueous vapours, which being collected in the form of clouds, are spread like a canopy over the horizon, to defend the subjacent regions from the direct rays of the sun. A great quantity of elementary fire is thus rendered insensible in the torrid zone, and is carried by the dispersion of the vapours to the north and to the south, where it is gradually communicated to the earth when the vapours are condensed."

That all this takes place, as the Doctor has advanced, cannot be denied; but, by allowing it, the difficulty is not removed in the smallest degree, as will appear from a due consideration of the phenomena which he himself has mentioned.—He owns that the sun communicates fire to the earth: the question is, What becomes of it, seeing the emission is continual? In summer, the air, the earth, and the water, are heated to a certain degree. On the sun's declining southward, the air first loses its heat. Whither does it go? It does not ascend into the higher regions of the atmosphere, for there are constantly found colder than the parts below. It does not descend to the earth and water; for there give out the quantity they had absorbed, as Dr Crawford observes. Neither does it go laterally to the southern regions; for they are constantly very hot, and ought to impart their heat to those farther north, instead of receiving any from them. How comes it then, that the atmosphere seems perpetually to receive heat without ever being satiated? or if the heat cannot be found going off either upwards, downwards, or sideways, how are we to account for its disappearance?

This question seems to be altogether unanswerable on the supposition that heat is occasioned by the mere presence of a fluid; but if we suppose it to be only a particular mode of action of an omnipresent fluid, the whole difficulty vanishes at once.—On this supposition indeed the question will naturally arise, Whence does this motion proceed, or by what is its action in general determined? Dr Berkenhout, in enumerating the properties of matter, exempts fire from two of those usually ascribed to other material substances, viz. gravitation and the vis inertia. "According to the philosophers (says he), matter cannot move without being either impelled or attracted. I doubt much whether this be true of fire, and whether, when uncombined, motion be not one of its essential properties.—Gravitation seems also to be no property of fire, which moves with equal facility in all directions, and may be accumulated in hard bodies to any degree without increasing their weight. Fire, being the cause of volatility, seems rather to be in constant counteraction to gravity."

But however essential we may suppose the motion of fire to be to it, there cannot be any self-existent mobility in its parts, otherwise it would soon be diffused equally throughout the universe, and the temperature of the whole reduced to an equilibrium. According to the present constitution of nature, we see that the distribution of heat is principally owing to the sun; and what we call its quantity, depends on the position of the sun with regard to terrestrial objects and the length of time they are exposed to his rays. Heat is not produced while the rays have a direct passage; and therefore fluids through which they pass easily, as air, are not heated by the rays of the sun. But when the rays are impeded in their course, and reflected in considerable quantity, a degree of heat takes place, which is always greater or less in proportion to the intensity of the rays.—In the reflecting substance, the heat will be comparatively greater in proportion to the quantity of rays which are absorbed or stopped in their course by it; but in any substance interposed between the sun and the reflecting body, the heat is proportional to the quantity of rays reflected.—Now it is plain, that when the particles of light fall upon any opaque substance, and enter its pores, which by their extreme subtilty they are well calculated to do, they must make an attempt to pass directly through it in their natural course; but as this cannot be done, they will push laterally, and in all directions, in consequence of being perpetually urged by the impulse of the light coming from the sun: and thus an action will be propagated in all directions as radii from a centre towards a circumference, which when it takes place in that subtle fluid always produces what we call heat.

In contemplating the system of nature, we perceive three kinds of fluids of extreme subtilty, and very identity much resembling one another, viz. fire, light, and electricity. That it should be agreeable to vulgar conceptions to suppose these all to be ultimately the same, is not surprising; and on examining the evidence of their identity, it will certainly be found exceedingly strong. They all agree in the property of exciting the sensation of heat in certain circumstances, and in not doing so in others. Fire, we know, in the common acceptation of the word, always does so; but when it assumes the latent and invisible state, as in the formation of vapour, it lays aside this seemingly essential property, and the vapour is cold to the touch.—Light, when collected into a focus by a burning-glass, i.e. when its rays converge towards a centre, and diverge or attempt to diverge from one, produces heat also; and so does the electric fluid; for it has been found that the aura converging from a very large conductor to the point of a needle, is capable of setting on fire a small cartridge of gunpowder, or a quantity of tinder, surrounding it*. There seems also to be a connection between fire and electricity.

* See Electricity. Theory.

Element of Fire.

Connection between fire or heat and electricity.

See Electricity.

Excessive electricity of the polar regions in winter.

Heat in summer becomes electric fluid in winter.

Why thunder and lightning take place in summer and not in winter.

Heat, light, cold, and electricity, the effects of one universal fluid.

Chemistry.

Fire and electricity in another way; for in proportion as heat is diminished, or the bodies are cooled, electricity succeeds in its place. Thus all electric bodies by heat become conductors of electricity, and cannot be excited or made to show any signs of containing that fluid; but as soon as the heat is removed, their electric property returns. Water is naturally a conducting substance: by being frozen its conducting power is lessened, which shows an approach to electricity; and, by being cooled down to 20° below 0° of Fahrenheit, the ice actually becomes electric, and will emit sparks by friction like glass*. The atmosphere is a natural electric: but by a certain degree of heat it loses this property, and becomes a conductor; nor is there any doubt that its electric properties are increased in proportion to the degree of cold imparted to it. In the winter time, therefore, we must consider the frozen surface of the earth, the water, and the atmosphere of the polar regions, as forming one electrical machine of enormous magnitude; for the natural cold of these countries is often sufficient to cool the water to more than 20° below 0°, and consequently to render it an electric. That this is really the case, appears from the excessively bright aurora borealis and other electric appearances, far exceeding anything observed in this country. In the summer time, however, no such appearances are to be seen, nor any thing remarkable except an excessive heat from the long continuance of the sun above the horizon. This quantity of heat then being succeeded by a proportionate quantity of electricity in winter, it is impossible to avoid concluding that the heat in summer becomes electric fluid in winter, which, going off through the celestial expanse, returns again to the grand source of light and heat from which it originally came; thus making room for the succeeding quantities which are to enliven the earth during the following summer.

Thus the disappearance of heat in winter, and of electricity in summer, in these countries, will be very naturally and easily accounted for. It is true, that the phenomena of thunder and lightning show the existence of this fluid in vast quantities during the summer season: but these phenomena are only partial, and though formidable to us, are trifling in comparison with the vast quantities of electric matter discharged by the continual flashing of the aurora borealis, not to mention the fire-balls and meteors called falling stars, which are very often to be seen in the northern countries. In the summer-time, the air which is an electric, heated by the rays of the sun, is excited or made to part with the fluid to the vapours contained in it; and it is the unequal or opposite electricity of the clouds to one another, or to the earth, which produces the lightning. But in winter, when the air, earth, and vapours, all become electric, they cannot discharge sparks from one to another as before; but the whole, as one connected and vast electrified apparatus, discharges the matter almost in a continued stream for many months.

From a consideration of these and other phenomena of nature, as well as of the best experiments which have hitherto been made, we must consider fire in the abstrusest of omnipotent fluids, of such subtlety as to pervade all terrestrial substances. When by any means it is made to diverge every way as from a centre, there it operates as heat; expands, rarifies, or burns, according to the intensity of its action. Proceeding in straight lines or parallel lines, or such as diverge but little, it acts Heat, as light, and shows none of that power discoverable in the former case, though this is easily discoverable by making it converge into a focus. In a quiescent state, or where the motion is but little, it presses on the surfaces of bodies, contracts and diminishes them every way in bulk, forces out the expanding fluid within their pores, and then acts as cold. In this case also, being obliged to fulfill the vehement action of that part of the fluid which is in motion, it flies with violence to every place where the pressure is lessened, and produces all the phenomena of Electricity.

§ 1. Of the Nature of Heat.

The manner in which the phenomena of heat may be solved and its nature understood, will appear from the following propositions.

1. It is in all cases observed, that when light proceeds in considerable quantity from a point, diverging as the radii of a circle from its centre, there a considerable degree of heat is found to exist, if an opaque body, having no great reflective power, is brought near that point.

2. This action of the light, therefore, may be accounted the ultimate cause of heat, without having recourse to any farther suppositions; because nothing else besides this action is evident to our senses.

3. If the point from which the rays are emitted is placed in a transparent medium, such as air or water, that medium, without the presence of an opaque body, will not be heated.

4. Another cause of heat, therefore, is the reflection of the parts of that body on which the light falls, to the action mentioned in Prop. 1. Where this reflection is weak, as in the cases just mentioned, the heat is either nothing, or very little.

5. If a body capable of reflecting light very copiously is brought near the lucid point, it will not be heated*.

6. A penetration of the light, therefore, into the substance of the body, and likewise a considerable degree of reflection on the part of that body to the action of the light, are the requisites to produce heat.

7. Those bodies ought to conceive the greatest degrees of heat into whose substance the light can best penetrate, i.e., which have the least reflective power, and which most strongly resist its action; which is evidently the case with black and solid substances.

8. By heat all bodies are expanded in their dimensions every way, and that in proportion to their bulk and the quantity of heat communicated to them.

9. This expansion takes place not only by an addition of sensible heat, but likewise of that which is latent. Of this last we have a remarkable instance in the case of snow mixed with spirit of nitre. The spirit of nitre contains a certain quantity of latent heat, which cannot be separated from it without effecting a change on the spirit itself; so that, if deprived of this heat, it would no longer be spirit of nitre.—Besides this, it contains a quantity of sensible heat, of a great part of which it may be deprived, and yet retain its characteristic properties as nitrous acid. When it is poured upon snow, the latter is immediately melted by the action of the latent heat in the acid. The snow cannot be melted or converted into water, without imbibing a quantity of latent heat, which it receives immediately from the acid which melts it. But the acid cannot part with the heat without decomposition; to prevent which, its sensible heat occupies the place of that which has entered the snow and liquefied it. The mixture then becomes exceedingly cold, and the heat forces into it from all the bodies in the neighbourhood; so that, by the time it has recovered that quantity of sensible heat which was lost, or arrived at the temperature of the atmosphere around it, it will contain a considerably larger quantity of heat than it originally did, and is therefore observed to be expanded in bulk. Another instance of this expansive power of latent heat is in the case of steam, which always occupies a much larger space than the substance from which it was produced; and this whether its temperature is greater or less than the surrounding atmosphere.

10. The difference between latent and sensible heat, then, as far as we can conceive, is, that the expansive power of the former is directed only against the particles of which the body is composed; but that of the latter is directed also against other bodies. Neither do there seem to be any difference at all between them farther than in quantity. If water, for instance, hath but a small quantity of heat, its parts are brought near each other, it contracts in bulk, and feels cold. Still, however, some part of the heat is retained among the aqueous particles, which prevents the fluid from congealing into a solid mass. But, by a continuation of the contracting power of the cold, the particles of water are at last brought to near each other that the internal or latent heat is forced out. By this discharge a quantity of air is also produced, the water is congealed, and the ice occupies a greater space than the water did; but then it is full of air-bubbles, which are evidently the cause of its expansion. The heat then becomes sensible, or, as it were, lies on the outside of the matter; and consequently is easily dissipated into the air, or communicated to other bodies. Another way in which the latent heat may be extricated is by a constant addition of sensible heat. In this case the body is first raised into vapour, which for some time carries off the redundant quantity of heat. But as the quantity of this heat is continually increased, the texture of the vapour itself is at last totally destroyed. It becomes too much expanded to contain the heat, which is therefore violently thrown out on all sides into the atmosphere, and the body is said to burn, or be on fire. See Combustion, Flame, and Ignition.

11. Hence it follows, that those bodies which have the least share of latent heat, appear to have the greatest quantity of sensible heat; but this is only in appearance, for the great quantity they seem to contain is owing really to their inability to contain it. Thus, if we can suppose a substance capable of transmitting heat through it as fast as it received it; if such a substance was let over a fire, it would be as hot as the fire itself, and yet the moment it was taken off, it would be perfectly cool, on account of its incapacity to detain the heat among the particles of which it was composed.

12. The heat, therefore, in all bodies consists in a certain violent action of the elementary fire within them tending from a centre to a circumference, and thus making an effort to separate the particles of the body from each other, and thereby to change its form or mode of existence. When this change is effected, bodies are said to be dissipated in vapour, calcined, vitrified, or burnt, according to their different natures.

13. Inflammable bodies are such as are easily raised in vapours; that is, the fire easily penetrates their parts, and combines with them in such quantity, that becoming exceedingly light, they are carried up by the atmosphere. Every succeeding addition of heat to the body increases also the quantity of latent heat in the vapour, till at last, being unable to resist its action, the heat breaks out all at once, the vapour is converted into flame, and is totally decomposed. See the article Flame, and Prop. 10.

14. Uninflammable bodies are those which have their parts more firmly connected, or otherwise disposed in such a manner, that the particles of heat cannot easily combine with them or raise them into vapour.

15. Heat therefore being only a certain mode of the action of elementary fire, it follows, that the capacity of a body for containing it, is only a certain constitution of the body itself, or a disposition of its parts, which can allow the elementary fire contained in it to exert its expansive power upon them without being dissipated on other bodies. Those substances which allow the expansive power of the fire to operate on their own particles are said to contain a great deal of heat; but those which throw it away from themselves upon other bodies, though they feel very hot, yet philosophically speaking they contain very little heat.

16. What is called the quantity of heat contained in any substance, if we would speak with the strictest propriety, is only the apparent force of its action, either upon the parts of the body itself, or upon other bodies in its neighbourhood. The expansive force of the elementary fire contained in any body upon the parts of that body, is the quantity of latent heat contained in it; and the expansive force of the fire exerted upon other bodies which touch or come near it, is the quantity of sensible heat it contains.

17. If what we call heat consists only in a certain action of that fluid called elementary fire, namely, its expansion, or acting from a centre to a circumference, it follows, that if the same fluid act in a manner directly opposite to the former, or press upon the particles of a body as from a circumference to a centre, it will then produce effects directly opposite to those of heat, i.e., it will then be absolute cold, and produce all the effects already attributed to Cold. See that article.

18. If heat and cold then are only two different modifications of the same fluid, it follows, that if a hot body and a cold one are suddenly brought near each other, the heat of the one ought to drive before it a part of the cold contained in the other, i.e., the two portions of elementary fire acting in two opposite ways, ought in some measure to operate upon one another as any two different bodies would when driven against each other. When a hot and a cold body therefore are brought near each other, that part of the cold body farthest from the hot one ought to become colder than before, and that part of the hot body farthest from the cold one ought to become hotter than before. For the same reason, the greatest degree of cold in any body ought to be no obstacle, or at least very little, to its conceiving heat, when put in a proper situation. Cold air, cold fuel, &c. ought to become as intensely heated, and nearly as soon, as that which is hotter.

The two last propositions are of great importance. When the first of them is thoroughly established, it will confirm beyond a doubt, that cold is a positive, as well as heat; and that each of them has a separate and distinct power, of which the action of its antagonist is the only proper limit; i.e., that heat can only limit the power of cold, and vice versa. A strong confirmation of this proposition is the experiment related by M. Geoffroy; an account of which is given under the article COLD. Another, but not so well authenticated, is related under the article CONGELATION.

—De Luc's observation also, mentioned by Dr Cleghorn, affords a pretty strong proof of it; for if the lower parts of the atmosphere are cooled by the pallage of the sun's rays at some distance above, and it hath been already shown that they do not attract the heat from the lower parts, it follows, that they must expel part of the cold from the upper regions.

The other proposition, when fully established, will prove, that heat and cold are really convertible into one another; which indeed seems not improbable, as we see that fires will burn with the greatest fierceness during the time of intense frosts, when the coldest air is admitted to them; and even in those dismal regions of Siberia, where the intense cold of the atmosphere is sufficient to congeal quicksilver, it cannot be doubted that fires will burn as well as in this country; which could not happen if heat was a fluid per se, and capable of being carried off, or absolutely diminished in quantity, either in any part of the atmosphere itself, or in such terrestrial bodies as are used for fuel.

§ 2. Of the general Effects of Heat.

Having said thus much concerning the nature of heat in general, we come now to a particular explanation of its several effects, which indeed constitute the whole of the active part of chemistry.—There are,

I. Expansion, or increase of bulk in every direction. This is a necessary consequence of the endeavour which the fluid makes to escape in all directions, when made to converge into a focus. The degree of expansion is unequal in different bodies, but in the same body is always proportionable to the degree of heat applied. There are two different instruments in use for ascertaining the degrees of expansion; and as we have already shown, that the degree of heat can only be known by the expansion, these effects of heat upon the instrument are usually taken for the degrees of heat themselves. These instruments are called the THERMOMETER and PYROMETER. The former is composed of a glass tube, with a globe or rather oval tube at one end, and exactly closed at the other; it is most usually filled with mercury or spirit of wine; but mercury is generally preferred on account of its expansions being more equable than those of any other fluid. It has the disadvantage, however, of being subject to congelation; which is not the case with spirit of wine, when very highly rectified.

Spirit-of-wine thermometers, therefore, ought not to be entirely disused, but seem rather a necessary part of the chemical apparatus, as well as those made with mercury.

As no thermometer made with any fluid can measure either the degrees of heat about the point at which it boils, or the degrees of cold below which it congeals, instruments have been contrived by which the expansion of solid bodies, though much less than what is occasioned by an equal degree of heat in a fluid, may become visible. These were usually called Pyrometers; but Mr Wedgewood has lately contrived a method of connecting the two together, in which the highest degree of heat, exceeding even that of a glass-house furnace, may be measured as accurately as the more moderate degrees by the common mercurial thermometer. See THERMOMETER.

Expansion in some cases does not appear to be the effect of heat, of which we have two remarkable instances, viz. of iron, which always expands in cooling after it has been melted; and of water, which expands with prodigious force in the act of freezing. The power with which iron expands in the act of passing from a fluid to a solid state, has never been measured, nor indeed does it seem easy to do so; but that of freezing water has been accurately computed. This was done by the Florentine Academicians, who having filled an hollow brass ball of an inch diameter with water, exposed it to a mixture of snow and salt, in order to congeal the water, and try whether its force was sufficient to burst the ball or not. The ball, being made very strong, resisted the expanding force of the water twice, even though a considerable part of its thickness had been pared off when it was perceived too strong at first. At the third time it burst; and by a calculation founded on the thickness of the globe and the tenacity of the metal, it was found that the expansive power of a sphere of water only one inch in diameter, was sufficient to overcome a resistance of more than 27,000 pounds, or 13 tons and a half.

A power of expansion so prodigious, little less than used as an double that of the most powerful steam-engines, and argument exerted in so small a body, seemingly by the force of cold, was thought to be a very powerful argument in favour of those who suppose cold to be a positive substance as well as heat; and indeed contributed not a little to embarrass the opposite party. Dr Black's discovery of latent heat, however, has now afforded by Dr a very easy and natural explication of this phenomenon. He has shown, that, in the act of congelation, water is not cooled more than it was before, but rather grows warmer; that as much heat is discharged, and passes from a latent to a sensible state, as, had it been applied to water in its fluid state, would have heated it to 135°. In this process the expansion is occasioned by a great number of minute bubbles suddenly produced. These were formerly supposed to be formed of cold in the abstract; and to be so subtle, that, infusing themselves into the substances of the fluid, they augmented its bulk, at the same time that, by impeding the motion of its particles upon each other, they changed it from a fluid to a solid. Dr Black, however, has demonstrated, that these are only air extracted during the congelation; and to the extraction of this air he very justly attributes the prodigious expansive force exerted by freezing water. only question, therefore, which now remains is, By what means this air comes to be extricated, and to take up more room than it naturally does in the fluid? To this we can scarce give any other answer, than that part of the heat which is discharged from the freezing water combines with the air in its unelastic state, and, by restoring its elasticity, gives it that extraordinary force, as we see also in the case of air suddenly extricated in the explosion of gunpowder. Thus expansion, even in the case of freezing, is properly an effect of heat; and must therefore be considered as a phenomenon uniformly and certainly attending the action of heat, and in all cases to be ascribed to it.

The only way in which the element or fluid of fire can be supposed to act, and the way in which we can have a rational idea of its being able to produce both heat and cold according to the diversity of its action, has been already explained so fully, that it is needless at present to enter into any further discussion of the subject. It will easily appear, that the capacity for containing heat is nothing different from the action of heat upon that body in expanding, and at last altering its form in such a manner, as either to be able to infuse itself among the particles in much greater quantity than before, still retaining its internal action, though the external one becomes imperceptible; or scattering them in such a manner, that it breaks forth in great quantity in its peculiar appearances of fire and light; in the former case producing vapour or smoke, and in the latter flame, as shall afterwards be more fully explained. It must likewise appear, that to determine the quantity of heat in any body is altogether impossible: and with regard to the lowest degree of heat, or a total expulsion of that fluid, so far from being able to determine what it is, the probability must be, that nature does not admit of any such thing; for if heat consists in the expansive action of a certain fluid, and cold in its opposite or contractile action, there is very little reason to suppose that the constitution of nature will allow any one of these actions entirely to cease, as it does not appear by what means it could again be renewed. Cold, as we have already seen, always tends to produce electricity; and the connection betwixt that and fire is so strong, that we cannot suppose the former to be carried to any great extreme without producing the latter. Whatever we may therefore suppose concerning the capacities of different bodies for containing heat, or concerning the point of total privation of heat, must be altogether void of foundation. A rule, however, has been given by Mr Kirwan for finding the point of total privation, which, together with its demonstration, we shall subjoin; and as it is necessary for the better understanding of this, to call to remembrance what has been said concerning the difference between the temperatures and specific heats of bodies, we shall insert an epitome of the doctrine from Mr Nicholson.

"If two equal bodies of different kinds and temperatures be brought into contact, the common temperature will seldom, if ever, be the mean betwixt the two original temperatures; that is to say, the surplus of heat in the hotter body will be unequally divided between them, and the proportions of this surplus retained by each body will express their respective dispositions, affinities, or capacities for heat.—If, therefore, a given substance, as for example fluid water, be taken as the standard of comparison, and its capacity for heat be called one, or unity, the respective capacities of their bodies may be determined by experiment, and expressed in numbers in the same manner as specific gravities usually are. And because it is established as well from reason as experiment, that the same capacity for heat obtains in all temperatures of a given body, so long as its state of solidity, fluidity, or vapour is not changed, it will follow, that the whole quantities of heat in equal bodies of a given temperature will be as those capacities. And as the respective quantities of matter, in bodies of equal volume, give the proportions of their specific gravities, so the respective quantities of heat in bodies of equal weight and temperature give the proportions of their specific heats.

"A greater capacity for heat, or greater specific heat, in a given body, answers the same purpose with respect to temperature as an increase of the mass; or the quantity of heat required to be added or subducted, in order to bring a body to a given temperature, will be as its capacity or specific heat.

"The capacities not only differ in various bodies, but also in the same body, according as it is either in a solid, fluid, or vaporous state. All the experiments hitherto made conspire to show, that the capacity, and consequently the specific heat, is greatest in the vaporous, least in the fluid, and least in the solid state.

"The quantity of heat that constitutes the difference between the several states, may be found in degrees of the thermometer. Thus, if equal quantities of water at $162^\circ$ and ice at $32^\circ$ of temperature be mixed, the ice melts, and the common temperature becomes $32^\circ$; or otherwise, if equal quantities of frozen and fluid water, both at $25^\circ$, be placed in a like situation to acquire heat from a fire, the water will become heated to $162^\circ$, while the ice melts without acquiring any increase of temperature. In either case the ice acquires $130^\circ$ of heat, which produces no other effect than rendering it fluid. Fluid water, therefore, contains not only as much more heat than ice, as is indicated by the thermometer, but also $130^\circ$, that is in some manner or other employed in giving it fluidity. And as fluid water cannot become ice without parting with $130^\circ$ of heat besides what it had above $32^\circ$ in its temperature; so also steam cannot become condensed into water without imparting much more heat to the matters it is cooled by, than water at the same temperature would have done.

"The heat employed in maintaining the fluid or vaporous form of a body, has been called latent heat, because it does not affect the thermometer.

"From the consideration of the specific heats of Mr Kirwan's theory, the same body in the two states of fluidity and solidity, and the difference between those specific heats, is deduced a method of finding the number of degrees which denote the temperature of any body immediately after congelation, reckoned from the natural zero, or absolute privation of heat. The rule is; multiply the degrees of heat required to reduce any solid to a fluid state, by the number expressing the specific heat of the fluid; divide this product by the difference between the numbers expressing the specific heat of the body in each state; the quotient will be the number..." Theory.

General Ef of degrees of temperature, reckoned from an absolute privation of heat.

"This theorem is Mr Kirwan's, and may be proved thus. Let \( s \) represent the required temperature of the body just congealed, \( l = \) the number of degrees that expresses the heat required to reduce it to fluidity, \( n = \) the specific heat of the solid, and \( m = \) the specific heat of the fluid. Then \( s + l : s : : m : n \). Whence

\[ s = \frac{m}{m-n} = \text{the temperature from the natural zero} \]

in thermometrical degrees of the fluid. But because the actual fall of the thermometer is to be produced by cooling the solid, must pay attention to its capacity. The quantity of heat required to produce a given change of temperature in a body is as its capacity; and consequently the changes of temperature, when the quantity of heat is given, will be inversely as the capacities: therefore, \( n : m : : \frac{ln}{m-n} : \frac{ln}{m-n} = s \).

which is the rule above mentioned.

"If the data \( l, m, \) and \( n, \) be accurately obtained by experiment, in any one instance, and the difference between the zero of Fahrenheit's scale and the natural zero be thence found in degrees of that scale, this difference will serve to reduce all temperatures to the numeration which commences at the natural zero. So that \( s \) being known in all cases, if any two of the quantities \( l, m, \) or \( n, \) be given in any body, the other may be likewise had. For \( l = \frac{sm - ln}{m}; \) and \( m = \frac{sn}{s-l} \)

and \( n = \frac{sm - lm}{s}. \)

"To give an example of this curious rule, let it be required to determine how many degrees of refrigeration would absolutely deprive ice of all its heat? The degrees of heat necessary to melt ice are 130; and the specific heats of ice and water are as 9 to 10. The number 130 multiplied by 10, produces 1300, and divided by the difference between 9 and 10 quotes 1300: therefore if ice were cooled 1300 degrees below 32°, or to—1268 of Fahrenheit's scale, it would retain no more heat."

II. Fluidity is another effect of heat, and is capable of taking place in all bodies hitherto known, when the fire is carried to a certain pitch. Theories have been invented, by which fluidity was ascribed to the smoothness and round figure of the particles whereof bodies were composed, and solidity to an angular or irregular figure. It has also been ascribed to a stronger degree of attraction between the parts of solids than of fluids. Dr Black, however, has shown, that in the case of melting ice, we are certainly to ascribe the acquired fluidity of the water to the abstraction of heat. This was determined by a decisive experiment, in which he exposed a Florence-flask full of water to the atmosphere in a warm room, when he found that the heat in the air evidently left it, to flow into the ice in the bottle, and reduced it to fluidity. The air thus deprived of its heat, he felt sensibly descending like a cold blast from the bottle, and continuing to do so as long as any of the ice remained unthawed; yet after it was all melted, the temperature of the fluid was no more than 32°. Different degrees of heat are requisite for converting different solids into fluids, for which see the Table of Degrees of Heat.

This theory receives an additional confirmation from the quantity of heat which is always known to be produced by the conversion of a fluid into a solid. And that this is really the case appears, 1. From what happens in the congelation of waters, it appears that ice is formed sensible very slowly, and with several circumstances which support the theory.—Thus, if we expose equal quantities of water to the air, which is perhaps 10° below frost, of a fluid and add to one of these a small quantity of salt or spirit of wine, and observe the cooling of each, we shall find them both grow gradually colder, until they arrive at the temperature of frost; after which the water containing the salt will continue to grow colder, until it has arrived at the temperature of the air, at the same time that only a small quantity of the other water is converted into ice. Yet were the common opinion just, it ought all to have been congealed by this time; instead of which, it is scarce grown a degree colder during the whole time. Its remaining at the same temperature for so long time, shows that it has been communicating heat to the atmosphere; for it is impossible that any body can remain in contact with another that is colder, without communicating heat to it. Whence then comes this heat? There must be some source adding to the sensible heat of the water, so as to keep up its temperature to the freezing point; and this source of heat must be very considerable; for it will continue to act for a very long time before the water is changed into ice; during all which time, even to the last drop, the water is not a degree colder than 32° of Fahrenheit's thermometer. This, therefore, is the latent heat of the water, which had formerly entered into it during its transition from ice to a fluid state.

A still stronger argument is derived from the following experiment; which evinces that the fluidity of water really depends upon its latent heat, and that of the theory from the sensible heat is only a mean or condition to its containing the latent heat. This experiment consists in exposing water contained in a covered beer-glass to fluid the air of a cold frosty night; and when the atmosphere is at the temperature of perhaps 10° or 12° below frost, the water will acquire that temperature without freezing; so that the fluidity of the water does not altogether depend on the quantity of sensible heat contained in it. The congelation, however, may be brought on by touching it with a bit of ice, with the extremity of a wire, by a shock upon the board, or otherwise disturbing it; and we then find the temperature suddenly raised up to 32°. This shows plainly, that the water has a disposition to retain the quantity of latent heat, upon which its fluidity must immediately and necessarily depend; and it retains it with a certain degree of force, so as to keep the water fluid in a temperature below that in which it usually parts with the latent heat and congeals. By disturbing it, however, we instantly bring on the congelation, which cannot take place without an extraction of the latent heat; which then, being changed into the ordinary or moveable heat, raises the thermometer as usual. The quantity of heat discharged from the first small portion of ice formed in the water is sufficient to prevent any more latent heat from separating, and consequently from any more ice being produced till more of the sensible heat is abstracted.

This doctrine extends not only to such bodies as are actually converted from a solid to a fluid, or from

General Effects of Heat.

A fluid to a solid state, but to such as are in a kind of middle state between solidity and fluidity; for every degree of softness depends on a certain degree of heat contained in the body. Thus, for instance, melted wax, allowed to cool slowly, soon becomes opaque and congealed; but it must be colder still before it attains its utmost degree of hardness. There is therefore a certain degree of heat below which every body is solid, and above which every one is fluid; the former being called the congealing, and the latter the melting point of bodies.

By making experiments upon different substances, the Doctor was convinced that latent heat is the universal cause of fluidity; and the doctrine holds good in all the experiments that have hitherto been made upon spermaceti, bees-wax, and some of the metals. If they are melted, allowed to cool slowly, and a thermometer be immersed into them, we find, that as long as they continue fluid, their sensible heat diminishes very fast; but as soon as they begin to grow solid, the sensible heat continues greater than that of the air to which they are exposed; and during all this time it is communicating heat to the air, without having its sensible heat diminished: for the latent heat within the fluid gradually receives a sensible form, and keeps up the temperature, proving a source of sensible heat, which is communicated to the neighbouring bodies as well as the surrounding air. The softness and ductility of bodies depend on this also.

III. Evaporation. A third effect of the action of heat is that of converting bodies into vapour, by which they are rendered specifically lighter than the surrounding atmosphere, and enabled to rise in it. To account for this, many theories have been invented; but that of Dr Black, who accounts for it, as well as fluidity from the absorption of latent heat, is now universally received. The circumstances by which he proves and illustrates his doctrine are the following:

1. When we attend to the phenomena of boiling water, in a tea kettle for instance, it may, when first put upon the fire, be about the temperature of 48° or 50°. In a quarter of an hour it will become heated to 212°. It then begins to boil, and has gained 162° of vapour in that time. Now, if the conversion of it into vapour depended on the quantity of sensible heat introduced, we may ask how long it will be necessary to raise it all in vapour? Surely another quarter of an hour should be sufficient; but this is far from being the case. Dr Black made some experiments upon this subject in conjunction with another gentleman. Having the opportunity of what is called a kitchen-table or a thick plate of cast iron, one end of which was made sensibly red-hot, they set upon this some iron vessels with circular flat bottoms, of about four inches diameter, and which contained a quantity of water. The temperature of the water was noted, as also when it began to boil; and when the whole of it was boiled away, it was found, that when set on the table its temperature had been 54°; in four minutes it began to boil, and in that space of time received 158° degrees of heat. Had the evaporation, therefore, depended merely on the quantity of sensible heat introduced, it ought to have been dissipated entirely in a single minute more. It was, however, 18 minutes in dissipating; and therefore had received 807 degrees of heat before it was all evaporated. All this time, therefore, while the water continued to boil, it was receiving a great quantity of heat, which must have been flowing equally fast out of it; for the vessel was no hotter, and the iron plate continued equally hot, the whole time. The vessels were of different shapes, some of them cylindrical, some conical, others widening upwards; one of the designs of the experiment being to show how far the evaporation was retarded by the particular form of the vessels. By suspending a thermometer in the mouth of one of the evaporating vessels, the heat of the steam was found to be exactly 212°; so that as the great quantity of heat absorbed was found neither to have remained in the water, nor to have been carried away by the steam in a sensible manner, we have nothing left to suppose, but that it flew off as one of the component parts of the steam in a latent state.

2. In an experiment to show the fixedness of the boiling point of water, Dr Black inclosed some of that fluid in a strong vial having a thermometer in it, and flopped close with a cork. By the application of heat he hoped now to be able to raise the thermometer some degrees above the boiling point, which would be the natural consequence of the confinement of the steam. When this was done, he pulled out the cork, and supposed that the water would now all fly out in vapour: but in this he was totally disappointed; a sudden and very tumultuous boiling ensued, which threw out some of the water; but though some quantity of steam likewise issued, the quantity of water was not considerably diminished. The vial had been heated to 20° above the boiling point, but almost instantly cooled down to 212°, when the cork was taken out.

3. Mr Watt, in making some experiments on the force of steam, had occasion to use Papin's digester, with a pipe proceeding from its side; the orifice of which was shut with a valve pressed down by one end of a lever. Thus he heated steam to 400° of Fahrenheit; after which, having suddenly struck off the lever, a quantity of steam flew out with considerable noise, and with such violence as to make an impression on the ceiling of the room; but this noise gradually diminished, and after ten minutes ceased entirely; and upon opening the machine, he found the greatest part of the water still remaining.

4. The change of sensible into latent heat in the formation of vapour, appears still more evident in the point of boiling of water in vacuo. Mr Boyle took a quantity of water which had been previously boiled to purge it of its air, and put it whilst hot under the receiver of an air-pump. In consequence of this it began again to boil, Boyle and continued boiling till it was only lukewarm, and it soon arrived at this temperature; so that in this case also the heat had disappeared during the conversion of the fluid into vapour. Others have repeated this experiment, as Boerhaave, Melschenbrock; and Robinson, Mr Robin, who lectures on chemistry in Glasgow, says that the heat diminishes very fast till it comes to 90° or 95°, which seems to be the boiling point of water in vacuo. As a considerable part of the heat thus disappears, and is to be discovered neither in the water nor in the vapour, we must conclude that it enters the latter as part of its composition.

5. Thus also we may understand some curious experiments made by Dr Cullen upon ether and other volatile Theory.

General Ef-fatile fluids. He employed some persons to make experiments upon the cold produced by evaporation; and willing to repeat them himself in vacuo, he put some of the most volatile liquors under the receiver of an air-pump. One of these was ether. It was contained in a glass, in which there was also placed some water. When the air was extracted, the ether began to boil, and to be converted into vapour, till it became so very cold that it froze the water contained in the vessel, though the temperature of the room was about 50°. Here therefore there was a quantity of heat which disappeared all of a sudden; which it is plain could not be owing to its having any communication with that of the atmosphere or other cold bodies, as they could not render it colder than they were themselves. Ether therefore is to be considered as a fluid so volatile, that were it not for the pressure of the atmosphere it would be perpetually in the state of vapour.

That this heat which enters into the vapour is led in great not destroyed, but remains in a latent state, is quantity by easily proved; for we find that a great quantity of heat is expelled from vapour when it is condensed again to form the body it composed originally. This is easily ascertained by observing the quantity of heat communicated to the water in the refrigeratory of a still by any given quantity of liquid which comes over. Thus, if the refrigeratory contain 100 pounds of water, and the distillation be continued till only one pound has come over, supposing the water in the refrigeratory to have received 8° of heat; it is plain, that if the whole of the quantity thus received could be thrown into one pound of water, the latter would be heated to 80°; which is sufficient to make an equal space of iron red-hot. But that this quantity of heat is received by the water in the refrigeratory has appeared from several experiments, which show that water, by being converted into vapour, absorbs between 800° and 900° of heat.

On this principle we may explain some curious experiments made by Mr Watt with regard to the evaporation of fluids in vacuo. That gentleman had formed a design of converting water into steam with less expense of fuel, which he imagined might be done by removing the pressure of the air from the water, which he thought would thus require a much smaller quantity of fuel to convert it into vapour. Dr Black, however, perceiving that only the small quantity of sensible heat the steam possessed could thus be carried off, informed him beforehand that his project would not be found attended with the advantages he imagined. The experiment, however, was made in the following manner: A still was procured of tinned iron, the body of which resembled that of a retort, with a vessel serving as a condenser; the whole apparatus being close, excepting a little hole in the extremity of the condensing vessel. He first exhausted this vessel of air by holding the condenser over the retort, in which some boiling water was contained, until it was entirely converted into steam. He then suddenly stopped the little hole, and removed the vessels from the fire; when, after they were cooled, there was a pretty perfect vacuum formed by the condensation of the steam. The retort was then put on the fire, and turned so that the pipe and condensing vessel should hang downward; and plunging them into cold water, General heat was applied to the still till the water boiled, as Effects of could be known by the noise. It was kept boiling, till a quantity of steam was pushed over and condensed with a very gentle heat, the still feeling little warmer than his hand. After a certain quantity had been distilled, the apparatus was removed, and he had noted the heat of the water in the refrigeratory; but though the steam all along came over with a gentle heat, he found the quantity communicated to the water in the refrigeratory to be surprisingly great, not less than 1000°; so that it would have been more than sufficient to heat the quantity of liquor which came over red-hot.

IV. Ignition, or the causing bodies to shine or emit light in the dark. This may be considered as a species of inflammation, and shall therefore be explained under that head: here we shall only observe, that ignition is a more steady and constant effect of heat than either the production of fluidity or vapour; and appears not only to be the same degree with regard to any particular body, but the same with regard to all kinds of matter. Dr Martin imagines, that a red-hot piece of iron is hotter than a red-hot piece of stone; but if you put into a crucible a hundred different kinds of matter, as metals, glasses, &c., that are capable of bearing a red heat, they will all begin to appear luminous about the same time, and their brightness will increase equally as their heat increases. But it is difficult to know at what point this begins, as we have no way of ascertaining the beginning or lowest degree of ignition but by the effect it produces on our sight, and we cannot be sure that we perceive the lowest degree of light; for we know that other animals see objects with such light as appears perfect darkness to us. Sir Isaac Newton's method of determining this has been already mentioned.

Dr Boerhaave entertained a notion, that some Metals may metals, after being once brought into a state of fusion, become hot after the possibility of this as a question, "Whether the heat of these metals can be increased after they are melted?" There brought in, however, the least doubt but that their heat may to fusion, be vastly increased after they are melted; and we know certainly that such as are of easy fusion may be heated to a vastly greater degree after being melted; and why may not those requiring stronger heats be the same? We are sure that this is the case with silver, which, after being melted, may be brought to such a heat as to become too dazzling for the eye to bear it. If Boerhaave's opinion were just, it would be impossible to cast any metal into moulds, because it must lose a little heat in being removed from the fire and in entering the mould; nor would they receive a proper impulsion if they did not contain a greater quantity of heat than was necessary for their fusion.

Ignition appears to be universal; and all bodies capable of supporting it without being converted into an elastic vapour that cannot be confined, are affected in the same way. Water, which in its ordinary state seems very little capable of enduring this heat, may be confined in strong vessels so as to become capable of melting lead, which is more than half way betwixt a sufficiently red heat and that of boiling water. Experiments with the eclipile show also that it can be made red-hot; for when the steam passes through burning fuel, it can- not miss of being made red-hot. Dr Black has also frequently seen the vapour of water heated by throwing it into the ash-pit of a furnace, so as to produce a very large and transparent flame in rising up through the vent. There is reason therefore to conclude, that ignition is one of the more general effects of heat, only that some bodies are incapable of it until they be reduced to a state of vapour.

V. The last of the effects of heat here to be taken notice of is inflammation. It differs from ignition in this, that the bodies subject to the latter gradually grow cooler as soon as they are taken out of the fire, without undergoing any considerable change; while those subject to inflammation become continually hotter and hotter, communicating a vast quantity of heat to others, and undergoing a kind of decomposition themselves, inasmuch, that by this means they have been thought to be reduced to their constituent principles or elements. Some substances indeed seem to be an exception to this, as in the open air they burn totally away, without leaving any residuum or producing any foot. These are spirit of wine, sulphur, and especially inflammable air; which last, by a proper mixture with dephlogisticated air, may be so totally consumed, that scarce a fiftieth part of the two will remain. On a careful examination of these substances, however, we find that there is by no means a total consumption, or indeed, properly speaking, any consumption at all, at least if we measure the quantity of matter by the weight of the substance employed. Thus, if we are at pains to collect the vapour of burning spirit of wine, we will find, that an aqueous dew is collected, which sometimes equals the spirit of wine itself in weight. With regard to sulphur, the case is still more evident; for the vapour of this, when collected, not only equals but greatly exceeds the weight of the sulphur employed; and on burning dephlogisticated and inflammable air together, as much water is found to be produced as nearly equals the weight of both airs. In like manner, when we collect the ashes, water, foot, and oil, procured by burning any of the common inflammable substances, we will find, that they in general exceed the weight of the matter employed. The great waste of bodies by fire, therefore, is owing to the dissipation of the volatile principles they contain, which are carried off and rendered invisible by being mixed with the atmosphere.

The process of inflammation has long been explained from the presence of a substance called Phlogiston in those bodies which are subject to it, and which is supposed to be the same in all bodies belonging to this class; the differences between them arising from the principles with which it is combined. This doctrine, which was first introduced by Stahl, has given occasion to such various and discordant theories, that the existence of phlogiston has been lately denied altogether by M. Lavoisier, who brought in a new method of solving the phenomena of fire, heat, and ignition, without any affluence from this principle.

The foundation of M. Lavoisier's doctrine is the drawn from increase of weight in metals by calcination. This increase he finds to be precisely, or very nearly so, proportionate to the decrease of weight in the air in which they are calcined. His theory, therefore, is, that in the act of calcination, the pure part of the air, which he calls the acidifying or oxygenous principle, unites with the metal, and converts it into a calx. In like manner, in substances truly inflammable, the heat and flame are supposed to proceed from the union of the pure air, or the oxygenous principle, with the substance, and converting it into those principles which are found to remain after inflammation. Thus the increased weight of the substance is easily accounted for; while the inflammation, in his opinion, is nothing more than a combination of the inflammable body itself with pure air, which has an attraction for it; and in confirmation of this it is urged, that when combustion is performed in empyreal or dephlogisticated air, the whole of the latter is absorbed; but in common atmospheric air only one fourth, being the quantity of pure air contained in it.

Other arguments in favour of this opinion are, that the calces of the perfect metals may be reduced without addition by the mere emission of the oxygenous principle, phlogiston (dephlogisticated air); by an union with which they all assume the form of a calx. Thus he evades a very strong argument used by the opposite party; who adduced, as a proof of the existence of phlogiston, the metals of charcoal in the reduction of metals to their proper form. A dispute indeed took place betwixt M. Lavoisier and Dr Priestley concerning the reduction of the whole of a mercurial calx formed by an union with the nitrous acid without addition; the Doctor insisting, that the whole could not be reduced by Priestley, mere heat, but that a very perceptible quantity was always lost; but on a thorough examination of the subject, the truth seemed rather to lie on M. Lavoisier's side. See Aerology.

Another theory, somewhat similar to that of Lavoisier's, has been published by Dr Luddock, in an inaugural Dissertation in 1784. In this he supposes two kinds of matter to exist in the universe; one he calls the principium proprium, the other the principium formabile; and it is this latter, which, according to our author, is the principle of mutability, or which, by being united in various proportions with the other, forms bodies of all the different kinds we see in nature. It is this principle, therefore, which he supposes to be absorbed in the calcination of metals, and not empyreal air, as M. Lavoisier supposes; and he contends, that this same principle extends throughout the whole system of nature, even to the utmost celestial bounds.

It would exceed the limits of this treatise to give an account of the various theories which have been invented, and the arguments used for and against them; nor indeed is there any occasion for doing so, as late experiments have reduced the dispute into a much narrower compass than before, and furnished the most decisive arguments in favour of the existence of phlogiston.

The greatest objection to the belief of this principle was, that it could neither be seen nor felt by our senses directly, nor discover itself indirectly by the existence of weight it communicated to the bodies with which it was united; on the contrary, the latter always became visibly lighter in proportion to the quantity they contained: and supposing that it was imagined, instead of being possessed of any specific gravity of its own, to be a principle of positiveness, such as that of heat or light may be reasonably supposed. This objection, however, is now entirely removed; and phlogiston in the abstract is found. found to be no subtile principle capable of eluding our researches, but one very common, and easily met with, being no other than common charcoal. In the last edition of this work, under the article PHLOGISTON, it was shown, that inflammable air, deprived of its elasticity, and combined with metallic substances, is really their phlogiston; and that in the inflammable bodies commonly used, what we call their phlogiston, is really their oil; and that which exists in charcoal, and cannot be driven off by distillation, is part of the empyreumatic or burnt oil of the subject which adheres so obstinately. A similar doctrine soon after appeared in the Philosophical Transactions for 1782, and the identity of phlogiston and inflammable air was clearly proved by Mr Kirwan. Still, however, it was insisted by the French philosophers and others, that no facts had been adduced against M. Lavoisier, nor any decisive proofs appeared of the existence of phlogiston as a substance per se. Facts of this kind, however, have now been discovered by Dr Priestley, and are related under the articles AEROLOGY, CHARCOAL, PHLOGISTON, &c. It is sufficient at present to mention, that he has been able to convert the purest spirit of wine, and one of the hardest metals, viz. copper, as well as several others, into a substance entirely resembling charcoal; that by means of the heat of a burning glass in vacuo, he has distilled this metallic charcoal, as well as the common kind, entirely into inflammable air, with the assistance only of a little water, and one of the hardest metals, viz. copper, as well as several others, into a substance entirely resembling charcoal; that by means of the heat of a burning glass in vacuo, he has distilled this metallic charcoal, as well as the common kind, entirely into inflammable air, with the assistance only of a little water.

The doctrine of phlogiston may be drawn from the total consumption of pure air in certain cases of combustion, for instance, in that of phosphorus, inflammable air, and iron. It must be observed, however, that in no case whatever is the air totally consumed; and phlogiston in that of inflammable air water is produced by the air in some union of the basis of the latter, that is charcoal, cases, with the basis of dephlogisticated air, the oxygenous principle of M. Lavoisier, and which appears to be one of the component parts of WATER. In the case of phosphorus, the latter is converted into an acid; and in all probability a quantity of water is also produced, by which part of it is converted into crystalline flowers. The case of the iron, therefore, alone remains to be considered. Dr Priestley's experiments on this subject are related at length under the article AEROLOGY, n° 67 et seq. In them the iron burnt briskly in dephlogisticated air, which, according to the common theory, should have indicated the expulsion of a great quantity of phlogiston; yet the whole residuum, of which the fixed air, produced by the supposed union of the phlogiston or principle of inflammability, was only a part, scarce amounted sometimes to one-fourteenth of the air originally employed.

This argument, however, instead of contradicting the existence of phlogiston, only shows, that in some cases the distillation of a very small quantity of phlogiston is necessary to inflammation; or that the aerial principle may combine with the iron in its metallic state. In this case only a very little quantity of the phlogiston of the iron was distilled; for it was not reduced to a calx, but to that kind of scoriae which flies off in scales by beating the metal when red-hot with a hammer. A decisive proof of this burning in was had by uniting iron thus combined with the dephlogisticated air with inflammable air. By this the metal was indeed reduced to perfect iron again; but water was produced at the same time from the union of the basis of the two airs, that of the reduction inflammable air being capable of furnishing a superfluous quantity, which united with the other into the flammable form of a fluid.

The existence of phlogiston being thus proved, and its nature ascertained, we may now proceed to determine the question, Whether the great quantity of heat the combustion of inflammable bodies produces from the bodies themselves, or from the air by which they must be admitted to them in order to make them burn? That the heat in this case proceeds from the atmosphere is evident; because in all cases of combustion there is a certain diminution undoubtedly takes place by means of the conversion of the dephlogisticated part of the atmosphere into fixed air. It is proved, under the article ELASTIC VAPOURS, that elementary fire is the universal cause of elasticity in fluids. By uniting a certain quantity of it with any substance, the latter at length attains an aerial or vaporous form; and it is this vapour alone which is inflammable*. Different vapours no doubt contain different quantities of these ingredients; but in all cases the basis of the dephlogisticated part of the atmosphere must must unite with the phlogiston of the inflammable body, or with something else, so that a decomposition may ensue; and it is this decomposition which produces the heat and light; for then the fire contained in the atmosphere having no longer any thing to absorb it, must appear in its proper form. But in those cases where there is a great quantity of phlogiston, and consequently much fixed air produced, the latter absorbs too much heat in a latent state, that the quantity communicated to surrounding bodies must be greatly diminished; and if by an excess of this ingredient, not only fixed air, but the phlogisticated kind and gross smoke be also produced, this diminishes the heat still farther by the great absorption, and will even destroy it altogether. The remedy for this is either to diminish the quantity of phlogiston, or to augment the quantity of air; which, by furnishing a greater quantity of dephlogisticated basis, affords an opportunity for the evolution of a greater quantity of heat. On the other hand, when the quantity of air is too great, the phlogistic matter cannot combine with the basis of the pure air in sufficient quantity to effect a decomposition; and therefore the heat is absorbed in a latent state, and the fire goes out.

From this theory, which is further illustrated under the articles Fire, Flame, Heat, Phlogiston, &c., we may not only have a rational idea of the manner in which inflammation is generally accomplished, but see why a fire may be put out both by too great a quantity of fuel, and by too great a quantity of air. We may also see why the solar beams and electric fluid, which contain no phlogistic matter, excite a much more powerful heat than any we can raise in our hottest furnaces. The difference between ignition and inflammation will now likewise appear; such bodies as are capable only of ignition containing little or no phlogiston, but inflammable bodies a great deal.

The following table shows the most remarkable degrees of heat from the congelation of mercury to that of Mr. Wedgewood's hottest furnace.

| Mercury freezes at | 40 | |-------------------|----| | Weak spirit of wine | 32 | | Brandy at | 10 | | Cold produced by snow and salt mixed | 0 | | Strong wine freezes at | 20 | | Vinegar freezes at | 27 | | Water freezes at | 32 | | Temperature of spring and autumn | 50 | | Ordinary summer weather | 65 | | Sultry heat | 75 | | Heat of human blood | 97 to 100 | | Feverish heat | 108 | | Bees wax melts | 142 | | Serum coagulates | 156 | | Spirit of wine boils | 174 | | Water boils | 212 | | Tin melts | 408 | | Bismuth melts | 460 | | Oil of vitriol boils | 550 | | Oil of turpentine boils | 561 | | Lead melts | 585 | | Quicksilver and linseed-oil boil | 600 | | Iron begins to shine in the dark | 635 | | Iron shines briskly in the dark | 750 | | Iron glows in the twilight | 884 |

Iron red-hot from a common fire | 1050 | Red heat fully visible in daylight according to Mr. Wedgewood | 1077 | Heat by which his enamel colours are burnt on | 1857 | Brafs melts | 3807 | Swedish copper melts | 4587 | Fine silver melts | 4717 | Fine gold melts | 5237 | Least welding heat of iron | 12777 | Greatest ditto | 13427 | Greatest heat of a common smith's forge | 17327 | Cast iron melts | 17977 | Greatest heat of Wedgewood's finest air-furnace | 21877 | Extremity of the scale of his thermometer | 32277 |

**Sect. II. Of the Doctrine of Elective Attraction, and of the different Objects of Chemistry.**

Before we proceed to give a general theory of the chemical changes which happen upon the mixtures of different attraction, bodies together, or exposing them singly to heat, we must observe, that all depend on certain qualities in bodies, by which some of them are apt to join together, and to remain united while they have an opportunity. The cause of these qualities is totally unknown; and therefore philosophers, after the example of Sir Isaac Newton, have expressed the apparent effect of this unknown cause by the word attraction. From them the word has been adopted by the chemists, and is now generally used in speaking of the phenomena which are observed in the mixture of different substances; but to distinguish it from other kinds, it is usually called Elective.

This attraction is not equally strong between all substances; in consequence of which, if any body is compounded of two others, and another is presented to it which has a greater attraction for one of the component parts than they have for one another, the substance will be decomposed. A new compound is then formed by the union of that third substance with one of the component parts or elements (if we please to call them so) of the first. If the attraction between the body superadded and either of the component parts of the other is not so strong as that between themselves, no decomposition will ensue; or if the third substance is attracted by both the others, a new composition will take place by the union of all the three.

The objects of chemistry, as we have already observed, are so various, that an enumeration of them all is impossible. To ease the mind, therefore, when speaking of them, and render more useful anything that is said or wrote on chemistry, it is necessary to divide them into different classes, comprehending in each class those bodies which have the greatest resemblance to one another, and to which one common rule applies pretty generally.—The division formerly used, was that of vegetables, animals, and minerals; but this has been thought improper, as there are many substances in each of those kingdoms which differ very widely from one another, and which are by no means subject to the same laws. The most approved method, Salts are either fusible, that is, capable of abiding the fire, and melting in a strong heat, without being dilipated; or volatile, that is, being dispersed in vapour with a small heat. Their other properties are, that they are soluble in water; not inflammable, unless by certain additions; and give a sensation of taste when applied to the tongue.

The most general characteristic of salts is, that they are all soluble in water, though some of them with much more difficulty than others. Most of them have likewise the property of forming themselves, in certain circumstances, into solid transparent masses of regular figures, different according to the different salt made use of, and which are termed crystals of that salt. In this state they always contain a quantity of water; and therefore the utmost degree of purity in which a salt can be procured, is when it has been well crystallized, and the crystals are freed of their superfluous moisture by a gentle heat. They generally appear then in the form of a white powder.

In the solution of salts in water, the first thing observable is, that the water parts with the air contained in it; which immediately rises to the top in the form of bubbles. This, however, is most remarkable when the salt is in the dry form we have just now mentioned, because there is always a quantity of air entangled among the interstices of the powder, which rises along with the salt; and this discharge of air is sometimes so great, as to be mistaken for an effervescence. From this, however, it is essentially different. See EFFERVESCENCE.

Another thing observable in the solution of salts is, that a considerable change happens in the temperature of the water in which they are dissolved; the mixture becoming either a good deal warmer or colder than either the salt or the water were before. In general, however, there is an increase of cold, and scarce any salt produces heat, except when it has been made very dry, and deprived of that moisture which it naturally requires; and thus the heating of salts by being mixed with water may be explained on the same principle with the heat produced by quicklime. See QUICKLIME.

After salt has been dissolved in a certain quantity by water, no more of that salt will be taken up unless the water is heated; and as long as the heat continues to increase, the salt will be dissolved. When the water boils, at which time it has attained its greatest heat, and will take up no more salt, it is then said to be saturated with that salt. This, however, does not prevent it from taking up a certain quantity of another salt, and after that perhaps of a third, or fourth, without letting go any of the first which it had dissolved. How far this property of water extends, has not yet been ascertained by experiments.

To the above rule there is only one exception known as yet; namely, common sea-salt: for water dissolves it in the very same quantity when cold as when boiling hot. It has been said by some, that all deliquescent salts, or those which grow moist on being exposed to the air, had the same property; but this is found to be a mistake.

This property of solubility, which all the salts possess in common, renders them easily miscible together; and separates the property by which most of them float in solution of fats, to crystals, renders those easily separable again which have no particular attraction for one another. This is likewise rendered still more easy by their requiring different proportions of water, and different degrees of heat, to suspend them; for by this they crystallize at different times, and we have not the trouble of picking the crystals of one out among those of the other.

The manner in which the solution of salts in water is effected, is equally unaccountable with most of the concerning other operations of nature. Sir Isaac Newton supposed that the particles of water got between those of the salt, and arranged them all at an equal distance from one another; and from this he also accounts for the regular figures they assume on passing into a crystalline form; because, having been once arranged in an orderly manner, they could not come together in disorder, unless something was to disturb the water in which they were suspended; and if any such disturbance is given, we find the crystals are by no means to regular as otherwise they would have proved. Others have thought that these figures depend on a certain polarity in the very small particles into which the salt is resolved when in a state of solution. These things, however, are merely conjectural; neither is it a matter of any consequence to a chemist whether they are right or wrong.

Though solution is that operation which salts undergo the most easily, and which should seem to affect them the least of any, a repetition of it proves nevertheless very injurious to them, especially if it is followed by quick evaporation; and the salt, instead of being crystallized, is dried with a pretty strong heat. Newman relates, that a pound of sea-salt was reduced, by 13 solutions and evaporation, to half an ounce; and even that was mostly earth. Where solution is required, therefore, it ought always to be done in close vessels, in which also the subsequent evaporation should be performed. (See EVAPORATION); and in all cases where crystallization is practicable, it ought to be preferred to violent evaporation.

The two great divisions of salts are into acids and alkalies. The former of these are known by their peculiar taste, which is called acid or sour. They are not found in a solid form; neither are any of them, except the acids of vitriol, of tartar, of phosphorus, and of borax, capable of being reduced to solidity. The others, when highly concentrated, that is, brought to the utmost degree of strength of which they are capable, always become an invisible vapour, permanently elastic, until it comes in contact with water, or some other substance with which they are capable of uniting. For such acids the name of salts seems less proper, as we can scarcely say that a vapour, which is already much more fluid than water, can be dissolved in that element.

The acids are divided into the mineral, the vegetable, and the animal; expressing their different origin, or where they are most commonly to be found. The mineral acids are commonly reckoned three; the vi- vitriolic, the nitrous, and the marine. To this the acid of borax ought to be added; but its weakness makes it much less taken notice of as an acid than the others. A Swedish chemist, however, Mr Scheele, hath lately added several others, which are afterwards taken notice of.

The vegetable kingdom affords only two distinct species of acids, at least without the assistance of some chemical operation. The one appears fluid, and when concentrated to the utmost degree becomes an invisible vapour. This is produced from fermented liquors, under the name of vinegar. An acid similar to this, and which is thought not to be essentially different from it, is extracted from most vegetables by distillation with a strong fire. The other is likewise a consequence of fermentation; and crusts on the bottom and sides of casks in which wine is put to depurate itself. In its crude state it is called tartar; and when afterwards purified, is called the cream, or crystals, of tartar. As for the various acids produced in the different chemical processes to be afterwards related, we forbear to mention them at present, it being justly suspected that some of them are artificial.

The animal acids, which have hitherto been discovered, are only two; the acid of ants, and that of urine, which is also the acid of phosphorus. The first of these is volatile; and consequently must be supposed a vapour when in its strongest state: the other is exceedingly fixed; and will rather melt into glaas than rise in vapours. Besides these, it is said an acid is contained in blood, in wafps, bees, &c.: but no experiments have as yet been made on these to determine this matter with any degree of precision.

The alkalis are of two kinds; fixed and volatile. The fixed kind are subdivided into two; the vegetable, and mineral or fossil alkali. The vegetable is so called, because it is procured from the ashes of burnt vegetables; the fossil, because it is found native in some places of the earth, and is the basis of sea-salt, which in some places is dug out of mines in vast quantity. They are called fixed, because they endure a very intense degree of heat without being dissipated in vapour, so as even to form a part of the composition of glaas. The volatile alkali is generally obtained by distillation from animal substances. In its pure state this alkali is perfectly invisible; but affects the sense of smelling to such a degree, as not to be approached with safety.

The acids and alkalis are generally thought to be entirely opposite in their natures to one another. Some, however, imagine them to be extremely similar, and to be as it were parts of one substance violently taken from each other. Certain it is, that when separated, they appear as opposite to one another as heat and cold. Their opposite action indeed very much resembles that of heat and cold, even when applied to the tongue; for the alkali has a hot, bitter, burning taste, while the acid, if not considerably concentrated, always gives a sensation of coldness. In their action too upon animal substances, the alkali dissolves, and reduces the part to a mucilage; while the acid, if not very much concentrated, tends to preserve it uncorrupted.

If an alkaline salt, and moderately strong acid in a liquid state, be mixed together, they will immediately unite; and, provided the alkali has not been deprived of its fixed air, their union will be attended with a very considerable effervescence: (see Aerology.) If the alkali has been deprived of air, no effervescence will ensue, but they will quietly mix together; but if a due proportion of each has been added, the liquor will neither have the properties of an acid nor an alkali, but will be what is called neutral. The bringing the liquor into this state, is called saturating the acid or alkali, or combining them to the point of saturation.

If the liquor after such a saturation be gently evaporated, a saline mass will be left, which is neither an acid nor an alkali, but a new compound formed by the union of the two, and which is called a perfect neutral salt. The epithet perfect is given it, to make a distinction between the salts formed by the union of an acid and an alkali, and those formed by the union of acids with earthy or metallic substances; for these will likewise unite with acids, and some of the compounds will crystallize into regular figures; but, because of their weaker union with these substances, the salts resulting from combinations of this kind are called imperfect.

All acids, the volatile sulphurous one excepted, change the blue infusions of vegetables, such as violet colours, to a red; and alkalis, as well as some of the changed by imperfect neutrals, change them to green. This is the acids and nicest test of an acid or alkali abounding in any substance, and seems the most proper method of determining whether a solution intended to be neutral really is so or not.

Though between every acid and alkali there is a very strong attraction, yet this is far from being the difference in all; neither is it the same between the fames of acid and alkali in different circumstances of the acid. When the acids are in a liquid state, and as free as possible of inflammable matter, between which and the nitrous and vitriolic acids there is a very strong attraction, the vitriolic will expel any of the rest from an alkaline basis, and take its place. Thus, if you combine the acid of sea-salt, or marine acid, to the point of saturation, with the fossil alkali, a neutral salt will be formed, which has every property of common salt; but, if you pour on a certain proportion of the vitriolic acid, the acid of sea-salt will immediately be expelled; and the liquor, upon being evaporated, will contain not the neutral salt formed by an union of the marine acid with the alkali, but another consisting of the vitriolic acid joined with that alkali, and which has quite different properties from the former.

When the acids and alkalis are applied to one another in a liquid state, the vitriolic acid always shows itself to be the most powerful; but when applied in a solid form, and urged with a violent heat, the case is very much altered. Thus, the acid of borax, commonly called fulgurative, is so weak as to be disengaged from its basis by every acid applied in a liquid form, that of tartar alone excepted; but if even the vitriolic acid combined with an alkali be mixed with this weak acid, then exsiccated, and at last urged with a vehement fire, the vitriolic acid will be disengaged from its basis, and rise in vapours, leaving the weaker acid in possession of the alkali. The same thing happens on adding the phosphorine or urinons acid, Theory.

Chemistry.

Acids unite with phlogiston.

With metals and earth.

Elective attractions.

§ 1. Of the Operations of Solution and Precipitation.

The chemical solution of solid bodies in acid or other menstrua, is a phenomenon which, though our familiarity with it has now taken off our surprise, must undoubtedly have occasioned the greatest admiration and astonishment in those who first observed it. It would far exceed the limits of this treatise to speak particularly of all the various circumstances attending the solution of different substances in every possible menstruum. The following are the most remarkable, collected from Mr Bergman's Dissertation on Metallic Precipitates.

1. On putting a small piece of metal into any acid, it is dissolved sometimes with violence, sometimes gently, according to the nature of the menstruum and of the metal to be dissolved.

2. The nitrous acid is the most powerful in its action. Solution and Precipitation.

Nitrous acid is the most violent in its operation.

Vitriolic acid acts more weakly than marine acid generally more weak than either, except when dephtogitated.

The action of marine acid, unless on some particular substances, is still more weak; but when dephtogitated, or deprived of part of the phlogiston essential to its constitution as an acid, it acts much more powerfully, and dissolves all the metals completely.

The other acids, as those of fluor, borax, with such as are obtained from the animal and vegetable kingdoms, are much inferior in their powers as solvents, unless in very few instances.

Metals vary very much in their degrees of solubility; some yielding to almost every menstruum, and others, as has been already observed, being scarce acted upon by the most powerful.

Zinc and iron are of the former kind, and gold and silver of the latter, eluding the marine; and gold, unless in one particular case, viz. when assayed by heat in a close vessel, the action of the nitrous acid also.

These metals, however, which in their perfect state resist the action of the most powerful menstrua, may be dissolved much more readily when deprived of a certain quantity of their inflammable principle. But though the separation of this principle in some degree renders metals more soluble, the abstraction of too much is fatal to it, particularly in the case of iron and tin, renders these metals almost entirely insoluble. Manganese is the most remarkable instance of this power of the phlogistic principle, in depriving metals of their solubility by its absence, or restoring it to them by its presence; for this substance, when reduced to blackness, cannot be dissolved by any acid without the addition of some inflammable matter; but when by the addition of phlogiston it has become white, may be dissolved in any acid.

The dissolution of metals by acids, even to their very last particle, is attended by a visible effervescence; but more obscure, and scarcely to be seen at all, when the solution proceeds slowly.

The elastic fluids extricated by these solutions are various, according to the nature of the acid and of the metal employed. With the nitrous, the fluid produced is commonly that called nitrous air; with vitriolic and marine acids the produce is sometimes inflammable air, sometimes otherwise, according to the nature of the metal acted upon.

Heat in a greater or smaller degree is always produced during the dissolution of metals; and the degree of it is in proportion to the quantity of the matter and the quickness of the solution; and hence, in small quantities of metal, and when the solution proceeds very slowly, the temperature of the mass is scarcely altered.

The calces of metals either yield no air at all, or only the aerial acid, unless when urged by a violent heat almost to ignition; when, by means of vitriolic or nitrous acid, they yield a quantity of pure air, after other elastic fluids, such as vitriolic, nitrous, or phlogisticated air. None of the dephtogitated air is usually produced by the marine acid in conjunction with metallic calces.

The solutions of some metals are coloured, others are not. The colour of the former is only that which is proper to the calx, but rendered more vivid by the moisture. Thus solutions of gold and platinum are yellow; those of copper, blue or green; solutions of nickel of a bright green; but those of cobalt are red, although the calx is black. We may observe that even this red colour may be heightened to blackness. Iron moderately calcined is green; but this rarely continues upon further dephtogitation.

The white calces of silver, lead, tin, bismuth, arsenic, antimony, and manganese, are dissolved without colour; but solutions of lead, tin, and antimony, are somewhat yellow, unless sufficiently diluted. Mercury, however, forms a singular exception to this rule; for the orange-coloured calx of this metal forms a colourless solution.

The metals yielding coloured solutions are gold, platinum, copper, iron, tin, nickel, and cobalt; the rest, if properly depurated, give no tinge. A solution of silver is sometimes of a blue or green colour at first, although there be no copper present; the vitriolic acid becomes blue with copper; the nitrous may be made either blue or green at pleasure; the marine varies according to the quantity of water with which it is diluted. Manganese, when too much dephtogitated, renders both the vitriolic and marine acids purple.

With regard to the cause of chemical solutions, our author observes, that though attraction must be looked upon as the fundamental cause, yet we may also lay it down as a maxim, that no metal can be taken up by an acid, and at the same time preclude the whole quantity of phlogiston which was necessary to it in its metallic state. A certain proportion of the principle of inflammation therefore may be considered as an obstacle which must be removed before a solution can take place. Thus, of all the acids, the nitrous attracts phlogiston the most powerfully, and separates it even from the vitriolic. A proof of this may be had by boiling sulphur slowly in concentrated nitrous acid. At length all its phlogiston may be separated, and the vitriolic acid will remain, deprived of its principle of inflammability. The extraordinary solvent powers of this acid, therefore, is conformable to the peculiarity of its nature in this respect. For this menstruum dissolves metals for solution with the greatest ease, most commonly without any affluence from external heat; which in some instances would be hurtful, by separating too much of phlogiston, as appears in the case of iron, tin, copper, and antimony; all of which may be so far dephtogitated as to be rendered extremely difficult of solution; for this reason it is very often unnecessary, as has already been observed, to temper the wards. activity of this menstruum by water. The vitriolic acid requires a boiling heat before it can act upon silver or mercury. The reason of this is, that by means of the heat, the watery part of the menstruum is diminished, its power is thereby increased, and the connection of the metallic earths with the inflammable principle diminished. Marine acid, which contains phlogiston as one of its constituent principles, must necessarily have little or no effect on those metals which retain their principle of inflammability very obstinately. But its watery part being diminished by boiling, it assumes an aerial form, and powerfully attracts a larger quantity of phlogiston than before; so that in a vaporous state it will dissolve metals, particularly silver and mercury, which in its liquid form it would scarcely be brought to touch. When deplogisticated as much as possible, it attracts phlogiston with prodigious avidity, dissolving all metals by its attraction for their phlogiston, and, uniting the inflammable principle to itself, refines the ordinary form of marine acid. When deplogisticated by means of nitrous acid in aqua regia, it dissolves gold and platinum. On the same principles may we account for its inferiority in power to the other acids.

It has already been observed that the metals differ much in their degrees of solubility, which is owing to the various degrees of force with which they retain their phlogiston. Those called perfect metals effectually resist calcination in the dry way. In this operation, the fire on the one hand, the great cause of the volatility of bodies, strenuously endeavours to expel the phlogiston; on the other hand, the basis of the deplogisticated part of the atmosphere (the acidifying principle of M. Lavoisier, and the principium foribile of Dr. Lavoisier) attracts the calx strongly. Experience, however, shows, that these two forces united, cannot decompose gold, silver, or platinum to any considerable degree. All the other metals yield to these forces when united, but not singly. Iron and zinc retain their inflammable principle so slightly, that any acid immediately acts upon them; but if the other metals be properly prepared for solution by being calcined to a certain degree, the acid will immediately take them up. Any further privation, however, would be injurious, and precipitate what was before dissolved. Thus the nitrous acid, when added to a solution of tin or antimony in marine acid, by its extraordinary attraction for phlogiston carries off such a quantity of it, that the calces of the metals are immediately precipitated.

The various elastic fluids which resemble air, and which are produced in plenty during the dissolution of metals, may be reduced to the following, viz., those excited by the vitriolic, nitrous, and marine acids, fluoric acid, vinegar, alkaline salts, and hepar sulphuris.

Pure vitriolic acid exposed to a violent heat, is indeed resolved into vapours, but of such a nature, that when the heat is gone, they condense again into an acid liquor of the same nature as before. But if any substance be added which contains phlogiston in a separable state, an elastic fluid is produced by means of fire, which is scarcely condensible by the most extreme cold, unless it comes in contact with water. This is called the volatile sulphurous acid, or vitriolic acid air, which may be totally absorbed by water. In this case the bond of union betwixt it and the phlogiston is so weak, that the latter soon flies off totally, and common vitriolic acid is regenerated.

The nitrous acid undergoes a similar change in a more obvious manner. Let a piece of silver, for instance, be put into a dilute nitrous acid, and the surface of the metal will instantly be covered with innumerable bubbles, which rising to the top of the liquor, there burst; and if collected, are found to be nitrous air. The nitrous acid saturates itself with phlogiston more completely than the vitriolic; therefore does not unite with the elastic fluid produced, or nitrous air, does not unite with water, and scarce retains any vestige of an acid water nature. The vitriolic acid, however, differs from the nitrous in this respect, that the phlogiston is absorbed by the latter even beyond the point necessary to obliterate its acid nature. In proof of this, our author adduces the decomposition of hepatic by means of nitrous air.

The marine acid exhibits different phenomena. It naturally contains phlogiston, and therefore can by its means be resolved into a kind of air somewhat similar to that produced by the vitriolic acid when artificially united to the same principle, and which has the same property, viz., that of remaining permanently elastic as long as it is kept from the contact of water. But as the acid we speak of naturally contains phlogiston, there is no necessity of adding more to produce this effect. In the mean time, the marine as well as nitrous air, when in its expanded state, attracts phlogiston, and that with wonderful avidity.

When the marine acid is deplogisticated, it yields another elastic fluid of a reddish brown colour, having tincted an odour like that of warm aqua regia. This does not unite with water, or only in very small quantity; and by the addition of a proper proportion of phlogiston may be reduced again to common marine acid. It is said that the marine acid may be deplogisticated by lead as well as by manganese, the nitrous acid, and arsenic.

The fluoric acid abounds with phlogiston, and therefore may, without any adventitious matter, be reduced acid to an elastic fluid. This air is easily distinguished from all others by its corrosion of glass whilst hot.

Vinegar also contains phlogiston; and for that reason, when well deplogisticated, may be reduced without addition into a permanently elastic fluid, called acetic air.

All these fluids seem to be nothing else, according to Mr Bergman, than the acids themselves expanded by phlogiston. "Perhaps (says he) the matter of heat and heat also enters their composition." The experiments lately made on these subjects, however, have put it beyond all doubt, that the expansive principle is not phlogiston but heat; nevertheless, it seems highly provable, that these elastic fluids do really consist of the acid united to phlogiston, and expanded by heat. This is also the case with the caustic volatile alkali, now called alkaline air.

In the hepatic air, it has been shown by Mr Bergmann, that sulphur exists which contains phlogiston; and exists in there is little reason to doubt that the expansive hepatic air power here is the same as in other cases. See Hepatic Air.

The heat generated during the solution of metals is by Mr Bergman supposed to be owing to the matter of heat which had been fixed in the metals; but it may with much more reason be supposed to proceed from the acid. Dr Black has demonstrated, that heat is universally the principle of fluidity; and all fluids, whether acid or not, are found to contain a great proportion of it. It is not probable that solids, even the most inflammable, contain an equal quantity; for it is always observed, that bodies in becoming fluid absorb heat, and throw it out again on becoming solid. Acids in all probability contain a much greater quantity than what is necessary to their fluidity; for we see that the nitrous acid, when poured upon snow, parts with as much heat as is necessary to dissolve the snow, at the same time that it still retains its fluidity. The case is not so with common salt, which is a solid: for though, in a mixture of salt and snow, the latter absorbs as much heat from the salt as is necessary for its own liquefaction; yet the salt could not be held in solution by a liquid of this temperature, were it not that an additional quantity is perpetually absorbed from the adjacent bodies, particularly the atmosphere. But were it possible to prevent this adventitious increase of heat, there is not the least reason to believe that the salt would be dissolved; for the strongest brine, when reduced to the temperature of 0° of Fahrenheit, is decomposed, the salt falling to the bottom in powder, and the water being converted into ice. Add to this also, that the cold produced by spirit of nitre and snow is much more intense than that produced by common salt and snow; which undoubtedly shows, that a solid does not readily part with as much heat as a fluid, and consequently cannot be supposed to contain as much. The solution of metals in acids also demonstrates, that the solid substance has not parted with heat, but absorbed it; for as soon as the solution becomes solid again, i.e., when it crystallizes, the temperature becomes higher than before.

The calces of metals have not that quantity of phlogiston that is necessary for their metallic state, but yet are not entirely destitute of it; therefore, in their solution, scarce any elastic fluid is generated, unless the fire be continued after efflorescence. Such as contain aerial acid, discharge it immediately in the same form as they had received it. It is remarkable, that Dr Priestley mentions a calx of lead, which, with the acid of phosphorus, produces an inflammable air. By means of the nitrous acid and evaporation to dryness, a pure air is produced. Sometimes a small portion of vitriolic acid air is obtained by means of a proper degree of fire from vitriolic acid, but a far greater quantity of pure air.

The solutions made by the menstrua above mentioned, contain a metallic calx intimately united with the acid, the quantity of phlogiston left being various according to the difference of the menstrua and of the temperature; but the performance of the operation either with or without intense heat, frequently occasions a remarkable difference. That metals are less calcined by the marine than by the nitrous acid, appears from pouring concentrated nitrous acid on tin or antimony; but the difference, if it actually does take place, is less visible in other metals.

Some modern chemists have denied this calcination of metals by solution. They have insisted, that the perfect metals ought to be excepted, as they do not yield to the most intense fire. On this subject, however, it may be observed, 1. That during their solution nitrous air is always generated, and that of a very perfect kind, which cannot happen without phlogiston; but in this case there is nothing present which can yield phlogiston except the metals. Therefore, for belief,

2. The metals, when precipitated from their menstrua by fixed alkalis, both with respect to their external calcination by appearance and internal properties, appear to be calcinated. Thus the precipitate of gold refuses to unite with mercury, and may be dissolved by marine acid and other simple menstrua, and that without the production of any elastic fluid. 3. Glases may be stained by these calces; but no metal in its perfect state can be taken up by glases.

The common objection is, that the calces of the Why the perfect metals may be reduced by heat alone without calces of the addition of charcoal. Many theories have been invented to solve this phenomenon. Some have supposed, that the matter of heat and light are the same produced with the phlogiston, and that thus the calces are reduced in the same manner as by charcoal or other substances usually termed phlogistic. But in this case we ought to find the calces of the imperfect metals also reduced by a long continuance of heat, as well as the more perfect; which, however, has never yet been known to take place. Some, among whose number is Dr Lewis, have imagined, that the porosity of the vessels, particularly those made of earthen ware, may be such as to admit the passage of phlogistic vapours through them; and he instances the revival of globules of lead in the middle of pieces of glass upwards of an inch in thickness, and that where there was not the least appearance of a crack. But from an experiment of Mr Kirwan's, to be afterwards related, it is much more probable that the reduction is effected by means of the phlogiston contained in one part of the calx attracted by another; by which means the latter is reduced to a perfect metal, while the former becomes somewhat more dephlogisticated. In consequence of this it appears, that the calx of the perfect metals is never totally reduced: for if the operation be performed in a glass retort, the bottom of it is always stained; which indicates the existence of a calx, in however little quantity.

The following fact, Mr Bergman says, has been Difficulty proposed to him as an inextricable dilemma. "Silver concerning cannot amalgamate with mercury except when in its the amal-metallic state, yet both saluted and nitrated silver are of silver taken up by mercury; it is therefore not calcined by solved by the acids, but adheres to them in its metallic form." Bergman. This, however, may be easily solved in the following manner. It is well known that the calx of copper, dissolved in the vitriolic acid, is precipitated in its metallic form on the addition of iron, and that by means of a double elective attraction; for the iron, dissolving in the acid, would form an inflammable air by its phlogiston, were not the copper present which takes it up, and thereby becomes insoluble as long as it retains it; but mercury has a stronger attraction for acids than silver: if therefore saluted or nitrated silver be triturated with mercury, the silver must be precipitated in a metallic state, and the mercury be calcined by being dissolved. This also takes place, provided there be moisture sufficient to foster the elective attractions. The acids frequently occasion precipitates, and that for various reasons. By means of elective attraction, mercury, silver, and lead, are taken from the nitrous acid by the addition of the marine or vitriolic. These acids form with the metals new compounds which are difficult of solution in water; they are therefore precipitated in greater or lesser quantity according to circumstances. The nitrous acid is capable of decomposing saluted tin and antimony by deplogilicating the calx of the metals too much; for when these are too much calcined, they cannot be dissolved in any menstruum, as has been already observed.

Metallic solutions are sometimes disturbed by the neutral salts formed by an union of alkalies with acids. Those which contain the vitriolic or marine acids decompose solutions of silver, mercury, or lead, in nitrous acid, and precipitate the metals. By forming a continuous triple combination, the vegetable as well as the volatile alkali, though saturated with vitriolic, nitrous, or marine acid, precipitate platina from aqua-regia; but when the basis is mineral alkali, the salt has no power of this kind. Some metallic salts can decompose some metallic salts, and precipitate their bases; which may happen whether the acid be different in the two salts or not.

Solution of gold affords an example of each of these cases. This is precipitated by martial vitriol; why the reason of which will appear from considering the nature of the precipitate: for this, when well washed, precipitated and dried, not only shows many shining gold-coloured particles, but also unites with mercury by trituration, dissolves in aqua-regia, but not in marine acid alone, together with other circumstances which evince a complete refucification of the gold. Martial vitriol, in its ordinary state, contains phlogiston, but very loosely adhering; so that the calx of gold may easily take it from the solution to supply the loss it had sustained during the solution. That this is the true foundation of the process, appears also from the following circumstances, that the weight of the gold is exactly recovered, and that deplogilicated vitriol will not precipitate this phlogistic metal. The reason that the surrounding aqua-regia leaves this precipitate untouched is, that the menstruum is diluted and weakened by a large quantity of water; for upon boiling it gently, so as to expel part of the water, the menstruum recovers its solvent power, and takes up the precipitate again.

It is somewhat more difficult to explain the reason why the solution of gold in aqua-regia should be precipitated by a solution of tin in the same menstruum. Here Mr Bergman first supposed that the tin had attracted a superabundance of acid, and taken it from the gold; which being therefore destitute of its proper quantity, must fall to the bottom: but on employing a solution containing a superabundant aqua regia, the same precipitation took place. The cause is therefore not in the menstruum. On examining the precipitate itself, we find nothing like the metallic splendor of gold, but that it entirely resembles a calx. It is easily found by its weight, indeed, that it cannot consist entirely of gold; and in fact chemical examination shows that it consists partly of tin. It cannot be dissolved by the marine acid alone, but is easily taken up by the addition of a little nitrous acid. It scarcely unites with mercury by trituration. These properties seem to indicate, that the gold has so far received phlogiston. gifton as to resist the marine acid until it receive the assistance of the nitrous; but its earthly appearance, and difficulty of uniting with mercury, evince that it is not in its complete metallic form. The following therefore, according to our author, seems to be the most easy and rational explanation. The solution of tin necessary for this operation must retain as much phlogiston as it possibly can, in a consistence with solubility. This is dropped into a solution of gold very much diluted; by which means the phlogiston remaining in the tin is more loosened, and of consequence more easily attracted by the gold calx, which is thereby brought to a state approximating to completion, so that it can no longer be retained by the menstruum; and the same happens to the tin, by means of the dephlogistication; they must both therefore fall to the bottom mixed intimately with one another. It is probable, says he, that in this case it is the tin which prevents the matter from uniting with mercury.

The metals precipitate one another after a certain order, which is the same in all acid menstrua. This precipitation is occasioned by a double elective attraction; for the metal to be precipitated exists in the solution in a calcined state; but being reduced by the phlogiston of the precipitant falls to the bottom, while at the same time the precipitant becomes soluble by calcination: but if the precipitant has been calcined so that a part of it being insoluble is mixed with the precipitate, the metallic splendor is wanting, and it puts on an earthy appearance. A pure precipitate is of the same weight with the metal before solution. The mixed precipitates are less frequently met with, yet gold precipitated by tin exhibits one of that kind.

Though the order in which the metals precipitate one another is constant and never inverted, yet there are many anomalous circumstances which occur in the matter. Thus zinc constantly prevails over iron; precipitate one iron over lead; lead over tin; tin over copper; copper over silver; silver over mercury, &c., yet it sometimes happens, that a metal which, according to the general rule, precipitates another in its metallic state from one menstruum, precipitates it from another in form of a calx, and not at all from a third. Thus zinc precipitates iron from marine acid in its metallic state, but from the nitrous only in form of a calx. Tin is precipitated by lead from the marine acid in its metallic state, but is not thrown down from the nitrous acid; and from the acetous is precipitated even by iron and zinc in form of a calx; solution of lead in vinegar is not precipitated by iron.

In Mr Bergman's experiments on this subject he employed the mineral alkali, as the degree of its saturation with fixed air was more constant. When he had occasion for a caustic alkali, he prepared it by a small quantity of burned lime kept in a clothe bottle; and the goodness of it was proved by its occasioning no precipitation in lime water. Phlogisticated alkali, or that by which Prussian blue is prepared, was also made use of. With these he made the following observations. Gold dissolved in aqua regia is precipitated by caustic alkali almost black; by the aerated, yellow, as well as by the phlogisticated, unless some iron be present, which frequently happens; but the whole of the gold is scarce ever precipitated, so that the weight cannot be ascertained.

Neither the caustic nor aerated mineral alkali precipitate one half of platina dissolved in aqua regia; the precipitate is of an orange colour, which on drying becomes brown. An equal proportion of alkali redissolves the precipitate, and the liquor becomes more dark; nay, the precipitation is so imperfect, that the alkalies matter seems to be dissolved even by neutral salts. The phlogisticated alkali does not precipitate the depurated solution, nor even make it turbid, but heightens the colour in the same manner as an excess of alkali.

Solution of silver in nitrous acid lets fall a white precipitate by the aerated alkali; brown by the caustic, and of an obscure yellow. By the nitrous and marine acids it lets fall a white precipitate, which with the former consists of more distinct particles, which grow black more slowly with the light of the sun.

Saluted mercury lets fall a red precipitate, or rather one of a ferruginous colour, by aerated alkali; but of a more yellowish or orange colour by the caustic. Nitrated mercury prepared without heat, yields a ferruginous precipitate with mineral alkali; a black with caustic; and when prepared with heat, it yields to caustic alkali an orange or reddish yellow precipitate. By phlogisticated alkali it is precipitated from all acids of a white colour; but turns of a brownish yellow when dry. Saluted mercury is very sparingly precipitated by this alkali. The precipitate by phlogisticated alkali is again dissolved, if too much of the precipitant be made use of.—Corrosive sublimate must be very cautiously precipitated by caustic, as well as aerated fixed alkali; for the part separated may again be dissolved by a large quantity of water. When too much alkali is used, a new compound arises of a peculiar nature.

Solution of lead in spirit of nitre is precipitated down white by aerated, caustic, or phlogisticated alkali; by using too much alkali, the precipitate by the phlogisticated kind is dissolved with a brownish yellow colour. Vitriol of lead and solution of lead in marine acid are precipitated white.

Blue solution of copper in spirit of nitre is precipitated by aerated fixed alkali; by the caustic of a greyish brown, which grows reddish by age. By phlogisticated alkali copper is precipitated of a greenish colour, which grows afterwards of a brownish red, and upon evaporation almost black. The aerial acid takes up a small quantity of copper during the precipitation, which is again deposited by the heat of boiling.

Aerated fixed alkali precipitates iron of a green colour from vitriolic and marine acid; but the precipitate becomes of a brownish yellow, especially on evaporation; with the caustic alkali it approaches more to black. In the precipitation some part is held in solution by the aerial acid, when the mild alkali is used. With phlogisticated alkali a Prussian blue is formed.

Tin is precipitated of a white colour by every alkaline salt, even by the phlogisticated kind; but at length some blue particles appear in the mixture: so that the whole, when collected and dried, appears of a light blue colour. That these blue particles are occasioned by iron appears by calcination; for they become ferru- Theory.

Solution and Precipitation.

Bismuth is thrown down of a fine white by water and alkalies, particularly the former; phlogisticated alkali throws down a yellow powder, which being mixed with blue particles occasioned by iron, at length appears green. This yellow sediment easily dissolves in nitrous acid.

Nickel is precipitated of a whitish green by fixed alkalies; by the phlogisticated alkali of a yellow; and by evaporation it is condensed into a dark brown mass.

Arsenic dissolved in acids, which prevent too great dephtogitication, may, to a certain degree, be precipitated white by the fixed alkali, even when phlogisticated, but the sediment is found soluble in water; yet nitrous acid, either alone, or joined with the marine, generally dephtogiticates the arsenical acid, which thereby becomes unfit for separation. Arsenic dissolved in marine acid, with the assistance of a little nitrous acid, deposited a white sediment on the addition of a large quantity of phlogisticated alkali. The sediment was mixed with Prussian blue. This was dissolved in water, and freed by frequent filtration from the blue particles; and at length, on evaporating to dryness, yielded a semipellucid mass.

Cobalt dissolved in acids is thrown down by fixed alkali, whether aerated or caustic, of a reddish blue, which grows darker on evaporation, especially when the former alkali has been used. Phlogisticated alkali throws down a powder of almost the same colour, which, upon evaporation, becomes of a reddish brown.

Zinc is precipitated white by aerated and caustic fixed alkalies, as also by the phlogisticated alkali; but this last becomes of a citron colour on evaporation: a small portion of aerial acid may easily escape during the precipitation.

Antimony is precipitated white by alkalies. When the phlogisticated alkali is used, some blue particles are almost always precipitated at the same time, though the regulus had been prepared without any iron. This operation should be cautiously conducted, lest some part be taken up by the alkaline salt.

Manganese procured by reduction from common magnesia nigra, generally renders menstruum brown, and with aerated alkali yields a yellowish brown sediment; with the caustic, one still darker; with the phlogisticated, first a blue, then a white, powder is separated, the mixture of which renders the mass a black green. To obtain a pure and white calx of manganese, we must dissolve in pure vinegar the precipitate thrown down by caustic alkali; for there still remains a quantity of iron which is taken up by the aerial acid. This acetous solution contains little or nothing of iron. That metal may also at first be separated by a small quantity of volatile alkali.

The common solution of the regulus is not perfectly precipitated by the aerated alkali; and upon evaporating the remaining liquor spontaneously to dryness, grains of a metallic splendour, and not unlike copper, are deposited on the glass. The nitrous acid attracts these readily, though they are only partially dissolved by it; but on the addition of zinc, nothing falls besides the manganese, though at first it is a little reddish. With phlogisticated alkali, we obtain a yellow precipitate like pure manganese, provided the solution has deposited the iron when too much dephtogiticated by age. But the new solution yields a precipitate almost like that which is obtained from common regulus. The yellow sediment may be dissolved in water.

The following is Mr Bergman's table of the quantities of precipitate of different metals, thrown down from various menstrua by the different alkalies. "On comparing the weights (says he), a question occurs in the concerning the cause of such enormous differences; weight of and it is plain, that this cause must be sought for in the precipitates themselves.—The fixed alkali saturated with aerial acid, when added to the solution, is taken up by the more powerful menstruum; and the weaker is of course expelled, and is absorbed by the calx as it falls, in greater or lesser quantity according to circumstances. That this is actually the case is easily demonstrated:—Let a bottle containing a quantity of nitrous acid be accurately weighed. Let there be put into it, for instance, 132 parts of lead precipitated by aerated alkali; and not only an effervescence will be observed, which continues until the very last particle is dissolved, but when the solution is finished, a deficiency of weight is discovered, which amounts nearly to 21, and which is undoubtedly owing to the extrication of aerial acid. But 132 - 21 = 111; a weight which still considerably exceeds that of the metal. Upon dilution nearly eight of water are discovered. There yet remain therefore three, which by violent heat are increased by seven; for 132 of the calx well calcined, yield 110. The whole increment of weight then does not depend on the water and aerial acid. The same thing is evinced by considering the precipitate of lead by the caustic alkali; in which case there can be no aerial acid, nor does any effervescence accompany the solution. If we suppose the quantity of water equal in both cases, yet even on this supposition the whole excess of weight is not accounted for; for 116 - 8 = 108. It is therefore probable, that the matter of heat is attached to the calx (A).—In proof of this opinion, and that caustic alkalies contain the matter of heat, our author adduces several arguments, of which the following is the strongest.—"Let the heat occasioned by the mixture of any acid and in favour of caustic alkali be determined by a thermometer; let the then an equal portion of the same menstruum be saturated with a metal; afterwards, on the addition of an equal quantity of caustic alkali, it will be found, either that no heat is generated, or a degree very much less than before.—Some of the matter of heat therefore is taken up and fixed, which also generally makes the colours of the precipitates more obscure; and in distillation with sal-ammoniac, communicates to the volatile alkali the quantity that had been taken away."

In this instance also, however, our author seems to have been deceived. It has already been observed, that in all solutions generating heat, it most probably comes from the fluid. Acids contain a quantity sufficient.

(A) This increase of weight is with more probability to be ascribed to a remainder of the acid. Chemistry

Solution and Precipitation

Sufficient not only for their own fluidity, but for rendering solid bodies fluid also. After they have dissolved the metal, however, this superfluous quantity is employed; and when the caustic alkali is added, if in a solid form, it is again employed in giving fluidity to the alkali; or if the alkali be already dissolved, the increased quantity of fluid makes the heat extricated less perceptible.

"What has been said of lead (continues our author), is also true of the other metals, a few excepted, which seem to take up little or no aerial acid; such are tin, antimony, gold and platinum.—But some precipitates retain also a quantity of the menstruum. Thus, corrosive mercury, precipitated by aerated alkali, retains a portion of marine acid, which cannot be washed off by water; but, by caustic alkali, the precipitate may be obtained, either free of the acid altogether, or in a great measure. In this case, as in many others, the aerial acid seems to generate a triple salt, scarce at all soluble. The presence of the marine acid is easily discovered by solution of silver in nitrous acid, if the menstruum has been pure. Hence we observe another difference in mercury precipitated from marine acid, according as we employ the aerated or caustic alkali; the latter, well washed, and put into volatile alkali, is scarcely changed in colour; but the former instantly grows white, generating a species of sal-ammoniac, but containing so little marine acid as not to be easily soluble in water. The calces which retain any of their former menstruum, generally give over on distillation a small portion of sublimate. The mercurial calx just mentioned, exposed to a sufficient degree of heat, is partly reduced to crude mercury, partly to mercurius dulcis, by means of its remaining marine acid. This mercurius dulcis did not exist in the precipitate; for in that case it would be easily discovered by acids in which it is not soluble, and would grow black with caustic alkali, neither of which take place, so that it must be generated during the distillation."

Mr Bergman concludes his dissertation, with an enumeration of the advantages resulting from the careful examination of metallic precipitates.—These are,

1. That thus the theory of the operation will be more perfectly understood. 2. We may discover the more useful and remarkable properties. 3. A foundation is thereby laid for effaying in the most way, from the bare knowledge of the weights. "It may be objected (says he), that the doctrine of the weights is very fallacious; that they vary in different precipitates; that by imperfect precipitation something remains in the liquor; and that sometimes extraneous matters remain in them. All this is true; but if the mode of operation be the same, the results of the experiments will be equally constant. Thus, let us suppose that a certain quantity of metal \(a\) precipitated in a certain manner, makes a weight \(b\); if that same manner be exactly employed, we may fairly conclude, that a quantity of precipitate \(nb\), occurring in any case, is correspondent to a quantity of perfect metal \(na\); though, in the fundamental experiment, the precipitation is either incomplete, or some extraneous matter may be present.

4. The nature of metals is thus illustrated. Platinum, nickel, cobalt, and manganese, are supposed by some to derive their origin from a mixture of other metals. But if iron necessarily enters into the composition of platinum, when the latter is dissolved in aqua regia, it ought to yield a Prussian blue on the addition of phlogisticated alkali; which indeed is the case when common platinum is employed, but not with that which is well depurated.

In like manner, if iron, adhering very obstinately to platinum is nickel, formed a great part of the latter, the precipitates obtained from it by alkalies could not differ greatly from martial precipitates so much as they do in colour, weight, and other properties. The same holds true for regulus of cobalt and manganese. The regulus obtained from lus of the latter contains about 0.08% of iron, which affects kel the mixture in the following manner. An hundred Cobalt or pounds dissolved in an acid menstruum, yields, by manganese treatment with phlogisticated alkali, a powder consisting partly of blue, partly of brownish yellow particles, Quantity equal in weight to 150 pounds; but eight pounds of tarate of iron yield 48 of Prussian blue, nearly \( \frac{1}{2} \) of the whole mass of precipitate: whence it follows, that 100 parts of pure from manganese yield to phlogisticated alkali scarcely 111; hence by i.e. nearly six times less than an equal weight of iron, cased alkali.

Lastly, by this method of examining precipitates, it may perhaps be possible to determine the unequal quantities of phlogiston in different metals; for a given weight of precipitating metal does not yield an equal weight of precipitate: thus, for instance, copper is capable of precipitating from nitrous acid four times its weight of silver."

| Precipitated by | Yielded Table of different dry precip. precip. | |----------------|---------------------------------| | Gold, | aerated mineral alkali - 106 | | | caustic - 110 | | Platina, | aerated mineral alkali - 34 | | | caustic - 36 | | Silver, | aerated mineral alkali - 129 | | | caustic - 112 | | Mercury, | aerated mineral alkali - 134 | | | caustic - 110 | | Lead, | aerated mineral alkali - 132 | | | caustic - 116 | | Copper, | aerated mineral alkali - 143 | | | caustic - 131 | | Iron, | aerated mineral alkali - 158 | | | caustic - 170 | | Tin, | aerated mineral alkali - 160 | | | caustic - 130 | | Bismuth, | aerated mineral alkali - 125 | | | caustic - 125 | | Nickel, | aerated mineral alkali - 135 | | | caustic - 128 | | Arsenic, | aerated mineral alkali - 250 | | | caustic - |

Arsenic, Mr Kirwan has made a great number of experiments on the attractive powers of the mineral acids to various substances, and greatly illustrated the operations both of solution and precipitation. Chemical attraction, he observes, "is that power by which the invisible particles of different bodies intermix and unite with each other so intimately, as to be inseparable by mere mechanical means." Thus it differs from the attraction of cohesion, as well as from that of magnetism and electricity, as not acting with the indifference observed to take place in these powers, but causing a body already united to another to quit that and unite with a third; whence it is called elective attraction. Hence attraction of cohesion often takes place betwixt bodies that have no chemical attraction for each other; as for instance, bismuth and regulus of cobalt, which cannot be made to unite together by fusion, though they cohere with each other so strongly, that they cannot be separated but by the blow of a hammer.

To determine the degrees of attraction betwixt different substances, M. Geoffroy laid it down as a general rule, that when two substances are united, and either quits the other to unite with a third, that which thus unites to the third must be said to have a greater affinity to it than to the substance it has quitted. In many cases, however, the seemingly single decomposition is in truth a double one. Thus, when the vitriolic acid expels the air from a fixed alkali, it does not necessarily follow, that the acid is more attracted by the alkali than the fixed air; for here though the latter resigns its place to the acid, yet the acid gives out its fire to the air; whence a decomposition might take place, even though the attractive powers of both the vitriolic and aerial acid to the alkali were equal.

To attain any certainty in this matter, therefore, it is necessary to determine the quantity and force of each of the attractive powers, and denote it by numbers. The necessity of this has been observed by Mr Morveau and Mr Wenzel, who have both proposed methods for answering the purpose; but Mr Kirwan has showed that both are defective: and he tells us, that the discovery of the quantity of real acid in each of the mineral acid liquors, with the proportion of real acid taken up by a given quantity of each basis at the point of saturation, led him unexpectedly to what seems the true method of investigating the quantity of attraction which each acid bears to the several bases to which it is capable of uniting: "for it was impossible (says he) not to perceive, 1. That the quantity of real acid necessary to saturate a given weight of each basis is inversely as the affinity of each basis to such acid. 2. That the quantity of each basis requisite to saturate a given quantity of each acid is directly as the affinity of such acid to each basis. Thus 100 grains of each of the acids require for their saturation a greater quantity of fixed alkali than of calcareous earths, more of this earth than of volatile alkali, more of this alkali than of magnesia, and more of magnetia than of earth of alum.

"If an acid be united to less of any basis than is requisite for its saturation, its affinity to the deficient part of its basis is as the ratio which that deficient part bears to the whole of what the acid can saturate. Thus, if 100 grains of vitriolic acid, which can saturate 110 of calcareous earth, be united only to 55, its affinity to the deficient 55 parts should be estimated one half of its whole affinity; but its affinity to the retained part is as its whole affinity."

To explain the decompositions in which these acids are concerned, we must consider, first, the powers explaining which resist any decomposition, and tend to keep the bodies in their present state; and, secondly, the powers effected by which tend to effect a decomposition and new union; acids alone, the former our author calls quiescent affinities, the latter divellent. A decomposition will therefore always take place when the sum of the divellent affinities is greater than the quiescent; and, on the contrary, no decomposition will happen when the sum of the quiescent affinities is greater than that of the divellent. All we have to do therefore is to compare the sums of each of these powers. The method our author takes to compare the affinities together is by the following table; in which the quantity of alkali, earth, &c. saturated by 100 grains of each of the mineral acids, is stated.

| Veg. fixed Mineral | Calc. Vol. Mag. Earth of Quantity | |-------------------|----------------------------------| | Vitriolic acid | 215 165 110 90 80 75 ken up by various bases | | Nitrous acid | 215 165 96 87 75 65 fes. | | Marine acid | 215 158 89 79 71 55 |

These numbers he considers as adequate expressions of the quantity of each of the affinities. Thus the affinity of the vitriolic acid to fixed vegetable alkali is to the affinity with which it adheres to calcareous earth as 215 to 110; and to that which the nitrous acid bears to calcareous earth as 215 to 96, &c. Hence we sum up the powers of affinity betwixt any number of the different substances, and account for their decompositions, as in the following example of the double decomposition, which takes place when a solution of each vitriolated tartar and solution of lime or chalk in nitrous acid are mixed together.

**Quiescent Affinities**

- Vitriolic acid to vegetable fixed alkali, 215 - Nitrous acid to calcareous earth, 96

Sum of quiescent affinities = 311

**Divellent Affinities**

- Vitriolic acid to calcareous earth, 110 - Nitrous acid to vegetable alkali, 215

Sum of divellent affinities = 325

Hence we see that a double decomposition must ensue. The same will be produced, if instead of vitriolated tartar we make use of Glauber's salt; for the sum of the the quiescent affinities is 261, of the divellent 275; with vitriolic ammoniac the sum of the quiescent is 186, of the divellent 195, &c. In mixing vitriolated tartar with solution of magnesia in nitrous or marine acids, a double decomposition takes place though invisibly, as the vitriolic Epsom salt is very soluble in water, and therefore cannot be precipitated like selenite. In the former case the sum of the quiescent powers is 290, of the divellent 295; in the second 286 and 295.

Other decompositions take place in the same manner; and from all the facts which our author had occasion to observe, he concludes, that the quantity of each affinity, as determined in the above table, coincides exactly with experience; and that these decompositions are perfectly consistent with the superior affinity which has been hitherto observed in the vitriolic and nitrous acids with fixed alkalies over the calcareous earths; nor do they infringe in the least the known laws of affinity, as has been insinuated by some chemists. One fact only, mentioned in Dr Crell's Journal, seems to be repugnant to what is here advanced; and that is, that if solutions of one part of alum and two of common salt be mixed together, evaporated, and set to crystallize, a Glauber's salt will be formed; though, in this case, the sum of the quiescent affinities is 233, and that of the divellent only 223. Mr Kirwan repeated this experiment without success; and Dr Crell himself owns that it will not succeed but in the most intense cold. If it does succeed at all, he says the decomposition must arise from a large excess of acid in the alum, which acted upon and decomposed the common salt; and this explanation is confirmed by the small proportion of Glauber's salt said to be obtained by this process; for from 30 lb. of common salt and 16 of alum, only 15 lb. of Glauber's salt were produced; whereas, if the whole of the alum had been decomposed, there should have been formed, according to Mr Kirwan's computation of the quantity of acid in the different salts, 29½ lb, or, according to Mr Bergman's, 22 lb. of Glauber's salt.

In some cases, the neutral salts have a power of uniting, without any decomposition, or with only a very small one, to a third substance; thus forming triple salts, and sometimes quadruple; which often causes anomalies that have not yet been sufficiently investigated. Volatile alkalies in particular are possessed of the power of uniting with neutral salts in this manner. Hence they seem to precipitate magnesia from Epsom salt, even when perfectly caustic; but this is owing to their combination with that salt, and forming a triple one, which is insoluble in water.

It seems extraordinary that, according to Mr Kirwan's table, the three mineral acids should have the same affinity to vegetable fixed alkalies, when it is well known that the vitriolic will expel either of the other two from an alkaline basis. In explication of this, Mr Kirwan observes, that nitre is decomposed by the marine acid; and that Glauber's salt and vitriolic ammoniac are decomposed by that of nitre; and that these salts, as well as cubic nitre and nitrous ammoniac, are decomposed by the marine acid.

Mr Kirwan is of opinion, that these decompositions are the effect of a double affinity, or at least of compound forces. He suspected that they arose from the different capacities of the acids for elementary fire; and to determine this matter, he made the following experiments, in which the decompositions were not discovered by crystallization, but by tests.

1. Having procured a quantity of each of the three mineral acids containing the same proportion of realments to acid, and reduced them to the temperature of 88° of this by the Fahrenheit, 100 grains of vitriolic acid, containing various degrees of real acid, was projected upon 480 grains of oil of tartar at the same temperature, by which the thermometer was raised to 138°.

2. An hundred grains of spirit of nitre, containing also 26.6, projected on 480 grains of oil of tartar, produced only 120° of heat.

3. An hundred grains of spirit of salt, the specific gravity of which was 1220, and which contained the usual proportion of real acid, raised the thermometer from 69 to 129.

"Hence (says he) it follows, that the vitriolic acid Vitriolic contains more specific fire, or at least gives out more acid consequently with fixed alkalies, than either the nitrous fire or marine; and therefore when the vitriolic acid comes into contact with either nitre or salt of Sylvius, its fire and vapours into these acids, which are thereby rarefied to a fine great degree, and are thus expelled from their alkaline basis, which is then seized on by the vitriolic."—Difficulty On this, however, it is obvious to remark, that, according to Mr Kirwan's explanation, the marine acid, as giving out more specific heat, ought to expel the nitrous from an alkaline basis; which, however, is not the case. Something else, therefore, besides the mere quantity of specific heat, must here be taken into consideration. Mr Kirwan, however, goes on to prove the truth of his theory by the following experiments.

4. To 400 grains of vitriolic acid, whose specific gravity was 1.362, sixty grains of nitre were added; on the nitrous which the thermometer fell from 68° to 60°. During the time of this deflection, the nitrous acid was not expelled; for some filings of copper, put into the mixture, were not acted upon in the least; but in five minutes afterwards they visibly effervesced, which showed that the nitrous acid began to be expelled; for the vitriolic acid does not act upon copper but by a boiling heat.

5. Sixty grains of nitre were put to 400 of oil of vitriol, whose specific gravity was 1.870; and the thermometer instantly rose from 68° to 105°, and the nitrous acid was expelled in a visible fume.—These experiments (says Mr Kirwan) prove, 1. That neutral salts are not decomposed by mere solution in an acid different from their own. 2. That the nitrous acid, being converted into vapour, had imbibed a large quantity of fire. But as the vitriolic acid, in both these experiments, was used in much larger quantities than was necessary to saturate the alkali of the dry nitre, sixty grains of the latter were put into 64 of the above mentioned dilute spirit of vitriol, which contained the same quantity of real vitriolic acid that the 60 grains of nitre did of the nitrous; with the addition of 40 grains of water and a few copper-filings. In less than two hours the copper was acted upon, and consequently the nitrous acid was expelled.

6. To 400 grains of oil of vitriol, of the specific gravity of 1.870, 100 grains of common salt were added. An effervescence immediately ensued, and and the marine acid rose in white vapours. A thermometer held in the liquor rose only 4 degrees, but in the froth it ascended to 10°, and fell again upon being replaced in the liquor. Hence Mr Kirwan concludes, that the vitriolic acid gives out its fire to the marine; and that this latter received more than it could absorb even in the state of vapour, and therefore communicated heat to the contiguous liquor. It appears to him also, that the nitrous and marine acids receive fire from the vitriolic, or are thrown into a vaporous state, or at least rarefied to such a degree as to be expelled from their alkaline basis, though their affinity with that basis may be equally strong with the vitriolic.

7. To ascertain the manner in which vitriolated tartar and Glauber's salt are decomposed by spirit of nitre, 60 grains of powdered tartar of vitriol were put into 400 of nitrous acid, whose specific gravity was 1.355, and which contained about 105 grains of real acid. The thermometer was not affected by the mixture; but in 24 hours the vitriolic acid was in part disengaged, as appeared by the acid mixture acting upon regulus of antimony, which neither pure vitriolic nor pure nitrous acid will do by themselves. On putting the same quantity of vitriolated tartar into 400 grains of spirit of nitre whose specific gravity was 1.478, the thermometer rose from 67° to 79°; the vitriolated tartar was quickly dissolved, and the regulus of antimony showed that the vitriolic acid was disengaged. Hence it appeared, that the nitrous acid, having the same affinity with the basis of vitriolated tartar as the vitriolic, but giving out, during the solution, more fire than was necessary to perform the solution, the vitriolic, receiving this fire, was disengaged: for as it cannot unite to alkalis without giving out fire; so when it receives back that fire, it must quit them. The reason why the nitrous acid, which specifically contains less fire than the vitriolic, gives out so much is, that its quantity in both these experiments is far greater than that of the vitriolic; it being in the first as 105 to 17, and in the last as 158 to 17.

8. To 60 grains of spirit of nitre, whose specific gravity was 1.355, Mr Kirwan added 1000 grains of water; and into this dilute acid put 60 grains of vitriolated tartar, containing exactly the same quantity of real acid that the 60 grains of nitrous acid did. In eight days the vitriolated tartar was almost entirely dissolved, and without any sign of its decomposition; and no nitre was found upon evaporating the liquor. Hence he concludes, that the nitrous acid can never decompose vitriolated tartar, without the assistance of heat, but when its quantity is so great that it contains considerably more fire, and by the act of solution is determined to give out this fire. This fact is also decomposed, in similar circumstances, by the marine acid; though still more slowly and with more difficulty than by the nitrous, as appears by the following experiments.

9. Into 400 grains of spirit of salt, whose specific gravity was 1.220, were put 60 grains of vitriolated tartar. The thermometer was not affected in the least, and the salt dissolved very slowly. Some pulverized bismuth was added to try whether the vitriolic acid was disengaged; and in 12 hours part of it was dissolved, so that it could not be precipitated by water. This showed, that part of the vitriolic acid was dislodged; for this semi-metal cannot be kept in solution when much diluted with water, excepting by a mixture of marine and vitriolic acids.

In this experiment the quantity of marine acid was much greater than that of the vitriolic; and therefore it was capable of dislodging it. This circumstance alone, however, is not sufficient; the acid must be disposed to give out by solution that quantity of fire which it is necessary the vitriolic should receive in order to its quitting the basis to which it is united; and therefore when Mr Cornette added two ounces of spirit of salt to half an ounce of vitriolated tartar already dissolved in water, no decomposition took place. The reason of this was, that as the vitriolated tartar was already dissolved, no cold nor heat was generated by the mixture; and therefore the spirit of salt could not give out any fire. Glauber's salt is more easily decomposed by marine acid than vitriolated tartar, on account of its being more easily soluble in spirit of salt; and likewise because its alkaline basis takes up an equal quantity of both acids: consequently the marine gives out more fire in uniting to the basis of Glauber's salt than on being united to that of vitriolated tartar. Vitriolic ammonia is also decomposed by means of marine acid; but in all these cases, the quantity of marine acid must greatly exceed that of the vitriolic contained in the salt to be decomposed; and it must be remarked, that according to the observations of Mr Bergman, the decomposition of Glauber's salt or vitriolic ammonia by this acid is never complete.

On the same principles the marine acid decomposes tartar which have the nitrous acid for their basis. Mr Cornette found, that cubic nitre was more easily decomposed by it than that which has vegetable alkaline salts for its basis. Accordingly, during the solution of prismatic nitre, only three degrees of cold were produced; but fix by the solution of cubic nitre; which shows that the spirit of salt gave out more fire in the latter case than in the former; and its quantity must always be greater than that of the nitrous acid contained in the mineral alkaline basis; because this basis requires for its saturation more of the marine than of the nitrous acid. The nitrous acid, however, in its turn decomposes salt of Sylvius and common salt; but it must always be in greater quantity than the marine acid to produce that effect.

10. Sixty grains of common salt being added to 400 of colourless spirit of nitre, whose specific gravity was 1.478, the mixture quickly effervesced and grew red, yet the thermometer rose but two degrees; which showed that the marine acid had absorbed the greater part of the fire given out by that of nitre; the decomposition was likewise hastened by the superior affinity of the nitrous acid to the alkaline basis of the sea-falt; hence the decomposition of sea-falt by means of nitre takes place without any solution; but spirit of salt will not decompose cubic nitre until it has first dissolved it. This mutual expulsion of the nitrous and marine acids by each other, is the reason why aqua-regia may be made by adding nitre or nitrous ammonia to spirit of salt, as well as by adding common salt or salt ammonia to spirit of nitre.

Selenite cannot be decomposed either by nitrous or marine marine acid; because it cannot be dissolved in either without the assistance of foreign heat. It must likewise be observed, that in all decompositions of this kind, when the liquor has been evaporated to a certain degree, the vitriolic acid expels in its turn the nitrous or marine acid to which it had already yielded its basis. The reason of this is, that the free part of the weaker acids being evaporated, the neutral salts begin to crystallize, and then giving out heat, the vitriolic absorbs it; and thus reacting upon them, expels them from the alkali or earth to which they are united.

Mr Kirwan found much more difficulty in determining the attractive powers of the different acids to the metals than to alkaline salts or earths. Some of the difficulties met with in this case arose from the nature of metallic substances themselves. Their calces when formed by fire always contain a quantity of air, which cannot be extracted from them without great difficulty, and is very soon re-absorbed; and if formed by solution, they as constantly retain a part of their solvent or precipitant; so that the precise weight of the metallic part can scarce be discovered. Our author, therefore, and because metallic calces are generally insoluble in acids, chose to have the metals in their perfect state: and even here they must lose a part of their phlogiston before they can be dissolved in acids, and a considerable part remains in the solution of the acid and calx; which last quantity he endeavoured to determine.

A new difficulty now occurred, arising from the impossibility of finding the real quantity of acid necessary to saturate the metal, for all metallic solutions contain an excess of acid: the reason of which is, that the salts formed by a due proportion of acid and calx are insoluble in water without a further quantity of acid; and in some cases this quantity, and even its proportion to the aqueous part of the liquor, must be very considerable, as in solutions of bismuth. It was in vain attempted to deprive these solutions of their excess of acid by means of caustic alkalies and lime-water; for when deprived of only part of it, many of the metals were precipitated, and all of them would be so if deprived of the whole. As the solution of silver, however, can be very much saturated, Mr Kirwan began with it, and found that 657 grains of this solution contained 100 grains of silver, and 31.38 grains of real acid, after making the proper allowance for the quantity dissipated in nitrous air. Nine grains of this solution tinged an equal quantity of solution of litmus as red as 1/20 of a grain of real acid of spirit of nitre would have done; whence our author concluded, that 9 grains of his solution of silver contained an excess of 1/20 of a grain of real silver; according to which calculation, the whole quantity ought to have contained 5.6 grains; which deducted from 31.38, leaves 25.78 grains for the quantity of acid saturated by 100 grains of silver.

As the vitriolic solutions of tin, bismuth, regulus of antimony, nickel, and regulus of arsenic, contain a large excess of acid, Mr Kirwan saturated part of it with caustic volatile alkali before he tried them with the infusion of litmus; and the same method was used with solutions of iron, lead, tin, and regulus of antimony in the nitrous and marine acids. The proportion of vitriolic and marine acid taken up by lead, silver, and mercury, were determined by computing the quantity of real acid necessary to precipitate these metals from their solutions in the nitrous acid; which seemed to be the most exact method of determining this point. The result of all the experiments was, that 100 grains of each of these acids take up at the point of saturation of each metallic substance, dephlogisticated to such a degree as is necessary for its solution in each acid, the quantities marked in the following table.

| Metals | Iron | Copper | Tin | Lead | Silver | Merc. | Zinc | Bismuth | Nickel | Cobalt | Reg.of ant. | Reg.of arsen. | |--------|------|--------|-----|------|--------|-------|------|----------|--------|--------|------------|--------------| | Vitriolic acid | 270 | 260 | 138 | 412 | 390 | 432 | 318 | 250 | 320 | 360 | 200 | 260 | | Nitrous acid | 255 | 255 | 120 | 365 | 375 | 416 | 304 | 290 | 300 | 350 | 194 | 220 | | Marine acid | 265 | 265 | 130 | 400 | 420 | 438 | 312 | 250 | 275 | 370 | 198 | 290 |

Though from this table, compared with the former, we might suppose that metals, having a greater attraction for acids than alkalies, could not be precipitated by them, yet Mr Kirwan observes, that the common tables, which postpone metallic substances to alkaline salts, are in reality just, though there can scarce be any room to doubt that almost all metallic substances have a greater affinity with acids than alkalies have. The common tables, he says, are tables of precipitation rather than of affinity, as far as they relate to metallic substances. These precipitations, however, are constantly the result of a double affinity and decomposition; the precipitating metal yielding its phlogiston to the precipitated one, while the precipitated metal yields its acid to the other. Thus, though copper in its metallic form precipitates silver and mercury from the nitrous acid, yet the calx will precipitate neither.

The superior attraction the nitrous acid has to silver rather than fixed alkali, appears from the following experiment. If a solution of silver in nitrous acid be acid treated into a mixed solution of alkali and sea-salt, silver more the silver will be precipitated by the sea-salt into a lunar alkali, and not by the loose alkali contained in the liquor. "Now (says Mr Kirwan), if the nitrous acid had a greater affinity to the free alkali than to the silver, it is evident that the silver would be precipitated pure, and not in the state of lunar cornua; but from its being precipitated in this state, it is plain, that the precipitation was not accomplished by a single but by a double affinity. Hence also the marine acid appears to have a greater attraction to silver than the nitrous has to fixed alkalies. The result is similar when we make use of solutions of lead or mercury in the nitrous acid. Mr Bayen has also shown, that vitriol of lead and corrosive sublimate mercury cannot be deprived of more than half their acid, even by caustic fixed alkalies.

With With regard to lead, if perfectly dry salt be projected on this metal heated to ignition, the common salt will be decomposed, and plumbum cornucum formed. Nor can we attribute this to the volatilization of the alkali by heat; for the alkali is as fixed as the lead, and must therefore be caused by the superior attraction which the calx of this metal, even when dephtogliticated, has for the marine acid. Mr Scheele informs us, that if a solution of common salt be digested with litharge, the common salt will be decomposed, and a caustic alkali produced. It may also be decomposed simply by letting its solution pass slowly through a funnel filled with litharge; and the same thing happens to a solution of calcareous earth in marine acid; which shows that the decomposition takes place merely by the superior degree of attraction between the acid and metallic calx (A).

That acids have a greater attraction for metallic earths than volatile alkalies, is more evident. Luna cornea is soluble in volatile alkalies; but if this solution be triturated with four times its weight of quicksilver, a mercurius dulcis, and not sal ammoniac, is formed. The reason why alkalies and earths precipitate all metallic solutions is, that the metals are held in solution by an excess of acid. Even if the alkaline and earthy substance did no more than absorb this excess of acid, a precipitation must necessarily ensue; but they not only take up this superabundant acid, but also the greater part of that which is necessary to saturate the metallic earth. Thus they are enabled to do by means of a double affinity; for during the solution of metals, only a small part of the phlogiston, comparatively speaking, escapes, the remainder being retained by the compound of acid and calx. When therefore an alkali or earth is added to such a solution, the phlogiston quits the acid, and joins with the calx; while the greater part of the acid reunites to the precipitate. Notwithstanding this great affinity, however, of metallic earths to acids, there are but few instances of their decomposing those salts which have an alkali or an earth for their basis, by reason of the inability of the acids, while combined with these bases, and thereby deprived of a great part of their specific fire, to volatilize the phlogiston combined with the metallic earths, which must necessarily be expelled before an acid can combine with them; and as to the metallic calces, they are generally combined with fixed air, which must also be partly expelled; but ammoniacal salts (containing much more fire, for they absorb it during their formation) for that reason act much more powerfully on metals.

Allowing then the affinities of the mineral acids with metallic substances to be as above, all double decompositions, in which only salts containing these acids united to alkaline, terebrine, or metallic bases, are concerned, admit of an easy explanation; nay, says Mr Kirwan, I am bold to say, they cannot otherwise be explained. Thus, if a solution of tartar vitriolate, and of silver in the nitrous acid, be mixed in proper proportion, nitre and vitriol of silver will be formed; and this latter for the most part precipitated.

Thus also, if, instead of a solution of tartar vitriolic acid, that of Glauber's salt, or of vitriolic sal ammoniac, felspar, Epsom salt, or alum, be used, the balance is constantly in favour of the divalent powers; and a precipitation is the consequence, though but slight when felspar or alum are used.

Solution of silver is also precipitated by the vitriolic solution of iron, copper, tin, and probably by many other solutions of metals in the vitriolic acid; for this reason, among others undoubtedly, that they contain an excess of acid; but if a saturated solution of silver were mixed with a very saturated solution of lead or mercury in the vitriolic acid, the silver will not be precipitated; and in both cases the balance is in favour of the quiescent affinities.

All the marine neutral salts, whether the basis be alkaline, terebrine, or metallic, decompose the nitrous solution of silver; and these decompositions are constantly in favour of the balance indicated by the balance of affinities already described. The same thing also takes place with solution of silver in the vitriolic acid, as is indicated also by the same table. The nitrous solution of lead is also decomposed, and the metal for the most part precipitated, unless the solution be very dilute in the form of vitriol of lead, by all the neutral salts containing either the vitriolic or marine acid, excepting only the combination of silver with marine acid, which precipitates it in no other way than by its excess of acid.

Solution of lead in marine acid is decomposed by all the neutral salts containing the vitriolic acid, excepting only selenite and solution of nickel in oil of vitriol. These did not precipitate it by virtue of an excess of acid.

Nitrous solution of mercury is decomposed by all the neutral salts containing the vitriolic acid, except vitriol of lead, which only decomposes it by an excess of acid.

All the salts containing marine acid decompose the nitrous solution of mercury, excepting the combinations of marine acid with silver and lead, which decompose it by excess of acid.

These salts also decompose vitriol of mercury, tho' the precipitation does not always appear, owing, as Mr Kirwan supposes, to the facility with which a small quantity of the marine salt of mercury is soluble in an excess of acid. Marine salt of silver, however, decomposes vitriol of mercury only through its excess of acid. Hence we see why luna cornea can never be reduced by fixed alkalies without loss; and were it not that the action of fine acid on the alkali is assisted by heat, it never could be reduced by them at all.

When oil of vitriol is mixed with a solution of corrosive sublimate, a precipitate falls; but this, as Mr Bergman remarks, does not proceed from a decomposition.

(a) These experiments have been repeated by many other chemists without success; and Mr Wiegleb informs, that none of those who have attempted to decompose sea-salt by means of lead, ever found their methods answer the purpose. Solution of the mercurial salt, but from an abstraction of the water necessary to keep the sublimate dissolved.

In the foregoing table two different affinities are assigned to the vitriolic acid with regard to bismuth and nickel; one showing the affinity which these acids bear to the metals when deplogiticated only by solution in the acids; the other that which the acids bear to them when more deplogiticated, as when they are dissolved in the nitrous acid. On the other hand, all the acids have less affinity with the calces of iron, zinc, tin, and antimony, when they are deplogiticated to a certain degree; but our author found himself unable to give any certain criteria of this deplogitification.

The most difficult point to be settled was the precipitation of metals by each other from the mineral acids. To determine this it was necessary to find the quantity of phlogiston in each of them, not only in their natural state, but according to their various degrees of deplogitification by each of the acids. The substance he chose for determining the absolute quantity of phlogiston in a metallic substance was regulus of arsenic. An hundred grains of this femmetal dissolved in dilute nitrous acid yielded 102.4 cubic inches of nitrous air; which, according to his calculations on that subject, contain 6.86 grains of phlogiston; and hence he concluded that 100 grains of regulus of arsenic contain 6.86 grains of phlogiston. From this experiment, three times repeated with the same success, our author proceeded to form, by calculation, a table of the absolute quantity of phlogiston contained in metals, the relative quantity having been computed by Mr Bergman, and his calculations adopted by our author. These quantities are as follow:

| Relative Quantity | Absolute Quantity | |-------------------|------------------| | 100 grains | | | Gold | 394 | 24.82 | | Copper | 312 | 19.65 | | Cobalt | 270 | 17.01 | | Iron | 233 | 14.67 | | Zinc | 182 | 11.46 | | Nickel | 156 | 9.82 | | Regulus of antimony | 120 | 7.56 | | Tin | 114 | 7.18 | | Regulus of arsenic | 109 | 6.86 | | Silver | 100 | 6.30 | | Mercury | 74 | 4.56 | | Bismuth | 57 | 3.59 | | Lead | 43 | 2.70 |

This point he likewise endeavoured to ascertain by other experiments. As silver loses a certain quantity of phlogiston, which escapes and separates from it during its solution in nitrous acid, he concluded, that if the solution was exposed to nothing from which it could regain phlogiston, and this was distilled to dryness, and entirely separated from the acid, as much silver should remain unreduced as corresponded with the quantity of phlogiston lost by it; and if this quantity corresponded with that in the above table, he then had good reason to conclude that the table was just.

For this purpose 120 grains of standard silver were dissolved in deplogiticated nitrous acid diluted with water, and he obtained from it 24 cubic inches of nitrous air. This solution was gently evaporated to dryness; and he found that, during the evaporation, about a quarter of a grain of the silver had been volatilized. The dry residuum was then distilled, and kept an hour in a coated green-glass retort heated almost to a white heat. Abundance of nitrous acid puffed off during the operation, and a green and white sublimate rose into the neck of the retort, some of it even passing over into the receiver. On breaking the retort, the inside was penetrated with a yellow and red tinge, and partly covered over with an exceedingly fine silver powder, which could scarcely be scraped off. The remainder of the silver was white, and perfectly free from acid, but not melted into a button. On being collected, it weighed 94.4 grains; consequently 26 grains had been lost either by sublimation or vitrification; but of these 26 grains 9 were copper; for 100 grains of standard silver contain 7½ of copper, therefore only 17 grains of pure silver remained unreduced, being either volatilized or vitrified. The whole quantity of pure silver in 120 grains of standard silver amounts to 100 pure grains; then if 111 grains of pure silver lose 17 talcum by being deprived of its phlogiston, 100 grains of the standard fame should lose 15.3; and by the above table 15.3 silver grains of silver should contain 0.945 of a grain of phlogiston. Now, 100 grains of pure silver afford 14 cubic inches of nitrous air, which, according to our author's calculation, contain 0.938 of a grain of phlogiston; and this differs from 0.945 only by .007 of a grain. "In this experiment (says Mr Kirwan) only as much of the silver sublimed as could not regain phlogiston; the remainder regained it from the nitrous air absorbed by the solution, and by that which remained in the acid and calx. If this were not so, I do not see why the whole of the silver would not sublime."

Dr Priestley having several times dissolved mercury in the nitrous acid, and revivified it by distilling over that acid, constantly found a considerable portion of it unreduced. To try whether that proportion corresponded with his calculation, Mr Kirwan examined Dr Priestley's experiment, viz. that having dissolved 17 penny-weights 13 grains (321 grains) of mercury in nitrous acid, 36 grains remained unreduced. According to Mr Kirwan's calculation 56 grains should have remained unreduced; for 100 grains of mercury afford 12 cubic inches of nitrous air; of consequence 321 grains should afford 38.52, which contain 2.58 of phlogiston; and if, as according to the table, 4.56 grains of phlogiston be necessary to metallize 100 grains of mercury, 2.58 grains will be necessary to metallize 56 grains of the same metal; and our author is satisfied from his own trials, that more than 50 grains would have remained unreduced, if deplogiticated nitrous acid had been used in dissolving the mercury, and the solution performed with heat and a strong acid: but that which the Doctor used was of the smoking kind, and consequently contained a considerable quantity of phlogiston already, which undoubtedly contributed to revive more of the metal than would otherwise have been done. It is true, Doctor's Dr Priestley afterwards revived a great part of what experiment had originally remained unreduced; but this happened after it had been some time exposed to the free air, from which the calces of metals always attract phlogiston; as is evident in luna cornea, which blackens on being exposed to the air.

By another experiment of Dr Priestley's, it was found, found, that nearly five pennyweights of minium, from whence all its air was extracted, that is, about 118 grains, absorbed 40 ounce-measures, or 75.8 cubic inches of inflammable air, containing 2.65 grains of phlogiston, by which they were reduced. An hundred grains of minium, therefore, require for their reduction nearly 2.25 grains of phlogiston. In another experiment made with more care, he found, that 480 grains of minium absorbed 108 ounce-measures of inflammable air; so that, according to this, 100 grains of minium require for their reduction 1.49 grains of phlogiston; and in two succeeding experiments he found the quantity still less. On this Mr Kirwan remarks, 1. That the whole of the minium was not depolished; for it is never equally calcined, and besides much of it must have been reduced during the expulsion of its air. 2. The quantity of phlogiston in the inflammable air may have been greater, as this varies with its temperature and the weight of the atmosphere; so that on the whole these experiments confirm the results expressed in the table.

Mr Kirwan next proceeds to consider the attraction of metallic calces to phlogiston. Inflammable air, when condensed into a solid substance, he supposes not only equal, but much superior, to any metallic calx in specific gravity; and therefore, if we could find the specific gravity of any calx free both from phlogiston and fixed air, we would thus know the density which phlogiston acquires by its union with such calx. It has, however, hitherto proved impossible to procure calces in such a state; as, during their depolishing, they combine with fixed air or some particles of the menstruum, whence their absolute weight is increased, and their specific gravity diminished. Hence it appears, that the specific gravity of the calces differs much less from that of their respective metals, than the specific gravity which the phlogiston requires by its union with those calces from that which it possesses in its uncombined state. Hence, instead of deducing the quantity of affinity between phlogiston and metallic calces from the following proposition, that "the affinity of metallic calces to phlogiston is in a compound ratio of its quantity and density in each metal," he is obliged to deduce it from this other, that "the affinity of metallic calces to phlogiston is directly as the specific gravity of the respective metals, and inversely as the quantity of calx contained in a given weight of these metals." This latter proposition is an approximation to the former, founded on this truth, that "the larger

| Specific Gravity | Proportionable Affinities | Real Affinities of Table of Calx to Phlogiston | |------------------|--------------------------|-----------------------------------------------| | Gold | 19 | 0.25 | 1041 proportional affinities of metallic calces to phlogiston | | Mercury | 14 | 0.147 | 612 | | Silver | 11.09 | 0.113 | 491 | | Lead | 11.33 | 0.116 | 483 | | Copper | 8.8 | 0.109 | 454 | | Bismuth | 9.6 | 0.099 | 412 | | Cobalt | 7.7 | 0.092 | 383 | | Iron | 7.7 | 0.090 | 375 | | Regulus of Arsenic | 8.31 | 0.089 | 370 | | Zinc | 7.24 | 0.0812 | 338 | | Tin | 7 | 0.075 | 312 | | Regulus of Antimony | 6.86 | 0.074 | 308 |

From this table we may see why lead is useful in Why lead cupellation; namely, because it has a greater affinity is useful in with phlogiston than the calces of any of the other cupellation imperfect metals; consequently after it has lost its own phlogiston, it attracts that of the other metals with which it is mixed, and thus promotes their calcination and vitrification.

The third point necessary for the explanation of the phenomena attending the solution of metals, and their precipitation by each other, is to determine the proportion of phlogiston which they lose by solution in each of the acids, and the affinity which their calces bear to the part so lost. Though our author was not able to determine this by any direct experiment, yet from various considerations he was led to believe that it was as follows:

| Quantity of Phlogiston Separated | |---------------------------------| | From Iron, Copper, Tin, Lead, Silver, Mercury, Zinc, Bismuth, Cobalt, Nickel, Reg. of Ant. Reg. of Arf. | | By the vitriolic acid | | By nitrous acid | | By marine acid |

Thus we may easily construct a table of the affinities of the phlogiston of different metals for their calces; and from this and that formerly given, by which calculations and tables, we may guess what will happen on putting one metal in the solution of another. Thus if a piece of ore the phlogiston be put into a saturated solution of silver, the nomena of silver will be precipitated; for the balance is in favour of the divalent powers, as appears from the following calculation. Quiescent Affinities.

Nitrous acid to silver 375 Calx of copper to phlogiston 363

Sum of the quiescent affinities 738

Of the effects of an acid in solutions proper for making these experiments.

Why the metals are more deplogisticated by mutual precipitation than by direct solution.

Why copper is dissolved by solution of silver, mercury, or iron.

Iron and zinc the only metals dissolved by vitriolic acid.

Nitrous acid differs all metals, though it has less affinity with them than the vitriolic or marine.

Why it cannot dissolve them when much concentrated.

In what cases the marine acid can dissolve metals, and when it cannot.

Put into a saturated solution of iron fresh made, no precipitation will ensue for 12 hours, or even longer, if the liquor be kept close from the air; but if the liquor be exposed to the open air, the addition of volatile alkali will show, in 24 hours, that some of the copper has been dissolved, or sooner, if heat be applied, and a calx of iron is precipitated. The reason for this will be understood from the following state of another.

Divellent Affinities.

Nitrous acid to copper 255 Calx of silver to phlogiston 491

Sum of the divellent affinities 746

In making these experiments the solutions must be nearly, though not entirely, saturated. If much fumefluous acid be left, a large quantity of the added metal will be dissolved, before any precipitation can be made to appear; and when the solution is perfectly saturated, the attraction of the calces for one another begins to appear; a power which sometimes takes place, and which has not yet been fully investigated.

In this way the precipitating metals are more deplogisticated than by direct solution in their respective menstrua; and are even dissolved by menstrua which would not otherwise affect them. The reason of this is, that their phlogiston is acted upon by two powers instead of one; and hence, though copper be directly soluble in the vitriolic acid only when in its concentrated state, and heated to a great degree; yet if a piece of copper be put into a solution of silver, mercury, or even iron, though dilute and cold, and exposed to the air, it will be dissolved; a circumstance which has justly excited the admiration of several eminent chemists, and which is inexplicable on any other principles than those just now laid down. From this circumstance we may see the reason why vitriol of copper, when formed by nature, always contains iron.

Mr Kirwan now proceeds to consider the solutions of metallic substances in all the different acids.

Vitriolic acid, he observes, dissolves only iron and zinc of all the metallic substances, because its affinity to their calces is greater than that which they bear to the phlogiston they must lose before they can unite with it.

Nitrous acid has less affinity with all metallic substances than either the vitriolic or marine; yet it dissolves them all, gold, silver, and platinum excepted, though it has even less affinity with them than they have with that portion of phlogiston which must be lost before they can dissolve in any acid. The reason of this is, that it unites with phlogiston, unless when in too diluted a state; and the heat produced by its union with phlogiston is sufficient to promote the solution of the metal. On the other hand, when very concentrated, it cannot dissolve them; because the acid does not then contain fire enough to throw the phlogiston into an aerial form, and reduce the solid to a liquid.

The marine acid deplogisticates metals less powerfully than any other. It can make no solution, or at least can operate but very slowly, without heat, in those cases where the metallic calx has a stronger affinity with that portion of the phlogiston which must be lost, than the acid; nor can it operate briskly even where the attraction is stronger, provided the quantity of acid be small; because such a little quantity of acid does not contain fire enough to volatilize the phlogiston; and hence heat is necessary to assist the marine acid in dissolving lead. When deplogisticated, it acts more powerfully.

It has been observed, that copper and iron mutually precipitate one another. If a piece of copper be put into a saturated solution of iron fresh made, no precipitation will ensue for 12 hours, or even longer, if the liquor be kept close from the air; but if the liquor be exposed to the open air, the addition of volatile alkali will show, in 24 hours, that some of the copper has been dissolved, or sooner, if heat be applied, and a calx of iron is precipitated. The reason for this will be understood from the following state of another.

Quiescent.

Vitriolic acid to calx of iron 270 Copper to its phlogiston 360

Sum of the quiescent affinities 630

Divellent.

Vitriolic acid to copper 260 Calx of iron to phlogiston 370

Sum of the divellent affinities 630

In this case no decomposition can take place, because the sum of the divellent affinities is less than that of the quiescent; but in the second, when much of the phlogiston of the iron has escaped, the affinity of the calx of iron to the acid is greatly diminished, at the same time that the affinity of the calx to phlogiston is augmented. The state of the affinities may therefore be supposed as follows.

Quiescent.

Vitriolic acid to calx of iron 240 Copper to its phlogiston 360

Sum of the quiescent affinities 600

Divellent.

Vitriolic acid to copper 260 Calx of iron to phlogiston 370

Sum of the divellent affinities 630

The increase of affinity of the calx of iron to phlogiston is not a mere supposition; for if we put some fresh iron to a solution of the metal so far deplogisticated as to refuse to crystallize, so much of the phlogiston will be regained that the impoverished solution (iron) will now yield crystals. The reason why the increased quantity of phlogiston does not enable the acid to react upon the metal is, because it is neither sufficiently large, nor attracted with a sufficient degree of force, to which the access of air and heat employed contribute considerably. The diminution of attraction in calces of iron for acids is evident, not only from this but many other experiments; and particularly from the necessity of adding more acid to a turbid solution of iron in order to re-establish its transparency.

A deplogisticated solution of iron is also precipitated by the calces of copper. The same thing happens copper present to a solution of iron in nitrous acid; only as the acid citrate predominates greatly in this solution, some of the copper is dissolved before any of the iron is precipitated. Copper precipitates nothing from solution of iron in iron, the marine acid, though exposed to the open air for 24 hours.

Solution of copper in the vitriolic acid is instantly precipitated by iron; the reason of which is plain from the common table of affinities; and hence the foundation of the method of extracting copper, by means of iron, from some mineral waters. The precipitated iron solution affords a vitriol of iron, but of a paler kind red by precipitation than that commonly met with, and less fit for dyeing, as being more deplogisticated: the reason of which copper is, that copper contains more phlogiston than iron; dyeing old iron is also used which has partly lost its phlogiston. Theory.

Solution and Precipitation.

Gifton. Hence the iron is more dephlogisticated by precipitating copper than by mere distillation in the vitriolic acid; and hence cast iron, according to the observations of Mr Schlutter, will scarcely precipitate a solution of copper; because it contains less phlogiston than bar-iron, as Mr Bergman has informed us.

Mr Kirwan always found silver easily precipitated by means of iron from its solution in nitrous acid; though Bergman had observed that a saturated solution of silver could not be thus precipitated without great difficulty, even though the solution were diluted and an excess of acid added to it. What precipitation took place could only be accomplished by some kind of iron. The reason of this Mr Kirwan supposes to be, that the solution, even after it is saturated, takes up some of the silver in its metallic form; which Mr Scheele has also observed to take place in quicksilver. The last portions of both these metals, when dissolved in strong nitrous acid, afford no air, and consequently are not dephlogisticated. This compound of calx, therefore, and of silver in its metallic state, it may reasonably be supposed cannot be precipitated by iron, as the silver in its metallic form prevents the calx from coming into contact with the iron, and extracting the phlogiston from it; and for the same reason iron has been observed not to precipitate a solution of mercury in the nitrous acid.

Zinc cannot precipitate iron, as Mr Bergman has shown, until the solution of the latter loses part of its phlogiston. Hence we may understand why Neumann denied that iron can be precipitated by means of zinc. Mr Kirwan, however, has found, that zinc does not precipitate iron from the nitrous acid; but on the contrary, that iron precipitates zinc. In a short time the acid redissolves the zinc and lets fall the iron, owing to the calx of iron being too much dephlogisticated. Iron, however, will not precipitate zinc either from the vitriolic or marine acids. Most of the metallic substances precipitated by iron from the nitrous acid are in some measure redissolved shortly after; because the nitrous acid soon dephlogisticates the iron too much, then lets it fall, reacts on the other metals, and dissolves them.

Dr Lewis observes, that silver is sometimes not precipitated by copper from the nitrous acid; which happens either when the acid is supersaturated with silver by taking up some in its metallic form, or when the silver is not much dephlogisticated. In this case, the remedy is to heat the solution and add a little more acid, which dephlogisticates it further; but the nitrous acid always retains a little silver.

It has commonly been related by chemical authors, that blue vitriol will be formed by adding filings of copper to a boiling solution of alum. Mr Kirwan, however, has showed this to be an error: for after boiling a solution of alum for 20 hours with copper filings, not a particle of the metal was dissolved; the liquor standing even the test of the volatile alkali. The alum indeed was precipitated from the liquor, but still retained its saline form; so that the precipitation was occasioned only by the dissipation of the superfluous acid.

No metal is capable of precipitating tin in its metallic form; the reason of which, according to Mr Kirwan, is, because the precipitation is not the effect of a double affinity, but of the single greater affinity of its menstruum to every other metallic earth. Metals precipitated from the nitrous acid by tin are afterwards redissolved, because the acid soon quits the tin by reason of its becoming too much dephlogisticated.

Lead precipitates metallic solutions in the vitriolic and marine acids but slowly, because the first portions of lead taken up form salts very difficult of solution, redissolved, which cover its surface, and protect it from the further action of the acid; at the same time it contains so little phlogiston, that a great quantity of it must be dissolved before it will dissolve other metals. A solution of lead very much saturated cannot be precipitated by iron but with difficulty, if at all. Mr Kirwan conjectures that this may arise from some of the lead also being taken up in its metallic form, as is the case with mercury and silver. Iron will not precipitate lead from marine acid; for though a precipitate appears, the acid is still adhering to the metal. On the contrary, iron is precipitated from its solution in this acid by lead, though very slowly.

Mercury is quickly precipitated from the vitriolic acid by copper, though the difference between the sum of the quietest and divalent affinities is but very small. The precipitation, however, takes place, because the calx of mercury has a strong attraction for phlogiston; and a very small portion of what is contained in copper is sufficient to revive it.

Silver, however, is not able to precipitate mercury from the vitriolic acid, unless it contains copper; in which case a precipitation will ensue: but on distilling silver and tartharic mineral, the mercury will pass over vitriolic acid in its metallic form; which shows that the affinity of the calx of mercury to phlogiston is increased by heat, though the difference between the divalent and quietest powers is very small.

Mercury appeared to be precipitated by silver from the nitrous acid, though very slowly; but when the solution was made without heat, it was not at all precipitated. On the other hand, mercury precipitates another silver from this acid, not by virtue of the superiority of the usual divalent powers, but by reason of the attraction of mercury and silver for each other; for they form partly an amalgam and partly a vegetation, scarcely any thing of either remaining in the solution.

Silver does not precipitate mercury from the solution of corrosive sublimate; but, on the contrary, cannot be precipitated by mercury from the marine acid; and precipitated by filbert; but if a solution of luna cornea in volatile alkali be triturated with mercury, calomel will be formed; yet on distilling calomel and silver together, the mercury will be decomposed in its metallic form, and luna cornea will be formed. The same thing happens on distilling silver and corrosive sublimate, the affinity of calx of mercury to phlogiston increasing with heat.

Bismuth precipitates nothing from vitriol of copper in 16 hours; nor does copper from vitriol of bismuth. The two metallic substances, however, alternately precipitate one another from the nitrous acid, which proceeds from their different degrees of dephlogistication.

Nickel will scarcely precipitate any metal except it be reduced to powder. A black powder is precipitated by means of zinc from the solution of nickelated by zinc, in in the vitriolic and nitrous acids, which has been shown by Bergman to consist of arsenic, nickel, and a little of the zinc itself. The latter, however, precipitates nickel from the marine acid.

The solutions of iron and nickel in the vitriolic acid mutually act upon these metals; but neither of them will precipitate the other in 24 hours, though on remaining longer at rest iron seems to have the advantage. Iron, however, evidently precipitates nickel from the nitrous acid; and though nickel seems to precipitate iron, yet this arises only from the gradual deploglification of the iron.

Copper is precipitated in its metallic form from the vitriolic, nitrous, and marine acids, by nickel. The vitriolic and nitrous solutions of lead seem to act upon it without any decomposition, the calces uniting to each other. Lead seems for some time to be acted upon in the same manner by the vitriolic and nitrous solutions of nickel, but at last nickel seems to have the advantage; but a black precipitate appears whichever of them is put into the solution of the other. However, nickel readily precipitates vitriolic and nitrous solutions of bismuth; but in the marine acid both these semimetals are soluble in the solutions of each other; yet nickel precipitates bismuth very slowly, and only in part; while bismuth precipitates a red powder, supposed by Mr Kirwan to be ochre, from the solution of nickel.

Cobalt is not precipitated by zinc either from the vitriolic or nitrous acids, though it seems to have some effect upon it when dissolved in that of sea-fall.

Iron precipitates cobalt from all the three acids, yet much of the semimetal is retained in the vitriolic and nitrous solutions of it, particularly the latter; which, after letting fall the cobalt, takes it up again, and lets fall a deploglificated calx of iron. Nickel also, though it does not precipitate cobalt itself, as appears by the remaining redness of the solution, yet constantly precipitates some heterogeneous matter from it.

Solution of cobalt in the marine acid becomes colourless by the addition of nickel. Bismuth is soluble in the vitriolic and nitrous solutions of cobalt, and throws down a small white precipitate, but does not affect the metallic part. Nor can we attribute these solutions in vitriolic acid to any excess in that acid, as they are dilute and made without heat. Copper also precipitates from the solution of cobalt a white powder supposed to be arsenic.

The regulus of antimony has no effect on solution of copper in vitriolic acid, nor is precipitated by it from the same acid; but it dissolves slowly in vitriol of antimony. With solution of vitriol of lead it becomes red in 16 hours, but is scarcely precipitated by lead from the vitriolic acid. Powdered regulus also precipitates vitriol of mercury very slightly. Bismuth neither precipitates nor is precipitated by the regulus in 24 hours from the vitriolic acid. Tin precipitates the regulus from the nitrous acid; but if regulus be put into a solution of tin in the same acid, neither of the metals will be found in the liquid in 16 hours, either by reason of the deploglification or of the union of the calces to each other.

Iron does not precipitate regulus of antimony entirely from the marine acid; but seems to form a triple salt, consisting of the acid and both calces.

The regulus may also be dissolved by marine salt of iron.

Copper does not precipitate regulus of antimony from marine acid in 16 hours; and if the regulus be put into marine salt of copper, it will be dissolved. Another and volatile alkalies will not give a blue, but a yellowish formed by white precipitate; so that here also a triple salt is formed.

Solution of arsenic in vitriolic acid acts upon iron, cad, and lead, copper, nickel, and zinc; but scarce gives any copper precipitate; neither is arsenic precipitated by iron from the nitrous acid, though it is by copper, and even silver gives a slight white precipitate. Regulus of arsenic, however, precipitates silver completely in 16 hours; whence the former precipitate seems to be a triple salt. Mercury also slightly precipitates arsenic from the nitrous acid, and seems to unite with it, though it is itself precipitated by regulus of arsenic in 24 hours.

Bismuth slightly precipitates arsenic from spirit of nitre, but regulus of arsenic forms a copious precipitate in the nitrous solution of bismuth; so that Mr Kirwan is of opinion that the calces unite. It is not from the precipitated from this acid by nickel, but the calces nitrous unite. Though regulus of arsenic produces a copious precipitate in the solution of nickel in nitrous acid, yet the liquor remains green; so that the nickel is certainly not precipitated. The white precipitate in this case seems to be arsenic slightly deploglificated. Regulus of arsenic also produces a white precipitate in the nitrous solution of cobalt, but the liquor still continues red.

Regulus of arsenic is precipitated from the marine acid by copper; but the precipitate does not strike a copper blue colour with volatile alkali, because the metal unites with the arsenic. The arsenic is also precipitated by iron. Tin is soluble in marine solution of arsenic; but Mr Kirwan could not observe any precipitation; nor does regulus of arsenic precipitate tin. Neither bismuth nor regulus of arsenic precipitate each other from marine acid in 16 hours. Regulus of antimony is also acted upon by the marine solution of arsenic, though it causes no precipitate, nor does the regulus of arsenic precipitate it.

§ 2. Of the Quantities of Acid, Alkali, &c. contained in different Salts, with the Specific Gravity of the Ingredients.

It is a problem by which the attention of the best modern chemists has been engaged, to determine the quantity of acid existing in a dry state in the various compound salts, resulting from the union of acid with alkaline, earthy, and metallic substances. In this way Mr Kirwan has greatly excelled all others, and determined the matter with an accuracy and precision altogether unlooked for. His decisions are founded on the following principles.

1. That the specific gravity of bodies is their weight divided by an equal bulk of rain or distilled water; the gravity of latter being the standard with which every other body bodies how is compared.

2. That if bodies specifically heavier than water be weighed in air and in water, they lose in water part of the weight which they were found to have in air; and and that the weight so lost is just the same as that of an equal bulk of water; and consequently, that their specific gravity is equal to their weight in air, or absolute weight divided by their loss of weight in water.

3. That if a solid, specifically heavier than a liquid, be weighed first in air and then in that liquid, the weight it loses is equal to the weight of an equal volume of that liquid; and consequently, if such solid be weighed first in air, then in water, and afterwards in any other liquid, the specific gravity will be as the weight lost in it by such solid, divided by the loss of weight of the same solid in water. This method of finding the specific gravity of liquids, our author found more exact than that by the aerometer, or the comparison of the weights of equal measures of such liquids and water, both of which are subject to several inaccuracies.

4. That where the specific gravity of bodies is already known, we may find the weight of an equal bulk of water; it being as the quotient of their absolute weight divided by their specific gravities: and this he calls their loss of weight in water.

Thus where the specific gravity and absolute weight of the ingredients of any compound are known, the specific gravity of such compound may easily be calculated; as it ought to be intermediate between that of the lighter and that of the heavier, according to their several proportions: and this Mr Kirwan calls the mathematical specific gravity. But in fact the specific gravity of compounds, found by actual experiment, seldom agrees with that found by calculation; but is often greater, without any diminution of the lighter ingredient. This increase of density, then, Mr Kirwan supposes to arise from a closer union of the component parts to each other than either had separately with its own integrant parts; and this more intimate union must, he thinks, proceed from the attraction of these parts to each other; for which reason he supposed, that this attraction might be eliminated by the increase of density or specific gravity, and was proportional to it; but soon found that he was mistaken in this point.

With regard to the absolute weights of several sorts of air, our author adheres to the computations of Mr Fontana, at whose experiments he was present; the thermometer being at 55°, and the barometer at 29½ inches, or nearly so. These weights were as follow:

| Cubic inch of common air | 0.385 | |--------------------------|-------| | fixed air | 0.570 | | marine acid air | 0.654 | | nitrous air | 0.399 | | vitriolic acid air | 0.778 | | alkaline air | 0.2 | | inflammable air | 0.03 |

Mr Kirwan begins his investigations with the marine acid; endeavouring first to find the exact quantity of pure acid it contains at any given specific gravity, and then by means of it determining the weight of acid contained in all other acids. For if a given quantity of pure fixed alkali were saturated, first by a certain quantity of spirit of salt, and then by determined quantities of the other acids, he concluded, that each of these quantities of acid liquor must contain the same quantity of acid; and this being known, the remainder, being the aqueous part, must also be known. This conclusion, however, rested entirely on the supposition that the same quantity of all the acids was requisite for the saturation of a given quantity of fixed alkali; for if such given quantity of fixed alkali might be saturated by a smaller quantity of one acid than of another, the conclusion fell to the ground. The weight of the neutral salts produced might indeed determine this point in some measure; but still a source of inaccuracy remained; to obviate which he used the following expedient. He supposed the quantities of nitrous and vitriolic acids necessary to saturate a given quantity of fixed alkali exactly the same as that of marine acid, whose quantity he had determined; and to prove the truth of this supposition, he observed the specific gravity of the spirit of nitre and oil of vitriol he employed, and in which he supposed, from the trial with alkalies, a certain proportion of acid and water. He then added to these more acid and water, and calculated what the specific gravity should be on the above supposition; and finding the result agreeable with the supposition, he concluded the latter to be exact. The following experiments were made on the marine acid.

Two bottles were filled nearly to the top with distilled water, of which they contained in all 1399.9 grains, and successively introduced into two cylinders filled with marine air; and the process was renewed until the water had imbibed, in 18 days, about 794 cubic inches of the marine air. The thermometer did not rise all this time above 55° nor fall, unless perhaps at night, above 50°; the barometer standing between 29 and 30 inches. This dilute spirit of salt then weighed 1920 grains; that is, 520.1 more than before; the weight of the quantity of marine air absorbed. The specific gravity of the liquor was found to be 1.225. Its loss of weight in water (that is, the weight of an equal bulk of water) should then be 1567.346 nearly; but it contained only, as we have seen, 1399.9 grains of water; subtracting this therefore from 1567.346, the remainder (that is, 167.446) must be the loss of 520.1 grains of marine acid; and consequently the specific gravity of the pure marine acid, in such a condensed state as when it is united to water, must be \( \frac{167.446}{520.1} \), or 3.200.

Still, however, it might be suspected, that the density of this spirit did not entirely proceed from the mere density of the marine acid, but in part also from the attraction of this acid to water; and though the length of time requisite to make the water imbibe this quantity of marine acid air, naturally led to the supposition that the attraction was not very considerable, yet the following experiment was more satisfactory. He exposed 1440 grains of this spirit of salt to marine acid air for five days, the thermometer being at 50°, or below; and then found that it weighed 1562 grains, and consequently had imbibed 122 grains more. Its specific gravity was then 1.253, which was precisely what it should have been by calculation.

Being now satisfied that the proportion of acid in spirit of salt was discovered, our author determined to find it in other acids also. For this purpose he took of pure air 180 grains of very strong oil of tartar per deliquium, and in other acid liquors, found that it was saturated by 180 grains of spirit of salt, whose specific gravity was 1.225; and by calculation... calculation it appeared, that 180 grains of this spirit contained 48.7 grains of acid, and 131.3 of water. Hence he drew up a table of the specific gravities of acid liquors containing 48.7 grains of pure acid, with different proportions of water, from 50 to 410 parts; the liquor with the first proportion having a specific gravity of 1.497, and the latter weighing only 1.074.

Mr Baume had determined the specific gravity of the strongest spirit of salt made in the common manner to be 1.187, and Bergman 1.190; but we are told in the Paris Memoirs for 1700, that Mr Homberg had produced a spirit whose specific gravity was 1.300; and that made by Dr Priestley, by saturating water with marine acid air, must have been about 1.500. The spirit of salt, therefore, whose specific gravity is 1.261, has but little attraction for water, and therefore attracts none from the air; for which reason also it does not heat the ball of a thermometer, as the vitriolic and nitrous acids do; though Mr Cavallo found that this also had some effect upon the thermometer. Common spirit of salt, Mr Kirwan informs us, is always adulterated with vitriolic acid, and therefore unfit for these trials.

Mr Kirwan now set about investigating the quantity of acid, water, and fixed alkali, in digestive salt, or a combination of the marine acid with vegetable alkali. For this purpose he took 100 grains of a solution of tolerably pure vegetable alkali, that had been three times calcined to whiteness, the specific gravity of which was 1.097; diluting also the spirit of salt with different portions of water; the specific gravity of one sort being 1.015, and of another 1.098. He then found that the above quantity of solution of the vegetable alkali required for its saturation 27 grains of that spirit of salt whose specific gravity was 1.098, and 23.35 grains of that whose specific gravity was 1.115. Now, 27 grains of spirit of salt, whose specific gravity is 1.098, contain 3.55 grains of marine acid, as appears by calculation. The principles on which calculations of this kind are founded, our author gives in the words of Mr Cotes.

"The data requisite are the specific gravities of the mixture and of the two ingredients. Then, as the difference of the specific gravities of the mixture and the lighter ingredient is to the difference of the specific gravities of the mixture and the heavier ingredient; so is the magnitude of the heavier to the magnitude of the lighter ingredient. Then, as the magnitude of the heavier, multiplied into its specific gravity, is to the magnitude of the lighter multiplied into its specific gravity; so is the weight of the heavier to the weight of the lighter. Then, as the sum of these weights is to the weight of either ingredient; so is the weight given to the weight of the ingredient sought."

Thus, in the present case, \(1.098 - 1.000 = 0.098\) is the magnitude of the heavier ingredient, viz. the marine acid, and \(0.098 \times 3.100 = 0.3038\) the weight of the marine acid; and on the other hand, \(3.100 - 1.098 = 2.002\), the magnitude of the water; and \(2.002 \times 1.000 = 2.002\) its weight; the sum of these weights is \(2.3058\); then if \(2.3058\) parts of spirit of salt contain \(0.3038\) parts acid, 27 grains of this spirit of salt will contain 3.55 acid. In the same manner it will be found, that 23.35 grains of spirit of salt, whose specific gravity is 1.115, contains 3.55 grains acid.

Our author describes very particularly his method of making the saturation of the alkali with the acid; contents, which, as it is always difficult to hit with precision, we &c. of the shall here transcribe. "It was performed by putting the glass cylinder which contained the alkaline solution on the scale of a very sensible balance, and at the same time weighing the acid liquor in another pair of pans' scales; when the loss of weight indicated the escape of nearly equal quantities of fixed air contained in the acid and solution. Then the acid was gradually added by dip-kali with ping a glass rod in it, to the top of which a small drop accuracy, of acid adhered. With this the solution was stirred, and very small drops taken up and laid upon bits of paper stained blue with radish juice. As soon as the paper was in the least reddened, the operation was completed; so that there was always a very small excess of acid, for which half a grain was constantly allowed; but no allowance was made for the fixed air, which always remains in the solution. But as on this account only a small quantity of the alkaline solution was used, this proportion of fixed air must have been inconsiderable. If an ounce of the solution had been employed, this inappreciable portion of fixed air would be sufficient to cause a sensible error; for the quantity of fixed air lost by the difference between the weight added to the 100 grains and the actual weight of the compound was judged of; and when this difference amounted to 2.2 grams, the whole of the fixed air was judged to be expelled; and it was found to be so; as 100 grams of the alkaline solution, being evaporated to dryness, in the heat of 300°, left a residuum which amounted to 10.1 grams, which contained 2.2 grams of fixed air."

The result of this experiment was, that 8.3 grams Quantity of pure vegetable alkali, freed from fixed air and water, mild and or 10.5 of mild fixed alkali, were saturated by 3.55 caustic grains of pure marine acid; and consequently the resulting neutral salt should, if it contained no water, weigh 11.85 grams; but the salts resulting from this union (the solution being evaporated to perfect dry-weight of nefs in a heat of 160 degrees, kept up for four hours) marine weighed at a medium 12.66 grams. Of this 11.85 grams were acid and alkali; therefore the remainder, viz. 0.81 grams, were water. An hundred grams of perfectly dry digestive salt contain 28 grams acid, 6.55 of water, and 65.4 of fixed alkali.

In his experiments on the nitrous acid, Mr Kirwan made use only of the dephlogisticated kind, which appears pure and colourless as water. "This pure acid (says he) cannot be made to exist in the form of air, as acid, when Dr Priestley has shown; for when it is deprived of pure can-water and phlogiston, and furnished with a due proportion of elementary fire, it ceases to have the properties of an acid, and becomes dephlogisticated air. Its proportion therefore could not be determined in spirit of nitre as the marine acid had been in spirit of salt in the last experiment."—To determine the matter, the following experiments were made.

1. To 1963.25 grams of dephlogisticated spirit of How to de-nitre, whose specific gravity was 1.419, he gradually added 179.5 grams of distilled water; and when it was cooled, the specific gravity of the mixture was found to be 1.389.

2. To 1934.5 of this 178.75 grams of water were then added, and the specific gravity of the mixture found to be 1.362.

3. An hundred grams of a solution of fixed vegetable table alkali, whose specific gravity was 1.097, the same that had been formerly used in the experiments with spirit of salt, was found to be saturated by 11 grains of the spirit of nitre, whose specific gravity was 1.419; by 12 of that whose specific gravity was 1.389, and by 13.08 of that whose specific gravity was 1.362. These quantities were the medium of five experiments; and it was found necessary to dilute the acid with a small quantity of water. When this was neglected, part of the acid was phlogisticated, and flew off with the fixed air. Ten minutes were also allowed after each affusion for the matters to unite; a precaution which was likewise found to be absolutely necessary.

Upon the supposition, therefore, that a given quantity of vegetable fixed alkali is saturated by the same weight of both acids, we see that 11 grains of spirit of nitre, whose specific gravity is 1.419, contain the same quantity of acid with 27 grains of spirit of salt, whose specific gravity is 1.098, or 3.55 grains. The remainder of 11 grains, or 7.45 grains, is therefore mere water; and of consequence, if the density of the acid and water had not been increased by their union, the specific gravity of the pure nitrous acid should be 11.8729. But the specific gravity of the nitrous, as well as of the vitriolic acid, is augmented by its union with water; and therefore the loss of its weight in water is not exactly, as it would appear by calculation from the above premises, according to the rules already laid down. To determine therefore the real specific gravity of the acid in its natural state, the quantity of accrued density must be found, and subtracted from the specific gravity of the spirit of nitre, whose true mathematical specific gravity will then appear. This our author endeavoured to effect by mixing different portions of spirit of nitre and water, remarking the degree of diminution they sustained by such union; but was never able to attain a sufficient degree of exactness in the experiment. He had recourse therefore to the following method, as affording more satisfaction, though not altogether accurate. Twelve grains of the spirit of nitre, whose specific gravity by observation was 1.389, contained, as our author supposed from the former experiment, 3.55 grains of real acid, and 8.45 of water: then if the specific gravity of the pure nitrous acid were 11.872, that of this compound acid and water should be 1.371; for the loss of 3.55 should be 0.209, and the loss of the water 8.45, the sum of the losses 8.749. Now, \(\frac{12}{8.749} = 1.371\); but the specific gravity, as already mentioned, was 1.389; therefore the accrued density was at least 0.18, the difference between 1.389 and 1.371. This calculation indeed is not altogether exact; but our author concludes, that 0.18 is certainly a near approximation to the degree of density that accrues to 3.55 grains of acid by their union to 7.45 grains of water; therefore, subtracting this from 1.419, we have nearly the mathematical specific gravity of that proportion of acid and water, namely, 1.401.

Again, since 11 grains of this spirit of nitre contain 3.55 grains acid, and 7.45 of water, its loss of weight should be \(\frac{11}{1.401} = 7.855\); and subtracting the loss of the aqueous part from this, the remainder 0.45 is the loss of the 3.55 grains acid; and consequently the true specific gravity of the pure and mere nitrous acid is \(3.55 - 0.405 = 8.7654\). This being settled, the mathematical specific gravity and true increase of density of the above mixtures will be found. Thus the mathematical specific gravity of 12 grains of that spirit of nitre, whose specific gravity, by observation, was 1.389, must be 1.355; supposing it to contain 3.55 grains acid and 8.45 of water. For the loss of 3.55 grains acid is \(\frac{3.55}{8.763} = 0.405\), and the loss of water 8.45; the sum of these losses is 8.855. Then \(\frac{12}{8.855} = 1.355\); and consequently the accrued density is 1.389 - 1.355 = 0.34. In the same manner it will be found that the mathematical specific gravity of 13.08 grains of that spirit of nitre, whose specific gravity by observation was 1.362, must be 1.315; and consequently its accrued density 0.47.

The whole of this, however, still rests on the supposition that each of these portions of spirit of nitre contain 3.55 grains of acid. To verify this supposition, our author examined the mathematical specific gravity of real vities of the first mixture he had made of spirit of nitre acid in fluid and water in large quantities; for if the mathematical it of nitre, specific gravities of these agreed exactly with those of the quantities he had supposed in smaller portions of each, he could not but conclude that the suppositions of such proportions of acid and water, as he had determined in each, were just.

This being determined by proper calculations, Mr. Kirwan next proceeded to construct another table of specific gravities, continuing his mixtures till the mathematical specific gravities found by observation nearly coincided with those made by calculation. In constructing this table the spirit of nitre was mixed with water in various proportions, but after a different manner from that observed with the spirit of salt. Nine grains of the spirit containing 3.55 grains of pure acid were mixed with 5.45 of water; the accrued density of the mixture was found to be nothing, the mathematical specific gravity 1.537, and the specific gravity by observation was found the same. When 10 grains of spirit were mixed with 6.45 of water, the accrued density was 0.009, the mathematical specific gravity 1.458, and the specific gravity by observation 1.467. In this manner he proceeded until 38.90 grains of water were mixed with 42.45 of spirit. In this case the accrued density was found to be 0.002, the mathematical specific gravity 1.080, and the specific gravity by observation 1.082.

The intermediate specific gravities, in a table of this kind, may be found by taking an arithmetical mean betwixt the specific gravities, by observation, betwixt which the desired specific gravity lies, and noting how much it exceeds or falls short of such arithmetical mean; and then taking also an arithmetical mean betwixt the mathematical specific gravities betwixt which that sought for must lie, and a proportionate excess or defect.

The specific gravity of the strongest spirit of nitre yet made, is, according to Mr. Baumé, 1.500, and according to Mr. Bergman 1.586.

Our author next proceeded to examine the propor-

Quantity of fixed alkali acid, water, and alkali in nitre determined.

Some experiments of the same kind had been made by M. Homberg; the results of which our author compared with those of his own. The specific gravity of the spirit of nitre which M. Homberg made use of was 1.349; and of this, he says, one ounce two drachms and 36 grains, or 621 troy grains, are required to saturate one French ounce (472.5 troy) of dry salt of tartar. According to Mr Kirwan's computation, however, 613 grains are sufficient; for the specific gravity lies between the specific gravities by observation 1.362 and 1.337, and is nearly an arithmetical mean between them. The corresponding mathematical specific gravity lies between the quantities marked in Mr Kirwan's table 1.315 and 1.286, being nearly 1.300. Now the proportion of acid and water in this is 2.629 of acid and 7.465 of water; for 8.765 - 1.300 = 7.465 of water, and 8.765 x 300 = 2.629 of acid; and the sum of both is 10.044. Now, since 10.5 grains of mild vegetable alkali require 3.53 grains of acid for their saturation, 472.5 will require 159.7; therefore if 10.044 grains of nitre contain 2.629 grains acid, the quantity of this spirit of nitre requisite to give 159.7 will be 613.2 nearly, and thus the difference with M. Homberg is only about eight grains.

M. Homberg says he found his salt, when evaporated to dryness, to weigh 186 grains more than before; but by Mr Kirwan's experiment, it should weigh but 92.8 grains more than at first; the cause of which difference will be mentioned in treating of vitriolated tartar, as it cannot be entirely attributed to the difference of evaporation.

He also affirms, that one ounce (472.5 Troy grains) of this spirit of nitre contains 141 grains of Troy of real acid. According to Mr Kirwan's computation, however, it contains only 123.08 grains of real acid. But this difference evidently proceeds from his neglecting the quantity of water that certainly enters into the composition of nitre; for he proceeds on this analogy, 621 : 186.6 :: 472.5 : 141.

Our author observes, that the proportion of fixed alkali assigned by him to nitre is fully confirmed by an experiment of Mr Fontana's inserted in Rozier's Journal for 1778. He decomposed two ounces of nitre by distilling it with a strong heat for 18 hours. After the distillation there remained in the retort a substance purely alkaline, amounting to 10 French drachms and 22 grains. Now two French ounces contain 945 grains Troy, and the alkaline matter 607 grains of the same kind; according to Mr Kirwan's computation the two ounces of nitre ought to contain 625 grains of alkali. Such a small difference he supposes to proceed from the loss in transferring from one vessel to another, weighing, filtering, evaporating, &c. Mr Kirwan also shows in a very particular manner the agreement of his calculations with the experiments of M. Lavoisier on mercury dissolved in spirit of nitre; but our limits will not allow us to insert an account of them.

When finding the quantity of pure acid contained in oil of vitriol, our author made use of such as was not deplogisticated; but, though pale, yet a little inclining to red. It contained some whitish matter, as contents, he perceived by its growing milky on the affusion of &c of the pure distilled water; but he imagines it was as pure as the kind used in all experiments.

To 2519.75 grains of this oil of vitriol, whose specific gravity was 1.819, he gradually added 180 grains more on of distilled water, and six hours after found its specific gravity to be 1.771.—To this mixture he again added 178.75 grains of water, and found its specific gravity, when cooled to the temperature of the atmosphere, to be 1.799, at which time it was milky. The same quantity of the oil of tartar above mentioned was then saturated with each of these kinds of oil of vitriol in the manner already described. The saturation was effected (taking a medium of five experiments) by 6.5 grains of that whose specific gravity was 1.819, by 6.96 grains of that whose specific gravity was 1.771, and by 7.41 of that whose specific gravity was 1.719.

It was found necessary to add a certain proportion of water to each of these sorts of oil of vitriol; for, oil of vitriol when they were not diluted, part of the acid was lost why phlogisticated, and went off with the fixed air; but necessary in knowing the quantity of water that was added, it was easily to find by the rule of proportion the quantity of each sort of vitriol that was taken up by the alkali. Hence it was supposed, that each of these quantities of oil of vitriol of different densities contained 3.55 grains of acid; as they saturated the same quantity of vegetable fixed alkali with 11 grains of spirit of nitre, which contained that quantity of acid.

It was next attempted to find the specific gravity of the pure vitriolic acid, in a manner similar to that by which the gravity of the nitrous acid was found; but as it cannot be had in the shape of air, unless when vitriolic united with such a quantity of phlogiston as quite alters its acid properties. The loss of 6.5 grains of oil of vitriol, whose specific gravity is 1.819, is $\frac{6.5}{1.819} = 3.572$; but as these 6.5 grains contained, besides 3.55 of acid, 2.95 of water, the loss of this must be subtracted from the entire loss; and then the remainder, or 0.622, is the loss of the pure acid part in that state or density to which it is reduced by its union with water. The specific gravity, therefore, of the pure vitriolic acid, in this state of density, is $\frac{3.55}{0.622} = 5.707$. But to find its natural specific gravity, we must find how much its density is increased by its union with this quantity of water; and in order to observe this, he proceeded as before with the nitrous acid. 6.96 grains of oil of vitriol, whose specific gravity was 1.771, contained 3.55 of acid and 3.41 of water; then its specific gravity by calculation should be 1.726; for the loss of 3.55 grains of acid is $\frac{3.55}{5.707} = 0.622$; the loss of 3.41 grains of water is 3.41; the sum of the losses 4.032; then 6.96 - 4.032 = 2.928; therefore the accrued density is 1.771 - 1.726 = 0.45. Taking this therefore from 1.819, its mathematical specific gravity will be 1.774. Then the loss of 6.5 grains of oil of vitriol, whose specific gravity by observation is 1.819, will be found to be $\frac{6.5}{1.774} = 4.663$; but of this, 2.95 grains are the loss. of the water it contains, and the remainder 0.714 are the loss of the mere acid part. Then \(\frac{355}{0.714}\) is nearly the true specific gravity of the pure vitriolic acid.

The specific gravity of the most concentrated oil of vitriol yet made, is, according to M. Baume and Bergman, 2.125.

Mr Kirwan now constructed a table of the specific gravities of vitriolic acids, of different strengths, in a manner similar to those constructed for spirit of salt and spirit of nitre; but for which, as well as the others, we must refer to Phil. Trans. vol. 71. He then proceeded to find the proportion of acid, water, and fixed alkali, in vitriolated tartar, as he had before done in sal digestivus and nitre.—He found the salts resulting from the saturation of the same oil of tartar, with portions of oil of vitriol, of different specific gravities, to weigh at a medium 12.45 grains. Of this weight only 11.85 grains were alkali and acid. The remainder, therefore, was water, viz. 0.6 of a grain. Consequently 100 grains of perfectly dry tartar vitriolate contain 21.58 grains acid, 4.82 of water, and 66.67 of fixed vegetable alkali.—In drying this salt, a heat of 240 degrees was made use of, to expel the adhering acid more thoroughly. It was kept in this heat for a quarter of an hour.

According to Mr Homberg, one French ounce, or 472.5 grains troy, of dry salt of tartar, required 297.5 grains troy, of oil of vitriol, whose specific gravity was 1.674, to saturate it; but by Mr Kirwan's calculation, this quantity of fixed alkali would require 325 grains; a difference which, considering the different methods they made use of for determining the specific gravities (Homberg's method by mensuration, giving it always less than Mr Kirwan's) the different defecation of their alkalies, &c. may be accounted inconsiderable.

The salt produced, according to Mr Homberg, weighed 182 grains troy above the original weight of the fixed alkali; but by Kirwan's experiment, it should weigh but 87.7 grains more. "It is hard to say (adds Mr Kirwan) how Mr Homberg could find this great excess of weight, both in nitre and tartar vitriolate; unless he meant by the weight of the salt of tartar the weight of the mere alkaline part distinct from the fixed air it contained: and indeed one would be tempted to think he did make the distinction; for in that case the excess of weight would be nearly such as he determined it."

From Mr Homberg's calculations, he inferred that one ounce (472.5 grains) of oil of vitriol contains 291.7 grains of acid. Mr Kirwan computes the acid only at 213.3 grains; but Homberg made no allowance for the water contained in tartar vitriolate; and imagined the whole increase of weight proceeded from the acid that is united in it to the fixed alkali. Now the aqueous part in 560 grains of tartar vitriolate amounts to 37 grains; the remaining difference may be attributed to the different degrees of defecation, &c.

On the acetous acid Mr Kirwan did not make any experiment; but by calculating from those of Homberg, he finds that the specific gravity of the pure acetous acid, free from superfluous water, should be 2.30. "It is probable (says Mr Kirwan), that its affinity to water is not strong enough to cause any irregular increase in its density; at least what can be expressed by three decimals: and hence its proportion of acid and water may always be calculated from its specific quantity and absolute weight."

An hundred parts of foliated tartar, or, as it should rather be called, acetous tartar, contain, when well dried, 32 of fixed alkali, 19 of acid, and 49 parts of water.—The specific gravity of the strongest concentrated vinegar yet made is 1.069.—It is more difficult to find the point of saturation with the vegetable than with the mineral acids, because they contain a mucilage that prevents their immediate union with alkalies; and hence they are commonly used in too great quantity: they should be used moderately hot, and sufficient time allowed them to unite.

From all the experiments above related, Mr Kirwan concludes, 1. That the fixed vegetable alkali takes up an equal quantity of the three mineral acids, and probably of all pure acids; for we have seen that 8.3 quantity of grains of pure vegetable alkali, that is, free from fixed air, take up 3.55 grains of each of these acids; consequently 100 parts of caustic fixed alkali would require 42.4 parts of acid to saturate them. But Mr Bergman has found that 100 parts of caustic fixed vegetable alkali take up 47 parts of the aerial acid; which, considering that his alkali might contain some water, differs but little from that already given. It should seem, therefore, that alkalies have a certain determined capacity of uniting to acids, that is, to a given weight of acids; and that this capacity is equally facilitated by a given weight of any pure acid indiscriminately. This weight is about 2.35 of the vegetable alkali.

2. That the three mineral acids, and probably all pure acids, take up 2.53 times their own weight of pure vegetable alkali, that is, are saturated by that quantity.

3. That the density accruing to compound substances, from the union of their compound parts, and exceeding its mathematical ratio, increases from a minimum, when the quantity of one of them is very small, in proportion to that of the other; to a maximum, when their qualities differ less: but that the attraction, on the contrary, of that part which is in the smallest quantity to that which is in the greatest, is at its maximum when the accrued density is at its minimum; but not reciprocally: and hence the point of saturation is probably the maximum of density and the minimum of sensible attraction of one of the parts. Hence no decomposition operated by means of a substance that has more affinity with one part of a compound than with another, the other, and these parts have with each other, can be complete, unless the minimum affinity of this third substance be greater than the maximum affinity of the parts already united. Hence also few decompositions are complete, unless a double affinity intervenes; and hence the last portions of the separated substance adhere so obstinately to that with which they were first united, as all chemists have observed.—that with which it has a greater affinity to phlogiston than the earths of the different metals have to it, yet they can never totally dephtlogiticate these acids, but only to a certain degree; so, though at never total atmospheric air, and particularly dephtlogiticated air, attracts phlogiston more strongly than the nitrous acid does, yet not even dephtlogiticated air can deprive the earths of nitrous acid totally of its phlogiston; as is evident from... the red colour of the nitrous acid, when nitrous air and dephlogisticated air are mixed together. Hence mercury precipitated from its solution in any acid, even by fixed alkalies, constantly retains a portion of the acid to which it was originally united, as Mr Bayen has shown. Thus also the earth of alum, when precipitated in like manner from its solution, retains part of the acid; and thus several anomalous decompositions may be explained.

409 Alkalies phlogisticated concentrated acids, oil of tartar, we may determine the quantity of real pure acid in any other acid substance that is difficultly decomposed; as the fatty acid, and those in vegetables and animals. For 10.5 grains of the mild pure acid in alkali will always be saturated by 3.55 grains of real acid; and reciprocally, the quantity of acid in any acid liquor being known, the quantity of real alkali in any vegetable alkaline liquor may be found.

Having thus determined the quantity of acid contained in the liquids of that kind usually employed in chemistry, as well as the specific gravities of the acids themselves, Mr Kirwan became desirous of investigating the gravity of fixed and volatile alkalies. But as these substances are not easily preserved from uniting themselves with fixed air, he was led to consider the gravity of this in its fixed state, as an element necessary for the calculation of the quantities of the alkalies.

To find the specific gravity of the fixed vegetable alkali, our author proceeded in a manner similar to that already described, excepting that he weighed it in ether instead of spirit of wine. The results of his experiments are,

1. That 100 grains of this alkali contain about 6.7 grains of earth; which, according to Mr Bergman, is siliceous. It passes the filter along with it when the alkali is not saturated with fixed air; so that it seems to be held in solution in the same manner as in the liquor silicium.

2. The quantity of fixed air in oil of tartar and dry vegetable fixed alkali is various at various times, and in various parcels of the same salt; but in the purer alkalies it may be reckoned at a medium 21 grains in 100; and hence the quantity of this alkali may very nearly be guessed at in any solution, by adding a known weight of any dilute acid to a given weight of such a solution, and then weighing it again; for as 21 is to 100, so is the weight lost to the weight of mild alkali in such solution. The specific gravity of mild and perfectly dry vegetable fixed alkali, four times calcined, free from siliceous earth, and containing 21 per cent. of fixed air, was found to be 5.0527. When it contains more fixed air the gravity is probably higher, except when it is not perfectly dry; and hence the specific gravity of this alkali, when caustic, was supposed by Mr Kirwan to be 4.234. For this reason the fixed alkalies, when united to aerial acid, are specifically heavier than when united either to the vitriolic or nitrous. Thus Mr R. Watson, in the Philosophical Transactions for 1770, informs us, that he found the specific gravity of dry salt of tartar, including the siliceous earth it naturally contains, to be 2.761; whereas the specific gravity of vitriolated tartar was only 2.636, and that of nitre 1.933. The reason why nitre is so much lighter than tartar vitriolate is, that it contains much more water, and the union of the acid with the water is less intimate.

Impure vegetable fixed alkalies, such as pearl-ash, pot-ashes, &c. contain more fixed air than the purer kind.

According to Mr Cavendish, pearl-ash contains 28.4 per cent. of fixed air. Hence in lime made from so much of these salts, of equal specific gravities with those of lighter than purer alkali, the quantity of saline matter will probably be in the ratio of 28.4 or 28.7 to 21; but this additional weight is only fixed air. Much also depends Quantity on their age; the oldest containing most fixed air. Our fixed air in author also gives a table of the specific gravities of different solutions of vegetable fixed alkali, in a manner similar to what he had done before with the acids. He begins mined with 64.92 grams of a solution containing 26.25 Mr Cave grains of salt, and 38.67 of water. The accrued density he finds to be .050, the mathematical specific gravity 1.445, and the specific gravity by observation 1.495. By continually diluting the solution containing the same quantity of salt, he brings the absolute weight of it at last to 344.94 grams, of which 317.49 are water; the accrued density 0.01, the mathematical specific gravity 1.064, and the specific gravity by observation 1.062.

In a subsequent paper on this subject, Philosophical Quarterly of Transactions, vol. 72, p. 179, our author corrects the acid taken small mistake concerning the quantity of acid taken up by mild fixed alkali by 10.5 grams of mild vegetable alkali. In his former exactly computations he had made no allowance for the small terned quantity of earth contained in this quantity of alkali; which, though inconsiderable in it, becomes of consequence where the quantities are large. The error, however, occasioned by this omission, isensible in his calculations concerning the quantities of acid, alkali, &c. contained in the neutral salts, as well as in that concerning the vegetable alkali. When the correction is properly made, he says, it will be found that 100 grains of such alkali, free from earth, water, and fixed air, take up 46.77 of the mineral acids, that is, of the mere acid part; and 100 grains of common mild vegetable alkali take up 36.23 grams of real acid. An hundred grains of perfectly dry tartar vitriolate contain 30.21 of real acid, quantity of 64.61 of fixed alkali, and 5.18 of water. Crystallized in vitriol tartar vitriolate loses only one percent. of water in a heat in lated tartar; which its acid is not separated in any degree; and tar therefore contains 6.18 of water. An hundred grams of nitre, perfectly dry, contain 30.86 of acid, 66 of alkali, and 3.14 of water; but in crystallized nitre the proportion of water is somewhat greater; for 100 grams of these crystals being exposed to a heat of 180° for two hours, lost three grams of their weight without exhaling any acid smell; but when exposed to a heat of 200 degrees, the smell of the nitrous acid is distinctly perceived. Hence 100 grams of crystallized nitre contain 29.89 of mere acid, 63.97 of alkali, and 6.14 of water. An hundred grams of digestive salt perfectly dry, contain 29.68 of marine acid, 63.47 of alkali, and 6.85 of water. One hundred grams of crystallized digestive salt lose but one grain of their weight before the smell of the marine acid is perceived; in digestive salt, and hence they contain 7.85 grams of water.

Another mistake, more difficult to be corrected, was his supposing the mixtures of oil of vitriol and water, and spirit of nitre and water, had attained their maximum of density when they had cooled to the tempera- ture of the atmosphere; which at the time he made the experiment was between 50° and 60° of Fahrenheit.

The mixture with oil of vitriol had been suffered to stand six hours; but when the acid was so much diluted as to occasion little or no heat, it was allowed to stand only for a very little time. Several months afterwards, however, many of these mixtures were found much denser than when he first examined them; and it was discovered, that at least twelve hours rest was necessary before concentrated oil of vitriol, to which even twice its weight of water is added, can attain its utmost density; and still more when a smaller proportion of water is used. Thus when he made the mixture of 259.75 grains of oil of vitriol, whose specific gravity was 1.819, with 180 of water, he found its density fix hours after 1.771, but after 24 hours it was 1.798: and hence, according to the methods of calculating already laid down, the accrued density was at least .064 instead of .045. But by using oil of vitriol still more concentrated, whose specific gravity was 1.8816, he was enabled to make a still nearer approximation; and found, that the accrued density of oil of vitriol, whose specific gravity is 1.819, amounts to 0.104, and consequently its mathematical specific gravity is 1.715. Six grains and a half of this oil of vitriol contained, as has been already observed, 3.55 of mere acid, and the remainder was water. The weight of an equal bulk of water is 3.79 grains; and subtracting from this the weight of the water that enters into the composition of the oil of vitriol, it will be found, that the weight of a bulk of water equal to the acid part is 0.84; and consequently the specific gravity of the mere acid part is 4.226. Thus, by constantly allowing the mixtures to rest at least 12 hours, until the oil of vitriol was diluted with four times its weight of water, and then only fix hours before the density of the mixtures was examined, he constructed another table, in which 1000 grains of liquor contained 612.05 of pure acid, 387.95 of water, the accrued density being .073, and the mathematical specific gravity 1.877. Increasing the quantity of water till the acid weighed 7000 grams, and the water 6387.95, he found the accrued density .059, and the mathematical specific gravity 1.669. By a similar correction of his experiments on the acid of nitre, he found its density to be 5.530; a similar table was constructed for it, for which we refer our readers to the 72d volume of the Philosophical Transactions.

These experiments were made when the thermometer stood between 50° and 60° of Fahrenheit; but, as it might be suspected that the density of acids is considerably altered at different degrees of temperature, he endeavoured to find the quantity of this alteration in the following manner: To calculate what this density would be at 55°, he took some dephlogisticated spirit of nitre, and examined its specific gravity at different degrees of heat; which was found to be as follows,

| Degrees of heat | Specific gravity | |-----------------|-----------------| | 30 | 1.4653 | | 46 | 1.4567 | | 86 | 1.4362 | | 120 | 1.4173 |

The total expansion of this spirit of nitre, therefore, from 30 to 120 degrees, that is, by 90° of heat, was 0.0527; for 1.4650 = 1.4123 + 0.0527. By which we see, that the dilatations are nearly proportional to the degrees of heat: for beginning with the first dilatation from 30 to 46 degrees, that is, by 16 degrees of heat, we find that the difference between the calculated and observed dilatations is only \( \frac{1}{100} \); a difference of no consequence in the present case, and which might arise from the immersion of the cold glass-ball filled with mercury in the liquor. In the next case the difference is still less, amounting only to \( \frac{1}{1000} \).

With another, and somewhat stronger spirit of nitre, the specific gravities were as follow:

| Degrees of heat | Specific gravity | |-----------------|-----------------| | 34 | 1.4750 | | 49 | 1.4653 | | 150 | 1.3792 |

Here also the expansions were nearly proportional to the degrees of heat; for 116° of heat, the difference between 34 and 150, produce an expansion of 0.0958; and 15° of heat, the difference between 34 and 49, produce an expansion of 0.0097; and by calculation 0.0123; which last differs from the truth only by \( \frac{1}{1000} \).

From this experiment we see, that the stronger the spirit of nitre is, the more it is expanded by the same degree of heat; for if the spirit of nitre of the last experiment were expanded in the same proportion as in the former, its dilatation, by 116 degrees of heat, weak, and should be 0.0679; whereas it was found to be 0.0958 why.

As the dilatation of the spirit of nitre is far greater than that of water by the same degree of heat, and as it confinits only of acid and water; it clearly follows, that its superior dilatability must be owing to the acid part: and hence the more acid that is contained in any quantity of spirit of nitre, the greater is its dilatability. We might therefore suppose, that the dilatation of nitre was intermediate betwixt the quantity of water it contains and that of the acid. But there exists another power also which prevents this simple result, viz. the attraction of the acid and water to each other, which makes them occupy less space than the sum of their joint volumes; and by this condensation our author explains his phrase of accrued density. Taking this into the account, we may consider the dilatation of the spirit of nitre as equal to those of the quantities of water and acid it contains, minus the condensation they acquire from their mutual attraction; and this rule holds as to all other heterogeneous compounds.

To find the quantities of acid and water in spirit of nitre, whose specific gravity was found in degrees of quantities temperature different from those for which the table was constructed, viz. 54°, 55°, or 56° of Fahrenheit, gained in the surest method is to find how much that spirit of nitre is expanded or condensed by a greater or lesser degree of heat; and then, by the rule of proportion, find what its density would be at 55°. But if this cannot be done, we shall approach pretty near the truth, if we allow \( \frac{1}{100} \) for every 1° degrees of heat above or below 55° of Fahrenheit, when the specific gravity is between 1.400 and 1.500, and \( \frac{8}{100} \) when the specific gravity is between 1.400 and 1.500.—The dilatations of oil and spirit of vitriol were found to be exceedingly irregular, probably by reason of a white foreign matter, which is more or less suspended or dissolved in it, according to its greater or lesser dilution; and and this matter our author did not separate, as he intended to try the acid in the state in which it is commonly used. In general he found that 15° of heat caused a difference of above 1° in its specific gravity, when it exceeds 1.800, and 1° when its specific gravity is between 1.400 and 1.300. The dilatations of spirit of salt are very nearly proportional to the degrees of heat, as appears by the following table.

| Degrees | Specific Gravity | |---------|-----------------| | 21° | 1.1916 | | 54° | 1.1860 | | 66° | 1.1820 | | 128° | 1.1631 |

Hence \( \frac{1}{15} \) should be added or subtracted for every 21° above or below 55°, in order to reduce it to 55°, the degree for which its proportion of acid and water was calculated. The dilatability of this acid is much greater than that of water, and even than that of the nitrous acid of the same density.

Our author next proceeds to consider the quantity of pure acids taken up at the point of saturation by the various substances they unite with.—He begins with the mineral alkali. Having rendered a quantity of this caustic in the usual manner, and evaporating one ounce of the caustic solution to perfect dryness, he found it to contain 20.25 grains of solid matter. He was assured, that the watery part alone exhaled during evaporation, as the quantity of fixed air contained in it was very small, and to dissipate this a much greater heat would have been requisite than that which he used. This dry alkali was dissolved in twice its weight of water; and saturating it with dilute vitriolic acid, he found it to contain 2.25 grains of fixed air; that being the weight which the saturated solution wanted of being equal to the joint weights of water, alkali, and spirit of vitriol employed.

The quantity of mere vitriolic acid necessary to saturate 100 grains of pure mineral alkali was found to be 60 or 61 grains; the saturated solution thus formed being evaporated to perfect dryness weighed 36.5 grains; but of this weight only 28.38 were alkali and acid; the remainder, that is, 8.12 grains, therefore, were water. Hence 100 grains of Glauber's salt, perfectly dried, contained 29.12 of mere vitriolic acid, 48.6 of mere alkali, and 22.28 of water. But Glauber's salt crystallized contains a much larger proportion of water; for 100 grains of these crystals heated red hot lost 55 grains of their weight; and this loss Mr Kirwan supposes to arise merely from the evaporation of the watery part, and the remaining 45 contained alkali, water, and acid, in the same proportion as the 100 grains of Glauber's salt perfectly dried above mentioned. Then these 45 contained 13.19 grains of vitriolic acid, 21.87 of fixed alkali, and 9.94 of water: consequently 100 grains of crystallized Glauber's salt contain 13.19 of vitriolic acid, 21.87 of alkali, and 64.94 of water.

On saturating the mineral alkali with dephlogisticated nitrous acid, it was found that 100 grains of the alkali took up 57 of the pure acid in the experiment he most depended upon; though in some others this quantity varied by a few grains: he concludes, therefore, that the quantity of alkali taken up by this acid nearly the same as that taken up by the vitriolic acid. Supposing this quantity to be 57 grains, then 100 contents, grains of cubic nitre, perfectly dry, contain 30 of acid, &c. of the 52.18 of alkali, and 17.82 of water: but cubic nitre crystallized contains something more water; for 100 grains of these crystals lose about four by gentle drying; therefore 100 grains of the crystallized salt contain 28.8 of acid, 50.9 of alkali, and 21.11 of water.

An hundred grains of mineral alkali require from By marine 63 to 66 or 67 grains of pure marine acid to saturate acid. it; but Mr Kirwan supposes that one reason of this variety is, that it is exceeding hard to hit the true point of saturation. Allowing 66 grains to be the quantity required, then 100 grains of perfectly dry common salt contain nearly 35 grains of real acid, 53 of alkali, and 13 of water; but 100 grains of the crystallized salt lose five by evaporation: so that 100 grains of these crystals contain 33.3 of acid, 50 of alkali, and 16.7 of water.

The proportion of fixed air, alkali, and water, was thus investigated: 200 grains of these crystals were of fixed air, dissolved in 240 of water; the solution was saturated alkali, and by such a quantity of spirit of nitre as contained 40 water, instead of pure nitrous acid; whence it was inferred that 17 of this saturated solution contained 70 of pure nitrous acid. The saturated solution weighed 40 grains less than the sum of its original weight, and that of the spirit of nitre added to it; consequently it lost 40 grains of fixed air. The remainder of the original weight of the crystals therefore must have been water, viz. 90 grains. Consequently 100 grains of these crystals contained 35 of alkali, 20 of fixed air, and 45 of water. This proportion differs considerably from that assigned by Mr Bergman and Lavoisier, which our author imputes to their having made use of soda Bergman recently crystallized; but Mr Kirwan's had been made and Lavoisier for some months, and probably lost much water and fixed air by evaporation, which altered the proportion of counted for the whole. According to the calculations of Bergman and Lavoisier, 100 grains of this alkali take up 80 of fixed air. The specific gravity of the crystallized mineral alkali, weighed in ether, was found to be 1.421.

The proportion of the different ingredients in volatile alkalies can only be had from the experiments of lately made by Dr Priestley concerning alkaline air. He informs us, that 1° of a measure of this, and one of volatile measure of fixed air, saturate one another. Then, supposing the measure to contain 100 cubic inches, 185 cubic inches of alkaline air take up 100 of fixed air; but 185 cubic inches of alkaline air weigh at a medium 42.55 grains, and 100 cubic inches of fixed air weigh 57 grains; therefore 100 grains of pure volatile alkali, free from water, take up 134 of fixed air.

On expelling its aerial acid from a quantity of this volatile alkali in a concrete state, and formed by sublimation, he found, that 53 grains of it were fixed air: according to the preceding calculation, 100 grains of it should contain 39.47 of real alkali, and 7.53 of water, the rest being fixed air.—On saturating a quantity with the vitriolic, nitrous, and marine acids, 100 grains of the mere alkali were found to take up 106 of mere vitriolic acid, 115 of the nitrous, and 130 of the marine acid. The specific gravity of the volatile alkali weighed in ether (b) was 1.4076. The proportion of water in the different ammoniacal salts could not be found on account of their volatility; but was supposed to be very small, as both volatile alkali and fixed air crystallize without the help of water when in an aerial state.

In making experiments on calcareous earth, it was first dissolved in nitrous acid; and after allowing for the loss of fixed air and water, 100 grains of the pure earth was found to take up 104 of nitrous acid; but only 91 or 92 of mere vitriolic acid were required to precipitate it from the nitrous solution.

Of the marine acid 100 grains of the pure calcareous earth require 112 for their solution. The liquor at first is colourless, but acquires a greenish colour by standing.

Natural gypsum varies in its proportion of acid, water, and earth; 100 grains of it containing from 32 to 34 of acid and likewise of earth, and from 26 to 32 of water. The artificial gypsum contains 32 of earth, 29.44 of acid, and 38.56 of water. When well dried, it loses about 24 of water; and therefore contains 42 of earth, 39 of acid, and 19 of water, per hundred.

Nitrous felselite (solution of calcareous earth in nitrous acid) carefully dried, contains 33.28 of acid, 32 of earth, and 34.72 of water.

The same quantity of marine felselite (solution of calcareous earth in marine acid), well dried, in such a manner as to lose no part of the acid, contain of the latter 42.56, of earth 38, and of water 19.44.

Magnesia, when perfectly dry and free from fixed air, cannot be dissolved in any of the acids without heat. Even the strongest nitrous acid did not act upon it in 24 hours in the temperature of the atmosphere; but in a heat of 180°, the mineral acids, diluted with four, or even six, times their quantity of water, had a very sensible effect upon it; but the quantity of acid dissipated by heat rendered it impossible to ascertain how much was necessary for solution, except by precipitation after it had been dissolved. For this purpose the caustic vegetable alkali was employed; by which it appeared that 100 grains of pure magnesia take up 125 of mere vitriolic acid, 132 of the nitrous, and 140 of the marine. All of these solutions appeared to contain something gelatinous; but none of them reddened vegetable blues; and that in the marine acid became greenish on standing for some time.

An hundred grains of perfectly dry Epson salt contain 45.67 of mere vitriolic acid, 36.54 of pure earth, and 17.83 of water. Solution of common Epson salt, however, reddens vegetable blues, and therefore contains an excess of acid. A like quantity of nitrous Epson, well dried, contains 35.64 of acid, 27 of pure earth, and 37.36 of water. The solution of marine Epson cannot be tolerably dried without losing much of its acid together with the water. The specific gravity of this earth is 2.3296.

Most writers on chemistry have said that earth of alum contains scarce any fixed air; but Mr Kirwan found that it contained no less than 26 per cent. though it had been previously kept red-hot for half an hour.

It dissolved with a moderate effervescence in acids until the heat was raised to 220°; after which the solution was found to have lost weight in the proportion above mentioned.

An hundred grains of this earth, deprived of the fixed air, require 133 of the pure vitriolic acid to dissolve them. The solution was made in a very dilute spirit of vitriol, whose specific gravity was 1.093, and in which the proportion of acid to the water was nearly as 1 to 14. It contained a slight excess of acid, turning the vegetable blues to a brownish red; but it crystallized when cold, and the crystals were of the form of alum. Our author, therefore, is of opinion, that this is the true proportion of acid and earth to be used in the formation of that salt, though there was not water enough to form large crystals. Perceiving that the liquor contained an excess of acid, more earth was added; but thus it was found impossible to prevent it from tingling vegetable blues of a red colour until a precipitation was formed; and even when this was the case, though one part of the salt fell in the form just mentioned, yet the rest would still redden vegetable blues as before; though here our author doubts whether this be a mark of acidity. An hundred grains of alum, when dried, contain 42.74 of acid, 32.14 of earth, and 25.02 of water; but crystallized alum loses 44 per cent. by deliquescence; therefore 100 grains of it contain 23.94 of acid, and 58.06 of water. An hundred grains of this pure earth take up, as near as can be judged, 153 of pure nitrous acid. The solution still reddened vegetable blues; but after the above quantity of earth was used, an insoluble salt began to precipitate. The solution, when cold, became turbid, and could not be rendered quite clear by 500 times its quantity of water.

An hundred and seventy-three grains of pure marine acid are required for the dissolution of 100 acid grains of earth of alum, but the liquor still reddened vegetable blues. After this an insoluble salt was formed; but it is difficult to ascertain the beginning of its formation precisely both in this and the preceding cases. The specific gravity of pure argillaceous earth, containing 25 per cent. of fixed air, is 1.9901.

In the experiments made by our author on metals, the acids employed were so far deploglificated as to be colourless; the metals were for the most part reduced to filings, or to fine powder in a mortar. They were added by little and little to their respective methods of distillation; much more being thus dissolved than if the whole had been thrown in at once, and the solution was performed in glass vials with bent tubes.

An hundred grains of bar-iron, in the temperature of 56°, require for their solution 190 grains of the real iron-taracid, whose proportion to that of the water, with the vitriolic which it should be diluted, is as 1 to 8, 10, or 12. It would act on iron, though its proportion were greater or lesser, though not so vigorously; but by applying a heat of 200° towards the end, 123 grains of

(b) The fixed and volatile alkalies were weighed in ether on account of their great solubility in water. of real acid would be sufficient. The air produced by this solution is entirely inflammable, and generally amounts to 155 cubic inches.

By the affluence of a strong heat, iron is also soluble in the concentrated vitriolic acid, though in smaller quantity; and instead of inflammable air, a large quantity of vitriolic air is produced, and a little sulphur is sublimed towards the end. The reason of this is, that the concentrated vitriolic acid, containing much less specific fire than the dilute kind, cannot expel the phlogiston in the form of inflammable air (which absorbs a vast quantity of fire), but unites with it when further dephlogisticated by heat, and thus forms both vitriolic air and sulphur. An hundred grains of iron dissolved without heat afford more than 400 of vitriol; and 100 grams of vitriol, when crystallized, contain 25 of iron, 20 of real acid, and 55 of water. When calcined nearly to redness, these crystals lose about 40 per cent. of water.

The calces of iron are soluble in the vitriolic acid according to the quantity of phlogiston they contain; the more phlogisticated being more readily soluble, and those which are dephlogisticated less so. The latter not only require more real acid for their solution, but afford only a thick liquor or magma by evaporation, instead of crystals like the others. Hence also solutions of iron, when newly made, diminish, and consequently phlogisticate, the superincumbent air by their gradual emission of phlogiston; at the same time that the calx, becoming more and more dephlogisticated, gradually falls to the bottom, unless more acid be added to keep it in solution.

An hundred grains of iron require for their solution in nitrous acid 142 grains of real acid, so diluted that its proportion to water should be as 1 to 13 or 14; and when this last proportion is used, the heat of a candle may be employed for a few seconds, and the access of common air prevented. Thus about 18 cubic inches of nitrous air are produced, the rest being absorbed by the solution, and no red vapours appear. But if the proportion of acid and water be as 1 to 3 or 10, a much greater quantity of metal will be dephlogisticated by the application of heat, though very little of it be held in solution. Thus, from 100 grams of iron Mr Kirwan has obtained 83.87 cubic inches of nitrous air; and by distilling the solution, a still greater quantity may be obtained which had been absorbed. The reason that nitrous solutions of iron or other metals yield no inflammable air is, because this acid has less affinity to water, and more to phlogiston, than the vitriolic, and likewise contains much less fire than either that or the marine (seen 278); and therefore unites with phlogiston, instead of barely expelling it. Hence also the vitriolic acid, though united with 30 times its weight of water, will still visibly act on iron, and separate inflammable air in the temperature of 55° whereas nitrous acid, diluted with 15 times its weight of water, has no perceptible effect on the metal in that temperature. The calces of iron, if not too much dephlogisticated, are also soluble in the nitrous acid.

Two hundred and fifteen grams of real marine acid are required for the solution of 100 grams of iron. When the proportion of water to the acid is as four to one, it effervesces rather too violently with the metal; and heat is rather prejudicial, as it volatilizes the acid. Contents, No marine air flies off; and the quantity of inflammable air is exactly the same as with diluted vitriolic acid. The calces of iron are also soluble in marine acid, and may be distinguished by their reddish colour Calces of when precipitated by fixed alkalies, while the precipitated iron precipitates of the metal are greenish.

An hundred and eighty-three grains of real vitriolic colour from acid are required to dissolve an hundred grains of copper; the proportion of acid to that of water being as 1 to 1.5, or at least as 1 to 1.7; and a strong heat must rise acid, also be applied. Mr Kirwan says he never could dissolve the whole quantity of copper; but to dissolve a given quantity of it, until greater heat must be employed in the dissolved by proportion of 28 to 100; but this residuum also is vitriolic acid, soluble by adding more acid. Copper dephlogisticated acid, in this manner is soluble by adding warm water to the mass.

By treating 128 grains of copper in this manner, we fail to obtain 11 cubic inches of inflammable air and 65 of ble and vitriolic acid air. When inflammable air was obtained, air obtained however, our author tells us the acid was a little more from aqueous. The reason why copper cannot be dephlogisticated by dilute vitriolic acid, or even by the concentrated kind without the affluence of heat, is its strong attraction to phlogiston, and the great quantity Why this it contains.

An hundred grains of vitriol of copper contain 27 ed upon of metal, 30 of acid, and 43 of water; 28 of which dilute vitriol are lost by evaporation or slight calcination. An acidic acid, hundred grains of copper, when dissolved, afford 373 of blue vitriol.

An hundred grains of copper require 130 of pure ingredients in nitrous acid for their dissolution. If the acid be too far diluted that its proportion of water be as 1 to 14, triol, the affluence of heat will be necessary, but not otherwise. This solution affords 67½ inches of nitrous copper diff. air.—The calces of copper are soluble in the nitrous acid.

A like quantity of this metal requires 1190 grains of real marine acid, as well as the affluence of a moderate heat, to dissolve them; the proportion of water being as 4½ to 1. By employing a greater heat, more of the acid will be requisite, as much more will be dissipated; the concentrated acid acts more vigorously.—Calces of copper are likewise soluble in the marine acid, though less easily than in the nitrous.

The vitriolic acid dissolves tin but in small quantity; Action of an hundred grams of the metal requiring for their solution 872 of real acid, whose proportion to water acid in tin, should not be less than 1 to 0.9. A strong heat is also required. When the action of the acid has ceased, some hot water should be added to the turbid solution, and the whole again heated. The metal is soluble in a more dilute acid, but not in such quantity.—The inflammable solution above mentioned affords 70 cubic inches of inflammable air.—The calces of tin, excepting that precipitated from marine acid by fixed alkalies, are insoluble in the vitriolic acid.

An hundred grams of tin require 1200 of real nitrous acid; whose proportion of water should be at least 25 to 1, and the heat employed not exceeding 60°. The quantity of air afforded by such solution is only 10 cubic inches, and it is not nitrous. The solution lution is not permanent; for in a few days it deposits a whitish calx, and in warm weather bursts the vial. The calces of tin are insoluble in this acid.

Four hundred and thirteen grains of pure marine acid are required to dissolve 100 grains of tin, the proportion of water being as 4½ to 1. The affluence of a moderate heat is also required. About 90 cubic inches of inflammable, and 10 of marine air, are afforded by the solution; but the calces of tin are nearly insoluble in this acid.

An hundred grains of lead require 600 grains of real vitriolic acid for their solution, the proportion being not less than 1 of acid to 5 of water; and it will still be better if the quantity of water be less; for which reason, as in copper, a greater quantity of metal should be employed than what is expected to be dissolved. A strong heat is also requisite; and hot water should be added to the calcined mass, though in small quantity, as it occasions a precipitation.—This metal is also soluble, but very sparingly, in dilute vitriolic acid. Its calces are something more soluble. An hundred grains of vitriol of lead, formed by precipitation, contain 73 of lead, 17 of real acid, and 10 of water.

With spirit of nitre, 78 grains of real acid are required for the solution of 100 of lead, with the affluence of heat towards the end. The proportion of acid to that of water may be about 1 to 11 or 12. This solution produces but eight cubic inches of air, which is nitrous. The calces of the metal are soluble in this acid; but less so when much dephlogisticated. An hundred grains of minium require 81 of real acid. An hundred grains of nitrous salt of lead contain about 6c of the metal.

Six hundred grains of the real marine acid are required for the solution of 100 grains of lead; the specific gravity of the acid being 1.111, though more would be dissolved by a stronger acid.—The calces of lead are more soluble in this acid than the metal itself. An hundred grains of minium require 327 of real acid; but white lead is much less soluble. The same quantity of plumbeum cornu, formed by precipitation, contain 72 of lead, 18 of marine acid, and 10 of water.

An hundred grains of silver require 530 of real vitriolic acid to dissolve them; the proportion of acid to water being not less than as 1 to 4½; and when such a concentrated acid is used, it acts slightly even in the temperature of 60°; but a moderate heat is required in order to procure a copious solution. The calces of silver formed by precipitation from the nitrous acid with fixed alkalies are soluble even in dilute vitriolic acid without the affluence of heat. An hundred grains of vitriol of silver, formed by precipitation, contain 74 grains of metal, about 17 of real acid, and 9 of water.

An hundred grains of the purest silver require for their solution 36 of nitrous acid, diluted with water in the proportion of one part of real acid to five parts of water, applying heat only when the solution is almost saturated. If the spirit be much more or much less dilute, it will not act without the affluence of heat. The last portions of silver thus taken up afford no air. Standard silver requires about 38 grains of real acid to dissolve the same proportion of it; and the solution affords 20 cubic inches of nitrous air; whereas 100 grains of silver revived from luna cornea afford about 14.

Mr Kirwan has never been able to dissolve silver in the marine acid, though Mr Bayen says he effected the dissolution of three grains and a half of it by digestion for some days with two ounces of strong spirit of salt. Newmann informs us also, that leaf-silver is corroded by the concentrated marine acid. It is dissolved, however, by the dephtogisticated spirit of salt, as well as by the phlogisticated acid when reduced to a state of vapour. An hundred grains of luna cornea contain 75 of silver, 18 of acid, and 7 of water.

Mr Kirwan found that kind of aqua regia to succeed best kind, best in the dissolution of gold, which was prepared by aqua regia for dissolving together three parts of the real marine acid for diluting with one of the nitrous acid. Both of them ought also to be as concentrated as possible; though, when this is the case, it is almost impossible to prevent a great quantity from escaping, as a violent effervescence takes place for some time after the mixture. Aqua regia made with common salt or sal ammoniac and spirit of nitre, is much less aqueous than that proceeding from an immediate combination of both acids; and hence it is the fittest for producing crystals of gold. Very little air is produced by the solution of this metal, and the operation goes on very slow. It is, however, better promoted by allowing it sufficient time, than by applying heat. An hundred grains of Quantity gold require for their solution 245 grains of real acid, the two acids being in the proportion above mentioned. Though soluble in the dephtogisticated marine acid, it is only in very small quantity, unless the acid be in a state of vapour; for in its liquid state it is too aqueous. In vitriolic and nitrous acids it is insoluble, tho' Calces of the calces are somewhat soluble in the nitrous, more gold soluble easily in the marine, but scarcely at all in the vitriolic in the vitriolic acid. Mr Kirwan says, that gold in its metallic state nitrous may be dissolved through the concentrated nitrous acid, tho' not dissolved in it; contrary to the opinion of other chemists, who have affirmed that a true dissolution takes place.

An hundred grains of mercury require for their solution 230 grains of real vitriolic acid, whose proportion in nitric acid is as 1 to 1½. A strong heat is also requisite, and the air produced is vitriolic. Precipitate per se is still less soluble.—An hundred grains with vitriolic acid of vitriol of mercury, produced by precipitation, contain 77 of metal, 19 of acid, and 4 of water.

In spirit of nitre, 100 grains of mercury are dissolved by 28 of real acid, whose proportion to the water of nitre it contains is as 1 to 1½. In this acid the solution takes place without heat; but it may also be dissolved in a much more dilute acid, provided heat be applied. About 12 cubic inches of air are produced when heat is not applied; but M. Lavoisier found the produce much greater. This, says Mr Kirwan, was evidently caused by his using red or yellow spirit of nitre, which already contains much phlogiston. Precipitate per se is much less easily dissolved in the nitrous acid, which Mr Kirwan supposes to be owing to the attraction of the aerial acid.

The marine acid, in its common phlogisticated state, does not act on mercury, at least in its usual state of fine acid concentration; though M. Homberg, in the Paris Memoirs for the year 1700, affirms, that he dissolved it by several months digestion in this acid. When dephtogisticated, it certainly acts upon it, though very weakly. Zinc requires for its solution an equal quantity of real vitriolic acid, whose proportion to that of water may be as 1 to 8, 10, or 12. Heat must be applied towards the end, when the saturation is almost completed. By the help of heat also this semimetal is soluble in the concentrated vitriolic acid, but a small quantity of black powder remains in all cases undissolved. An hundred cubic inches of inflammable air are produced. An hundred grains of vitriol of zinc contain 20 of zinc, 22 of acid, and 58 of water. The calces of zinc, if not exceedingly dephlogisticated, are also soluble in this acid.

An hundred and twenty-five grains of real nitrous acid, whose proportion to water is that of 1 to 12, are required for the solution of 100 grains of this semimetal, applying heat slightly from time to time. A concentrated acid dissolves less of the metal, as a great quantity of the menstruum escapes during the effervescence. No nitrous air can be procured, the acid being partly decomposed during the operation. The calces of zinc, if not too much dephlogisticated, are likewise dissolved by the nitrous acid.

An hundred grains of zinc require for their dissolution 210 grains of real marine acid, the proportion of it to the water being as 1 to 9. If a more concentrated spirit of salt be made use of, a considerable part of it will be dissipated during the effervescence, and consequently more will be required for the solution. The calces of zinc are also soluble in the marine acid.

Only three grains of bismuth were dissolved by 200 of oil of vitriol, whose specific gravity was 1.863, though a strong heat was used at the same time. A greater quantity was indeed slightly dephlogisticated; but when the gravity of the acid was reduced to 1.200, only a single grain of the metal was dissolved by 400 of it. The calces of this semimetal are much more soluble. Four cubic inches of vitriolic air were afforded by the solution of three grains of bismuth.

In spirit of nitre, 100 grains of real acid are only required to dissolve 100 grains of the metal. The proportion of water to the acid ought to be as 8 or 9 to 1; in which case a gentle heat may be applied. The solution affords 44 cubic inches of nitrous air. The calces of bismuth are also soluble in this acid.

Only three or four grains of it were dissolved by 400 of marine acid, whose specific gravity was 1.220.

About four grains of nickel were dissolved in an hundred of the concentrated vitriolic acid with the assistance of a strong heat; but its calces are much more soluble. An hundred grains of nickel require for their solution 112 of real nitrous acid, whose proportion to water is as 1 to 11 or 12. The product of nitrous air is 79 inches. The calces are also soluble. A moderate heat is necessary for the dissolution of the metal; but a concentrated acid acts so rapidly, that much of it is dissipated.—Only four or five grains of nickel are dissolved by 200 of spirit of salt whose specific gravity was 1.220. An acid of this degree of strength acts without the assistance of heat, though a weaker acid requires it, and dissolves still less of the calces.

The calces of nickel are also soluble with difficulty in this acid.

Four hundred and fifty grains of real vitriolic acid, whose proportion to water is not less than 1 to 15, are required for the dissolution of 100 grains of co-rent acid; but, assisted by a heat of 270° at least. A solution of cobalt is obtained by pouring warm water on the dephto-vitriolic gaficated mass.—The calces of cobalt, however, are acid; more soluble; so that even a dilute acid will serve.

In spirit of nitre, the like quantity of cobalt requires With spirit 220 grains of real acid, whose proportion to water is 1 to 4; giving a heat of 180° towards the end.—The calces of the metal are soluble in the nitrous acid.

An hundred grains of spirit of salt, whose specific gravity is 1.178, dissolves, with the assistance of heat, of salt; two grains and a half of cobalt; and a greater quantity will be dissolved by an acid more highly concentrated.—The calces of cobalt are more soluble.

An hundred grains of regulus of antimony require Regulus of their solution 725 grains of real vitriolic acid, antimony whose proportion to water is as 1 to 7, assisted by vitriol acid; a heat of 400°. A large quantity of regulus should be put into the acid; and the resulting salt requires much water to dissolve it, as the concentrated acid lets fall much when water is added to it. A less concentrated acid will likewise dissolve this semimetal, but in smaller quantity. The calces of antimony, even diaphoretic antimony, are somewhat more soluble. Nine hundred grains of real nitrous acid are required for the solution of 100 grains of regulus; the proportion of acid to the water of the solvent being as 1 to 12, and assisted by an heat of 110°; but the solution becomes turbid in a few days. The calces are much less soluble in this acid.—Only one grain of the regulus is dissolved by 100 of spirit of salt, whose specific gravity liable in the was 1.220, with the assistance of a slight heat; and marine that which is only 1.178 dissolves still less; but Mr. Kirwan is of opinion that the concentrated acid would, in a long time, and by the assistance of a gentle heat, dissolve much more. The calces dissolve more easily in the marine acid.

Eighteen grains of regulus of arsenic are dissolved Regulus of in a heat of 250° by 200 grains of real vitriolic acid, arsenic with whose specific gravity is 1.871. About seven of these vitriolic parts crystallize on cooling, and are soluble in a large quantity of water. The calces of arsenic are more soluble in this acid.—An hundred and forty grains of real nitrous acid are requisite for the solution of 100 grains of regulus of arsenic; the proportion of acid to the water being as 1 to 11. The solution affords 102 cubic inches of nitrous air, the barometer being at 30 and the thermometer at 60°. Calces of arsenic are likewise soluble in this acid.

An hundred grains of spirit of salt, whose specific gravity is 1.220, dissolve a grain and an half of regulus of salt, of arsenic; but the marine acid, in its common state, that is, when its gravity is under 1.173, does not at all affect it. The arsenical calces are less soluble in this than in the vitriolic or nitrous acids.

§ 3. Of the Quantity of Phlogiston contained in different Substances.

Having gone through all the various bases with which acids are usually combined, and ascertained the quantity Quantity of quantity of different ingredients contained in the compound resulting from their union, we ought next to give an account of our author's experiments on phlogiston; but as his sentiments on that subject are taken notice of elsewhere, we shall content ourselves with briefly mentioning the very ingenious methods by which he discovers the quantities of it contained in various kinds of air and in sulphur.

Having proved that inflammable air, in its concrete state, and phlogiston are the same thing, Mr Kirwan proceeds to estimate the quantity contained in nitrous air in the following manner.

An hundred grains of filings of iron, dissolved in a sufficient quantity of very dilute vitriolic acid, produced, with the assistance of heat gradually applied, 155 cubic inches of inflammable air; the barometer being at 29.5, and the thermometer between 56° and 60°. Now, inflammable air and phlogiston being the same thing, this quantity of inflammable air amounts to 5.42 grains of phlogiston.—Again, 100 grains of iron dissolved in deplogisticated nitrous acid, in a heat gradually applied and raised to the utmost, afford 83.87 cubic inches of nitrous air. But as this nitrous air contains nearly the whole quantity of phlogiston which iron will part with (it being more completely deplogisticated by this than any other means), it follows, that 83.87 cubic inches of nitrous air contain at least 5.42 grains of phlogiston. But it may reasonably be thought, that the whole quantity of phlogiston which iron will part with is not expelled by the vitriolic acid, but that nitrous acid may expel and take up more of it. To try whether this was really the case, a quantity of green vitriol was calcined until its basis became quite infipid; after which, two cubic inches of nitrous air were extracted from 64 grains of this ochre; and consequently 100 grains would yield 3.12 cubic inches of nitrous air. If 83.87 cubic inches of nitrous air contain 5.42 of phlogiston; then 3.12 cubic inches of this air contain 0.2 of phlogiston. The nitrous acid, therefore, extracts from 100 grains of iron two-tenths of a grain more phlogiston than vitriolic acid does. Therefore 83.87 cubic inches of nitrous air, containing nearly the whole phlogiston of the iron, have 5.62 of this substance. Hence 100 cubic inches of nitrous air contain 6.7 grains of phlogiston."

With regard to the quantity of phlogiston in fixed air, after proving at length that it is composed of deplogisticated air united to the principle of inflammability, Mr Kirwan ascertains the quantity of the latter in the following manner: "Dr Priestley, in the fourth volume of his Observations, p. 380, has satisfactorily proved, that nitrous air parts with as much phlogiston to common air, as an equal bulk of inflammable does when fixed in the same proportion of common air. Now, when inflammable air unites with common air, its whole weight unites to it, as it contains nothing else but pure phlogiston. Since, therefore, nitrous air phlogisticates common air to the same degree that inflammable air does, it must part with a quantity of phlogiston, equal to the weight of a volume of inflammable air, similar to that of nitrous air. But 100 cubic inches of inflammable air weigh three grains and a half; therefore 100 cubic inches of nitrous air part with 3.5 grains of phlogiston, when they communicate their phlogiston to as much common air as will take it up. In this process, however, the Quantity of nitrous air does not part with the whole of the phlogiston it contains, as appears by the red colour it constantly affumes when mixed with common or deplogisticated air; which colour belongs to the nitrous acid, combined with the remainder of its phlogiston, whence the acid produced is always volatile.

One measure of the purest deplogisticated air and two of nitrous air occupy but \( \frac{1}{10} \) of one measure, as Dr Priestley has observed. Suppose one measure to contain 100 cubic inches, then the whole, very nearly, of the nitrous air will disappear (its acid uniting to the water over which the mixture is made), and 97 cubic inches of the deplogisticated air, which is converted into fixed air by its union with the phlogiston of the nitrous air; therefore 97 cubic inches of deplogisticated air take up all the phlogiston which 200 cubic inches of nitrous air will part with; and this we have found to be seven grains; therefore a weight of fixed air equal to that of 97 cubic inches of deplogisticated air, and 7 of phlogiston, will contain seven grains of the latter. Now, 97 cubic inches of deplogisticated air weigh 40.74 grains; to which adding 7, we have the whole weight of the fixed air = 47.74 grains, = 83.755 cubic inches; and consequently 100 cubic inches of fixed air contain 8.357 grains of phlogiston, the remainder being deplogisticated air. An hundred grains of fixed air therefore, contain 14.661 of phlogiston, and 85.339 of elementary or deplogisticated air. Hence also 100 cubic inches of deplogisticated air are converted into fixed air by 7.2165 grains of phlogiston, and will be then reduced to the bulk of 86.34 cubic inches.

To find the quantity of phlogiston in vitriolic acid air, our author pursued the following method.

1. He found the quantity of nitrous air afforded by a given weight of copper, when dissolved in the deplogisticated nitrous acid, and by that means how much phlogiston it parts with.

2. He found the quantity of copper which a given quantity of the deplogisticated vitriolic acid could dissolve; and observed, that it could not entirely saturate itself with copper without deplogisticating a further quantity which it does not dissolve.

3. He found how much it deplogisticates what it thoroughly dissolves, and how much it deplogisticates what it barely calcines.

4. How much inflammable air a given quantity of copper affords when dissolved in the vitriolic acid to the greatest advantage.

5. He deducts from the whole quantity of phlogiston expelled by the vitriolic acid the quantity of it contained in the inflammable air; the remainder shows the quantity of it contained in the vitriolic acid air.

The conclusion deduced from experiments conducted after this manner is, that 100 cubic inches of vitriolic air contain 6.6 grains of phlogiston, and 71.2 grains of acid; and 100 cubic inches of this air weighing 77.8 grams, 100 of it must contain 8.48 grams of phlogiston, and 91.52 of acid.

To find the quantity of phlogiston in sulphur, Mr Kirwan proposed to estimate that of the fixed air produced during its combustion. For this purpose he firmly tied and cemented to the open top of a glass-bell a large bladder, destined to receive the air expanded by combustion, which generally escapes when this Quantity of this precaution is not used. Under this bell, containing about 3000 cubic inches of air, a candle of substances sulphur, weighing 347 grains, was placed; its wick, which was not consumed, weighing half a grain. It was supported by a very thin concave plate of tin, to prevent the sulphur from running over during the combustion; and both were supported by an iron wire fixed in a flask in a tub of water. As soon as the sulphur began to burn with a feeble flame, it was covered with the bell, the air being squeezed out of the bladder. The inside of the bell was soon filled with white fumes, so that the flame could not be seen; but in about an hour after all the fumes were thoroughly sublimed, and the glass became cold, as much water entered the bell as was equal to 87.2 cubic inches; which space our author concludes to have been occupied by fixed air, and which must have contained 7.287 grains of phlogiston. The candle of sulphur being weighed was found to have lost 20.75 grains; therefore 20.75 grains of sulphur contain 7.287 of phlogiston, besides the quantity of phlogiston which remained in the vitriolic air. This air must have amounted to 20.75 - 7.287 = 13.463 grains, which, as already shown, contain 1.41 grains of phlogiston. Therefore the whole quantity of phlogiston in 20.75 grains of sulphur is 8.428; of consequence 100 grains of sulphur contain 59.39 of vitriolic acid, and 40.61 of phlogiston.

The quantity of phlogiston contained in marine acid air was found by the following method.—Eight grains of copper dissolved in colourless spirit of salt afforded but 4.9 inches of inflammable air; but when the experiment was repeated over mercury, 91.28 cubic inches of air were obtained. Of these only 4.9 cubic inches were inflammable; and consequently the remainder, 86.38 inches, were marine air, weighing 56.49 grains.—Now, as spirit of tartar certainly does not dephlogisticate copper more than the vitriolic acid does, it follows, that these 4.9 cubic inches of inflammable air, and 86.38 of marine air, do not contain more phlogiston than would be separated from the same quantity of copper by the vitriolic acid; and since 100 grains of copper would yield to the vitriolic acid 4.32 grains of phlogiston, 8.5 grains of copper would yield 0.367 grains of phlogiston. This therefore is the whole quantity extracted by the marine acid, and contained in 91.28 cubic inches of air; and, deducting from this the quantity of phlogiston contained in 4.9 cubic inches of inflammable air = 0.171 grains, the remainder, viz. 0.367 - 0.171 = 0.196, is all the phlogiston that can be found in 86.38 cubic inches of marine air. Then 100 cubic inches of it contain but 0.227 of a grain of phlogiston, 65.173 grains being acid.—Hence we see why it acts so feebly on oils, spirit of wine, &c., and why it is not dislodged from any basis by uniting with phlogiston, as the vitriolic and nitrous acids are, its affinity to it being inconsiderable.

§ 4. Remarks on the Doctrines of the Quantity and Specific Gravity above delivered.

To this doctrine of the specific gravity and quantity of acid contained in different substances, Mr Keir has made several objections. 1. Mr Kirwan supposes, that marine acid gas is the pure and solid marine acid deprived of all water and other matter. Its apparent dryness in this respect, however, is no argument that it really contains no water; for water itself, reduced to a state of vapour, possesses no moistening property. There is great reason to believe that water is a constituent part of some gases, and it is certain that all of them are capable of holding it in solution. As moist materials, therefore, are employed in the preparation of marine acid air, there seems no reason to believe, that in any way in which Mr Kirwan could obtain it, there was reason to suppose it perfectly free of water; in which case the density of the acid would be greater, and its quantity smaller than he supposes.

2. A considerable part of the density of the acid absorbed in the experiment, probably arose from the condensation which always accompanies the union of a concentrated acid with water. Mr Kirwan allows this to be the case with the nitrous and vitriolic acids, but thinks it too inconsiderable to deserve notice in the marine. His reasoning, however, does not appear satisfactory, or his experiments on the subject conclusive. He observes, that the length of time taken up in effecting an union between the marine gas and water, is no argument against their attracting one another strongly when once united; and it is certain that part of this acid gas is very quickly absorbed by water. He also finds fault with his accuracy in calculation; and affirms, that if matters are fairly stated, the real density of the marine acid gas will be considerably less than Mr Kirwan makes it.

3. A great obstacle even to an approximation towards the real density of the acid, arises from the condensation which the water, as well as the acids, must suffer in the process; and in this case, where a general condensation takes place, he asks, "How shall we determine the part of the condensation that belongs to the water, and the part that the acid retains?" This, with other considerations, makes Mr Keir "doubt of the possibility of solving the question concerning the actual density of pure and solid acids." The investigation of the question, indeed, he does not consider as a matter of great consequence, as every useful application may be obtained, by first investigating the comparative strengths of different portions of the same acid rendered more or less dilute; and then by finding out the strength of the vitriolic, nitrous, and marine acids of known densities, so that they may be compared together. "Homberg (says he) has the merit of making the first effort towards this investigation. Bergman and Wenzel have supplied the defect of Homberg, by taking into consideration the gas united with alkaline substances; and Mr Kirwan, by using determinate quantities of acid liquors of known densities, has considerably improved the method of Bergman: and whoever succeeds these able chemists in this inquiry, may avail himself greatly of their labours, particularly those of Mr Kirwan." He concludes with stating the results of the inquiries made by the chemists above mentioned; on which he makes the following remarks.

"The discordancy of these results is very striking, great difference gives but an humiliating representation of the preferences in our present knowledge in chemistry. A great part of the difference arises undoubtedly from the different views in which these authors considered the dryness or purity of the acids. Mr Kirwan, as we have seen, endeavoured to find their density and quantity in a state of perfect dryness and purity; which he supposed to exist in the marine acid gas: with which he compared and inferred the densities and quantities of the nitrous and vitriolic acids, upon the supposition that equal quantities of these several acids are saturated by a given weight of fixed alkali. Besides the uncertainty of his principles, from which he deduces the density and quantity of the marine acid, his applications from thence to deduce the densities of the pure nitrous and vitriolic acids, being founded on the above supposition, must partake of its defects. The alkali which he happened to fix on as the standard by which he compared the strengths of the different acid liquors, in order to determine the quantity of real acid they contained, and thence to determine their density in a solid state, was the fixed vegetable. Having found that 100 grains of his real marine acid could saturate 215 grains of this alkali, he infers, that the same proportion is applicable to the other acids; and accordingly we find that 100 grains of each of the pure and real mineral acids are saturated by an equal quantity, viz. 215 grains of this alkali. But if we examine the other columns of his table, we shall at once see, that, in other substances soluble by acids, this equality does not exist; and that every such substance has a ratio peculiar to itself, with respect to the proportions of these acids necessary for its saturation. It is evident, therefore, that if Mr Kirwan had fixed on the mineral alkali, the volatile alkali, lime, or any other substance, as a standard, instead of vegetable alkali, his determination of the densities of the real vitriolic and nitrous acids would have been different; and as no reason can be assigned why the vegetable alkali or any other substance should have the prerogative over the rest, it is obvious that there can be no such general standard, but that each substance possesses solely the capacity of determining the proportions of the several acids necessary for its saturation.

"The other chemists were contented to consider as the pure and dry acid, that which actually remains in the neutral salt, after this has been rendered as dry as possible by exposure to a red heat: and having made their alkalies as dry as they could, they supposed these alkalies to retain the same weight in the dried neutral salt; and that the augmentation of the weight gained by the alkali during the formation of the neutral salt showed the weight of the dry acid. The uncertainty which affects this method arises from the different capacities which different neutral salts may possess of retaining more or less water, either as a constituent part of the dry salt, or merely by the strength of adhesion or affinity. Nevertheless, this method being founded solely on experiment, without any theoretical inductions, seems to furnish some approximation, not perhaps of the absolute quantity of the acids in their driest possible state, but of the acids as they actually exist in these salts comparatively with each other. Though the disagreements between Bergman's and Wenzel's results are little in comparison of the difference between them and Kirwan's, yet as their experiments were made nearly in the same manner, and upon the same grounds, there seems to be sufficient reason to wish for a careful repetition of their experiments, or of others with the same view, and less liable to objections.

"The only difference in the methods employed by these two celebrated chemists consisted in the mode of saturation. Bergman probably used the common method, but Wenzel employed a very peculiar one. He added to his alkali a greater quantity of acid than was necessary for the saturation; and after the alkali was dissolved, he added a lump of zinc, or of oyster-shell, in order to saturate completely the superfluous acid. By observing how much of the zinc or oyster-shell the acid dissolved, and knowing how much of these substances was soluble in his acid by former experiments, he inferred the quantity of acid left for the saturation of the alkali. Having thus ascertained the quantity necessary to saturate the alkali, he mixed together the proper proportions of these, and formed his neutral salt by evaporating the mixture and drying the salt with a red heat. Perhaps the difference in the results obtained by these two chemists might arise from their different modes of saturation. The common method of ascertaining the point of saturation by means of litmus or other blue vegetable juices, appears sufficiently exact, is simpler, and therefore preferable to that used by Wenzel.

"The standard for comparing the strengths of acids, and likewise of alkalies with one another, may be either an acid or an alkaline substance; and if we had one of each, the proportion of whose quantities requisite for their mutual saturation were well ascertained, the convenience in making the experiments would be obvious, and the certainty greater. Alkaline, and the earthy substances that are soluble in acids, are seldom pure enough for this purpose. They generally contain quantities, which are not constant, of fixed air, siliceous earth, magnesia, neutral salts, and inflammable matter, which render any of those that are commonly met with unfit for the purpose without a very skilful and careful purification. The chemists who have made experiments to determine the proportions of acids and alkalies requisite for each other's saturation, have scarcely been explicit enough in explaining the means of purifying the alkalies which they employed; for those in commerce are quite uncertain in strength and purity; and as to the general rules for making allowances for any heterogeneous substances they may contain, they are quite inapplicable to delicate experiments. No other method seems proper for ascertaining the purity of alkalies but that of crystallization; of which both the vegetable and mineral alkalies are susceptible, especially the latter, which on account of its being more easily reducible into crystals, is therefore preferable. These alkaline crystals, however, are not fit to be used as a standard, because they either are apt to be insufficiently dried, or, upon exposure to air, to lose a part of the water of their crystallization, and to fall into powder. Even if they should be taken, as is possible with due care, at the exact state of dry but entire crystals, another uncertainty arises from a property which seems to be common to them all, namely, that of retaining a greater or smaller quantity of water, according to the degree of heat in which they were crystallized; the colder the weather the greater quantity of water entering into the composition of the crystals. It seems possible, however, to make a pretty accurate standard of mineral alkali in the following preparing manner: Let the alkali be purified by repeated foli-

Remarks on the former Doctrines.

tion and crystallization, using only such as are formed first, and rejecting the remaining liquors. Let the pure crystals be exposed to a dry air until they have completely effloresced or fallen into a dry white powder; which alteration may be facilitated by bruising the crystals, and changing the surface of the powder. Let this powder be then exposed for a certain and determinate time to a constant heat, as that of boiling water for 12 hours; letting the surface exposed be in some given proportion, suppose of a square inch to an ounce of the powder of crystals, and let it be stirred every two hours. When thus dried, let them be put while hot into a bottle, and well stoppered. This powder I have found to be an uniform and constant standard for ascertaining the strength of acids; and also, by comparison by means of acids, of other alkaline substances."

With regard to an acid standard, our author recommends oil of vitriol; which, he says, as it comes from the hands of the British manufacturers, is of the specific gravity of about 1.846, but soon becomes weaker, unless carefully kept from the external air; and in general he rates it at 1.844. One part of this acid mixed with nine of water, is of a very convenient strength for use; and as every ten grains of the mixture contain one of the standard acid, the computations are thus rendered easy; and by these standards, the strength of all acids, alkalies, and substances soluble in acids, may be measured and compared together.

To determine the specific gravity of liquors with accuracy, our author recommends the method of weighing them in a phial fitted with a glass-flopper, which can only enter a certain length into the neck. In this way, he observes, no other inconvenience can ensue than the slight one, that the glass-flopper, by very frequent use, is apt to wear itself and the neck of the phial also; so that after a great number of experiments, it will at last diminish, in some measure, the capacity of the phial itself. This, however, is but very trifling, and may be corrected at any time. Mr Keir has besides found, that after some hundreds of experiments, the error amounted only to one quarter of a grain in 101 grains.

"The methods hitherto practised (says he) for ascertaining the quantities of acids and alkalies contained in neutral salts, seem to be liable to several objections besides those above mentioned, arising from the different proportions of water remaining in a neutral salt, after exposure to a red heat, which heat is also very indefinite. In boiling the saturated mixture of acid and alkali to dryness, and afterwards in exposing this salt to a red heat, it has been supposed that nothing but water is expelled; and some chemists, who have given the results, have also determined the weight of the alkali which enters into the neutral mixture, by evaporating to dryness an equal quantity of the alkaline solution which had been employed in the saturation, and weighing the dry solution, on the supposition that nothing is expelled but water. It is certain, however, that in the evaporation both of alkalies and neutral salts, a considerable portion of the saline matter is elevated towards the end, when the liquor becomes concentrated and acquires a degree of heat considerably above that of boiling water. The following method appears best for determining the relative quantities of acid and alkali, or other substance existing in neutral salts.

"To a given number of grains, suppose 100 of the standard vitriolic acid, or to a proportionable quantity of any other acid, add as much of the alkali or other soluble substance as is requisite for the saturation, and note the quantity required, which suppose to be 150 grains. We have thus a solution of the neutral salt, which is the object of the experiment; the quantities of acid and basis contained in which are known, and the general proportion of the quantity of the acid to its basis in the neutral salt determined, viz. as 100 to 150. The next thing to be discovered is the weight of the dry neutral salt contained in this solution, in order to know the proportion of the dry neutral salt to its acid and basis. For this purpose, let a given quantity of the same neutral salt, either in the state of crystals or dried to any given degree, be dissolved in water. Let this solution be brought to the same density as the former, by adding water to the heavier of the two; then, by knowing the weight of each solution, and the quantity of dry neutral salt which was actually dissolved in one of them, the quantity contained in the other may be deduced; and thence the quantities of standard acid, or of other acid proportioned to it, and of the alkali employed, or other soluble substance contained in a given quantity of the neutral salt, are determined; also the quantity of water contained in the neutral salt, that is greater or less than what is contained in the quantity of acid employed, will be known, over and above any water that may have been contained in the alkali or other basis of the neutral salt; the quantity of which water, if any, cannot be determined.

"By this method may be ascertained the proportion of the acid, of the basis, and of the neutral salt, to each other; not indeed the quantity of acid and of alkali deprived of all water, but the quantity of acid, equal in intensity of acidity to a known portion of the standard acid; and also the quantity of such alkali or other soluble substance as was employed; the relative strength of which is known from its ratio to the standard acid."

The translator of Wiegley's System of Chemistry totally disagrees with Mr Kirwan's calculation of the quantity of phlogiston contained in sulphur; but as his calculation objection seems to arise rather from an inclination to the antiphlogistic doctrine than a real discussion of the subject, this can have but little weight. It is possible indeed that Mr Kirwan may have over-rated the quantity of phlogiston this substance contains, which is indeed larger than that allowed by other chemists.

"Brandt (says the translator), who has been most generally followed, reckons it only at $\frac{1}{3}$; and it has always appeared to me, that the weight of phlogiston in sulphur is almost infinitely small." His objection proceeds on a maxim which he thinks he has demonstrated, viz. that sulphur is composed, not of the vitriolic acid and phlogiston, but of the base of vitriolic acid and phlogiston. No experiments hitherto made, however, have been able to show this base distinct from the acid; nor have we any reason to suppose that the increase of weight in the vitriolic acid above the sulphur from Theory.

from which it is produced, arises from anything besides the accession of mere water, which the air parts with during the combustion. Hence, if the sulphur is burnt in a very moist air, the quantity of acid obtained will be four or five times the weight of the sulphur.

Sect. IV. Earths.

These are divided into five classes: 1. Absorbent, alkaline, or calcareous earths; 2. Argillaceous earths or clay; 3. The flinty; 4. The fusible earths; and 5. The talc.

1. The first class comprehends all those that are capable of being converted into lime. They are found of various degrees of hardness; but none of them are capable of totally resisting the edge of a knife, or striking fire with steel. They are found to consist of a very friable earth, joined with a large quantity of air and some water. They effervescence with an acid when poured on them; by which they are distinguished from all other kinds of earth, except the argillaceous. When calcined by a strong fire, they part with the water and air which they contained, and then acquire a great degree of causticity, lose their power of effervescing with acids, and become what is a calquicklime. They are soluble in acids, but not equally so in all. The vitriolic and tartaric acids form compounds with them very difficultly soluble; the felsites, formed by the vitriolic acid and calcareous earth, requiring, according to Mr Beaumé, an ounce of water to dissolve a single grain of it. The solubility of the tartaric felsite hath not yet been determined.—With the other mineral acids, the calcareous earths become easily soluble; and by proper management form concretes which appear luminous in the dark, and are called phosphoric.

2. The argillaceous earths differ from the calcareous, in not being convertible into quicklime. When mixed into a paste with water, and exposed to the fire, they shrink remarkably, crack in many places, and become excessively hard. By being gently dried in the open air before they are turned, they do not crack, and thus may be formed into vessels of any shape. Of this kind of earth are formed all the brown fort of earthen ware. The purest kind of argillaceous earth naturally found, is that whereof tobacco-pipes are made.

All the argillaceous earths are soluble in acids. With the vitriolic they dissolve into a gelatinous tough liquor very difficultly crystallizable; but which, on the addition of some fixed or volatile alkali, may be shot into crystals of the salt called alum. With the other acids they form affluegent salts of a similar nature.

The attraction between the argillaceous earths and acids is very weak, yielding not only to alkaline salts both fixed and volatile, but even to some metals, particularly iron; but these earths have as yet been but little the subject of chemical examination in this way. They have a remarkable property of absorbing the colouring matter of cochineal, Brazil-wood, &c., as have also the calces of some metals.

Both the calcareous and argillaceous, and indeed all earths when pure, resist the utmost violence of fire; but when mixed together will readily melt, especially if in contact with the burning fuel. Dr Lewis having made covers to some crucibles of clay and chalk mixed together, found that they melted into a yellow glass, before the mixtures in the crucibles were fused in the least. But though they melted thus readily when in contact with the fuel, it was with great difficulty he could bring them to a transparent glass when put into a crucible.

The other species of earths, viz. the flinty, fusible, and talc, being no other way the subjects of chemistry than as they are subservient to the making of glass, all that can be said of them will most properly come under that article. For their different species, see Mineralogy.

Besides the above mentioned species of earths, there are others which may be called anomalous, as having some resemblance of the calcareous and argillaceous, and yet being essentially different from them. These are the white earth called magnesia alba, the earth of burnt vegetables, and that produced from burning animal substances.

Magnesia alba was at first prepared from the thick liquor remaining after the crystallization of nitre; and is now found to be contained in the liquor called bittern, which is left after the separation of common salt from sea-water. In the former case it was united with the nitrous, in the latter with the vitriolic, acid. It is also found naturally in the soft kind of stone called fleatics or "soap stone;" and in the concrete used for taking spots out of cloths, called French chalk. It differs from the calcareous earths, in not acquiring any causticity when deprived of its air, of which it contains so large a quantity as to lose two-thirds of its weight when calcined. From the argillaceous it differs in not burning hard when mixed with water, nor forming a tough ductile paste. It is easily soluble in all the acids, even the vitriolic; with which it forms the bitter purging salt commonly called Effom salt, from its being first discovered in the waters of Epom. With all the other acids it likewise forms purgative compounds, which are either very difficultly or not at all crystallizable.—Like other pure earths, it cannot be melted by itself; but, on proper additions, runs into a beautiful green glass.

The earth of burnt vegetables is thought by Dr Lewis to be the same with magnesia alba; but on trying the common wood ashes, they were found to be very different. This kind of earth is fusible, by reason of the alkaline salts contained in it. Animal earth is both very difficult of solution in acids, and impossible to be melted in the strongest fire. It dissolves, however, in acid liquors, though slowly; but the nature of the compounds formed by such an union are as yet unknown. The softer parts of animals, such as blood, flesh, &c., are said to yield a more soluble earth than the others. Animal earth has lately been supposed to be compounded of calcareous earth and phosphoric acid; but this opinion is shown to be erroneous under the article Bones. The phosphoric acid produced from these, is with reason supposed to be only the vitriolic acid changed.

Sect. V. Inflammable Substances.

These comprehend all vegetable, animal, and some mineral substances. They are distinguished from all others, others, by emitting a gross thick smoke and flame, when a certain degree of heat is applied. To this, however, spirit of wine and all preparations from it are exceptions. They burn without the least smoke; and if a glass bell is held over the burning spirit, no foot is formed, only a quantity of water is found condensed on its sides. Even the grocer's oils, if slowly burnt with a very small flame, will yield no foot; and an exceeding great quantity of water, fully equal in weight and bulk to the oil employed, may be obtained from them. We can scarcely, however, credit, that so great a quantity of water comes from the oil; as this would be a real transmutation; and we know that, besides water, the oils contain also some quantity of fixed air, as well as earth. It is probable, therefore, that, as it is impossible to sustain flame without a decomposition of that part of the air which rushes in to support it, part of the water in this case comes from the air, which always contains moisture in abundance.

Inflammable matters, on being burnt, generally leave behind a small quantity of earthly matter called ash; but to this, spirit of wine, camphor, the more volatile oils, and the mineral oil called naphtha, are exceptions. Vegetable substances, when distilled in close vessels, give out a quantity of air, some acid, and an empyreumatic oil, leaving behind a black spongy mass called charcoal. To this too there are a few exceptions, viz., spirit of wine, and the preparations from it, camphor, and perhaps some of the more volatile oils, or naphtha. Animal substances yield only a very fetid empyreumatic oil, and volatile alkali.

In general, all inflammable matters are acted upon with some violence by the vitriolic and nitrous acids, excepting only camphor and naphtha. With the vitriolic acid, when in a liquid state, they render it volatile and sulphureous; if in a dry state, they form actual sulphur. With the nitrous, they first impart a high colour and great degree of volatility to the acid; then a violent flame ensues, if the matter is attempted to be dried. With spirit of wine the effects are considerably different; and very volatile compounds are formed, which are called ether, on account of their exceeding great disposition to rise in vapour. Similar compounds are likewise produced, but with more difficulty, from the marine acid and concentrated vinegar. The sal sedativus of borax mixes with spirit of wine, and causes it burn with a green flame; but does not seem to produce any other change upon it. How the acid of phosphorus and of ants act upon spirit of wine, is not exactly known; but that of tartar by digestion with it, is converted into the acetic acid. With any other inflammable matter, the phosphoric acid reproduces phosphorus.

There are two singularities observed among the inflammable substances. One is that bituminous matter called amber, which yields a volatile salt of an acid nature on distillation: When combined with alkalies, this acid is found to yield compounds similar to those made with the acetic acid and alkali. The other is, that gum called benzoin, which is used as a perfume, and yields by sublimation a kind of volatile salt in fine shining crystals like small needles, and of a most grateful odour. These dissolve very readily in spirit of wine; but not at all in water, unless it is made very hot; so that they seem to contain more oily than saline matter. Neither the nature of these flowers, however, nor that of the salt of amber, is fully known.

Sect. VI. Metalline Substances.

These are distinguished from all other bodies by their great specific gravity, exceeding that of the most dense and compact stones. The heaviest of the latter do not exceed the specific gravity of water in a greater proportion than that of 4 to 1; but tin, the lightest of all the metals, exceeds the specific gravity of water in the proportion of 7 to 1. They are also the most opaque of all known bodies, and reflect the rays of light most powerfully.

Metallic bodies possess the quality of dissolving in metals and uniting with acid salts, in common with earths liable to alkalis; but, in general, their union is less perfect, and they are more easily separable. They effervescence with acids, as well as calcareous earths and alkalies; but their effervescence is attended with very different appearances. In the effervescence of acids with alkalies, or with calcareous earths, there is a discharge of the fluid called fixed air, which is so far from being inflammable, that it will immediately extinguish a candle, or other small flame immersed in it. The mixture also is notably diminished in weight. When a metallic substance is dissolved in an acid, the weight of the mixture is never very much diminished, and sometimes it is increased. Thus, an ounce of quicksilver being slowly dropped into as much aquafortis as was sufficient to dissolve it, and the solution managed so as to take up almost a whole day, the whole was found to have gained seven grains. There is also a remarkable difference between the nature of the vapour discharged from metals and that from alkalies; the former, in most cases, taking fire and exploding with violence; the latter, as already observed, extinguishing flame.

The metallic substances, at least such as we are able to decompose, are all composed of a certain kind of phlogiston. The earthy part by itself, in whatever way it is procured, goes by the name of calx. The other principle has already been proved to be the same with charcoal. When these two principles are separated from one another, the metal is then said to be calcined. The calx being mixed with any inflammable substance, such as powdered charcoal, and urged with a strong fire, melts into metal again; and it is then said to be reduced, or revivificated: and this takes place whether the metal has been reduced to a calx by dissolution in an acid, or by being exposed to a violent fire. If, however, the calcination by fire has been very violent and long continued, the calx will not then so readily unite with the phlogiston of the charcoal, and the reduction will be performed with more difficulty. Whether, by this means, viz., a long continued and violent calcination, metallic earths might entirely lose their property of combining with phlogiston, and be changed into those of another kind, deserves well to be inquired into.

When a metallic substance is dissolved in any kind of acid, and an alkali or calcareous earth not deprived of its fixed air is added, the alkali will immediately be attracted by the acid, at the same time that the fixed acids. ed air contained in the alkali is disengaged, and the calx of the metal, having now no acid to keep it dissolved, immediately joins with the fixed air of the alkali, and falls to the bottom. Something similar to this happens when metals are calcined by fire. In this case, there is a continual decomposition of the air which enters the fire; and the fixed air contained in it, being, by this decomposition, set loose, combines with the calx; whence, in both cases, there is a considerable increase of weight. If the air is excluded from a metal, it cannot be calcined even by the most violent fire.

When a metal is precipitated by a mild alkali, or by the increase of an uncalcined calcareous earth, the reason of the increase of weight is very evident; namely, the adhesion of the fixed air to the metallic calx; but, though it is not so much increased when precipitated by caustic alkali, or by quicklime, there is nevertheless a very evident increase, which is not so easily accounted for. M. Lavoisier has mentioned some experiments made on mercury and iron dissolved in aquafortis, which deserve to be taken notice of, as in a great measure accounting for the phenomenon already mentioned of the solution of metalline substances gaining an addition of weight; and likewise show the proportion of increase of weight with the mild, or calcined calcareous earth.

Exactly 12 ounces of quicksilver (says he) were put into a matrafs, and 12 ounces of spirit of nitre poured on it. Immediately a spontaneous effervescence ensued, attended with heat. The red vapours of the nitrous acid arose from the mixture, and the liquor assumed a greenish colour. I did not wait till the solution was entirely accomplished before I weighed it; it had lost one drachm 18 grains. Three hours after, the mercury was nearly all dissolved; but having again weighed the solution, I was much astonished to perceive that it had increased instead of being diminished in weight; and that the loss, which was one drachm 18 grains at first, was now only 54 grains. The next day the solution of the mercury was entirely finished, and the loss of weight reduced to 18 grains; so that in 12 hours the solution, though confined in a narrow necked matrafs, had acquired an augmentation in weight of one drachm. I added some distilled water to my solution, to prevent it from crystallizing; the total weight of it was then found to be 48 ounces 1 drachm and 18 grains.

I weighed separately, in two vessels, 8 ounces 15 grains of the above solution, each of which portions, according to the preceding experiment, ought to contain 2 ounces of nitrous acid and 2 ounces of quicksilver. On the other side, I prepared 6 drachms 36 grains of chalk, and 4 drachms 36 grains of lime; these proportions having been found by former experiments just necessary to saturate two ounces of nitrous acid. I put the chalk in the one vessel, and the lime in the other.

An effervescence attended the precipitation by chalk, but without heat; the mercury precipitated in a light yellow powder, at the same time the chalk was dissolved in the nitrous acid. The precipitation by the lime was effected without effervescence, but with heat; the mercury was precipitated in a brownish powder. When the precipitates were well subsided, I decanted off the liquors from them, and carefully edulcorated them. After which, I caused them to be dried in a heat nearly equal to that in which mercury boils.

The precipitate by the chalk weighed 2 ounces 2 drachms 45 grains; that by the lime weighed 2 ounces 1 drachm 45 grains.

Sixteen ounces of the nitrous acid, the same as employed in the former experiments, were placed in a matrafs, and some iron filings gradually added. The effervescence was brisk, attended with great heat, red vapours, and a very rapid discharge of elastic fluid: the quantity of iron necessary to attain the point of saturation was 2 ounces 4 drachms; after which, the loss of weight was found to be 4 drachms 19 grains. As the solution was turbid, I added as much distilled water as made the whole weight of the solution to be exactly 6 pounds.

I took two portions, each weighing 12 ounces of the above solution, and containing 2 ounces of nitrous acid, and 2 drachms 36 grains of iron filings. I placed them in two separate vessels. To one were added 6 drachms 36 grains of chalk; and to the other 4 drachms 36 grains of flaked lime, being the quantities necessary to saturate the acid.

The precipitation was effected by the chalk with effervescence and tumefaction, that by the lime without either effervescence or heat. Each precipitate was a yellow brown rust of iron. They were washed in several parcels of distilled water, and then dried in an heat somewhat superior to that used in the last experiment.

The precipitate by the chalk, when dried, was a greyish rust of iron, inclining even to white by veins. It weighed 6 drachms 35 grains. That by the lime was rather yellower, and weighed 4 drachms 69 grains.

The result of these experiments (says M. Lavoisier) are, 1. That iron and mercury dissolved in nitrous acid acquire a remarkable increase of weight, whether they be precipitated by chalk or by lime. 2. That this increase is greater in respect to iron than mercury. 3. That one reason for thinking that the elastic fluid contributes to this augmentation is, that it is constantly greater when an earth is employed saturated with elastic fluid, such as chalk, than when an earth is used which has been deprived of it, as lime. 4. That it is probable that the increase of weight which is experienced in the precipitation of lime, although not so great as that by chalk, proceeds in part from a portion of the elastic fluid which remains united to the lime, and which could not be separated by the calcination.

But though we are naturally enough inclined to think that the increase of weight in the precipitates formed by lime proceeded from some quantity of elastic fluid or fixed air which remained combined with the lime, it is by far too great to be accounted for in this way, even according to the experiments mentioned by M. Lavoisier himself, and which, from the manner in which they are told, appear to have been performed with the greatest accuracy. He found, that 1 ounce 5 drachms and 36 grains of flaked lime contained 3 drachms and 3 quarters of a grain of water, and only 16 grains and an half of elastic fluid were separable from it. In the experiments above related, where only 4 drachms and 36 grains were employed, the quantity of elastic fluid could not exceed 6 or 8 grains. Yet the calx was increased in mercury by no less than 105 grains, and in iron by 203 grains; a quantity quite unaccountable from the elastic fluid or fixed air which we can suppose to be contained in the lime made use of. It is much more probable, that the increased weight of metallic precipitates, formed by lime, arises from an adhesion of part of the acid.

Metals are found to be compounded of a kind of earth mixed with the inflammable principle or phlogiston; and, by a dissipation of the latter, all metallic bodies, gold, silver, and platinum excepted, are capable of being reduced to a calx, but very different degrees of heat are required for calcining them. Lead and tin begin to calcine as soon as they are melted, long before they are made red-hot. The same happens to the femimetals bismuth and zinc; the latter indeed, being combustible, cannot bear a greater heat in open vessels than that which is barely sufficient to melt it. Iron and copper require a red heat to calcine them; though the former may be made partly to calcine by being frequently wetted in a degree of heat considerably below that which is sufficient to make it red.

Most metals undergo a kind of spontaneous calcination in the open air, which is called their rusting; and which has given occasion to various conjectures. But M. Lavoisier has shown, that this arises from the fixable part of the atmosphere attaching itself to their earthly part, and discharging the phlogiston. According to him, no metallic body can rust but where there is an absorption of air; and consequently metals can be but imperfectly rusted when kept under a receiver.

If two metals are mixed together, the compound generally turns out more fusible than either of them was before the mixture. There are indeed great differences in the degrees of heat requisite to melt them. Thus, lead and tin melt below that degree of heat which is required to make quicksilver or linseed oil boil. Silver requires a full red heat, gold a low white heat, copper a full white, and iron an extreme white heat, to make it melt. The femimetal called bismuth melts at about 460° Fahrenheit's thermometer, and tin at about 422°. When mixed in equal quantities, the compound melted at 283°. When the tin was double the bismuth, it required 334° to melt it; with eight times more tin than bismuth, it did not melt under 392°. If to this compound lead is added, which by itself melts in about 540°, the fusibility is surprisingly increased. Mr Holmberg proposed for an anatomical injection a compound of lead, tin, and bismuth, in equal parts; which he tells us keeps in fusion with a heat so moderate that it will not singe paper. Sir Isaac Newton contrived a mixture of the above-mentioned metallic substances, in such proportions that it melted and kept fluid in a heat still smaller, not much exceeding that of boiling water. A compound of two parts of lead, three parts of tin, and five of bismuth, did but just stiffen at that very heat, and so would have melted with very little more; and when the lead, tin, and bismuth, were to one another in the proportions of 1, 4, and 5, the compound melted in 246°. We have seen, however, a piece of metal compounded of these three, the proportions unknown, which melted, and even underwent a slight degree of calcination, in boiling water, and barely stiffened in a degree of heat so gentle that the hand could almost bear it.

A slight degree of calcination seems to give the solubility acids a greater power over metallic substances; a greater makes them less soluble; and if long and violently calcined, they are not acted upon by acids at all. Of all the acids, the marine has the greatest attraction for metallic calces, and volatilizes almost every one of them.

Sulphur readily unites with most metals, destroys their malleability, and even entirely dissolves them. On gold and platinum, however, it has no effect, till united with a fixed alkaline salt, when it forms the compound called hepatic sulphuris; which is a very powerful solvent, and will make even gold and platinum themselves soluble in water, so as to pass the filter. This preparation is thought to be the means by which Moses dissolved and gave the Israelites to drink the golden calf which they had idolatrously set up.

When a metal is dissolved in an acid, it may be precipitated, not only by means of calcareous earths and alkalis, but also by some other metals; for acids do not attract all metals with equal strength; and it is remarkable, that when a metal is precipitated by another, the precipitate is not found in a calcined state, but in a metallic one. The reason of this is, that the precipitating metal attracts the phlogiston which is expelled from that which is dissolving, and immediately unites with it, so as to appear in its proper form. The various degrees of attraction which acids have for the different metals is not as yet fully determined. The best authenticated are mentioned in the Table of Affinities or Elective Attractions (Sect. IX.)

Metalline substances are divided into metals and ferrometals. The metals which are distinguished from ferrometals by their malleability or stretching under the hammer, are in number seven; gold, silver, copper, iron, lead, tin, and platinum. To these is added quicksilver; which Mr Brown's experiments have shown to be a real malleable metal, as well as others, but requiring so little heat to keep it in fusion, that it is always found in a liquid state. The ferrometals are bismuth or tin-glaas, zinc, regulus of antimony, and cobalt, nickel, and arsenic. This last substance is now discovered to be compounded of an acid of a peculiar kind and phlogiston; and as the quantity of arsenic of the latter is great or small, the arsenic affumes either a metallic or saline form. It likewise unites with sulphur, with which it forms a compound of a red or yellow colour, according as more or less sulphur is used. This compound is easily fusible; though the arsenic, by itself, is so volatile as to go off in vapour rather than melt. In common with the salts, it possesses the properties of dissolving in water, and uniting itself to alkalies. Water will dissolve about 1/10 of its weight of pure arsenic; but if arsenic is boiled in a strong alkaline lixivium, a much greater proportion will be dissolved. Indeed strong alkaline lixivia will dissolve ### Chemistry

#### Chemical Characters or Symbols

| Symbol | Description | |--------|-------------| | △ Fir. | Fir. | | △ Air. | Air. | | ▽ Water. | Water. | | ▽ Earth. | Earth. | | £△ Flexible Air. | Flexible Air. | | m.△ Mephitic Air. | Mephitic Air. | | ▽ Clay. | Clay. | | ▽ Gypsum. | Gypsum. | | ▽ Calcaceous Earth. | Calcaceous Earth. | | Ψ CV; T Quicklime. | Quicklime. | | ▽ Vitrifiable, or Siliceous Earths. | Siliceous Earths. | | ▽ Fluors, or Fusible Earths. | Fusible Earths. | | X Talk. | Talk. | | M▽ Magnesia. | Magnesia. | | A▽ Earth of Alam. | Earth of Alam. | | ▽ Sand. | Sand. | | ○ Gold. | Gold. | | ▽ Silver. | Silver. | | ▽ Copper. | Copper. | | ▽ Tin. | Tin. | | ▽ Lead. | Lead. | | ▽ Mercury. | Mercury. | | ▽ Iron. | Iron. | | ▽ Zinc. | Zinc. | | B; W; 8 Bismuth. | Bismuth. | | ▽ Antimony. | Antimony. | | ▽ Regulus of Antimony. | Regulus of Antimony. | | ▽ Arsenic. | Arsenic. | | ▽ Regulus of Arsenic. | Regulus of Arsenic. | | K 8 Cobalt. | Cobalt. | | N Nickel. | Nickel. | | S.M. Metallic Substances. | Metallic Substances. | | C.Calx. | Calx. | | ▽ Orpiment. | Orpiment. | | ▽ Cinnabar. | Cinnabar. | | L.C. Lapis Calaminaris. | Lapis Calaminaris. | | ▽ Tully. | Tully. | | ▽ Vitriol. | Vitriol. | | ▽ Sea Salt. | Sea Salt. | | 8; ▽ Sal Gem. | Sal Gem. | | ▽ Nitre. | Nitre. | | S.S. Sedative Salt. | Sedative Salt. | | X, ▽ Sal Ammoniac. | Sal Ammoniac. | | ▽ Alum. | Alum. | | ▽ Tartar. | Tartar. | | ▽ Alkali. | Alkali. | | ▽ Fixed Alkali. | Fixed Alkali. | | ▽ Volatile Alkali. | Volatile Alkali. | | ▽ Mild fixed Alkali. | Mild fixed Alkali. | | ▽ Caustic fixed Alkali. | Caustic fixed Alkali. | | ▽ Mild vol. Alkali. | Mild vol. Alkali. | | ▽ Caustic vol. Alkali. | Caustic vol. Alkali. | | ▽ Potash. | Potash. | | ▽ Acids. | Acids. | | ▽ Vinegar. | Vinegar. | | ▽ Vitriolic Acid. | Vitriolic Acid. | | ▽ Nitrous Acid. | Nitrous Acid. | | ▽ Marine Acid. | Marine Acid. | | F; F Aquafortis. | Aquafortis. | | R; R Aqua Regia. | Aqua Regia. | | ▽ Vol. Sulphureous Acid. | Vol. Sulphureous Acid. | | ▽ Phosphoric Acid. | Phosphoric Acid. | | V Wine. | Wine. | | V Spirit of Wine. | Spirit of Wine. | | R Rectified V. | Rectified V. | | ▽ Ether. | Ether. | | ▽ Lime Water. | Lime Water. | | ▽ Urine. | Urine. | | ▽ Oil. | Oil. | | ▽ Essential Oil. | Essential Oil. | | ▽ Fixed Oil. | Fixed Oil. | | ▽ Sulphur. | Sulphur. | | ▽ Hepar of Sulphur. | Hepar of Sulphur. | | ▽ Phosphorus. | Phosphorus. | | ▽ Phlogiston. | Phlogiston. | | ▽ Soap. | Soap. | | ▽ Verdigris. | Verdigris. | | ▽ Glass. | Glass. | | ▽ Cupul Mortuum. | Cupul Mortuum. | | ▽ Powder. | Powder. | | E Ashes. | Ashes. | | B ABath. | Bath. | | BM; WB Water bath. | Water bath. | | AB Sand bath. | Sand bath. | | VB Vapor bath. | Vapor bath. | | ▽ An Hour. | An Hour. | | ▽ 1 Day. | 1 Day. | | ▽ A Night. | A Night. | | ▽ A Month. | A Month. | | ▽ Amalgam. | Amalgam. | | ▽ To Distill. | To Distill. | | ▽ To Sublime. | To Sublime. | | ▽ To Precipitate. | To Precipitate. | | ▽ Retort. | Retort. | | XX An Alembic. | Alembic. | | ▽ Crucible. | Crucible. | | SSS Stratum Super Stratum. | Stratum Super Stratum. | | C.C. Cornu Cerui Hartshorn. | Hartshorn. | | ▽ Bottle. | Bottle. | | ▽ Grain. | Grain. | | ▽ Scruple. | Scruple. | | ▽ Dram. | Dram. | | ▽ Ounce. | Ounce. | | ▽ Pound. | Pound. | | ▽ Pennyweight. | Pennyweight. |

*Abbott Sculp.* Theory.

Waters, &c., solve a part of almost every metalline substance, except gold, silver, and platina; but, excepting copper, which may be formed into crystals by means of the volatile alkali, none of them will assume a crystalline form when united with alkalies. Arsenic, on the contrary, unites very readily with fixed alkalies, and shoots with them into a neutral salt. If it is mixed with nitre, it unites itself to the alkaline basis of that salt, and expels the acid in very volatile fumes, which are difficulty condensed into a blue liquor. The reason of this is the great attraction between the nitrous acid and phlogiston, which are always disposed to unite when a proper degree of heat is applied. Was the phlogiston contained in large quantity in the arsenic, and the heat sufficiently great, a violent deflagration would ensue; but as the acid of arsenic attracts the alkaline part of the nitre, at the same time that the nitrous acid attracts the phlogiston, a double decomposition ensues, in a less degree of heat than would otherwise be necessary; and the nitrous acid arises in a very volatile state, as it always is when combined with phlogiston, which is the occasion of the blueness in aquafortis so produced. The arsenic is also decomposed by being deprived of its proper quantity of phlogiston; in consequence of which its acid attaches itself to the fixed alkali of the nitre, and forms a neutral arsenical salt. For the extraction of metallic substances from their ores, and the various methods of refining them, see METALLURGY.

SECT. VII. Waters.

The pure element of water, like that of fire, is so much an agent in most chemical operations, as to be itself very little the object of practical chemistry. Some late experiments, however, have shown that this fluid really consists, in part at least, of phlogiston, and an invisible substance which forms the basis of pure air; and consequently water is generated in the deflagration of dephlogisticated air; but as the basis of the former cannot be perceived by itself, we can as yet say nothing about it. Waters, therefore, can only be the objects of chemistry, in consequence of the impurities they contain; and as these impurities are most commonly of the saline kind, it is impossible that any general theory can be given of waters, distinct from that of the salts contained in them; which all depend on the general properties belonging to salts, and which we have already mentioned. Anything that can be said with regard to waters, then, must be postponed to the particular consideration of the properties of each of the saline bodies with which water is capable of being adulterated. We shall therefore refer entirely to the article WATER in the order of the alphabet, for what can be said on this subject.

SECT. VIII. Animal and Vegetable Substances.

The general chemical properties of these have been already taken notice of under the name of inflammable substances. They agree in giving out a very thick fetid oil, when distilled by a strong fire; but in other respects they differ very considerably. Most kinds of vegetables give out an acid along with the oil; but all animal substances (ants, and perhaps some other insects, excepted) yield only a volatile alkali. Some kinds of vegetables, indeed, as mustard, afford a volatile alkali on distillation, similar to that from animal substances; but instances of this kind are very rare, as well as of animals affording an acid. Both animal and vegetable substances are susceptible of a kind of fermentation, called putrefaction, by which a volatile alkali is produced in great plenty: there is, however, this remarkable difference between them, that many vegetable substances undergo two kinds of fermentation before they arrive at the putrefactive stage. The first is called the vinous, when the ardent spirits are produced, which we have already mentioned when speaking of inflammable substances. This is succeeded by the acetous, wherein the vegetable acid called vinegar is produced in plenty; and lastly, the putrefactive stage succeeds when a volatile alkali is only produced; not the smallest vestige either of ardent spirits or of vinegar remaining. On the other hand, animal substances seem susceptible only of the putrefactive fermentation; no instance having ever occurred where there was the least drop, either of ardent spirit or of vinegar, produced from a putrid animal substance. (See Fermentation and Putrefaction.)

SECT. IX. Of the Chemical Characters, and Tables of Elective Attraction.

The numerous marks or characters by which the ancient chemists used to denote many different substances, of marks were invented rather from a superstitious and fantastic principle than from any real necessity; or, perhaps, like the enigmatical language used by the alchemists, they have thereby sought to conceal their mysteries from the vulgar. In contriving these marks, they affected a great deal of ingenuity; intending them as symbols of the qualities possessed by each of the different substances. A circle being supposed the most perfect figure, was therefore used to represent the most perfect metal in nature, that is, gold. Silver being likewise a perfect and indestructible metal, is placed next to gold; but, on account of its inferiority, is expressed only by a crescent, as if but half gold. A circle was likewise used to denote salt of any kind, as being something elaborate and perfect. A cross was used to denote acrimony of any kind, and consequently employed for the acrimonious salts of vitriol, alkali, &c. Hence all the inferior metals have the cross somehow or other combined with the marks designed to represent them. Thus, the mark for quicksilver denotes, that it hath the splendor of silver, the weight of gold, but its perfection is hindered by an acrimony represented by the cross at bottom, &c. Fire is represented by an equilateral triangle, having one of its angles uppermost. This may be considered as a rude representation of flame, which is always pointed at top. Water, again, is represented by a triangle, with an angle downwards, showing the way in which that element exerts its strength, &c. All these marks, however, as they were of no real use at first, so they are now becoming every day more and more neglected. Such of them, however, as may most readily occur in chemical books are represented and explained on Plate CXXXII.

The French chemists have of late attempted to introduce a kind of new chemical language; and by adopting it themselves, may perhaps make it at last universal. Tables of affinities, or elective attractions, are but of late invention. They are consequences of an improved state of chemistry, when the different substances were found to act upon one another in most cases according to a fixed and settled rule. The most approved table of this kind for a long time was that composed by Mr Geoffroy. It was, however, found to be very incomplete, not only as to its extent, but likewise as heat and some other circumstances were found to vary the attractions considerably, and sometimes even to reverse them. Other tables have been constructed by Mr Gellert, &c., but none hath yet appeared so complete but that many additions may be made to it. The following is that at present exhibited by Dr Black in his course of chemistry.

1. Vitriolic Acid. Copper Phlogiston Terra ponderosa Fixed alkali Calcareous earth Zinc Iron Tin Copper Quicksilver Silver Volatile alkali Magnesia Earth of alum.

2. Nitrous Acid. Fixed alkali Calcareous earth Zinc Iron Lead Tin Copper Quicksilver Silver Volatile alkali.

3. Marine Acid. Fixed alkali Calcareous earth Zinc Iron Lead Tin Copper Regulus of antimony Quicksilver Silver Spirit of wine Volatile oils Gold.

4. Sulphur. Fixed alkali Calcareous earth Iron Nickel

5. Hepar Sulphuris is partially decomposed by Quicksilver Solution of fixed alkali Lime-water Volatile alkali.

6. Fixed Air. Calcareous earth Fixed alkali Magnesia Volatile alkali.

7. Alkaline Salts. Vitriolic acid Nitrous acid Marine acid Acetous acid Volatile vitriolic acid Sedative salt Fixed air Sulphur Exprefled oils.

8. Calcareous Earth. Vitriolic acid Nitrous acid Marine acid Acid of tartar Acetous acid Sulphureous acid and sedative salt Sulphur.

9. Metallic Substances, Lead and Regulus of Antimony excepted. Marine acid.

Vitriolic acid Nitrous acid Sulphur and acetous acid.

10. Lead. Vitriolic acid Marine acid Nitrous acid Acetous acid Exprefled oils.

11. Regulus of Antimony. Vitriolic acid Nitrous acid Marine acid Acetous acid.

12. Arsenic. Copper Lead Tin Silver Regulus of antimony Quicksilver Arfenic. Zinc Iron Copper Tin Lead Silver Gold.

13. Regulus of Antimony. In consequence of heat, sedative salt and the other solid acids decompose vitriolated tartar, nitre, and sea-salt.

Double Elective Attractions; which, in some cases, may be considered as exceptions to the foregoing table.

I. Those which happen in mixtures of watery substances.

1. Acids Calc. earths, or metallic substances Vitriolic or marine acids

2. Alkalies or earths Lead Nitrous, marine, or acetous acids Silver

3. Vitriolic, nitrous, or acetous acids Volatile alkali

4. Acids Nitrous, marine, or acetous acids Calcareous earths

II. Those which happen in distillations or sublimations, and require heat.

1. Vol. alkali Acids

2. Vol. alkali Vitriol. acid Vol. alkali Nitrous, marine, or vitriolic acids

Fixed-air Calcareous earths. Nitrous, marine, or acetous acids Fixed alkali. Acetous acid Fixed alkali, or absorbent earths. Theory.

Chemical Operations.

4. Reg. of antimon. Marine acid Sulphur Quicksilver.

III. Those which happen in mixtures by fusion.

1. Tin Iron Silver Lead. 2. Copper Sulphur Gold Lead. 3. M. S. Sulphur Gold Reg. of ant.

The first of these tables requires very little explanation. The names printed in small capitals, are those of the substances which have the affinity with or attract those below them. Thus, vitriolic acid attracts most powerfully the phlogiston, or inflammable principle; next, fixed alkali; then, calcareous earth; and so on, in the order in which they are marked.—The tables of double elective attractions cannot be made quite so difficult; though an explanation of one example will make this likewise easy to be understood. Thus in Table I. the first case is, "If a combination of acids with calcareous earths or metallic substances is mixed with a combination of volatile alkali and fixed air, the acids will unite themselves to the volatile alkali, and the fixed air to the calcareous earth or metallic substance."

Sect. X. Of the different Operations in Practical Chemistry, and the proper Instruments for performing each.

The most remarkable operations in chemistry, and by which the greatest changes are made upon those bodies which are the objects of that science, may be comprehended under the following names. 1. Solution. 2. Filtration. 3. Precipitation, or coagulation. 4. Evaporation. 5. Crystalization. 6. Distillation. 7. Sublimation. 8. Deflagration. 9. Calcination. 10. Fusion. 11. Maceration, or digestion. To which we may add, 12. Trituration, or levigation.

Before we proceed to a particular account of each of these operations, it is necessary to take notice, that there are two different things proposed by those who enter on the practice of chemistry. Some have nothing farther in view than the enlargement of their knowledge, or making improvements in arts which are to be practised by others for their own advantage. Others design to follow chemistry as a trade, by which they hope to enrich themselves, or to get a comfortable livelihood. But the apparatus and utensils necessary for performing the very same operations are exceedingly different when experiments only are to be made, from what they must be when these operations are performed with a view to profit; and so great is this difference, than those who pursue chemistry with a view to advantage, will always find themselves very considerable losers if they follow the plan of an apparatus or a laboratory designed only for making experiments. Along with the apparatus, therefore, which is commonly described in chemical books, and proper only for experiments, we shall also give that which is necessary for preparing great quantities of any chemical article in the way of trade.

In general, those who practice chemistry merely with an experimental view, ought, as much as possible, to make use of glass vessels, as not being liable to be corroded by the most powerful solvents; and, by their transparency, giving an opportunity of observing what passes within them during the operation. But by those who practise chemistry with a different view, these vessels ought, with equal care, to be avoided, on account of their expense and brittleness. This last quality, indeed, is possessed by glass in so eminent a degree, that glass vessels will sometimes fly to pieces, and that with considerable violence, when standing by themselves, and nothing touching them. The principal objects which a chemist ought to have in view, in performing his operations, ought to be to save time and fuel, especially the former; and for this purpose, he would find himself a considerable gainer, though he should be at much greater expense in his apparatus than he would otherwise have occasion for.

On the subject of chemical vessels Dr Black observes, that "with regard to the material of which these are composed, we are very much at a loss; and indeed there are no such materials in nature as are capable of answering the purposes of chemists in absolute perfection.—The qualities are, 1. Transparency, to allow us to see the changes going on; 2. The power of resisting the action of acids and corrosive substances; 3. That they bear sudden alterations of heat and cold without breaking; 4. That they be strong, in order to confine elastic vapours; and, 5. That they bear very great heat without melting. As these qualities, however, are not to be met with united in any one substance, the chemists are obliged to have recourse to different substances which possess some of them differently. There are, glass, metal, and earthen ware. Good glass is possessed of the two first properties, but has had the inconvenience of being apt to crack and fly into pieces, on any sudden transition from heat to cold, or from cold to heat. The best method of remedying this defect, is to have the glass made very thin, and vessels of a round figure, that it may be all heated as equally as possible; as it is the unequal application of the heat which causes it break. Another requisite in the choice of chemical glasses, is that they be well annealed. If this is not done, the glass will either immediately fly to pieces, or be liable to break on the smallest accident. That such glasses should be liable to be broken on every slight occasion, is a phenomenon that has hitherto received no explanation. If you touch them with a diamond, with a piece of flint, glass, &c., or expose them to the heat of the sun, they break immediately. Dr Black has had great vessels of glass, which broke immediately on his throwing a little sand into them to clean them. This manifestly depends upon the same principles as the qualities of what are called glass tears.

Glass when well annealed is universally to be preferred, where great and sudden changes of heat, or much strength, are not required. Flint-glass is the best; but the coarser kinds, as bottle-glass, are very apt to break.

The metals have the third and fourth qualities in perfection, but are deficient in all the rest. The bad qualities of metals are, that they are liable to be corroded by acids and other bodies, as is the case with iron and copper; though this is in some chemical vessels. measure remedied by tinning; which, though it wants some of the qualities from its melting too soon, yet resists the action of many acid substances without being so readily injured by them; but it is not entirely free from this imperfection, and is liable to be somewhat corroded and rusted. In nice operations, therefore, recourse is had to silver and even to gold vessels.

Earthen ware possesses only the fifth quality in perfection, viz. that of bearing a violent heat without fusion. The basis of these vessels is clay, which, when good, is very convenient for the formation of vessels, and it has been used from the earliest ages of chemistry for this purpose. The requisite qualities are, 1. A considerable degree of toughness when mixed with water. 2. A great degree of hardness when burnt in the fire with a violent degree of heat. The best kind of clay thus contracts a degree of hardness scarcely inferior to flint, as is the case with that of which tobacco-pipes are made; but most other kinds, such as that of which bricks are constructed, are apt to melt with a strong heat into a spongy matter. Clay, however, can seldom be used alone; for when burnt to extreme hardness, the vessels are very liable to crack. This is remedied by mixing sand reduced to a particular degree of fineness, with the clay of which the vessels are made. For this purpose both the finest and the coarsest particles of the sand must be thrown away.

Another substance known by the name of black lead, used in the making of pencils, resists the fire exceedingly. This, however, does not contain an ore of lead, but sulphur, and some mineral substances; when mixed with clay, however, it makes it resist the fire surprisingly. But there are some particular cases in which neither sand nor black lead can be used as a material; for the sand is easily corroded by acid matters, and the black lead would produce other inconveniences. Clay is therefore to be taken in its unburnt state, reducing it to a powder like sand; then burning this powder with a violent heat, so as to convert it into sand. Mixing it then with raw clay, it forms a composition which answers very well for making chemical vessels, and may be employed in those particular cases where sand would not answer. Pott of Berlin has written upon the different kinds of earthen ware proper to be employed in the construction of chemical vessels. There is a French translation of it in four or five volumes. In cases where the utmost compactness of texture is required, porcelain vessels are to be chosen; which is composed of the finest clay, mixed with a stony matter, that has the quality of melting in a violent heat, and gives more compactness to the clay than it is naturally capable of receiving; but these are rather too costly for most operations. Reaumur has taught a way of converting glass into porcelain.

We shall now proceed to a particular description of each of the operations above mentioned.

I. Solution. By this is understood the dissolving a solid substance in a fluid, so that the solid shall totally disappear, and become part of a transparent liquor. This operation applies particularly to salts, earths, and metals; as well as to several unctuous and inflammable substances. For performing this operation in a small way, common vials are in many cases sufficient. Where

the solution is attended with effervescence and a diffusion of vapours, the long-necked glasses called matrasses, or bottle-heads, (fig. 5.), are necessary. Florence flasks are indeed exceedingly well adapted for this operation, as being of the proper shape, and capable of bearing heat so well, that they may be filled with any fluid, and set on a common fire like a metallic vessel. Solution is much promoted by agitating the vessel, and by heat. In some cases, indeed, it will not take place till the mixture becomes very hot; and in such cases it will be proper to make the fluid boiling hot by itself, and then slowly to add the substance to be dissolved.

When large quantities of saline matter are to be dissolved, metallic vessels must be used; but before any are made use of for this purpose, it will be necessary to make an experiment whether the salt receives any impregnation from the metal of which the vessel intended to be made use of is formed; and if this is found to be the case, it must not be used. The metals most liable to be corroded by saline bodies are iron and copper; and indeed, unless it be for the single purpose of dissolving fixed alkaline salts, iron vessels seem totally unfit for saline solutions of any kind. Copper vessels are also very liable to be corroded, and to communicate very mischievous qualities to the liquors which corrode them; for which reason, they ought never to be made use of for the purposes of solution. The metal least liable to be corroded, next to gold and silver, is lead; and therefore a chemist ought rather to provide himself with leaden vessels than those of any other metal. But though lead is not apt to be corroded by many kinds of salts, there are some which are found to act upon it, and to form therewith a very dangerous poison. The vegetable acid of vinegar is particularly apt to receive a dangerous impregnation from this metal; and therefore no solution of any salt containing this acid ought to be made in leaden vessels. It appears to be very little affected by the vitriolic or marine acids; and therefore any saline substance containing either of these acids may be safely enough dissolved in vessels made of lead.

In order to save time in making solutions, the vessels ought to be as large as possible; though even in this there must be a certain limit: for two small vessels filled with water will sooner acquire the necessary degree of heat than one large one; and in proportion as the vessel is made more capacious, the sides and bottom must be thicker, which considerably increases the expense. Fifteen or twenty English gallons is the utmost capacity of which they ever will be required; and is rather above what will on most occasions be necessary. They ought to be of a conical figure, round at the bottom; and to have a cover of thick plate-iron all around that part which is exposed to the action of the fire, that the lead may not bend on the application of heat, which it would otherwise be very apt to do. When the solution is to be made, the leaden vessel is first to be filled up with water so far as to have room for the quantity of salt intended to be dissolved; a fire is then to be applied so as to make it boil; and then the salt is to be added slowly, so as scarcely to hinder the boiling; for if a great quantity was thrown in at once, so as to cool the liquor very much, great part of the salt would concrete on the bottom, in such Chemical Operations

a manner as not only to be very difficultly soluble, but even to endanger the melting of the vessel. It is of some consequence also to avoid the hot steam which proceeds from the boiling water, and which influes with great force from a narrow-mouthed vessel such as we have been describing. That the operator may be out of the reach of this, and likewise dissolve the salt in a regular and gradual manner, without any danger of its concreting on the bottom, it will be proper to have a leaden, or even a wooden, vessel, with a long handle; which is to be filled with the substance to be dissolved, then immersed in the boiling liquor, and shaken about in it, till the salt is made into a kind of thick pap, which will be in no danger of concreting. It will also be proper not to saturate the water perfectly with salt; for it will in that case be impossible to hinder part of it from settling on the bottom, where it soon acquires such a degree of heat as to melt the lead. Before any saline substance is put into water for solution, it ought to be pounded and sifted through a hair sieve.

Where large quantities of metal are to be dissolved in acids, especially the nitrous acid, glass vessels are in a manner indispensable; although the common stoneware bottles, especially those made in Holland, will answer the purpose very well, as not being liable to corrosion, and not so apt to break as the glass vessels are. They may be got of such a size as to hold three or four gallons: but no vessel in which metallic solutions are made ought ever to be above half full.

In solutions of oily and inflammable substances, cast iron vessels are perhaps the most proper of any; though copper ones are generally preferred. The copper is excessively soluble in oil, especially if it is left to cool in such a vessel; but iron is not soluble in any inflammable matter except sulphur. Copper has, however, this advantage over iron, that it is sooner cooled, as the vessels made of copper are thinner than they can be made of cast iron: so that if too great heat is applied to a copper vessel, it may be easily remedied by taking it off the fire; but in a cast iron vessel the heat continues so long as may sometimes produce dangerous consequences, even after the fire is removed.

Dr Black observes, that for the purpose of solution, if no particular nor uncommon consequence follow the application of the two bodies to each other, and if none of them be very volatile, any glass or porcelain vessel that can resist the action of the substances will answer the purpose; but it often happens that they break out into violent ebullition, which produces steam; and here a common vessel is not so proper, as we would wish to have the vapour confined or condensed. We therefore choose a close vessel that will bear the heat suddenly produced by the mixture, or the heat that may be necessary to promote the action of such bodies upon one another. Of this kind is the phiala chemica, or matras, in which the vapours will have time to circulate and to be condensed again, without being allowed to escape. Where the matter is in small quantity, smaller vessels somewhat of the same form are used, as Florentine flasks, which bear sudden changes of heat and cold remarkably well, on account of their thinness. In order to promote the action of bodies, it is sometimes necessary to make the fluids boil; and for this purpose we must have a matras with a large neck, or apply another vessel to it that will receive the steam, and give them still more room for their condensation, and direct them to fall back again, when condensed, into the matras. This is called circulation. Macquer describes another vessel called the pelican, which has been made use of for this purpose; but it is hardly ever employed, on account of its being troublesome to procure and manage it; and the advantages arising from it may be obtained by a more simple apparatus.

To this head we must refer Papin's digester, which Papin's digester is represented Fig. 4. It is generally made of copper, very thick and strong, open at the top, with a lid fitted to it, which applies very exactly. There are usually two projections on the side, designed to make the lid go in a particular manner, but they are unnecessary. There are other two, to which are fitted the two sides of a cross bar BB; in which cross bar there is a strong screw D, by which the lid can be pressed down very strongly. Its use is to force water to bear a stronger heat than it can do under the ordinary pressure of the atmosphere. It is sometimes furnished with an apparatus for letting out the steam, lest it should be in danger of bursting the vessel. A pipe is passed through the lid which is fitted with a valve, on which passes a lever at a very small distance from its centre of motion; and this can be made to press on the valve with different weights, according to the distance of these weights from the centre. In one constructed by Dr Black, there was another pipe below, into which a thermometer could be introduced, in order to measure the degree of heat to which the steam was raised. This machine was pretty much employed some time ago, and its effects were much admired; but we find that most things which can be dissolved in this way, can likewise be dissolved in the ordinary way by boiling water, provided it is continued for a longer time, as animal bones, from which the gelatinous parts are indeed extracted very quickly by this vessel; but the same change is produced by boiling them in water for a long time in the ordinary degree of heat.

II. Filtration. This operation is generally the attendant of solution: very few substances, of the saline kind especially, are capable of being dissolved without leaving some impurities, from which they must be freed; and the doing of this, so as to render the solution perfectly transparent, is what is understood by the word filtration.

For purposes merely experimental, a glass funnel and piece of paper are generally sufficient. The paper is formed into a conical cap, which being placed in the funnel with its point downwards, the funnel is then placed in the mouth of a vial; and the solution or other liquor to be filtered is poured into the paper cap, through which the liquor passes transparent, leaving its impurities on the paper. For the purpose of filtration, paper has come into such general use, that a particular kind of it is prepared under the name of filtering paper. This is of a reddish colour; but Dr Lewis prefers the whitish grey paper which comes from Holland about the pill boxes, as not giving any colour to the solutions which pass through it.

This operation, though apparently so simple and easy, easily, is nevertheless attended with very troublesome circumstances, on account of the great time it takes up. Even where very small quantities of liquor are to be filtered, merely for experiment's sake, the impurities frequently settle on the paper too soon, and obstruct its pores to such a degree, that the operator is often quite wearied out; often, too, the paper breaks; and thus the whole is spoiled, and the operation must be begun over again.

To avoid these inconveniences, another method of filtration hath been proposed; namely, to use a number of cotton threads, the ends of which are to be immersed in the liquor, and the other ends are to hang over the side of the vessel which contains it, and to hang lower than the surface of the liquor. By this means they will act as so many capillary typhons, (see Syphon); the liquor will arise in them quite pure, and be discharged from their lower extremities into a vessel placed to receive it. That the liquor may flow freely into the cotton, it will be proper to wet the threads before they are used.

In point of efficacy, no doubt, this method excels every other; and where the operator has abundance of time and patience, may be proper for experiments; but, in the way of trade, such a contrivance is evidently useless. For filtering large quantities of liquor, therefore, recourse has been had to large funnels; earthen cullenders, or basins full of holes in the bottom, lined with filtering paper; and to conical bags of flannel or canvas.

The inconveniences attending funnels, when used only in the way of experiment, are much greater when they are employed for filtering large quantities of liquor; and therefore they are generally laid aside. The earthen cullenders, too, do not answer any good purpose; nor indeed does filtration through paper in general succeed well. The conical flannel or canvas bags are greatly preferable; but they have this inconvenience, that the pressure of the liquor is directed chiefly against one particular point, or a small part of the bottom, and therefore the impurities are forcibly driven into that place; and thus the operation becomes insufferably tedious.

The best method of obviating the inconveniences of filtration seems to be the following. Let a wooden frame of about three feet square be made, having four holes, one in each corner, about three quarters of an inch in diameter. This frame is to be supported by four feet, the ends of which must project an inch or two through the holes. Thus the whole may be occasionally let up and taken down, so as to go into very little compass; for if the feet are properly placed, each with a little projection outwards, there will be no danger of its falling. A square piece of canvas must also be procured, somewhat less than the wooden frame. On each corner of it there must be a very strong loop, which slips on one of the projecting ends of the feet, so that the canvas may hang a little slack in the middle of the frame. The liquor to be filtered is now poured into the canvas, and a vessel placed underneath to receive it. At first it will pass through very foul; but being returned two or three times, will become perfectly transparent, and will continue to run with great velocity, if the filter is kept constantly full. A filter of the size just now mentioned will contain ten gallons of liquid; which is a very great advantage, as the heat of such a quantity of liquor is not soon dissipated, and every solution filters much faster when hot than when allowed to cool.

The advantages of a filter of this kind above others arise from the pressure of the liquor being more equally diffused over a large space, by which the impurities are not forced so strongly into the cloth as to stop it up entirely. Yet even here, where large quantities of liquor require filtration, the cloth is apt to be flopped up so as to make the operation not a little tedious and disagreeable. It will be proper therefore to have several cloths, that one may be applied as soon as another is taken off.

To promote the operation of filtration, it is very proper to let the liquors to be filtrated settle for some time; that so their grosser feculencies may fall to the bottom, and thus there will be the fewer to retard the last part of the operation. Sometimes, however, these feculencies refuse to settle till after a very long time; and where this happens to be the case, a little powdered quicklime thrown into the boiling liquor remarkably promotes the separation. This, however, can only be used in certain cases.

In some cases, the discovery of a ready way of filtering a large quantity of liquor would be a matter of filtering great consequence; as where a town is supplied with large quantities of river water, which is generally far from being clear, and often imparts a disagreeable colour to clothes washed with it. Some years ago, a scheme was proposed by a chemist for filtering muddy water in any quantity. His method was, to have a large cask covered over in the bottom with straw to the depth of some inches, and then filled up with sand. This cask was entirely open at one end, and had a hole in the other, which, by means of a leaden pipe, communicated with a large reservoir of the water to be filtered, and which stood considerably higher than the cask. The water which descended through the pipe into the cask, having a tendency to rise up to the same level with that in the reservoir, would press violently against the sand, and, as he thought, run over the mouth of the cask perfectly filtrated, and free from its impurities. By this contrivance, indeed, a very violent pressure was occasioned, if the height of the reservoir was considerable: but the consequence was, not a filtration, but a greater degree of impurity in the water; for the sand was forced out of the cask along with it, and, however confined, the water always rose as muddy as it went in.

Where water is to be filtered in large quantity, as for the purposes of a family, a particular kind of soft spongy stones, called filtering stones, are employed. These, however, though the water percolates through them very fine, and in sufficient quantity at first, are liable to be obstructed in the same manner as paper, and are then rendered useless. A better method seems to be, to have a wooden vessel, lined with lead, three or four feet wide at top, but tapering so as to end in a small orifice at the bottom. The under part of the vessel is to be filled with very rough sand, or gravel, well freed from earth by washing. Over this, pretty fine sand may be laid to the depth of 12 or 14 inches, but which must likewise be well freed from earthy particles. particles. The vessel may then be filled up to the top with water, pouring it gently at first, lest the sand should be too much displaced. It will soon filter through the sand, and run out at the lower orifice exceedingly transparent, and likewise in very considerable quantity. When the upper part of the sand begins to be stopped up, so as not to allow a free passage to the water, it may occasionally be taken off, and the earthy matter washed from it, when it will be equally serviceable as before.

III. Precipitation, or Coagulation. This operation is the very reverse of solution, and is the bringing a body suddenly from a fluid to a solid state. It differs from crystallization, in that it generally requires less time; and in crystallization the substance assumes regular figures, whereas precipitates are always in the form of powders.

Precipitation is generally preceded by solution and filtration: it is used for separating earths and metals from the acids which had kept them suspended. When a precipitation is made of the more valuable metals, glass vessels are to be used. When earths, or the imperfect metallic substances, are to be precipitated in large quantity, wooden ones answer every purpose. If a metal is to be precipitated by an alkali, this salt must first be dissolved in water, then filtered, and gradually added to the metallic solution. If particular circumstances do not forbid, the salt for precipitation should be chosen in its caustic state, or deprived of its fixed air, because then a very troublesome effervescence is avoided. To promote the operation also, the mixture, if contained in a glass, is to be shaken; or if in any other vessels, to be well stirred after every addition of alkali. If an earth is employed to precipitate a metal, the mixture must be in a manner constantly stirred or shaken, in order to promote the precipitation; and if one metal is to be precipitated by another, that which is used as a precipitant must be beaten into thin plates, that so they may be frequently cleaned from the precipitating metal, which would otherwise very soon totally impede the operation.

Sometimes a precipitation ensues on the addition of water or spirit of wine: but in most cases care must be taken not to add too much of the substance which is used to precipitate the other; because, in such a case, the precipitate may be dissolved after it has been thrown down. Thus, though volatile alkali will separate copper from aquafortis, it will as effectually dissolve the precipitate, if too much of it is used, as the acid itself. It is proper, therefore, to proceed cautiously, and examine a small quantity of the liquor from time to time. If an addition of the precipitant throws down any more, it will be proper to add some more to the whole solution.

It is seldom or never that precipitation can be performed so perfectly, but that one or other of the ingredients will prevail; and though they should not, a new compound, consisting of the acid united with the alkali, or other substance used for precipitation, is contained in the liquor through which the precipitate falls. It is proper, therefore, to wash all precipitates; otherwise they can never be obtained perfectly pure, or free from a mixture of saline substances. This is best done by pouring the whole into a filter, and letting the fluid part run off, as long as it will drop, without shaking the cloth. Some water is then to be cautiously poured all over the surface of the precipitate, so as to disturb it as little as possible. This water will push before it the saline liquor which is mixed with the powder, and render it much purer than before. A second or third quantity of water may be used, in order to wash off all the saline matter. This is called edulcorating the precipitate.

IV. Evaporation. This operation consists in evaporating the most fluid or volatile parts of any substance by means of heat. It most generally succeeds solution and filtration, being a preparatory for the operation of crystallization.

For the evaporation of saline solutions, which have been already filtered, and which it is of consequence to preserve from even the least impurities, distilling vessels are unquestionably the most proper; both as, by their means, the solution will be kept perfectly free from dust, and as the quantity of liquor evaporated can be known with certainty by measuring that which comes over. This also is probably the most expeditious method of evaporating, and which requires the least fuel. (See the detached articles Evaporation and Distillation.) With regard to vessels for evaporation, the same thing must be applicable which was mentioned above under Solution. No saline liquor must be evaporated in a vessel which would be corroded by it; and hence iron vessels are absolutely improper for evaporations of any kind of saline liquor whatever.—Lead is in this case the metal most generally useful. It must only be used, however, where the evaporation is not carried to dryness; for, on account of the great fusibility of this metal, nothing could be effused in it without great danger of its melting. Where a saline liquor therefore is to be perfectly effused, the evaporation, if performed in lead vessels, must be carried on so far only as to form a saline pellicle on the surface of the liquor. It is then to be drawn off; for which purpose, all evaporating vessels should have a cock near the bottom. The liquor must now be put into a number of stone-ware basins, set on warm sand, where the effusion may be finished.

V. Crystallization. This, though commonly accounted one of the processes in chemistry, is in reality only a natural one, and which the chemist can only prepare for, leaving the operation entirely in the hands of nature.—By crystallization is meant the separation of a salt from the water in which it has been dissolved, in transparent masses regularly figured, and differently formed, according to the different nature of the salts.

This process depends upon the constitution of the atmosphere more than any other; and therefore is difficult to be performed, nor does it always succeed equally well; neither have there yet been laid down any rules whereby beautiful and regular crystals can with certainty be formed at all times.

As the different salts assume very different figures when crystallized, they are not subject to the same general rules in crystallization. Nitre, Glauber's salt, vitriol of iron, and many others, crystallize best on having their solutions set in a cold place after proper evaporation. Sal polychrest, and common salt, require the solution to be kept as hot as the hand can bear it during the time of crystallizing. Soluble tartar too, and other deliquescent salts, require to be kept warm while this operation is going on; and there are many saline substances, such as the combinations of calcareous earths and magnesia with acids, which can scarcely be crystallized at all.

Mr Beaumé has discovered, that when two or more salts are dissolved in the same quantity of water, when one crystallizes, the crystals of that salt will not contain the least quantity of any of the others; neither, although the liquor was acid or alkaline, will the crystals for that reason be either acid or alkaline, but will remain perfectly neutral; and the acid or alkaline liquor which adheres to the outside of the crystals may be absorbed by merely spreading them on filtering paper.—Hence we are furnished with a better method of shooting salts into large and well formed crystals than merely by dissolving them in water; namely, by adding to the solutions, when set to crystallize, a certain quantity of acid or alkaline liquor, according to the nature of the salts themselves. These additions, however, are not equally proper for all salts; and it is not yet determined what kinds of salts ought to be crystallized in alkaline, and what in acid liquors.—Soluble tartar and Seignette's salt crystallize best when the liquor is alkaline. Sal soda, sal glaucum, and sal polychrest, require an acid if crystallized in the cold; but sal polychrest forms into very fine and large crystals when the solution is alkaline, and kept as hot as the hand can easily bear.

The best general direction that can be given with regard to the regular crystallization of salts is, that they ought to be set to crystallize in as large a quantity at once as possible; and this, as far as we have observed, without any limit; for by this means, the crystals are formed much larger and better figured than they possibly can be by any other method hitherto known.—As to the form of the vessels in which salts are to be crystallized, little can be said with certainty. They are generally flat, and wider at top than at the bottom. The only proper material, in the large way, is lead.

VI. Distillation. This is a kind of evaporation; only in such a manner, that the part of the liquor evaporated is not dissipated in the air, but preserved by making the steam pass through a spiral pipe, which goes through a large vessel full of cold water, or into cold glass receivers.

This is one of the most common chemical operations; and as there are a variety of subjects which require to be distilled, there is consequently a considerable variety both in the form of the distilling vessels to be used on different occasions, and likewise in the materials of which they are made, as well as the management of the fire during the time of the operation.

The most simple and easily performed distillation is that by the common copper still, (fig. 3). It consists of two parts; one called the body, and the other the head. The body is a cylindrical vessel of copper, which is sometimes tinned over in the inside; but where distillation is performed without any regard to the residuum, the tinning is useless. The upper part of the body terminates in a kind of arch, in the middle of which is a circular aperture, about one half, or something less, in diameter, of the breadth of the whole body.—Into this aperture, a round head, Chemical made likewise of copper, is fitted, so as to be removable at pleasure. In the top, or sometimes in the side of the head, is inserted a pewter pipe, which communicates with a spiral one of the same metal, that passes through a large wooden vessel, called the refrigeratory, filled with cold water; each of its ends projecting a little above and below. The still is to be filled two thirds full of the substance to be distilled, the head put on, and the junctures well closed with a mixture of linted meal and water, or common flour or chalk and water will answer the same purpose. This mixture is called the luting, or lute. A fire being kindled under the still, the vapours will arise; and, being condensed by the cold water through which the spiral pipe called the worm passes, will run in a stream more or less strong as the fire is more or less hastily urged, and is caught in a receiver set underneath.

This kind of distilling vessels is proper for procuring the essential oils of vegetables, vinous spirits from fermented liquor, and for the rectification of these after they are once distilled. Even the acetic acid may be very conveniently distilled in a copper vessel, provided the worm and all the descending parts of the pipe which communicates with it be of pewter, otherwise a mischiefous impregnation of copper would be communicated to the distilled vinegar. The reason of this is, that copper is not dissolved by vinegar, or in very small quantity, when that acid is boiled in it; but if the metal is exposed to the action of the acid when cold, or to its vapours, a considerable dissolution takes place. For this reason, too, the still must be washed out after the operation while it continues hot, and must likewise be very carefully freed from the least remains of acid, otherwise it will be much corroded.

Copper-stills ought to be of as large a size as possible; but Dr Lewis very justly observes, that, in common ones, the width of the worm is by no means proportionable to the capacity of the still; hence the vapour which issues from a large surface being violently forced through a small tube, meets with too much resistance as sometimes to blow off the still-head. This inconvenience is ridiculously endeavoured to be prevented by strongly tying or otherwise forcing down the head; by which means, if the worm should happen to be choked up, a terrible explosion would ensue; for no ligatures, or any other obstacle whatever, have yet been found strong enough to resist the elastic force of steam; and the greater obstacle it has to overcome, the greater would the explosion be.—Dangers of this kind might be totally avoided by having the worm of a proper degree of wideness.

Sometimes, however, matters are to be distilled, mineral as well as mineral acid spirits, which would corrode any kind of metallic vessels; and for these only earthen, or clay vessels, the closest kind of stone-ware, can be used. These are more easily condensed than the steams of aqueous or vinous liquors, and therefore do not require to be passed through a pipe of such a length as is used for condensing the steams from the common still. In these cases, where a violent heat is not necessary, and the distillation is to be performed in glass vessels, the retort is used (fig. 4.) When a fluid is to be put into this vessel, the retort must be laid upon its back on sand, or any other soft matter that will support it without breaking. A funnel must also be procured with a long stem, and a little crooked at the extremity, that the liquor may pass at once into the belly of the retort, without touching any part of its neck; otherwise the quantity which adhered to the neck would pass into the receiver when the retort was placed in a proper situation for distilling, and foul the produce. When the vessel is properly filled, which ought never to be above two thirds, it is to be set in a sand bath; that is, in an iron pot, of a proper thickness, and covered over in the bottom, to the depth of one or two inches, with dry sand. When the retort is put in, so as to stand on its bottom, the pot is to be filled up with sand, as far as the neck of the retort. A glass receiver is then to be applied, which ought to be as large as possible, and likewise pretty strong; for which reason it will be proper not to let the capacity of it be above what is necessary to hold ten gallons. In the hinder part of it should be drilled a small hole, which may be occasionally shut by a small wooden peg. The mouth of the receiver ought to be so wide as to let the nose of the retort enter to the middle of it, or very near to it; for if the vapors are discharged very near the luting, they will act upon it much more strongly than when at a distance. It is likewise proper to have the neck of the retort as wide as may be; for this has a very great effect in the condensation, by presenting a larger surface to the condensing vapor.

The luting for acid spirits ought to be very different from that used in other distillations; for these will penetrate the common lutes so as to make them liquid and fall down into the receiver. Some have used retorts, the necks of which were ground to the receivers with emery; but these are very difficult to be procured, and are expensive, and consequently have never come into general use. Various kinds of lutes have been proposed, but the preference seems due to a mixture of clay and sand. We are not to understand, however, that every kind of clay is fit for this purpose; it must only be such as is not at all, or very little, affected by acids; and this quality is only possessed by that kind of which tobacco-pipes are made. Trial ought to be made of this before the distillation is begun, by pouring a little nitrous acid on the clay intended to be the use of. If a violent effervescence is raised, we may be sure that the clay is unfit for the purpose. Finely powdered alabaster would answer extremely well, had it the ductility of clay. As this kind of lute remains soft for a considerable time, it ought to be farther secured by a bit of rag spread with some strong cement, such as quicklime mixed with the white of an egg, &c. Matters, however, ought to be managed in such a manner, that the luting may give way, rather than the vessels burst; which would not only occasion a certain loss of the materials, but might endanger the persons who were standing by.

The iron pots commonly used for distillations by the sand-bath, or balneum mariae, are commonly made very thick; and are to be sold at large founderies, under the name of sand-pots. The shape of these, however, is by no means eligible: for, as they are of a figure nearly cylindrical, if the retort is of such a size as almost to fill their cavity, it cannot be put into them when full, and often pretty heavy, without great danger of touching the sides of the pot; and in this case, touching and breaking are synonymous expressions. It is much better, therefore, to have them in the figure of a punch-bowl; and the common cast-iron kettles, which may be had much cheaper than the sand-pots usually sold, answer extremely well. If the distilling vessel is placed in a pot filled with water, the distillation is said to be performed in a water-bath, or balneum mariae.

When the matter to be condensed is very volatile, a number of open receivers with two necks, called adopters (fig. 7.), may be used, with a close receiver at the end. Each of these adopters must be fitted with as much care as when only a single receiver is made adobe, use of. Vessels of a similar kind were formerly much used by chemists for particular sublimations, under the name of adobes.

Formerly, instead of retorts, a vessel called a cucurbit, (fig. 5., and 6.) with a head like the common still, called an alembic, were used; but the more simple figure of the retort gives it greatly the preference. It is but seldom that vessels of this kind are useful, which will be taken notice of when describing the particular operations: and if at any time an alembic head should be necessary, its use may be superseded by a crooked glass tube, which will answer the purpose equally well.

Sometimes a very violent fire is required in distillations by the retort. Here, where it is possible, glass or earthen vessels should be avoided, and iron pots substituted in their stead. The hardest and best cast iron, however, will at last melt by a vehement heat; and therefore there is a necessity for using earthen ware, or coated glass. This last is better than most kinds of earthen ware, as being less porous; for when the vessel is urged by a very intense heat, the glass melts, and forms a kind of semivitreous compound with the inside of the coating, so that its figure is still preserved, and the accidental cracks in the luting are filled up.

For coating of vessels, mixtures of coloethan of triol, sand, iron filings, blood, chopped hair, &c., have glasses been recommended. We cannot help thinking, however, that the simple mixture of tobacco-pipe clay and sand is preferable to any other; especially if, as Dr Black directs, that part next the glass is mixed with charcoal dust.

The proportions recommended by the Doctor for luting the joints of vessels, are four parts of sand and one of clay; but for lining the insides of furnaces, and, we should think, likewise for coating glass vessels, he directs 6 or 7 of sand to 1 of clay; that the contraction of the clay in drying may thereby be the more effectually prevented. Besides this, he directs a mixture of three parts of charcoal-dust with one of clay, to be put next the furnace itself, as being more apt to confine the heat; but possibly the first composition might be sufficient for glasses.

The coating of large glasses must be a very troublesome and tedious operation; and therefore coated glass is never used but in experiments. When large distillations are to be performed in the way of trade, recourse must be had either to iron pots, or to earthen ware. ware. Of the most proper kinds of earthen ware for resisting violent heats, we shall take notice under the article Fusion.

In all distillations by the retort, a considerable quantity of air, or other incondensible vapour, is extracted; and to this it is absolutely necessary to give vent, or the vessels would be burst, or the receiver thrown off. For this purpose, Dr Lewis recommends an open pipe to be inserted at the luting, of such an height as will not allow any of the vapour to escape; but this we cannot approve of, as by that means a constant communication is formed between the external atmosphere and the matters contained in the retort and receiver, which is at all times to be avoided as much as possible, and in some cases, as the distillation of phosphorus, would be very dangerous. The having a small hole drilled in the receiver, which is to be now and then opened, must answer the purpose much better, although it takes more attendance; but if the operator is obliged to leave the vessels for some time, it will be convenient either to leave the little hole open, or to contrive it so that the wooden peg may be pushed out with less force than is sufficient to break the tube.

VII. Sublimation. This, properly speaking, is only the distillation of a dry substance; and therefore, when volatile matters, such as salt of hartshorn, are to be sublimed, the operation is performed in a glass retort set in a sand bath, and the salt passes over into the receiver. The cucurbit and alembic were formerly much in use for this purpose; and a blind head, without any spout, was applied. A much simpler apparatus, however, is now made use of. A globe made of very thin glass, or an oblong vessel of the same kind, answers the more common purposes of sublimation. For experiments, Florence flasks are excellent; as being both very cheap, and having the necessary shape and thinness requisite for bearing the heat without cracking. The matter to be sublimed must not, on almost any occasion, take up more than a third part of the subliming vessel. It is to be set in a sand-bath, that the heat may be more equally applied than it could otherwise be. The heat must be no greater, or very little, than is necessary for sublimation, or it will be in danger of flying out at the mouth of the subliming vessel, or of choking it up so as to burst. The upper part of the vessel, too, must by no means be kept cool, but slightly covered with sand, that the matter may settle in a kind of half-melted state, and thus form a compact hard cake, which is the appearance sublimes are expected to have. Hence this operation requires a good deal of caution, and is not very easily performed.

VIII. Deflagration. This operation is always performed by means of nitre, except in making the flowers of zinc. It requires open vessels of earth or iron; the latter are very apt to be corroded, and the former to imbibe part of the matter. To perform this process with safety, and without loss, the nitre ought to be mixed with whatever matter is to be deflagrated with it, and thrown by little and little into the vessel previously made red-hot. If much is put in at once, a great deal will be thrown out by the violent commotion; and to perform this operation in close vessels is in a manner impossible, from the prodigious quantity of elastic vapour generated by the nitre. Care must also be taken to remove the whole mixture to some distance from the fire, and not to bring back any spark from the quantity deflagrating, with the spoon which puts it in; otherwise the whole would irremediably be consumed at once.

IX. Calcination. This is the subjecting any matter to a heat so violent as to dissipate some part of it, without melting what remains. It is often practised on metallic substances, particularly lead, for obtaining the calx of that metal called minium, or red lead.

This operation, as indeed all other chemical ones, is best performed in large quantities, where a particular furnace is constructed for purpose, and a fire kept on day and night without interruption. The flame is made to play over the surface of the metal, and it is continually stirred so as to expose different parcels of it to the action of the heat.

X. Fusion. This is when a solid body is exposed to such a degree of heat as makes it pass from a solid to a fluid state; and as different substances are possessed of very different degrees of fusibility, the degrees of melting heat are very various.

Besides the true fusion, there are some kinds of salts which retain to a large proportion of water in their crystals, as to become entirely fluid upon being exposed to a very small degree of heat. This is commonly called the watery fusion; but is really a solution of the salt in that quantity of water retained by it in its crystalline form; for such salts afterwards become solid by the evaporation of the water they contained; and then require a strong red heat to melt them thoroughly, or perhaps are absolutely infusible.

Of all known substances, unctuous and inflammable ones become fluid with the least heat; then come the more fusible metals, lead, tin, and antimony; then some of the more fusible salts; and then the harder metals, silver, gold, copper, and iron; then the mixtures for making glas; and last of all, the metal called platinum, which has hitherto been incapable of fusion, except by the violent action of the sun-beams in the focus of a large burning glass. This substance seems to be the most refractory of all others, even the hardest flints melting into glass long before it. (See Platina.)

Fusion of small quantities of matter is usually performed in pots called crucibles; which, as they are required to stand a very violent heat, must be made of the most refractory materials possible.

The making of crucibles belongs properly to the potter; but as a chemist ought to be the judge of their proper composition, we shall here give some account of the materials for different attempts to make these vessels of the necessary strength.

All earthen vessels are composed, at least partly, of that kind which is called the argillaceous earth or clay, because these only have the necessary ductility, and can be formed into vessels of the proper form. Pure clay is, by itself, absolutely unfusible; but is exceedingly apt to crack when exposed to sudden changes of heat and cold. It is also very apt to melt when mixed with other substances, such as calcareous earths, &c. When mixed in a certain proportion with other materials, they are changed by violent heat into a kind of half-melted substance, such as our stone-bottles. They cannot be melted completely, however, by almost any fire; they are also very compact, and will contain the most fusible substances, even glas of lead itself; but as they are very apt to crack from sudden changes of heat and cold, they are not so much used; yet, on particular occasions, they are the only ones which can be made use of.

The more dense any kind of vessels are, the more apt they are, in general, to break by a sudden application of heat or cold: hence crucibles are not, in general, made of the greatest density possible; which is not at all times required. Those made at Hesse, in Germany, have had the best reputation for a long time. Mr Pott, member of the Academy of Sciences at Berlin, hath determined the composition of these crucibles to be, one part of good refractory clay, mixed with two parts of sand, of a middling fineness, from which the finest part has been fitted. By fitting the finer particles from the sand, too great compactness is avoided: but at the same time this mixture renders them apt to be corroded by vitrifying matters kept a long time in fusion; for these do not fail to act upon the sand contained in the composition of the crucible, and, forming a vitreous mass, at last run through it.

This inconvenience is prevented, by mixing, instead of sand, a good baked clay in grofs powder. Of a composition of this kind are made the glas-house pots, which sometimes sustain the violent heat employed in making glas for several months. They are, however, gradually consumed by the glass, and become constantly more and more thin.

As the containing vessel, however, must always be exposed to a more violent heat than what is contained in it, crucibles ought to be formed of such materials as are not vitrifiable by the heat of any furnace whatever. But from the attempts made to melt platina, it appears, that of all known substances it would be the most desirable for a melting vessel. Hessian crucibles, glas-house pots, Sturbridge clay, in short every substance which could be thought of to resist the most violent heat, were melted in such a manner as even to stop up the pipes of large bellows, while platina was not altered in the least; and Messrs Macquer and Beaumé have shown, that though platina cannot be melted so as to cast vessels of it, it may nevertheless be cupelled with lead so as to become malleable, and thus vessels might otherwise be made from that substance. The extreme scarcity of this mineral, however, leaves as yet little room to hope for anything from it, though Mr Achard has found a method of forming crucibles from this refractory substance. It consists in moulding the precipitate made with sal ammoniac into the form of a crucible, and then applying a sudden and very violent heat, which fuses this calx.

Mr Pott has made so many experiments upon clays mixed with different substances, that he has in a manner exhausted the subject. The basis of all his compositions was clay. This he mixed in different proportions with metallic calcareous earths, calcareous earths, talc, amiantus, asbestos, pumice-stones, tripoli, and many others; but he did not obtain a perfect composition from any of them. The best crucibles, according to Scheffer, cannot easily contain metals dissolved by sulphur, in the operation of parting by means of sul-

phur. They may be made much more durable and Chemical folid, by steeping them a few days in linseed-oil, and Operations, strewing powdered borax upon them before they are dried.

The result of Mr Pott's experiments are: 1. Crucibles made of fat clays are more apt to crack when exposed to sudden heat, than those which are made of lean or meagre clays. Meagre clays are those which contain a considerable quantity of sand along with the pure argillaceous earth: and fat clays are those which contain but little. 2. Some crucibles become porous by long exposure to the fire, and imbibe part of the contained metals. This may be prevented, by glazing the internal and external surfaces; which is done by moistening these with oil of tartar, or by strewing upon them, when wetted with water, powdered glas of borax. These glazings are not capable of containing glas of lead. 3. Crucibles made of burnt clay grossly powdered, together with unburnt clay, were much less liable to crack by heat than crucibles made of the same materials where the burnt clay was finely powdered, or than crucibles made entirely of unburnt clay. 4. If the quantity of unburnt clay be too great, the crucible will be apt to crack in the fire. Crucibles made of 10 ounces of unburnt clay, 10 ounces of grossly powdered burnt clay, and three drachms of calcined vitriol, are capable of retaining melted metals, but are pervaded by glas of lead. The following composition is better than the preceding: Seven ounces of unburnt clay, 14 ounces of grossly powdered burnt clay, and one drachm of calx of vitriol. These crucibles may be rendered more capable of containing glas of lead, by lining their internal surfaces, before they are baked, with unburnt clay diluted with water. They may be further strengthened by making them thicker than is usually done; or by covering their external surfaces with some unburnt clay, which is called arming them. 5. The composition of crucibles most capable of containing the glas of lead, was 18 parts of grossly powdered burnt clay, as much unburnt clay, and one part of fusible spar. These crucibles must lead, not, however, be exposed too suddenly to a violent heat. 6. Crucibles capable of containing glas of lead very well, were made of 24 parts of unburnt clay, four parts of burnt clay, and one part of chalk. These require to be armed. 7. Plume alum powdered, and mixed with whites of eggs and water, being applied to the internal surface of a Hessian crucible, enabled it to retain for a long time glas of lead in fusion. 8. One part of clay, and two parts of Spanish chalk, made very good crucibles. The substance called Spa-

nish chalk is not a calcareous earth, but appears to be a kind of fleates. 9. Two parts of Spanish chalk, and one part of powdered tobacco-pipes, made good lining for common crucibles. 10. Eight parts of Spanish chalk, as much burnt clay, and one part of litharge, made solid crucibles. 11. Crucibles made of black lead are fitter than Hessian crucibles for melting metals; but they are so porous, that fused salts pass entirely through them. They are more tenacious than Hessian crucibles, are not so apt to burst in pieces, and are more durable. 12. Crucibles placed with their bottoms upwards, are less apt to be cracked during the baking, than when placed differently. 13. The paste of which crucibles are made, ought not to be too moist; Chemical moist; else, when dried and baked, they will not be sufficiently compact: hence they ought not to be so moist as to be capable of being turned on a potter's lathe; but they must be formed in bras or wooden moulds.

On this subject Dr Lewis hath also made several observations; the principal of which are, 1. Pure clay softened to a due consistence for being worked, not only coheres together, but sticks to the hands. In drying, it contracts 1 inch or more in 12; and hence it is very apt to crack, unless it is dried exceeding slowly. In burning, it is subject to the same inconvenience, unless very slowly and gradually heated. When thoroughly burnt, if it has escaped those imperfections, it proves solid and compact; and so hard as to strike fire with steel. Vessels made of it are not penetrated by any kind of liquid; and resists salts and glazes brought into the thinnest fusion, excepting those which by degrees corrode and dissolve the earth itself, as glaze of lead; and even this penetrating glaze is resisted by it better than by almost any other earth; but, in counterbalance to these good qualities, they cannot be heated or cooled, but with such precautions as can rarely be complied with in the way of burnings, without cracking, or flying in pieces.

2. Clay that has been once exposed to any considerable degrees of heat, and then powdered, has no longer any tenacity. Fresh clay, divided by a due proportion of this powder, proves less tenacious than by itself; not sticking to the hands, though cohering sufficiently together. It shrinks less in drying, is less apt to crack, and less susceptible of injury from alterations of heat and cold; but at the same time is less solid and compact. Considerable differences are observed in these respects; not only according to the quantity of dividing matter, but according as it is in finer or coarser powder.

3. Vessels made with a moderate proportion of fine powder, as half the weight of the clay, are compact and solid, but still very apt to crack, from sudden heat or cold; those with a larger proportion, as twice or thrice the quantity of the clay, are free from that imperfection, but so friable as to crumble between the fingers. Nor does there appear to be any medium between a disposition to crack and to crumble; all the compounds made of clay and fine powders having the one or the other, or both imperfections. Coarser powders of the size of middling sand, form, with an equal weight of clay, compounds sufficiently solid, and much less apt to crack than the mixtures with fine powders. Two parts of coarse powder, and one of clay, prove moderately solid, and but little disposed to crack: a mixture of three parts and one, tho' heated and cooled suddenly, does not crack at all, but suffers very fluid substances to transude through it; solidity, and resistance to quick vicissitudes of heat and cold, seeming here also to be incompatible.

4. Pure clay, mixed with pure clay that has been burnt, is no other than one simple earth; and is neither to be melted nor softened, nor made in any degree transparent with the most intense fires.

5. Mixtures of clay with gypseous earths burn whiter than clay alone; in certain proportions, as two parts of clay to three of gypsum, they become, in a moderate fire, semi-transparent, and in a strong one they melt.

6. Calcareous earths in small proportion bake tolerably compact and white; and added to other compositions, seem to improve their compactness. If the quantity of the calcareous earth nearly equals that of the clay, the mixture melts into a yellow glass; if it considerably exceeds, the product acquires the qualities of quicklime.

7. Vessels made from clay and sand, in whatever proportion, do not melt in the strongest fire; but they sometimes bend or soften, so as to yield to the tongs. Glazes in thin fusion penetrate them by dissolving the sand. If gypseous or calcareous earths are urged in such crucibles with a vehement heat, the vessels and their contents run all into one mass. In moderate fires, these vessels prove tolerably compact, and retain most kinds of salts in fusion: but they are liable to crack, especially when large; and do not long sustain melted metals, being burnt by their weight. Such are the Hessian crucibles.

8. Mixtures of clay and black-lead, which seems a species of tale, are not liable to crack from alternations of heat and cold; but are extremely porous. Hence black-lead crucibles answer excellently for the melting of metals, and stand repeated fusions; whilst salts flowing thin, transude through them almost as water through a sieve: sulphureous bodies, as antimony, corrode them.

9. Pure clay, softened with water, and incrusted on earthen vessels, that have been burnt, does not adhere to them, or scales off again upon exposure to the fire; applied to unburnt vessels, it adheres and incorporates. Divided clay unites with them in both states. Vitreous matters, melted in vessels of pure clay, adhere so firmly as not to be separated; from vessels of divided clay they may be knocked off by a hammer.

10. The saline fluxes which promote the fusion of clay, besides the common ones of all earths, alkali and borax, are chiefly arsenic fixed by nitre, and the fusible salt of urine; both which have little effect on the other earths though mixed in a large proportion. Nitre, which readily brings the crystalline earths into fusion, and sal mirabile and sandiver, powerful fluxes for the calcareous earths, do not perfectly vitrify with clay. Burnt clay does not differ in these respects from such as has not been burnt; nor in that singular property of vitrifying with gypseous or calcareous earths, without any saline or metallic addition; the utmost vehemence of fire seeming to destroy only its ductility, or that power by which it coheres when its parts are moistened with water.

But though it seems impossible to make perfect vessels from mixtures of clay in its two different states, of burnt and unburnt, more is to be hoped from the mixtures which are employed in making porcelain. Manufactories of this kind of ware have been attempted in different countries, (see Porcelain); and in some places the qualities requisite for chemical vessels have been given to it in a very surprising degree. The count de Lauraguais, a French nobleman, and member of the academy of sciences, has distinguished himself in a very eminent manner by attempts of this kind. The translator translator of the chemical dictionary affirms us, that he had it from a gentleman of undoubted veracity, that this nobleman having heated a piece of his porcelain red hot, threw it into cold water, without breaking or cracking it.

The most useful attempt, however, for the purposes of chemistry, seems to be the discovery by Mr Reaumur of converting common green glass into porcelain. This was published as long ago as the year 1739; yet we have scarce heard of any chemist, no not Dr Lewis himself, who has made trial of chemical vessels formed of this sort of porcelain, although the very use to which Mr Reaumur thought the preparation could be applicable was that of bringing chemical vessels to a degree of perfection which could not otherwise be done. The following is the result of Mr Reaumur's experiments.

Green glass, surrounded with white earthy matters, as white sand, gypsum, or plaster of Paris, &c. and exposed to a considerable heat not strong enough to alter its figure, as that of a potter's furnace, acquires different shades of blue, and by degrees begins to grow white. On breaking the glass, the white coat appears to be composed of fine, white, glossy, satin-like fibres, running transversely, and parallel to one another; the glass in the middle being scarcely altered. On continuing the cementation, the change proceeds further and further, till at length the white fibrous parts from both sides meet in the middle, and no appearance of glass remains. By this means, entire vessels of glass may be changed into porcelain.

The substance into which glass is thus converted, is opaque, compact, internally of great whiteness, equal to that of the finest china-ware; but, externally, of a much duller hue. It is considerably harder than glass, much less fusible in the fire, and sustains alterations of heat and cold without injury. Vessels of it, cold, bear boiling liquids; and may be placed on the fire at once, without danger of their cracking. "I have put a vessel of this porcelain (says the author) into a forge, surrounded it with coals, and kept vehemently blowing for near a quarter of an hour; I have melted glass in this vessel, without its having suffered any injury in its figure." If means could be found of giving the outside a whiteness equal to the internal part, glass vessels might thus be converted into a valuable kind of porcelain, superior to all that have hitherto been made. Chemistry, says he, may receive from this discovery, in its present state, such vessels as have been long wanted; vessels which, with the compactness and impenetrability of glass, are also free from its inconveniences.

The common green glass bottles yield a porcelain of tolerable beauty; window-glasses, and drinking-glasses, a much inferior one; while the finer kinds of crystalline glasses afforded none at all. With regard to the cementing materials, he found white sand and gypsum, or rather a mixture of both, to answer best. Coloured earths generally make the external surface of a deeper or lighter brown colour; foot and charcoal, of a deep black, the internal part being always white.

The account of this kind of porcelain given by Mr Reaumur, induced Dr Lewis, who had also observed the same changes on the bottom of glass-retorts exposed to violent heat in a sand-bath, to make further experiments on this matter; an account of which he has published in his Philosophical Commerce of Arts. The results of his experiments were, 1. Green glass, cemented with white sand, received no change in a heat below ignition. 2. In a low red heat, the change proceeded exceeding slowly; and in a strong red heat, approaching to white, the thickest pieces of glass bottles were thoroughly converted in the space of three hours. 3. By continued heat, the glass suffered the following progressive changes: first, its surface became blue, its transparency was diminished, and a yellowish hue was observable when it was held between the eye and the light. Afterwards it was changed a little way on both sides into a white substance, externally still bluish; and, as this change advanced still further and further within the glass, the colour of the vitreous part in the middle approached nearer to yellow: the white coat was of a fine fibrous texture, and the fibres were disposed nearly parallel to one another, and transverse to the thickness of the piece: by degrees the glass became white and fibrous throughout, the external bluishness at the same time going off, and being succeeded by a dull whitish or dun colour. By a still longer continuance in the fire, the fibres were changed gradually from the external to the internal part, and converted into grains; and the texture was then not unlike that of common porcelain. The grains, at first fine and somewhat glossy, became by degrees larger and duller; and at last the substance of the glass became porous and friable, like a mass of white sand slightly cohering. 4. Concerning the qualities of this kind of porcelain, Dr Lewis observes, that, while it remained in the fibrous state, it was harder than common glass, and more able to resist the changes of heat and cold than glass, or even porcelain; but, in a moderate white heat, was fusible into a substance not fibrous, but vitreous and smooth, like white enamel: that when its texture had become coarsely granulated, it was now much softer and unfusible; and lastly, that when some coarsely granulated unfusible pieces, which, with the continuance of a moderate heat, would have become porous and friable, were suddenly exposed to an intense fire, they were rendered remarkably more compact than before; the solidity of some of them being superior to that of any other ware.

It seems surprising that this able chemist, who on this other occasions had the improvements of the arts foject still much at heart, did not put some vessels of this kind of porcelain to other severe trials, besides attempting to fuse it by itself with a violent fire: for though pieces of it were absolutely unfusible, we are not sure but they might have been corroded by alkaline salts, acids, calcareous earths, or glass of lead; nay, it should seem very probable that they would have been so: in which case they would not be much superior to the vessels made from earthy materials. When a first-rate chemist publishes anything in an imperfect state, inferior ones are discouraged from attempting to finish what he has begun; and thus, notwithstanding that these experiments have been so long published, nobody has yet attempted to investigate the properties of this kind of porcelain, by getting chemical vessels made of it, and trying how they answer for crucibles, or retorts. All that has been said concerning the proper materials for crucibles, must likewise be applicable to the materials for retorts, which are required to stand a very violent heat. Mr Reaumur's porcelain bids fairest for answering the purpose of retorts, as well as crucibles. The great disadvantage of the common earthen ones, is, that they suffer a quantity of volatile and penetrating vapours to pass through them. This is very observable in the distillation of phosphorus; and though this substance has not hitherto been used for any purpose in medicine, and very little in the arts, its acid only being sometimes used as a flux, if vessels could be made capable of containing all the items, and at the same time bearing the heat necessary for its distillation, phosphorus, perhaps, might be obtained in such quantity, as to show that it is a preparation not altogether useless.

With regard to stone-ware vessels, and all those in which the composition of sand or flint enters, we shall only further observe, that they will be corroded by fixed alkaline salts, especially of the caustic kind, in a very moderate heat. Dr Black, having evaporated some caustic leys in a stone-ware basin, and then melted the dry salt in the same vessel, found it so corroded, as afterwards to be full of small holes; and he found nothing to resist the action of this salt so well as silver. On the subject of chemical vessels, we have now, however, to add the improved earthen ware of Mr Wedgwood; in which the properties of compactness, infusibility, and the power of resisting sudden changes of heat and cold, are said to be united, so that it promises to be a very valuable addition to the chemical apparatus.

11. Maceration, or Digestion. This is the mixing two bodies, generally a solid and a fluid, together, and then exposing them to a moderate degree of heat for a considerable length of time, so that they may have the better opportunity of acting upon one another. Digestion is usually performed in the glases already mentioned, called matrasses or bolt-heads; and is done in a heat. When any of the substances are very volatile, as spirit of wine; or when the matter requires to be heated so considerably that a quantity of vapour will be raised, the necks of the bolt-heads ought to be pretty long; or a tin pipe may be inserted, of sufficient length to prevent the escape of any part of the steam.

12. Levigation. This is the reducing any body to a very fine powder, which shall feel quite soft between the fingers or when put into the mouth. It is performed by grinding the substance upon a flat marble stone, with some water, or by rubbing it in a marble mortar. In the large way, levigation is performed by mills drawn by horses, or driven by water; some of them are so small as to be turned by the hand. They consist of two smooth stones, generally of black marble, or some other stone equally hard, having several grooves in each, but made to run in contrary directions to one another when the mill is set in motion. The matter being mixed with water, is put in by a funnel, which is fixed into a hole in the upper stone, and turns along with it. The under millstone has round it a wooden ledge, whereby the levigating matter is confined for some time, and at length discharged, by an opening made for that purpose, when it has accumulated in a certain quantity.

In this operation, when the matters to be levigated are very hard, they wear off a part of the mortar, or stones on which they are levigated; so that a substance perfectly hard, and which could not be worn by any attrition, is as great a desideratum for the purposes of levigation, as one which could not be melted is for those of fusion. Dr Lewis proposes the porcelain of Mr Reaumur as an improvement for levigating planes, mortars, &c., because, while in its fibrous state, it is considerably harder than glass, and consequently much less liable to abrasion by the harder powders.

In many cases levigation is very much accelerated by what is called elutriation. This is the method by which many of the painters colours are prepared of the requisite fineness; and is performed by mixing any substance, not totally reduced to the necessary degree of fineness, with a sufficient quantity of water, and stirring them well together. The finer parts of the powder remain some time suspended in the water, while the groarser particles fall to the bottom. The separation is then easily made, by pouring off the water impregnated with these fine parts, and committing the rest to the levigating mill, when it may again be washed; and this may be repeated till all the powder is reduced to the utmost fineness. Substances soluble in water cannot be levigated in this manner.

Of Chemical Furnaces.

The two general divisions we have already mentioned of those who practice chemistry, namely, those who have no other view than mere experiment, and those who wish to profit by it, render very different kinds of furnaces necessary. For the first, those furnaces are necessary which are capable of acting upon a small quantity of matter, yet sufficient for all the changes which fire can produce, from simple digestion to the most perfect vitrification. For the others, those are to be chosen which can produce the same changes upon very large quantities of matter, that as much may be done at once as possible.

To avoid the trouble and expense of a number of portable furnaces, a portable one hath long been a desideratum among those chemists who are fond of making experiments. One of the best of those, if not the very best, that hath yet appeared, is that described in Shaw's edition of Boerhaave's chemistry, and represented fig. 1.

This furnace is made of earth; and, as the workmanship of a furnace requires none of the neatness or elegance which is required in making potters vessels, any person may easily make a furnace of this kind for himself, who has time and patience for so doing. With regard to the most proper materials, all that we have said concerning crucibles and retorts must be applicable to the materials for constructing a furnace; only here we need not care so much for the porosity, or disposition to crumble, as when crucibles or other distilling vessels are to be made.

Plate-iron is commonly directed for the outside of portable furnaces; but we cannot help thinking this is a very needless expense, seeing the coating which Chemical it necessarily requires on the inside may be supposed to harden to such a degree as soon to support itself, without any assistance from the plate-iron. This will be the least necessary, if we consider, that, for the thickness of the walls of any furnace where a considerable heat is wanted, two or three inches are by no means sufficient. When the inside of a furnace is heated, the walls, if very thin, are soon penetrated by the heat, and great part of it by this means dissipated in the air. If they are of a sufficient thickness, the heat cannot penetrate so easily; and thus the inner part of the furnace preserves the heat of the fuel, and communicates it to the contained vessel. In the construction of a portable furnace, therefore, it will be convenient to have all parts of it six inches thick at least. This will also give it a sufficient degree of strength; and, as it is formed of several different pieces, no inconvenience can follow from the weight of each of them taken separately.

In Boerhaave's chemistry, this furnace is represented as narrower at the bottom than at the top; but we cannot suppose any good reason for such a form, seeing a cylindrical one must answer every purpose much better, as allowing a larger quantity of air to pass through the fuel, and likewise not being so apt to be overturned as it necessarily must be where the upper part is considerably heavier than the lower. We have, therefore, given a representation of it as of a cylindrical form.

The furnace consists of five or more parts. C represents the dome, or top of the furnace, with a short earthen funnel E for transmitting the smoke. B, B, B, are moveable cylinders of earth, each provided with a door D, D, D. In Boerhaave's chemistry these doors are represented as having iron hinges and latches; but they may be formed to more advantage of square pieces of earth, having two holes in the middle, by which they may be occasionally taken out, by introducing an iron fork. In like manner, the domes and cylinders, in Boerhaave's chemistry, are represented with iron handles; but they may be almost as easily taken off by the cheaper contrivance of having four holes in each, two directly opposite to one another, into which two short forks may be introduced when the parts are to be separated.

In the lowermost cylinder is to be placed an iron grate, a little below the door, for supporting the fire. In the under part is a small hole, big enough for introducing the pipe of a pair of good perpetual bellows, when the fire is to be violently excited. Dr Lewis prefers the organ-bellows to any other kind.

When the bellows is used, the whole must stand upon a close cylinder A, that the air may be confined, and made to pass through the fuel. By having more bellows, the fire may be excited to a most intense degree. In this case, the pipe of every one of them must enter the cylinder B.

Each of the cylinders should have, in its upper part, a round hole, opposite to its door, for carrying off the smoke, by means of a pipe inserted into it, when the furnace is used for distillations by the sand-bath. Each cylinder ought likewise to have a semicircular cut in the opposite sides, both above and below, that when the under cut of the upper cylinder is brought directly above the upper cut of the lower one, a perfect circle may be formed. These are for giving a passage to the necks of retorts, when distillation by the retort is to be performed. The holes may be occasionally filled with stopples made of the same materials with the body of the furnace.

The most convenient situation for a furnace of this kind would be under a chimney; the vent of which might be easily stopped up by a broad plate of iron, in which a hole ought to be cut for the reception of the earthen tube of the dome. By this means the use of a long tube, which at any rate must be very troublesome, might be easily avoided, and a very strong blast of air would pass through the fuel. If it is found convenient to place the furnace at some distance from the chimney, a plate-iron pipe must be procured to fit the earthen pipe of the dome, and carry the smoke into the chimney. This pipe will also be of use, when the furnace is used for distillations by the sand-bath; it must then be inserted into the hole opposite to the door of any of the cylinders, and will convey away the smoke, while the mouth of the cylinder is totally covered with a sand-pot.

For portable furnaces, Dr Lewis greatly recommends the large black crucibles, marked No 60, on account of their resisting a violent heat, and being very easily cut by a knife or saw, so that doors, &c., may be formed in them at pleasure. The bottom of one of these large ones being cut out, a grate is to be put into the narrow part of it. For grates, the doctor recommends cast-iron rings, having each three knobs around them. These knobs go into corresponding cavities of the outer rings, and the knobs of the outermost rest on the crucible, which is to be indented a little to receive them, that so the grate may rest the more firmly, and the furnace not be endangered from the swelling of the iron by heat. When this is to be made use of as a melting-furnace, and a violent heat to be excited, another crucible must be inverted on that which contains the fuel, which serves instead of the dome of the last mentioned furnace; and as whatever is said of it must likewise be applicable to the two crucibles when placed above one another, we need give no farther description of the doctor's portable furnace.

No doubt, the great experience of Dr Lewis in chemical matters must give very considerable weight to their use to anything he advances; and the warmth with which he recommends these furnaces must convince us, that he has found them abundantly answer the purposes of experiments. We cannot help thinking, however, that where a very great and lasting heat is to be given, the thinness, and even the form, of these crucibles, is some objection to their use. It is certain that such a permanent, or, as the workmen call it, a solid heat, can never be given where the walls of a furnace are thin, as when they are of sufficient thickness. They are also very apt to burst with great heat; and, for this reason, Dr Lewis desires his furnace to be strengthened with copper hoops. This disposition to burst proceeds from the inner parts, which are more intensely heated than the outer, expanding more than these do, and consequently bursting them. Hence the doctor desires his furnace to be strengthened also by putting it within another crucible of a larger size, and the intermediate space to be filled up with a mix- Chemical ture of sifted ashes and water. For most chemical processes, where only a small degree of heat is requisite, these furnaces answer beyond anything that has hitherto been attempted. The whole is to be supported by an iron ring with three feet.

Dr Black's Dr Black has contrived a furnace in which all these inconveniences are avoided. Two thick iron plates, above and below, are joined by a thinner plate, forming the body of the furnace, which is of an oval form. The upper part is perforated with two holes; the one, A, pretty large, which is the mouth of the furnace, and which is of a circular form; the other behind it, B, of an oval form, and designed for fastening the end of the vent which is screwed down upon it. The undermost thick plate has only one large circular opening G near to the middle, but not altogether so, being nearer to one side of the ellipse than the other, where the round hole in the top is placed; so that a line passing this circular hole has a little obliquity forwards. The ash-pit H is likewise made of an elliptical form, and a very small matter widened; so that the bottom of the furnace is received within the ellipse. A little below, there is a border E that receives the bottom of the furnace; and except the holes of the damping-plate DD, the parts are all closed by means of soft lute, upon which the body of the furnace is pressed down; by which means the joining of the two parts, and of all the different pieces, are made quite tight; for the body, fire-place, ash-pit, vent, and grate, are all separable from one another. As the furnace comes from the workman, the grate is made to apply to the outside of the lower part. It consists of a ring laid on its edge, and then bars likewise laid on their edges; and from the outer ring proceed four pieces of iron, by means of which it may be screwed down; so it is kept out of the cavity of the furnace, and preserved from the extremity of the heat. Thus it lasts much longer, and is indeed hardly liable to any decay; for by being exposed to the cool air, it is kept cool, that it is never hurt by the heat of the fuel. The sides, which are made of plate iron, must be fitted within, to confine the heat, and preserve them from its action.

To adapt this to the various operations of chemistry, we may observe, that for a melting furnace it is very convenient; we need only provide a cover for the opening above, which is made the door; and which, being immediately over the grate, is convenient for introducing the substances to be acted upon, and for allowing us to look into the vessel and take it out. This cover may be a piece of tile, or two bricks rendered flat and square. Dr Black commonly uses a kind of lid with a rim containing a quantity of lute; and to augment the heat, we may increase the height of the vent. It can be employed in most operations in the way of effaying; and the situation of the door allows us to see the substances very readily. It does not admit the introduction of the muffle; but can be employed in all those operations where the muffle is made use of; and in Cornwall in England such a furnace is made use of for effaying of metals. To preserve the substance from the contact of the fuel, they cut off about a third part of the length of a brick, and then put it on one end on the middle of the grate. They choose their fuel of large pieces, that the air may have free passage through it, and open a little of the door, which occasions a stream of air to flow in; and this strikes upon the substance and produces the effect desired; so that it may be used in the calcination of lead to convert it into litharge. It also answers very well in operations for producing vapour. If we desire to employ it in distillations which require an intense heat, the earthen retort is to be suspended by means of an iron ring having three branches standing up from it, and which hangs down about half a foot from the hole; so that the bottom of the retort rests upon the ring, and is immediately hung over the fuel; and the opening between the mouth of the furnace and retort is filled up with broken crucibles and potholders, which are covered over with ashes that transmit the heat very slowly; so it answers for distillations performed with the naked fire. Dr Black has sometimes caused them be provided with a hole in the side, from which the neck of the retort may be made to come out; and in this way has distilled the phosphorus of urine, which requires a very strong heat. For distillations with retorts performed with the sand-bath, there is an iron pot fitted for the opening of the furnace, which is set on and employed as a sand-pot. The vent of the furnace then becomes the door; and it answers very well for that purpose; and is more easily kept tight than if it were in the side, and may be kept close with a lid of charcoal and clay. In like manner it answers well for the common still, which may be adapted to it; part of it being made to enter the open part of the furnace, and hang over the fire, as in Plate CXXXIII. fig. 7. and 8. that the bottom part of that still may be made to enter; and the vent becomes the door, by which fresh fuel may be added. Indeed it is seldom necessary to add fresh fuel during any operation. In the ordinary distillations it is never necessary; and even in distilling mercury, phosphorus, &c., it generally contains enough to finish the operation; so effectually is the heat preserved from loss or dilution, and so very slow is the consumption of the fuel.

For luting this and other furnaces, the doctor finds nothing preferable to a simple mixture of sand and clay. The proportions for standing the violence of fire are four parts of sand to one of clay; but when designed for the lining of furnaces, he uses six or seven of sand to one of clay, the more effectually to prevent the contraction of the latter; for it is known from experiments, that clay, when exposed to a strong heat, contracts the more in proportion to its purity. The sand settles into less bulk when wet, and does not contract by heat, which it also resists as well as the clay itself.

Besides this outside lining next the fire, Dr Black uses another to be laid on next the iron of the furnace; and this consists of clay mixed with a large proportion of charcoal dust. It is more fit for containing the heat, and is put next to the iron, to the thickness of an inch and a half. That it may be pretty dry when first put in, he takes three parts by weight of the applying charcoal dust, and one of the common clay, which must be mixed together when in dry powder, otherwise it is very difficult to mix them perfectly. As much water is added as will form the matter into balls; and these are beat very firm and compact by means of a hammer upon the inside of the furnace. The other lute is then spread over it to the thickness of about half an... Theory.

Chemical Furnaces.

an inch, and this is also beat solid by hammering; after which it is allowed to dry slowly, that all cracks and fissures may be avoided; and after the body of the furnace is thus lined, the vent is screwed on and lined in the same manner. It must then be allowed to dry for a long time; after which a fire may be kindled, and the furnace gradually heated for a day or two. The fire is then to be raised to the greatest intensity; and thus the luting acquires a hardness equal to that of free-stone, and is afterwards as lasting as any part of the furnace (A).

When furnaces are used in the large way, they are always built of brick, and each particular operation has a furnace allotted for itself. The melting-furnace, where very large quantities of matter are not to be melted at once, requires only to be built of brick in such a form as we have already described; only, as it would perhaps be troublesome to procure a dome of the proper figure, the forefront of it may be left entirely open for the admission of melting vessels. The opening may be closed up with bricks and earth during the operation. There is no necessity for having the inside of a circular form; a square one will answer the purpose equally well. According to the author of the Chemical Dictionary, when the internal diameter D C of such a furnace is 12 or 15 inches, the diameter of the tube G I 8 or 9 inches, and its height 18 or 20 feet, and when the furnace is well supplied with fuel, an extreme heat is produced; in less than an hour the furnace will be white and dazzling like the sun; its heat will be equal to the strongest glass-house furnace; and in less than two hours will be melted whatever is fusible in furnaces. The hottest part is at H F, 4 or 6 inches above the grate. A plate-iron tube may be advantageously supplied by a short chimney of bricks, built under a pretty high vent, so as the whole may easily be stopped, except that passage which transmits the smoke of the furnace. By this means a very strong current of air will be made to pass through the fuel.

On this subject Dr Black informs us, that Mr Pott of Berlin employs one almost similar to the above, for making experiments on earthen ware; by which he showed that many substances formerly reckoned infusible, might nevertheless be melted by fire raised to a very intense degree; and that several of these bodies, when mixed together, form compounds which may be melted without any difficulty. From this a tube arises to some height, and there is an additional tube which may be put on to the height of above 10 feet. The making the fire-place is narrow below, but widens towards the middle, and contracts again at top, for the sake of the vessels which are put into it, and which are wider at top than at bottom. Thus the vessel is equally heated, and there is room above for containing a quantity of fuel, which defends as fast as it is consumed. Different reasons have been assigned for this form: thus Dr Boerhaave imagines that the melting furnace should be made of a parabolic form, and Macquer that it should be in the form of an ellipse; and that the crucible should be placed in one of the foci, where they imagined the heat would be concentrated; but it is very plain, that the materials are such as are not capable of reflecting the rays of heat in a regular manner; and even though they could do so, it would be to no purpose, because the heat and light do not come from any single point, but from a great number, striking the furnace in all possible directions, and which must consequently be reflected in directions as numerous. The furnace is made of iron lined with clay; and as it is difficult to beat out the iron into this roundish form, it may as well be made cylindrical; and it is easy to give the inside what form we please by means of a luting of clay; neither need the dome have the roundish form, but may be simply made conical. The vent should be made about two-thirds of the diameter of the furnace, or such as will give an area of about one-half the grate. A small portable furnace of this kind is very convenient for ordinary crucibles; the largest of which are only about four or five inches high; the widest part of the furnace may be beat out about 10 inches diameter; and when made of thin plate iron, and lined within, are very convenient, and may be heated at very little expense of fuel. But for heating much larger vessels, it is proper to construct them of brick, when they have pretty much the same form; only it is necessary to make them square, and round on the inside with a luting of sand and clay. The top is generally made flat, and covered over with two or three bricks; the vent goes a little backwards, and then is raised to a proper height. Where the vessel to be heated is very large, it is common to leave the front open for putting in the vessel; and then to build it up with bricks, clay, and sand; which can be easily pulled down again when the operation is over.

There are some cases in which it is necessary to have a rapidity of inflammation even beyond what this furnace can give; and in these we have recourse to bellows of various constructions, by which the air can be compressed, and made to enter the fuel with great velocity. These again are sometimes wrought by water; but there is another machine which produces a greater effect, viz. the water-blast, described by Lewis in his Commercium Philosoph. Technicum.

The colipile too may be employed for driving air instead of air, the same effect is not produced; and the true manner in which this instrument increases the inflammation is by driving air through the fuel; the steam from the vessel spreading and mixing with the air, and driving it before it, makes it strike upon the fuel.

Chemists have generally believed that a wide and high ash-hole greatly increases the power of a melting furnace; but this advantage is found to be merely imaginary, as well as that of introducing the air through a long tube to the ash-hole; unless where the furnace is placed in a close room, so that it is necessary to furnish a greater blast of air than can otherwise have access.

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(A) These furnaces, of different sizes, from 30s. to 50s. price, may be purchased from John Sibbald Smith in Edinburgh; who has had the advantage of making them under the immediate inspection of Dr Black. For the form of the furnaces necessary in essaying and smelting of ores or making glass, see Essaying, Glass, and Smelting.

When large stills, sand-pots, &c. are to be fixed with a view to daily use, it is a matter of no small consequence to have them put up in a proper manner. The requisites here are, 1. That the whole force of the fire should be spent on the distilling vessel or sand pot, except what is necessarily imbibed by the walls of the furnace. 2. That the vessel should be set in such a manner as that they may receive heat even from the furnace walls; for a still which contains any liquid can never be made so hot as a piece of dry brick. 3. It is absolutely necessary that the force of the fire be not allowed to collect itself upon one particular part of the vessel; otherwise that part will soon be destroyed. 4. The draught of air into furnaces of this kind ought to be moderate; only so much as will prevent smoke. If a strong blast of air enters, not only a great part of the heat will be wasted by going up the chimney, but the outside of the vessel will be calcined every time the fire is kindled, and thus must be soon rendered unfit for use.

There are few of the common workmen that are capable of building furnaces properly; and it is very necessary for a chemist to know when they are properly done, and to make the workmen act according to his directions. As the still, or whatever vessel is to be fixed, must have a support from the furnace on which it is built, it is evident the whole of its surface cannot be exposed to the fire. For this reason many of these vessels have had only their bottom exposed to the fire, no more space being left for the action of the heat, than the mere circular area of the still bottom; and the fire, passing directly through a hole in the back part of the building, which communicated with a chimney, and consequently had a strong draught, scarce spent any of its force on the still, but went furiously up the chimney. By this means an extraordinary waste of fuel was occasioned; and that part of the still-bottom which was next the chimney receiving the whole force of the flame, was soon destroyed. Attempts were made to remedy this inconvenience, by putting the fire something forward, that it might be at a greater distance from the chimney, and consequently might not spend its force in the air. This too was found to avail very little. A contrivance was then fallen upon to make the vent pass round the body of the still in a spiral form. This was a considerable improvement; but had the inconvenience of making the fire spend itself uselessly on the walls of the furnace, and besides wasted that part of the still which touched the under part of the vent. A much better method is to build the back part of the furnace entirely close, and make the fire come out through a long narrow opening before; after which it passes out through a flue in the back and upper part of the furnace into the chimney.

The only inconvenience of this form is, that the vent must either be very wide, or it is apt to choke up with foot, which last is a very troublesome circumstance. If the vent is made very wide, a prodigious draught of air rushes through the fuel, and increases the heat to such a degree as to calcine the metal of which the still is made; and, on the other hand, nothing can be more disagreeable than to have the vent of a furnace stopped up with foot. These inconveniences, however, are totally avoided by making two small vents, one on each side of the distilling vessel, which may communicate with a chimney by means of two tubes either of plate-iron or formed with clay or bricks, which may be occasionally taken off if they happen to be choked up. The vessel is to be suspended by three trunnions, so that the whole surface may be exposed to the fire, excepting a ring the thickness of a brick all round; so that a very strong heat will be communicated although the furnace draws but little. The two small vents on each side will draw the flame equally; and by this means the most equable heat can be preserved, and may be pushed so far as to make the whole bottom and sides of the vessel intensely red. Such a construction as this is more especially useful for sand-pots, and those which are used for distilling alkaline spirits from bones.

In the use of the furnaces hitherto described, the attendance of the operator is necessary, both for inspecting the processes, and for supplying and animating the fuel. There are some operations, of a slower kind, that require a gentle heat to be continued for a length of time; which demand little attendance in regard to the operations themselves, and in which, of consequence, it is extremely convenient to have the attendance in regard to the fire as much as possible dispensed with. This end has been answered by the furnace called athanor; but the use of it has been found attended with some inconveniences, and it is now generally laid aside.

Sundry attempts have been made for keeping up a lamp for continued heat, with as little trouble as in the athanor, nace. by the flame of a lamp; but the common lamp-furnaces have not answered so well as could be wished. The lamps require frequent snuffing, and smoke much; and the foot accumulated on the bottom of the vessel placed over them, is apt, at times, to fall down and put out the flame. The largeness of the wick, the irregular supply of oil from the reservoir by jets, and the oil being suffered to sink considerably in the lamp, so that the upper part of the wick burns to a coal, appeared to be the principal causes of these inconveniences; which accordingly were found to be in great measure remedied by the following construction.

The lamp consists of a brass pipe 10 or 12 inches Fig. 8, long, and about a quarter of an inch wide, inserted at one end into the reservoir of the oil, and turned up at the other to an elbow, like the bole of a tobacco-pipe, the aperture of which is extended to the width of near two inches. On this aperture is fitted a round plate, having 5, 6, or 7 small holes, at equal distances, round its outer part, into which are inserted as many pipes about an inch long; into these pipes are drawn threads of cotton, all together not exceeding what in the common lamps form one wick: by this division of the wick, the flame exposes a larger surface to the action of the air, the fuliginous matter is consumed and carried off, and the lamp burns clear and vivid.

The reservoir is a cylindric vessel, eight or ten inches wide, composed of three parts, with a cover on the top. The middle partition communicates, by the lateral pipe, with the wicks; and has an upright Chemical right open pipe soldered into its bottom, whose top reaches as high as the level of the wick; so that, when this part is charged with oil, till the oil rises up to the wicks in the other end of the lamp, any further addition of oil will run down through the upright pipe into the lower division of the reservoir. The upper division is designed for supplying oil to the middle one; and, for that purpose, is furnished with a cock in the bottom; which is turned more or less, by a key on the outside, that the oil may drop fast enough to supply the consumption, or rather faster, for the overplus is of no inconvenience, being carried off by the upright pipe; so that the oil is always, by this means, kept exactly at the same height in the lamp.

For common uses, the middle division alone may be made to suffice; for, on account of its width, the sinking of the oil will not be considerable in several hours burning. In either case, however, it is expedient to renew the wicks every two or three days; oftener or seldom according as the oil is more or less foul; for its impure matter, gradually left in the wicks, occasions the flame to become more and more dull. For the more convenient renewing of them, there should be two of the perforated plates; that when one is removed, another, with wicks fitted to it, may be ready to supply its place.

One of the black-lead pots, recommended by Dr Lewis for his portable furnace, makes a proper furnace for the lamp. If one is to be fitted up on purpose for this use, it requires no other aperture than one in the bottom for admitting air, and one in the side for the introduction of the elbow of the lamp. The reservoir stands on any convenient support without the furnace. The stopper of the side aperture consists of two pieces, that it may be conveniently put in after the lamp is introduced; and has a round hole at its bottom fitting the pipe of the lamp. By these means, the furnace being let upon a trevett or open foot, the air enters only underneath, and spreads equally all round, without coming in streams, whence the flame burns steady. It is not advisable to attempt raising the heat higher than about the 450th degree of Fahrenheit's thermometer; a heat somewhat more than sufficient for keeping tin in perfect fusion. Some have proposed giving a much greater degree of heat in lamp-furnaces, by using a number of large wicks; but when the furnace is so heated, the oil emits copious fumes, and its whole quantity takes fire. The balsam, or other vessel including the subject-matters, is supported over the flame by an iron ring, as already described in the sand-bath and still; a bath is here particularly necessary, as the subject would otherwise be very unequally heated, only a small part of the vessel being exposed to the flame. Since the new invention of Argand's lamps, which perfectly consume the oil, attempts have been made to construct lamp-furnaces on their principles; though, on the whole, it is to be doubted whether they are preferable to the above construction or not.

**Part II. Practice.**

**Sect. I. Salts.**

§ 1. Of the Vitriolic Acid, and its Combinations.

The vitriolic acid is never found pure, but always united with some proportion, either of phlogiston or metallic and earthy substances. Indeed there is scarce any kind of earth which does not contain some portion of this acid, and from which it may always some way or other be separable. When pure, the vitriolic acid appears in the form of a transparent colourless liquor. By distilling in a glass retort, the aqueous part arises, and the liquor which is left becomes gradually more and more acid. This operation is generally called the rectification, or dephlegmation, of the acid. After the distillation has gone on for some time, the water adheres more strongly to what remains in the retort, and cannot be forced over without elevating part of the acid along with it. The remaining acid, being also exceedingly concentrated, begins to lose its fluidity, and puts on the appearance of a clear oil. This is the state in which it is usually sold, and then goes by the name of oil of vitriol. If the distillation is still farther continued, with a heat below 60° of Fahrenheit's thermometer, the acid gradually loses more and more of its fluidity, till at last it congeals in the cold, and becomes like ice. In this state it is called the icy oil of vitriol. Such exceedingly great concentration, however, is only practised on this acid for curiosity. If the heat be suddenly raised to 620°, the whole of the acid rises, and generally cracks the receiver. Clear oil of vitriol is immediately turned black by an admixture of the smallest portion of inflammable matter.

The icy oil of vitriol, and even that commonly sold, attracts the moisture of the air with very great force. Mr Newmann relates, that having exposed an ounce of this acid to the air, from September 1736 to September 1737, at the end of the twelvemonth it weighed seven ounces and two drachms; and thus had attracted from the air above five times its own weight of moisture. This quantity, however, seems extraordinary; and it is probable, that in so long a time some water had been accidentally mixed with it; for Dr Gould, professor at Oxford, who seems to have tried this matter fully, relates, that three drachms of oil of vitriol acquired, in 57 days, an increase only of six drachms and an half. The acid was exposed in a glass of three inches diameter; the increase of weight the first day was upwards of one drachm; in the following days less and less, till, on the fifty-sixth, it scarce amounted to half a grain. The liquor, when saturated with humidity, retained or lost part of its acquired weight according as the atmosphere was in a moist or dry state; and this difference was so sensible as to afford an accurate hygrometer. Hoffman having exposed an ounce and two scruples in an open glass-dish, it gained seven drachms and a scruple in 14 days.

This acid, when mixed with a large quantity of productive water, makes the temperature something colder than before; but if the acid bears any considerable proportion. Vitriolic Acid and its Combinations.

Quantity of alkali saturated by it.

Effects on the human body.

Difficulty of procuring it by itself.

Pyrites, where found.

I. From Pyrites, with the making of Copperas, and obtaining the pure Oil of Vitriol from it.

Pyrites are found in large quantity in the coal-mines of England, where most of the copperas is made. They are very hard and heavy substances, having a kind of brass appearance, as if they contained that metal; and hence they are called brasses by the workmen. A very large quantity of these is collected, and spread out upon a bed of stiff clay to the depth of three feet. After being some time exposed to the air, the uppermost ones lose their metallic appearance, split, and fall to powder. The heaps are then turned, the under part uppermost, so as to expose fresh pyrites to the air. When they are all reduced to powder, which generally requires three years, the liquor, which is formed by the rain-water running from such a large mass, becomes very acid, and has likewise a flaky vitriolic taste. It is now conveyed into large cisterns lined with clay, whence it is pumped into a very large flat vessel made of lead. This vessel, which contains about 15 or 20 tons of liquor, is supported by cast-iron plates about an inch thick, between which and the lead a bed of clay is interposed. The whole rests upon narrow arches of brick, under which the fire is placed. Alongside the liquor, about half a ton or more of old iron is put into the evaporating vessel. The liquor, which is very far from being saturated with acid, acts upon the iron, and, by repeated filling up as it evaporates, dissolves the whole quantity. By the time this quantity is dissolved, a pellicle is formed on the surface. The fire is then put out; and as such a prodigious quantity of liquor does not admit of filtration, it is left to settle for a whole day, and then is let off by a cock placed a little above the bottom of the evaporating vessel, so as to allow the impurities to remain behind. It is conveyed by wooden spouts to a large leaden cistern, five or six feet deep, sunk in the ground, and which is capable of containing the whole quantity of liquor. Here the copperas crystallizes on the sides, and on sticks put into the liquor. The crystallization usually takes up three weeks. The liquor is then pumped back into the evaporating vessel; more iron, and fresh liquor from the pyrites, are added; and a new solution takes place.

Copperas is used, in dyeing, for procuring a black colour; and is an ingredient in making common ink. It is also used in medicine as a corrosive, under the name of salt of lead; but before it is used with this intention, it is redissolved in water, and crystallized, with the addition of a little pure oil of vitriol. Whether it is at all mended by this supposed purification, either in appearance or quality, is very doubtful.

This proceeds furnishes us first with a very impure vitriolic acid, which could not be applied to any useful purpose; afterwards with an imperfect neutral salt, called green vitriol, which is applicable to several purposes where the pure acid itself could not be used; but still the acid by itself is not to be had without a very troublesome operation.

Though this acid adheres very strongly to iron, it is capable of being expelled from it by fire; yet not without a very violent and long-continued one. If we attempt to distil green vitriol in a retort, it swells and boils in such a manner by the great quantity of water contained in its crystals, that the retort will almost certainly crack; and though it should not, the salt would be changed into an hard flaky mass, which the fire could never sufficiently penetrate so as to extract the acid. It must therefore be calcined previous to the distillation. This is best done in flat iron-pans, set over a moderate fire. The salt undergoes the wa- Vitriolic Acid by fusion; (See Fusion); after which it becomes opaque and white. By a continuance of the fire, it becomes brown, yellow, and at last red. For the purpose of distillation, it may be taken out as soon as it has recovered its solidity.

The dry vitriol, being now reduced to powder, is to be put into an earthen retort, or rather long neck (a kind of retort where the neck issues laterally, that the vapours may have little way to ascend), which it may nearly fill. This retort must be placed in a furnace capable of giving a very strong heat, such as the melting furnace we have already described. A large receiver is to be fitted on; and a small fire made in the furnace, to heat the vessels gradually. White fumes will soon come over into the receiver, which will make the upper part warm. The fire is to be kept of an equal degree of strength, till the fumes begin to disappear, and the receiver grows cool. It is then to be increased by degrees; and the acid will become gradually more and more difficult to be raised, till at last it requires an extreme red, or even white, heat. When nothing more will come over, the fire must be suffered to go out, the receiver be unluted, and its contents poured into a bottle fixed with a glass stopper. A sulphurous and suffocating fume will come from the liquor, which must be carefully avoided. In the retort, a fine red powder will remain, which is used in painting, and is called calcotar of vitriol. It is useful on account of its durability; and, when mixed with tar, has been employed as a preservative of wood from rotting; but Dr Lewis prefers finely powdered pit-coal. As a preservative for masts of ships, he recommends a mixture of tar and lamp-black; concerning which he relates the following anecdote:

"I have been favoured by a gentleman on board of a vessel in the East Indies, with an account of a violent thunder-storm, by which the main-mast was greatly damaged, and whose effects on the different parts of the mast were pretty remarkable. All the parts which were greased or covered with turpentine were burnt in pieces: those above, between, and below the greased parts, as also the yard-arms, the round-top or scaffoldings, coated with tar and lamp-black, remained unhurt."

Oil of vitriol, when distilled in this manner, is always of a black colour, and must therefore be rectified by distillation in a glass retort. When the acid has attained a proper degree of strength, the blackness either flies off, or separates and falls to the bottom, and the liquor becomes clear. The distillation is then to be discontinued, and the clear acid which is left in the retort kept for use.

This was the first method by which the vitriolic acid was obtained; and from its being distilled from vitriol has ever since retained the name of oil of vitriol. Green vitriol is the only substance from which it is practicable to draw this acid by distillation; when combined with calcareous earths, or even copper (though to this last it has a weaker attraction than to iron), it relieves the fire most obliquely. When distillation from vitriol was practised, large furnaces were erected for that purpose, capable of containing an hundred long necks at once; but as it has been discovered to be more easily procurable from sulphur, this method has been laid aside, and it is now needless to describe these furnaces.

II. To procure the Vitriolic Acid from Sulphur.

This substance contains the vitriolic acid in such plenty, that every pound of sulphur, according to Mr Kirwan's calculation, contains more than one-half of acid in pure acid; which being in a state perfectly dry, is consequently of a strength far beyond that of the most highly rectified oil of vitriol. Common oil of vitriol requires to be distilled to one-fourth of its quantity before it will coagulate when cold; and even in this state it undoubtedly contains some water. No method, however, has as yet been fallen upon to condense all the steams of burning sulphur, at least in the large way, nor is any other profitable way of decomposing sulphur known than that by burning; and in this way produced the most successful operators have never obtained more than 14 ounces of oil from a pound of sulphur.

The difficulties here are, that sulphur cannot be burnt but in an open vessel; and the stream of air, obviating which is admitted to make it burn, also carries off the acid which is emitted in the form of smoke. To avoid this, a method was contrived of burning sulphur in large glass globes, capable of containing an hoghead or more. The fume of the burning sulphur was then allowed to circulate till it condensed into an acid liquor. A greater difficulty, however, occurs here; for though the sulphur burns very well, its steams will never condense. It has been said, that the condensation is promoted by keeping some warm water continually smoking in the bottom of the globe; and even Dr Lewis has asserted this: but the steam of warm water immediately extinguishes sulphur, as we have often experienced; neither does the fume of burning sulphur seem at all inclined to join with water, even when forced into contact with it. As it arises from the sulphur, it contains a quantity of phlogiston, which in a great measure keeps it from uniting with water; and the defloration is not something to make the sulphur burn freely, but to deprive the fumes of the phlogiston they contain, and render them miscible with water. For this purpose nitre has been advantageously used. This consumes a very large quantity of the phlogiston contained in sulphur, and renders the acid easily combustible: but it is plain that few of the fumes, comparatively speaking, are thus deprived of the inflammable principle; for the vessel in which the sulphur and nitre are burnt, remains filled with a volatile and most suffocating fume, which extinguishes flame, and issues in such quantity as to render it highly dangerous to stay near the place. It has been thought that nitre contributes to the burning of the sulphur in close vessels; but this too is a mistake. More sulphur may be burnt in an oil of vitriol globe without nitre than with it, as we have often experienced; for the acid of the sulphur unites with the alkaline basis of the nitre, and forms therewith an uninflammable compound, which soon extinguishes the flame, and even prevents a part of the sulphur from being burnt either at that time or any other.

In the condensation of the fumes of sulphur by means of nitre, a remarkable effervescence happens, which naturally leads us to think that the condensation is between the nitrous and nitrous fumes. Vitriolic Acid and its Combinations.

Dr Lewis is of opinion, that the acid thus obtained is perfectly free from an admixture of the nitrous acid; but in this he is certainly mistaken; for, on rectifying the acid produced by sulphur and nitre, the first fumes that come over are red, after which they change their colour to white. How the nitrous acid should exist in the liquor, indeed, does not appear; for this acid is totally destructible by deflagration with charcoal; but it does not follow, that because the nitrous acid is destroyed when deflagrated with charcoal, it must likewise be so if deflagrated with sulphur. Indeed it certainly is not; for the clystus of nitre made with sulphur is very different from that made with charcoal.

The proportions of nitre to the sulphur, used in the large oil of vitriol works, are not known, every thing being kept as secret as possible by the proprietors. Dr Lewis reckons about five pounds of nitre to an hundred weight of sulphur; but from such experiments as we have made, this appears by far too little. An ounce and an half, or two ounces, may be advantageously used to a pound of sulphur. In greater proportions, nitre seems prejudicial.

A very great improvement in the apparatus for making oil of vitriol, lies in the using lead vessels instead of glass globes. The globes are so apt to be broken by accident, or by the action of the acid upon them, that common prudence would suggest the use of lead to those who intend to prepare any quantity of vitriolic acid, as it is known to have no little effect upon the metal. The leaden vessels, according to the best accounts we have been able to procure, are cubes of about three feet, having on one side a door about six inches wide. The mixture of sulphur and nitre is placed in the hollow of the cube, in an earthen faucer, set on a stand made of the same materials. The quantity which can be consumed at once in such a vessel is about two ounces. To prevent the remains from sticking to the faucer, it is laid on a square bit of brown paper. The sulphur being kindled, the door is to be close shut, and the whole let alone for two hours. In that time the fumes will be condensed. The door is then to be opened; and the operator must immediately retire, to escape the suffocating fumes which issue from the vessel. It will be an hour before he can safely return, and introduce another quantity of materials, which are to be treated precisely in the same manner.

Where oil of vitriol is made in large quantities, the slowness of the operation requires a great number of globes, and constant attendance day and night. Hence the making of this acid is very expensive: The apparatus for a large work usually costs L1500.

Vitriolic Acid Combined,

I. With Fixed Alkali. Dilute a pound of oil of vitriol with ten times its quantity of water; dissolve also two pounds of fixed alkaline salt in ten pounds of water, and filter the solution. Drop the alkali into the acid as long as any effervescence arises; managing matters so that the acid may prevail. The liquor will now be a solution of the neutral salt called vitriolated tartar, which may be procured in a dry form, either by evaporation or crystallization. In case the latter method is made use of, some more alkali must be added when it is set to evaporate, for this salt crystallizes best in an alkaline liquor.

Other methods, besides that above described, have been recommended for preparing vitriolated tartar; particularly that of using green vitriol instead of pure vitriolic acid. In this case the vitriol is decomposed by the fixed alkali: but as the alkali itself dissolves the calx of iron after it is precipitated, it is next impossible to procure a pure salt by such a process; tartar, neither is there occasion to be solicitous about the preparation of this salt by itself, as the materials for it are left in greater quantity than will ever be demanded, after the distillation of spirit of nitre.

Vitriolated tartar is employed in medicine as a purgative; but is not at all superior to other salts which are more easily prepared in a crystalline form. It is very difficultly soluble in water, from which proceeds the difficulty of crystallizing it: for if the acid and alkali are not very much diluted, the salt will be precipitated in powder, during the time of saturation.—It is very difficult of fusion, requiring a strong red heat; but, notwithstanding its fixedness in a violent fire, it mixes with the steam of boiling water in such a manner as to be almost totally dilutated along with it by strong boiling.—This salt has been used in making glass; but with little success, as the glass wherein it is an ingredient always proves very brittle and apt to crack of itself.

II. With volatile alkali. Take any quantity of volatile alkaline spirit; that prepared with quicklime is preferable to the other, on account of its raising no effervescence. Drop into this liquor, contained in a bottle, diluted oil of vitriol, shaking the bottle after every addition. The saturation is known to be complete by the volatile smell of the alkali being entirely destroyed. When this happens, some more of the spirit must be added, that the alkali may predominate a little, because the excess will fly off during the evaporation. The liquor, on being filtered and evaporated, will shoot into fine fibrous plates like feathers. This salt, when newly prepared, has a fulphurous smell, and a penetrating pungent taste. It readily dissolves in water, and increases the coldness of the liquor; on standing for a little time, it begins to separate from the water, and... Vitriolic acid vegetate, or arise in efflorescences up the sides of the glaas. It easily melts in the fire; penetrates the common crucibles; and if sublimed in glaas vessels, which requires a very considerable heat, it always becomes acid, however exactly the saturation was performed.

This salt has been dignified with the names of Glau-ber's secret sal ammoniac, or philosophaic sal ammoniac, from the high opinion which some chemists have entertained of its activity upon metals; but from Mr Pott's experiments, it appears, that its effects have been greatly exaggerated. It dissolves or corrodes in some degree all those metals which oil of vitriol dissolves, but has no effect upon those on which that acid does not act by itself:

Gold is not touched in the least, either by the salt in fusion, or by a solution of it: the salt added to a solution of gold in aqua-regia occasions no precipitation or change of colour. On melting the salts with inflammable matters, it forms a sulphurous compound, which dissolves gold in fusion, in the same manner as compositions of sulphur and fixed alkaline salt. Melted with silver, it corrodes it into a white calx, which partially dissolves in water: it likewise precipitates silver from its solution in aquafortis. It acts more powerfully on copper; elevates a part of the metal in sublimation, so as to acquire a bluish colour on the surface; and renders the greatest part of the residuum soluble in water. This solution appears colourless, so that it could not be supposed to hold any copper; but readily discovers that it abounds with that metal, by the blue colour it acquires on an addition of volatile alkali, and the green calx which fixed alkalies precipitate. In evaporation it becomes green without addition. Iron is corroded by this salt in fusion, and dissolved by boiling in a solution of it. Zinc dissolves more freely and more plentifully. Lead unites with it, but does not become soluble in water. Tin is corroded, and a part of the calx is soluble in boiling water. Of regulus of antimony also a small portion is made soluble. Alkalies precipitate from the solution a bluish powder. Calcined bismuth-ore treated with its equal weight of the salt, partly dissolved in water into a pale red liquor, which became green from heat, in the same manner as tinctures made from that ore by aqua-regia. The undissolved part yielded still, with frit, a blue glaas. On treating manganese in the same manner, aluminoous crystals were obtained; the undissolved part of the manganese gave still a violet colour to glaas.

III. With Calcareous Earth. This combination may be made by saturating diluted oil of vitriol with chalk in fine powder. The mixture ought to be made in a glaas; the chalk must be mixed with a pretty large quantity of water, and the acid dropped into it. The glaas must be well shaken after every addition, and the mixture ought rather to be over saturated with acid; because the superfluous quantity may afterwards be washed off; the selenite, as it is called, or gypsum, having very little solubility in water.

This combination of vitriolic acid with chalk or calcareous earth, is found naturally in such plenty, that it is seldom or never made, unless for experiment's sake, or by accident. Mr Pott indeed says, that he found

some slight differences between the natural and artificial vitriolic acid and its properties of the latter.

The natural gypsums are found in hard, semitransparent masses, commonly called alabaster, or plaster of Paris. (See Alabaster, Gypsum, and Plaster.) By exposure to a moderate heat, they become opaque, and very friable. If they are now reduced to fine powder, and mixed with water, they may be cast into moulds of any shape; they very soon harden without shrinking; and are the materials whereof the common white images are made. This property belongs likewise to the artificial gypsum, if moderately calcined.

Mr Beaumé has observed, that gypsum may be dissolved in some measure by acids; but is afterwards separable by crystallization in the same state in which it was before solution, without retaining any part of the acids. This compound, if long exposed to a pretty strong heat, loses great part of its acid, and is converted into quicklime. In glaas vessels it gives over no acid with the most violent fire. It may be fused by suddenly applying a very intense heat. With clay it soon melts, as we have observed when speaking of the materials for making crucibles. A like fusion takes place when pure calcareous earth is mixed with clay; but gypsum bubbles and swells much more in fusion with clay than calcareous earth.

From natural gypsum we see that vitriolated tartar may be made, in a manner similar to its preparation from green vitriol. If fixed alkaline salt is boiled with any quantity of gypsum, the earth of the latter will be precipitated, and the acid united with the alkali. If a mild volatile alkali is poured on gypsum contained in a glaas, and the mixture frequently shaken, the gypsum will in like manner be decomposed, and a phlogistic sal ammoniac will be formed. With the caustic volatile alkali, or that made with quicklime, no decomposition ensues.

IV. With Argillaceous Earth. The produce of Alum of this combination is the astringent salt called alum, the ancients much used in dyeing and other arts. It has different name from the Latin word alumen, called στερνοποια by the Greeks; though by these words the ancients expressed a talcaceous substance containing very little alum, and that entirely enveloped in a vitriolic matter. The alum used at present was first discovered in the oriental parts of the world; though we know not when, or on what occasion. One of the most ancient alum-works of which we have any account was name of that of Rocca, now Edessa, a city of Syria; and from rock alum this city was derived the appellation of Rock-alum; an expression so little understood by the generality, that it has been supposed to signify rock alum. From this, and some works in the neighbourhood of Constantinople, as well as at Phoca Nova, now Foya Nova, near Smyrna, the Italians were supplied till the middle of the 15th century, when they began to set up works of a similar kind in their own country. The first Italian alum-work was established about 1459 by Bartholomew Perdix, or Permix, a Genoese merchant, who had up in Italy, discovered the proper matrix, or ore of alum, in the island of Ischia. Soon after the same material was discovered at Tolfa by John de Castro, who had visited the alum manufactories at Constantinople. Vitriolic A-ving observed the ilex aquifolium to grow in the neighbourhood of the Turkish manufactories, and finding the same near Tolfa, he concluded that the materials for alum were to be found there also; and was quickly confirmed in his suspicions by the taste of the stones in the neighbourhood. These alum-works prospered exceedingly, and their success was augmented by an edict of Pope Pius II. prohibiting the use of foreign alum.

In Spain, England, and Sweden.

Its component parts first discovered by Meff, Boulduc and Geoffroy.

The component principles of this salt were long unknown; but at last Meff's Boulduc and Geoffroy discovered, that it consisted of argillaceous earth supersaturated with vitriolic acid. This is confirmed by the experiments of other chemists. It is found to reddish the tincture and paper of turnsole; and on taking away the superabundant acid, it loses its solubility and all the other properties of alum. Mr Morveau, indeed, will not admit of a superabundance of acid in alum, by which he thinks would necessarily be separated by edulcoration and crystallization; and he is of opinion with Mr Kirwan, that the turning vegetable juices red is not any unequivocal sign of the presence of an acid. In the present case, however, we certainly know that there is a superabundance of acid, and that a certain portion of the vitriolic acid adheres to the clay less tenaciously than the remainder. If we put a piece of iron into a solution of alum, it will attract this portion of acid; and the vitriolated clay, when deprived of the superfluous quantity, will fall down to the bottom in an insoluble powder.

Alum in its ordinary state contains a considerable quantity of water, and crystallizes by proper management into octahedral and perfectly transparent and colourless crystals. When exposed to a moderate fire, it melts, bubbles, and swells up; being gradually changed into a light, spongy, white mass, called burnt alum. This, with the addition of some vitriolic acid, may be crystallized as before. The principles it contains, therefore, are water, vitriolic acid, and argillaceous earth. The proportions may be ascertained in the following manner. 1. The water and superfluous vitriolic acid may be dissipated by evaporation, or rather distillation; and the loss of weight sustained by the salt, as well as the quantity of liquid which comes over into the receiver, shows the quantity of aqueous phlegm and unsaturated acid. 2. By combining this with as much caustic fixed alkali as is sufficient to saturate the acid which comes over, we know its proportion to the water; and by redistilling this new compound, we have the water by itself. 3. The earth may be obtained by precipitation with an alkali in its caustic state, either fixed or volatile: but this part of the process is attended with considerable difficulty; for the alkalies first absorb the superfluous acid, after which the earth combined to saturation with the acid falls to the bottom, and the digestion with the alkaline salt must be continued for a very considerable time before the acid is totally separated. By analysing alum in this manner, Mr Bergman determined the principles of alum to be 38 parts of vitriolic acid, 18 of clay, and Vitriolic Acid and its Combinations.

It has been a question among chemists, whether the earth of alum is to be considered as a pure clay or not. The salt was extracted from common clay by Messrs Hellot and Geoffroy. The experiment was repeated with success by Mr Pott; but he seemed to consider it rather as the production of a new substance during the operation, than a combination of any principle already existing with the vitriolic acid. Margraf, however, maintains from some very accurate experiments, demonstrated that all kinds of clay consist of two principles mechanically mixed; one of which constantly is the pure earth of alum. This opinion is espoused by Bergman; who concludes, that since an equal quantity of it may be extracted from clay by all the acids, it can only be completely mixed with these clays; for if it was generated by the parts of all menstrua during the operation, it must be procured in different quantities, if not of different qualities also, according to the difference of the solvents made use of. Notwithstanding this, the matter seems to be rendered somewhat obscure by an experiment of Dr Lewis. Lewis's experiment, "Powdered tobacco-pipe clay (says he) being boiled in a considerable quantity of oil of vitriol, and the boiling show that continued to dryness, the matter when cold discovers clay under very little taste, or only a slight acidulous one. Exposed to the air for a few days, the greatest part of it was changed into luminous efflorescences tending exactly like alum. The remainder, treated with fresh earth of oil of vitriol, in the same manner exhibits the same phenomena till nearly the whole of the clay is converted into an altringent salt." Hence he concludes, that the clay is in some degree changed before the alumino-fusible is produced. Without this supposition, indeed, it is difficult to see why the salt should not be produced immediately by the combination of the two principles. An hundred parts of crystallized alum require, according to Mr Bergman, in a mean heat of 1412 parts of distilled water, but in a boiling heat only 75 of the same parts for its solution. The specific gravity of alum, when computed from the increase of bulk in its solution, is 2.071 when the air-bubbles are abstracted; but if they are suffered to remain, it is no more than 1.757. These bubbles consist of aerial acid, but cannot be removed by the air-pump, though they fly off on the application of heat.

The ores from which alum is prepared for sale, according to Mr Bergman, are of two kinds; one containing the alum already formed, the other its principles united by roofing. What he calls the aluminous schift, is nothing but an argillaceous schift impregnated with dried petroleum, from whence the oil is easily extracted by distillation; but by applying proper menstrua it discovers several other ingredients, particularly an argillaceous martial substance, frequently amounting to ¼ of the whole; a siliceous matter amounting to ½; and commonly also a small proportion of calcareous earth and magnesia; the rest being all pyritous. By roasting Howchan ore the bituminous part is destroyed and the pyrites decomposed; on which part of the vitriolic acid adheres to the iron of the pyrites, and the rest to the pure clay of the schift, forming green vitriol with the former, and alum with the latter. If any calcareous earth or magnesia are present, gypsum and Epsom salt will be produced at the same time. No salt is obtained by Practice.

Vitriolic Acid and its Combinations.

The presence of pyrites is generally necessary for the production of alum.

Ores containing alum readily formed, to be met with in volcanic countries.

Aluminous ores at Solfatara in Italy.

Aluminous ores at Solfatara in Italy.

Aluminous ores at Solfatara in Italy.

Alum fulphur and vitriol extracted from the same ore.

Alum flake found at York in England.

Mr Bergman's directions for the preparation of alum.

Use of roasting the ore.

By lixiviating this schilt before calcination, though Mr Bergman thinks nothing more is necessary for the production of the salt but the presence of a pyrites. This, he tells us, is generally dispersed through the mass in form of very minute particles, though it sometimes appears in small nuclei. The goodness of the ore, therefore, depends on the proper proportion of the pyrites to the clay, and its equal distribution through the whole. The most dente and ponderous is most esteemed, while that which contains too much pyrites as to be visible is rejected as having too much iron. The ore which produces less than four pounds of alum from 100 of the ore does not pay the expense of manufacturing in Sweden. Sometimes this kind of ore produces salts without the application of fire; but this must be attributed to a kind of spontaneous calcination.

That species of ore which contains the principles already united into alum, according to Mr Bergman, is to be met with only in volcanic countries; and of this kind are the principal Italian ores of alum, particularly that employed at Tolfa near Cingelos, for boiling the Roman alum. Mr Monnet, however, is of opinion, that even this ore does not contain alum perfectly formed, but a combination of nearly equal parts of clay and sulphur, which, by exposure to air during calcination, is converted into alum. He found a little marl earth also contained in it, to which he ascribes the reddish colour of that alum. The aluminous ores at Solfatara in Italy consist of old lava whitened by the phlogisticated vitriolic acid. The clay thus becomes a component part of the aluminous salt, and the mass effloresces in the same manner, and for the same reason, as the mass left after boiling tobacco-pipe clay in oil of vitriol mentioned by Dr Lewis. Mr Bergman, who examined this ore, found, that 100 pounds of it contained eight of pure alum, besides four of pure clay; and that the remainder was filicose. This proportion, however, must be very variable, according to the quantity of rain which falls upon the ore.

A variety of aluminous ores are to be met with in different parts of the world. In Haffia and Bohemia this salt is obtained from wood impregnated with bitumen. At Helsingborg in Scania, a turf is found consisting of the roots of vegetables mixed with nuts, straw, and leaves, often covered with a thin pyrites cuticle, which, when elixited, yields alum: Even the sulphureous pyrites is generally mixed with an argillaceous matter, which may be separated by menstrua. In some places, sulphur, vitriol, and alum are extracted from the same material. The sulphur rises by distillation; the residuum is exposed to the air till it effloresces, after which a green vitriol is obtained by lixiviation, and alum from the same liquor, after no more vitriol will crystallize. The alum flake, from which this salt is made near York in England, contains a considerable quantity of sulphur; and therefore produces alum on the principles already mentioned.

Mr Bergman has given very particular directions for the preparation of this salt from its ores, and minutely describes the several operations which they must undergo. There are,

1. Roasting: This is absolutely necessary in order to destroy the pyrites; for on this the formation of the alum entirely depends; as the sulphur of the pyrites will not part with its phlogiston without a burning heat in the open air. By long exposure to the air, indeed, the same effect will follow; but unless the ore be of a particular kind, and loose in texture, so that the air can freely pervade it, the process we speak of cannot take place. The hard ores, therefore, cannot be treated in this manner; and the earthy ores are not only unfit for spontaneous calcination, but for roasting also, as they will not allow the air to pervade them and extinguish the fire. Such as are capable of spontaneous calcination, should be supplied with some quantity of water, and laid on a hard clay bottom, as directed for making green vitriol. The roasting is performed in Sweden in the following manner. Small pieces of the ore are thrown upon a layer of burning sticks to the thickness of half a foot. When the sticks are consumed, these are covered, nearly to the same thickness, with pieces burned before and four times den.

Lixiviating: Thus, strata are alternately laid of such a thickness, and at such intervals of time, that the fire may continue, and the whole mass grow hot and smoke, but not break out into flame. The upper strata may sometimes be increased to a double thickness on account of the long continuance of the fire. When eight strata are laid, another row is placed contiguous to the former; when this is finished, a third; and so on until the heap be of a proper size, which rarely requires more than three rows. When the ore is once roasted, it still contains so much phlogiston that water acts but little upon it; but after the operation is two or three times repeated, the ore yields its principles more freely; the roasting may even be repeated to advantage till the whole be reduced to powder. The bitumen keeps up the fire; for which reason alternate layers of the crude ore are used; and in rainy weather these layers of unburnt ore should be thicker. An heap, 20 feet broad at the base, two feet at the top, and consisting of 26 rows, is finished in three weeks, but requires two or three months to be well burned, and three weeks to cool. The greater pyritous nuclei explode like bombs. In this process the sulphur of the pyrites is slowly consumed, and the phlogisticated acid, penetrating the mass, is fixed; after which the remaining phlogiston is gradually dissipated. The chief danger of art consists in moderating the heat in such a manner as to avoid with safety the two extremes; for too small a fire would not be capable of forming the salt, while a heat too strong would destroy it by melting the ore. The scoria is insoluble in water, and therefore thrown away as useless. They are produced by violent winds, or by a strong heat too much closed up; for it is necessary to make holes in the red strata, that the fire may reach the black stratum which is to be laid on.

Another method of burning was invented by the celebrated Rinnan, and is practised at a place called Gar, method of burning the phyllite in Sweden. There the ore itself is set on fire; and after burning is boiled, and yields alum in the same manner as the former. The heaps are formed in the following manner: First the schilt, burning from the furnace, is laid to the depth of four feet; if the fire be slow, then wood is added; after that a thin stratum of elixited schilt; the third consists of schilt not burned; and the fourth of elixited schilt a foot and a half thick; after that the burning schilt, and so on. This method, however, is attended with some inconveniences. The vitriolic acid is partly dissipated by the fire, and thus... the quantity of alum is diminished; so much schilt also is requisite in this method that it cannot all be elixated; and thus the heap must be perpetually increasing.

The hard ores containing bitumen, such as those of Tolfa, are burned upon wood for some hours like limestone, until they become pervious to water, and effloresce. The fire is extinguished as soon as the flame becomes white, and the smell of sulphurous acid begins to be perceived. When the ore cools, those particles which were nearest to the fire are placed outermost, and those which had been outermost within, the fire being again lighted. The ore is sufficiently burned when it can be broken with the hands. It is then heaped up near certain trenches, and watered five times a day, particularly when the sun shines clear; the operation being destroyed by a continued rain and cloudy sky. In some places the ore is first burned and afterwards elixated; neither is there any way of knowing the proper methods of managing it but by experiment.

2. Elixation. This is performed in some places with hot, and at others with cold, water. At Garphyttan in Sweden, where the latter method is chosen, the receptacles, in the year 1772, were of hewn stone, having their joints united by some cement capable of resisting the liquor. Every set consisted of four square receptacles disposed round a fifth, which was deeper than the rest. The first receptacle is filled with roasted schilt, and the ore lies in water for 24 hours; the water is then drawn off by a pipe into the fifth; from thence into the second, containing schilt not yet washed; from that, in like manner, after 24 hours, through the fifth into the third, and so into the fourth. The lixivium is then conveyed to the fifth, and allowed to stand in it; and lastly, is drawn off into a vessel appropriated for its reception.—In other places the water passes over the schilt that has been washed three times for six hours; then that which has been twice washed, next what has been once washed, and lastly, the ore which has been newly roasted. Those who superintend the alum manufactories are of opinion that the alum is destroyed by passing the water first over the newly burnt ore, and then over that which has been previously elixated.

The lixivium, before boiling, ought to be as richly impregnated with alum as possible, in order to save fuel, though this is frequently neglected. In some places the taste is used as the only criterion; but in others the weight of water which fills a small glass bottle is divided into 64 equal parts, each of which is called in Sweden a panning; and the quantity by which the same bottle, full of lixivium, exceeds it when filled with water, is supposed to indicate the quantity of salt dissolved.—This method may undoubtedly be reckoned sufficiently accurate for work conducted on a large scale; and though Mr Bergman gives formulae by which the matter may be determined to a ferocious exactness, it does not appear that such accuracy is either necessary or indeed practicable in works conducted in a great way.

Those who manage the alum manufactories assert, that the cold lixivium ought to be made no richer than when the weight of the bottle filled with lixivium exceeds it when filled with water by 4½ pannings, which shows the water to be loaded with ⅓ of its Vitriolic A weight of alum. If the overplus amounts to ¾ pan, it is niggings, which indicates its containing ⅔ of salt, crytals are then depoited.—Congelation is of no use to concentrate the aluminous lixivium; for water saturated with alum freezes almost as readily as pure water.

3. Boiling the ley for crystallization. The Confinery being first brought from the pits through canals evaporation of the for the purpose, is put into a leaden boiler, at the back vessel, of which is a reservoir, out of which the loss sustained by evaporation is constantly supplied, so that the surface of that in the boiler continues always nearly at the same height. Various signs are used by different manufacturers to know when the ley is properly evaporated: some determining the matter by the floating of a new laid egg; others by dropping a small quantity on a plate, and observing whether it crystallizes on cooling; and lastly, others weigh the lixivium in the bottle above-mentioned. The boiling is supposed to be proper nished if the increase of weight be equal to 20 pans strength of evaporation; that is, if the water be loaded with ⅓ of its own weight. It might, however, take up above ⅔ of its weight, or nearly 27 pannings; but as it has to be depurated by standing quiet before the crystals are formed, the liquor must not be fully saturated with salt.

The lixivium, when sufficiently concentrated by Of the first evaporation, flows through proper channels into coolers, where it is allowed to rest for about an hour to free it from the grossest sediment; after which it is put into wooden or stone receptacles to crystallize. In eight or ten days the remaining liquor, commonly called mother ley, or magistral water, is let off into another vessel. A great number of crystals, generally small and impure, adhere to the bottom and sides of the vessel, which are afterwards collected and washed in cold water.

When a sufficient quantity of the small crystals are collected, they must then be put into the boiler for de-puration. They are now distilled in as small a quantity of water as possible; after which the lixivium is poured into a great tub containing as much as the boiler itself. In 16 or 18 days the hoops of the tub are loosed, and the aluminous mass bound with an iron ring; and in 28 days more the residuum of the solution is let out through a hole, and collected in a trench; after which the saline mass, which at Garphyttan in Sweden amounts to 26 tons, is dried and sold as depurated alum. The boiler emptied for the first crystallization is next filled two-thirds full with the magistral lixivium; and as soon as the liquor arrives at the boiling point, the other third is filled with crude lixivium, with which the evaporation is also constantly supplied. A certain quantity of the aluminous impurities left by washing the salts of the first crystallization in water is then added, and the above described process repeated. Only the first boiling in the spring is performed with the crude lixivium alone, the rest are all done as just now related.—Mr Bergman remarks, that the time required for crystallization may be shortened. The reservoirs used in the proper form of the Sweden for this purpose (he says), are deep, and narrow at the top; on which account they are not only long Vitriolic acid in cooling, but the evaporation, which is absolutely necessary for the crystallization, goes on very slowly, excepting in extremely warm weather, at the same time that the doors and windows are disposed in such a manner as to direct a current of air along the surface. In Italy he tells us that conical reservoirs are used with the wide part uppermost.

It is remarkable, that pure alum cannot be obtained in very considerable quantity by merely evaporating and cooling the ley. The reason of this is, that the lixivium sometimes acquires such a consistence, that it both crystallizes with difficulty, and produces impure crystals. The cause was unknown till the time of Mr Bergman, who has shown that it proceeds from an excess of vitriolic acid. Hence also we may see the reason why alkaline salts, volatile alkali in its pure state, or even putrefied urine, when added to this thick solution, produce good crystals of alum when they cannot be obtained otherwise. It is remarkable that this impediment to crystallization is not removed by mineral alkali, though it is so by the vegetable and volatile alkalis, which is a phenomenon hitherto unexplained. According to our author, however, an addition of pure clay, to absorb the superabundant acid, is preferable to any other; and indeed it is reasonable to think so, as the union of vitriolic acid and pure clay forms the salt defined, which is not the case with any of the alkalis.—To ascertain this, he made the following experiments.

1. He dissolved 215 grains of pure alum in distilled water, in a small cucurbit, and evaporated it over the fire till the surface of the liquor stood at two marks, which indicated, in a former evaporation, that it was fit for crystallization. 2. Having poured out this into a proper glass vessel, he dissolved other 215 grains, and added to the solution 24½ grains of concentrated vitriolic acid. 3. This solution being likewise poured out, the experiment was repeated a third time, with the addition of 53 grains of vitriolic acid; and the glasses being at last set in a proper place for crystallization, the first yielded 155½, the second 130, and the third 100½ grains of alum.

This shows that an excess of vitriolic acid impedes the crystallization of the alum; but to determine how far this could be remedied by the addition of clay, further experiments were necessary. Having therefore employed a magistral residuum, in which the excess of acid was nearly in the proportion already related, he added two drachms of clay in fine powder to a kanne, or Swedish cantharns, of the liquor: he boiled the mixture for ten minutes; and on separating the clay that remained, he found that 25½ grains were dissolved, which indicates an increase of 14½ grains of alum. On gently boiling the liquor for half an hour, 75 grams of the clay were dissolved, which indicated an increase of 41½ grams of alum.

The addition of clay must therefore be much preferable to that of alkaline salts, not only as the former produces a considerable increase of alum, but also as there is no danger of adding too much; for we have already shown, that when the liquor is entirely deprived of its superabundant acid, the neutralized clay is insoluble in water. The earth itself, however, dissolves so slowly, that there is not the least danger of the acid being oversaturated by simply boiling them together.

Alum, as commonly made, though depurated by a second crystallization, yet is almost always found contaminated by dephlogisticated vitriol; whence it grows yellow, and deposits an ochre in solution when old. Alum generally contains iron, and is even so in dyeing where dark colours are required; but where the more lively colours are wanted, everything vitriolic must be avoided. This is done triol, by the addition of pure clay, which precipitates the iron, and produces an alum entirely void of any noxious or heterogeneous matter. Nor is this contrary to the laws of chemical attraction; for though iron is dition of dissolved by a solution of alum, and the earthy base of pure clay, alum precipitated, and though in a solution of vitriol and alum the white earth falls first on an addition of alkali, and then the ochre; this happens only in consequence of employing phlogisticated or metallic iron, or such as is but very little dephlogisticated; for if the inflammable principle be any further diminished, the attraction is thereby so much weakened, that the clay has a greater attraction for the vitriolic acid than the iron. The truth of this may be proved in many different ways. Thus, let a portion of alum be dissolved in a solution of highly dephlogisticated vitriol, and an alkali then added, the ochre of the vitriol will be first deposited, and then the clay: and provided there be a sufficient quantity of the latter, the iron will all be precipitated; and hence we see that an aluminoous solution mixed only with one of dephlogisticated vitriol may readily be freed from it.

But a solution of alum containing perfect vitriol cannot be freed from it effectually either by clay or alkali; for the former effects no decomposition, and the latter, although it can destroy the vitriol, will undoubtedly decompose the alum in the first place. As long, therefore, as the solution is rich in alum, it may be employed in the common manner; but when the vitriolic salt begins to predominate, it must either be crystallized in its proper form, or be destroyed in such a manner as to produce alum, which may be accomplished in the following manner. Let the lixivium be reduced to a tenacious mass with clay, phlogiston and formed into cakes, which must be exposed in an abattoir to the open air. Thus the phlogiston, which is powerfully attracted by the dephlogisticated part of vitriol, the atmosphere, by degrees separates from the iron, while the clay is taken up by its superior attraction for the acid. The calcination is accelerated by fire; but it must be cautiously employed, lest the acid should be expelled.

In the alum manufactories in Sweden, a considerable quantity of vitriolated magnesia, or Epsom salt, may be mixed with the alum. Mr Bergman directs this to be separated by means of an uncalcined calcareous mother liquor; falling down to the bottom with the acid in form of a felsitic matter. This must be added to the boiling liquor gradually, lest the effervescence should cause the mass to swell and run over the top of the vessel. A just proportion destroys both the aluminoous and vitriolic salt, on being properly agitated and heated; neither is there any danger of the Epsom salt. Vitriolic acid being decomposed in this process, the uncalcined earth being unable to separate the magnesia from the acid. Were this method followed in the Swedish manufactories, he is of opinion, that as much Epsom salt might be produced from them as would supply the consumpt of that kingdom.

With regard to the quantity of superfluous acid found in the magistral lixivium, Mr Bergman informs us, that it amounted to five ounces in one kanne; so that in a single boiler there is nearly 250 lb. But vitriol, when well dephlogisticated, retains its acid so loofly that it may be easily separated by fire. He has no doubt, therefore, that if the surface of such a lixivium were first increased in order to let the phlogiston evaporate, the liquor might afterwards be advantageously committed to distillation for the sake of its acid.

From what has been above delivered, the necessity will be sufficiently apparent of not continuing the coction even with pure clay to perfect saturation of the liquor; and this is further confirmed by M. Beaumé, who relates, that having boiled four ounces of earth of alum with two ounces of the salt, in a sufficient quantity of water, the acid became saturated to such a degree with earth, that the liquor lost its aluminous taste entirely, and assumed that of hard spring water. After filtration and evaporation, only a few micaceous crystals, very difficult of solution, were formed by letting the liquor stand for some months.

Dr Sieffert informs us, that by boiling half an ounce of alum with half a drachm of flaked lime, cubical crystals of alum may be obtained.

VI. With Magnesia. The earthy substance called magnesia alba is never found by itself, and consequently this combination cannot originally take place by art. The vitriolic acid, however, is found combined with magnesia in great plenty in the bitter liquor which remains after the crystallization of common salt; from whence the magnesia is procured by precipitating with a fixed alkali. If this liquor, which, when the common salt is extracted, appears like clean oil of vitriol, is set by for some time in a leaden vessel, a large quantity of salt shoots, very much resembling Glauber's sal mirabile. This salt is in many places sold instead of the true Glauber's salt; and is preferred to it, because the true sal mirabile calcines in dry air, which the spurious kind does not. If after the first crystallization of the bitter, the remainder is gently evaporated farther, a fresh quantity of Glauber's salt will shoot; and if the liquor is then halily evaporated, a salt will still be crystallized; but instead of large regular crystals, it will concrete into very small ones, having something of the appearance of snow when taken out of the liquid. These salts are essentially the same, and are all used in medicine as purgatives. The salt shot into small crystals is termed Epsom salt, from its being first produced from the purging waters at Epsom in England. The bitter affording this kind of salt in such great plenty, these waters were soon neglected, as they yielded it but very sparingly, and the quantity prepared from them was insufficient for the demand. Neumann says, that having infusoried 100 quarts of Epsom water, he scarce obtained half an ounce of salt matter. According to Mr Scheele's experiments, if a solution of Epsom and common salt be mixed together, a double decomposition ensues, and the mixture contains Glauber's salt and a combination of magnesia with marine acid. From this lixivium the Glauber's salt may be crystallized in winter, but not in summer; a great degree of cold being necessary for this purpose. From twelve pounds of Epsom salt and six of common salt, Mr Scheele obtained, in a temperature three degrees below the freezing point, six pounds of Glauber salt; but in a degree of cold considerably greater, the produce was seven pounds and three quarters.

VI. With Silver. Oil of vitriol boiled on half its weight of silver-filings, corrodes them into a saline mass. This substance is not used in medicine nor in the arts. The only remarkable property of it is, that it has a very strong attraction for mercury; coagulating and hardening as much quicksilver as the acid weighed at first. If the hard concrete be diluted with fresh acid, it melts easily in the fire, and does not part with the mercury in the greatest heat that glass vessels can sustain. The vitriolic acid, by itself, strongly retains mercury, but not near so much as when combined with silver.

Silver thus corroded by the vitriolic acid, or precipitated by it from the nitrous, may in great part be dissolved, by cautiously applying a very little water at a time; and more effectually by boiling in fresh oil of vitriol.

VII. With Copper. With this metal the vitriolic acid cannot be combined, unless in its concentrated state, and strongly heated. If pure oil of vitriol is boiled on copper filings, or small pieces of the metal, it dissolves it into a liquor of a deep blue colour, which easily crystallizes. The crystals are of a beautiful blue colour, and are sold under the name of blue vitriol or Roman vitriol.

Where sulphur is found in great plenty, however, Blue vitriol, Roman vitriol is made by stratifying thin plates of copper with sulphur; and upon slowly burning the sulphur, its acid corrodes the copper. The metal is then to be boiled in water, that the saline part may be dissolved. The operation is to be repeated till all the copper is consumed; and all the saline liquors are to be evaporated together to the crystallizing point. By this method, however, a great part of the acid is lost; and in Britain, where the sulphur must be imported, we should think the pure acid preferable for those who prepare blue vitriol.

This salt, on being exposed to the fire, first turns white, then of a yellowish red colour. On urging it on distillation with a strong fire, the acid slowly exhales, and a dark red calx of copper remains. The whole of the vitriolic acid cannot be expelled from copper by heat: as much of it still remains as to render a part of the metal soluble in water. After this soluble part has been extracted, a little acid is still retained, amounting to about $\frac{1}{3}$ of the calx.

Vitriol of copper is employed in medicine as a caustic, in which respect it is very useful; but when used internally, is dangerous, as indeed all the preparations of copper are found to be. It has, nevertheless, according cording to Neumann, been recommended in all kinds of intermittents, and the lepra. The smallest portion, he says, occasions a sickness and nausea; somewhat larger, reaching and violent vomitings, accompanied often with convulsions. If the quantity taken has been considerable, and is not soon discharged by vomiting, the stomach and intestines are corroded, intense pains, inflammations, and death, succeed.

VIII. With Iron. The vitriolic acid does not act upon this metal till considerably diluted. Common oil of vitriol requires to be mixed with ten or twelve times its quantity of water before it will act briskly on the metal. In this state it effervesces violently with iron filings, or small bits of the metal, and a great quantity of inflammable vapour is discharged (see A18). The liquor assumes a fine green colour; and by evaporation and slow cooling, very beautiful rhomboidal crystals are formed. These are named salt of steel, and are used in medicine; but for the salt made with the pure acid and iron, the common copperas, made with the impure acid extracted from pyrites, is commonly substituted. This is generally esteemed a venial fraud, and no doubt is so in medicinal respects; but when it is considered, that, by this substitution, common copperas is imposed on the ignorant, at the price of 2s. per pound, the affair appears in a different light.

Pure vitriol of iron is originally of a much more beautiful appearance than common copperas, and retains its colour much better; the reason of which is, that the salt thus prepared has more phlogiston than the copperas. If either of the kinds, however, are exposed to the air for a sufficient length of time, part of the acid is dissipated, and the vitriol becomes yellowish or brownish. If the salt is now dissolved in water, a brown precipitate falls, which is part of the iron, in a calcined state. If the liquor is separated from this precipitate by filtration, a similar one forms in a short time, and by long standing a considerable quantity sublimes. According to Dr Lewis, the precipitation is greatly expedited by a boiling heat; by which more of the metal separates in a few minutes than by standing without heat for a twelvemonth. This change takes place in no other metallic solutions.

The calx of iron, precipitated by quicklime from green vitriol, appears, when dry, of a yellow colour; and is recommended in the Swedish transactions, instead of yellow ochre, as a colour for house-painting. Solutions of green vitriol are also recommended for preserving wood, particularly the wheels of carriages, from decay. When all the pieces are fit for being joined together, they are directed to be boiled in a solution of vitriol for three or four hours; and then kept in a warm place for some days to dry. By this preparation, it is said, wood becomes so hard, that moisture cannot penetrate it; and that iron nails are not so apt to rust in this vitriolated wood as might be expected, but last as long as the wood itself.

IX. With Tin. This metal cannot be dissolved in the vitriolic acid, but in the same manner as silver; namely, by boiling concentrated oil of vitriol to dryness upon filings of the metal. The saline mass may then be dissolved in water, and the solution will crystallize. The salt, however, formed by this union, is not applied to any useful purpose. A salt of tin, indeed, formed by the union of vitriolic acid with this metal, Vitriolic acid has been recommended for some medical purposes, and processes are given for it in the dispensaries; but they have never come much into practice.

X. With Lead. While lead is in its metallic state, the vitriolic acid acts very little upon it, either in a diluted or concentrated state; but if the metal is dissolved in any other acid, and oil of vitriol added, a precipitation immediately ensues, which is occasioned by the combination of vitriolic acid with the lead. This precipitate will be more or less white as the metal is more or less deprived of its phlogiston by calcination before solution. If a little strong spirit of nitre is poured upon litharge, which is lead calcined to a white colour, the greatest degree possible without vitrification, the acid unites itself to the metal with considerable effervescence and heat. Some water being now poured on, and the phial containing the mixture shaken, a turbid solution of the litharge is made. If a little oil of vitriol is then added, it throws down a beautifully white precipitate; and the acid of nitre, being left at liberty to act upon the remaining part of the litharge, begins anew to dissolve it with effervescence. When it is again saturated, more oil of vitriol is to be dropped in, and a white precipitate is again thrown down. If any of the litharge is still undissolved, the nitrous acid, being set at liberty a second time, attacks it as at first; and by continuing to add oil of vitriol, the whole of the litharge may be converted into a most beautiful and durable white. Unfortunately this colour cannot be used in oil, though in water it seems superior to any. If the process is well managed, an ounce of spirit of nitre may be made to convert several pounds of litharge into a white of this kind.

XI. With Quicksilver. The dissolution of quicksilver in vitriolic acid cannot be performed but by a concentrated oil and strong boiling heat. The metal is first corroded into a white calx, which may afterwards be easily dissolved by an addition of fresh acid. Every time it is dissolved, the mercury becomes more and more fixed and more difficult to dry. If the extraction and dissolution has been repeated several times, the matter becomes at last so fixed as to bear a degree of red heat. This combination is the basis of a medicine formerly of some repute, under the name of turpith mineral. The process for making turpith mineral is given by the author of the Chemical Dictionary as follows:

"Some mercury is poured into a glass retort, and Turpith upon it an equal quantity of concentrated oil of vitriol, mineral, or more, according to the strength of the acid. These matters are to be distilled together, in the heat of a sand-bath, till nothing remains in the retort but a dry saline mass, which is a combination of the vitriolic acid and mercury. The acid which passes into the receiver is very suffocating and sulphurous; which quantities it receives from the phlogiston of the mercury. The white saline mass which is left at the bottom of the retort is to be put into a large vessel; and upon it are to be poured large quantities of hot water at several different times. This water weakens the acid, and takes it from the mercury; which is then precipitated towards the bottom of the vessel, in form of a very shining yellow powder. The water with..." Vitriolic Acid and its Combinations.

which it is washed contains the acid that was united with the mercury, and likewise a little mercury rendered soluble by means of the very large quantity of acid.

Most chemists have believed, that a portion of vitriolic acid remains united with the turbith mineral, only too little to render it soluble in water. But Mr. Beaumé, having examined this matter, affirms, that turbith mineral contains no acid, when it has been sufficiently washed; and that, by frequently boiling this preparation in a large quantity of distilled water, not a vestige of acid will adhere to it."

Dr Lewis, who is of opinion that the whole of this mercurial calx is soluble in a very large quantity of water, defies the water with which it is washed to be impregnated with some alkaline salt; which makes the yield of turbith greater than when pure water is used. The author of the Chemical Dictionary also observes, that the precipitate remains white till well freed from the acid; and the more perfectly it is washed, the deeper yellow colour it acquires.

XII. With Zinc. This semifinal is not acted upon by the vitriolic acid in its concentrated state; but, when diluted, is dissolved by it with effervescence, and with the extrication of an inflammable vapour in the same manner as iron. Neumann observes, that, during the distillation, a grey and blackish spongy matter fell to the bottom; but, on standing for some days, was taken up, and dissolved in the liquor, nothing being left but a little yellowish dust scarcely worth mentioning. Six parts of oil of vitriol, diluted with an equal quantity of water, dissolves one part of zinc.

The product of this combination is white vitriol; which is used in medicine as an ophthalmic, and in painting for making oil-colours dry quickly: what is used for this purpose, however, is not made in Britain, but comes from Germany. It is made at Goslar by the following process. An ore containing lead and silver, having been previously roasted for the obtaining of sulphur (see Metallurgy), is lixiviated with water, and afterwards evaporated in leaden boilers, as for the preparation of green vitriol: but here a regular crystallization is prevented; for when the salt has assumed any kind of crystalline form, these crystals are made to undergo the watery fusion in copper caldrons. It is then kept constantly stirring till a considerable part of the moisture is evaporated, and the matter has acquired the consistence of fine sugar. White vitriol generally contains some ferruginous matter, from which it may be entirely freed by some fresh zinc; for this semifinal precipitates from the vitriolic acid all other metallic substances; but notwithstanding this strong attraction, the vitriolic acid is more easily expelled by distillation from white than green or blue vitriol. Towards the end of the distillation of white vitriol, the acid arises exceedingly concentrated, though sulphureous: so that, if mixed with common oil of vitriol, it will heat it almost as much as oil of vitriol heats water.

XIII. With Regulus of Antimony. To combine vitriolic acid with regulus of antimony, the same method must be used, as directed for uniting it with quicksilver, for making turbith mineral, viz. to employ a very concentrated acid, and to distil in close vessels. The same phenomena also occur in this case as in making turbith mineral; a very suffocating sulphureous acid rises, and, as Mr. Geoffroy observes, a true sulphur sublimes into the neck of the retort; a white, saline, tumefied mass remains in the vessel; and when the vessels are united, a white fume issues, as in the smoking spirit of libavus. See Combinations of marine acid with tin, infra.

XIV. With Regulus of Cobalt. From a combination of Regulus of the vitriolic acid with cobalt, a red salt may be obtained. To procure it, one part of cobalt, reduced to a very fine powder, may be mixed with two or three of concentrated acid, diluting the liquor after it has been digested for 24 hours, and then filtering and evaporating it.

XV. With Arsenic. Neumann relates, that powdered white arsenic being distilled in a retort with oil of vitriol, a transparent sublimate like glass arose, which in a few days lost its transparency, and became opaque like the arsenic itself. The arsenic remaining in the retort sustained an open fire without any sensible alteration. The author of the Chemical Dictionary says, that if a concentrated vitriolic acid is distilled over arsenic, the acid which comes over smells exactly like marine acid. When the solution is distilled till no more acid rises, the retort is then almost red-hot, and no arsenic is sublimed; but it remains fused at the bottom of the retort; and, when cold, is found to be an heavy, compact mass, brittle and transparent as crystal-glass. This kind of arsenical glass, exposed to the air, soon loses its transparency from the moisture it attracts, which dissolves and partly deliquesces it. This deliquium is extremely acid.—By digesting one part of arsenic with two of concentrated oil of vitriol, diluting the solution with water, and then filtering and evaporating, we obtain a yellowish salt which shoots into pyramidal, transparent, and shining crystals. None of the three last mentioned combinations have been found applicable to any useful purpose.

XVI. With Oil. The product of this combination is a thick black substance, very much resembling balsam of sulphur in colour and consistence; to which it is sometimes substituted. If this substance is distilled with a gentle heat, great part of the acid becomes volatile, and evaporates in white fumes, having a pungent smell resembling that of burning sulphur. This goes by the name of volatile or sulphureous vitriolic acid; and a salt was formerly prepared from it by saturation with fixed alkali, which was thought to possess great virtues. From its inventor it was called the sulphureous salt of Stahl. The most singular property of this volatile acid is, that though the vitriolic in its fixed state is capable of expelling any other acid from its basis, the volatile one is expelled by every acid, even that of vinegar. It is very difficultly condensible, as we have already taken notice; and, when mixed with water, seems scarcely at all acid, but rather to have a bitterish taste.

Several methods have been proposed for procuring this acid from burning sulphur, which yields it in its highest degree of volatility, as well as concentration, but the produce is so exceedingly finial, that none of them are worth mentioning. Dr Priestley has given very good directions for obtaining the volatile vitriolic acid in the form of air. His method was, to pour, on some oil of vitriol contained in a phial, a very small quantity of oil olive; as much as was sufficient to cover it. He then applied the proper apparatus for the reception of air in quicksilver (see Air); and, holding a candle to the phial, the volatile vitriolic acid rushed out in great quantity. Had he received this air in water, instead of quicksilver, the consequence would have been, that some part of it, at least, would have been absorbed by the water, and a sulphureous acid liquor produced. This seems indeed almost the only method of procuring the sulphureous vitriolic acid of any tolerable strength; but it is never required in the form of a liquor, except for experimental purposes. The only useful property hitherto discovered about this kind of acid is, that it is remarkably destructive of colours of all kinds; and hence the fumes of sulphur are employed to whiten wool, &c.

XVII. With Phlogiston of charcoal. If charcoal is mixed with concentrated vitriolic acid, and the mixture distilled, the same kind of acid is first obtained, which comes over when oil is used; and towards the end, when the matter begins to grow dry, a true sulphur sublimes. The best way, however, of producing sulphur from the vitriolic acid is by combining it, when in a perfectly dry state, with the phlogiston. By this means sulphur may very readily be made at any time. The process is generally directed to be performed in the following manner.

Reduce to fine powder any quantity of vitriolated tartar. Mingle it carefully with a 16th part of its weight of charcoal-dust. Put the whole into a covered crucible set in a melting furnace. Give a heat sufficient to melt the salt; and when thoroughly melted, pour it out on a flat stone. The vitriolated tartar and charcoal will now be converted into a sulphureous mass similar to a combination of alkaline salts with sulphur. See Alkaline Salts, below.

XVIII. With Spirit of wine. The result of this combination is one of the most extraordinary phenomena in chemistry; being that fluid, which, for its extreme degree of volatility, was first distinguished by the name of ether; and now, since a liquor of the like kind is discovered to be preparable from spirit of wine by means of other acids, this species is distinguished by the name of vitriolic ether. The method of preparing this subtle liquor recommended by Mr. Beaumé, seems to be the best of any hitherto discovered.

Mix together equal parts by weight, of highly rectified spirit of wine and concentrated oil of vitriol, or somewhat more than two measures of spirit of wine with one of the acid. The mixture is to be made in a flint glass retort, the bottom and sides of which are very thin, that it may not break from the heat which is suddenly generated by the union of these two substances. The spirit of wine is first put into the retort, and then the acid is poured in by a glass-funnel, so that the stream may be directed against the side of the glass; in which case it will not exert much of its force on the spirit, but will lie quietly below at the bottom. The retort is now to be very gently shaken, that the acid may mingle with it by little and little. When the mixture is completed, very little more heat will be necessary to make the liquor boil.

This mixture is to be distilled with as brisk and quick a heat as possible; for which reason, immediately after the acid and spirit are mixed, the retort should be put into a sand furnace heated as much as the mixture is. The distillation should be continued only till about one third of the liquor is come over; if it is continued farther, part of the vitriolic acid rises in a sulphureous state. In the retort a thick, black, acid matter remains, which is similar to a combination of oil of vitriol with any inflammable matter, and from which a little sulphur may be obtained. Along with the sulphureous acid, a greenish oil, called oleum vitrioli dulcis, arises, which has a smell compounded of that of the ether and sulphureous acid; and Mr. Beaumé has shown that it is compounded of these two; for if it is rectified with an alkali, to attract the acid, it is changed into ether. If, after the distillation of the ether, some water be poured into the retort, the liquor by distillation may be brought back to the state of a pure vitriolic acid.

As the fumes of the ethereal liquor are exceedingly volatile, and at the same time a quick fire is necessary to the success of the operation, the receiver must be carefully kept cool with very cold water or with snow. Care must also be taken to prevent any of the sulphureous acid fumes from coming over; but as it is impossible to prevent this totally, the liquor requires rectification. This is the more necessary, as a part of the spirit of wine always rises unchanged. From this acid the liquor is easily set free, by adding a small quantity of alkaline salt, and re-distilling with a very gentle heat; but as spirit of wine is likewise very volatile, the distillation must be performed in a very tall glass. Dr. Black recommends a matrass, or bolt-head, with a tin-pipe adapted to the head, so as to convey the fumes at a right angle, to be condensed in the receiver. When this fluid is to be prepared in great quantities, the ether, by proper management, may be made to equal half the weight of the spirit of wine employed. Mr. Dollfus has made many important experiments on this subject; of which the following is an abstract: 1. Two pounds of vitriolic acid were mixed with as much of spirit of wine, and the mixture distilled with a very gentle fire. The first ten ounces that came over consisted of a liquor strongly impregnated with ether, and of an agreeable odour. This was put by itself and marked A. It was followed by a stronger ethereal liquor, of which a small quantity only would mix with water. Of this there were 12 ounces, which were also put by themselves, and marked B. By continuing the process two ounces more were obtained, which smelled of sulphur, and were marked C. The distillation was now continued with a view to concentrate the vitriolic acid, when three drachms of a thicker kind of ether were found swimming on a weak sulphureous acid. This thick liquid was not in the least volatile, and in consistence resembled an expressed oil. 2. Twenty-four ounces of spirit of wine were now added to the residuum of the former distillation, and the process recommenced. The first seven ounces that came over were poured to the dulcified spirit marked A. Next passed over ten ounces of a tolerably pure ether, which was mixed with the contents of B; besides two ounces that had a sulphureous smell, which were mixed with C. By a repeated dephlegmation of what remained in the retort were obtained five ounces of a weak sulphureous acid; and the remainder being again mixed with 20 ounces of spirit of wine, yielded first six ounces of the liquor marked A; then four ounces of pure ether put into that marked B; and after that another ounce marked C. By continuing the distillation four ounces of weak sulphureous acid were obtained, on which floated a little oil of wine. 3. The remainder, which was very thick, and covered with a slight pellicle, was mixed with 20 ounces of spirit of wine, and yielded five ounces of dulcified spirit marked A; eight ounces of pure ether marked B; and at last one ounce of the same, which had rather a sulphureous smell. This was followed by a few drops of acid; but the remainder frothed up with such violence, that an end was put to the operation, in order to prevent its passing over into the receiver.

By these four distillations there were obtained from six pounds of spirit of wine and two of oil of vitriol, 28 ounces of dulcified spirit of vitriol and 38 of ether; which last, when rectified by distillation over manganese, yielded 28 ounces of the best ether. At the end of this distillation were produced 13 ounces of weak acetous acid; and the liquor of the last running marked C, afforded, by rectification, four ounces of good ether. The sulphureous acid liquor yielded four ounces of weak acetous acid, and three drachms of naphtha resembling a distilled oil in consistence.

By these processes the vitriolic acid was rendered quite thick and black; its weight being reduced to 24 ounces. The blackness was found to be owing to a powder which floated in the liquid, and could neither be separated by subliming to the bottom nor rising to the top. The liquor was therefore diluted with eight ounces of water, and filtered through powdered glais; by which means the black substance was collected, partly in powder, and partly in grains of different sizes. It felt very soft between the fingers, and left a stain upon paper like Indian ink; but though washed with 24 ounces of water, still tafted acid. Half an ounce of it distilled in a retort yielded a drachm and an half of weak acetous mixed with a little sulphureous acid; the residuum was a black coal, which by calcination in an open fire for a quarter of an hour, yielded 25 grains of white ashes, consisting of felsite, calcareous earth, and magnesia. A drachm of it digested with nitrous acid, which was afterwards distilled from it, and then diluted with distilled water and filtered, yielded a few crystals, which appeared to be genuine salt of tartar, an insoluble felsite being left behind.

On rectifying the vitriolic acid freed from the black matter and diluted with eight ounces of water, nine ounces of sulphureous acid were first obtained, after which followed an ounce of acid rather high-coloured, and then the vitriolic acid quite colourless. It now weighed only 193 ounces, and its specific gravity was but 1.723, while that of the acid originally employed had been 1.989.

On repeating the process with six pounds of spirit of wine to two of oil of vitriol, the first 12 ounces that came over were spirit of wine almost totally unchanged; then two ounces smelling a little of ether; and afterwards two pounds, of which about one third were ether. When about five pounds had been drawn off, the distilling liquor began to smell sulphureous; and after nine ounces more had been drawn off, the frothing up of the matter in the retort obliged him to put an end to the operation. The acid was then filtered through pounded glais as before, and afterwards committed to distillation. The three first ounces were a weak sulphureous acid; then followed an ounce more concentrated, and of a red colour; then another of a yellowish cast; after which the rest of the acid came over quite colourless. The whole weighed 27 ounces, and the specific gravity of it compared with distilled water was as 1.667 to 1.000.

Ether is the lightest of all known fluids, except air; and is so volatile, that in vacuo its boiling point is 20° below zero of Fahrenheit's thermometer. If a small quantity is poured out on the ground, it instantly evaporates, diffusing its fragrance all through the room, and scarce perceptibly moistening the place on which it fell. It difficulty mixes with water, as being of an oily nature: ten parts of water, however, will take up one part of ether. Its great volatility renders it serviceable in nervous diseases, and removing pains, when rubbed on with the hand, and kept from evaporating immediately. By spontaneous evaporation, it produces a great degree of cold. (See Evaporation and Congelation). The most extraordinary property, however, is, that if gold is dissolved in aqua-regia (see Metallic Substances, below), and ether added to the solution, the gold will leave the acid and permanently unite with the ether. The exceeding great volatility of ether renders it very easily inflammable even on the approach of flame; and therefore it ought never to be distilled, or even poured from one vessel to another, by candle-light. If a less quantity of the vitriolic acid is added to the spirit of wine than what is sufficient to produce ether, the product is called spiritus vitrioli dulcis. The following experiment made by Wallerius, induced him and others to think, that the vitriolic acid was convertible into the nitrous.

"Some salt of tartar (says he) being mixed with the dulcified spirit of vitriol, or perhaps with the favour of ether (for the author expresses himself a little ambiguously), the full bottle stopp'd with a cork, tied over with bladder, and laid on its side; on standing for four to nitrous months, the greatest part of the spirit was found to acid, have escaped, and the salt was shot into hexangular prismatic crystals resembling nitre. It tasted strongly of the spirit, but had no other particular taste. Laid on a burning coal, it crackled, exploded with a bright flash, and flew into the air. He afterwards found, that by adding to the spirit a drop or two of any acid, the salt crystallizes the sooner; that in this case it has a sourish taste, but in other respects is the same with that made without acid. This salt-petre (says the author) promises, from the violence of its explosion, to make the strongest gun-powder in the world, but a very dear one. Though the experiment should not be applicable to any use in this way, it will probably contribute to illustrate the generation of nitre: as it palpably shows nitre, that is, the acid or characteristic part of nitre, produced from the vitriolic acid and phlogiston."

We cannot here help again regretting that chemists of superior abilities should sometimes leave very important discoveries, only half finished, so that chemists of an inferior rank know not what to make of them. Had Wallerius, Wallerius, who seems more than once to have been in possession of this salt, only poured on it a few drops of oil of vitriol, the peculiar colour and smell of the fumes must have been a much more convincing proof of the reality of the transmutation than that of mere declamation; because the latter can be otherwise accounted for.

It is certain, that many substances, water itself not excepted, will explode with great violence if suddenly heated beyond what they are able to bear. If spirit of wine is confined in a close vessel, it will also by means of heat burst it as effectually as water; and as the vapours of this substance are inflammable, the explosion will be attended with a flash if any flame is near. In like manner ether, on the approach of a candle, takes fire, and goes off in a flash like lightning; but this happens, not from anything nitrous, but from its great volatility and inflammability. If therefore the vapours of the ethereal liquor are confined, and heat is applied suddenly to the containing vessel, their great volatility will cause them make an instantaneous effort against the sides of it, which increasing with a swiftness far beyond that of aqueous or spiritious vapours, will make a much quicker as well as a much stronger explosion than either of them; and if a flaming substance is near, the explosion will be attended with a bright flash like that of the ether itself.

In the experiment now before us, the salt tasted strongly of the spirit, or ether, from which it was made. The spirit was therefore confined in the crystals of salt; and his volatile liquor, which, even under the pressure of the atmosphere, boils with the heat of 100° Fahrenheit, was, in a confined state, subjected to the heat of a burning coal; that is, to more than ten times the degree of heat necessary to convert it into vapour. The consequence of this could be no other, than that the particles of salt, or perhaps the air itself, not being capable of giving way soon enough to the forcible expansion of the ether, a violent explosion would happen, and the salt be thrown about; which accordingly came to pass, and might very reasonably be expected, without anything nitrous contained in the salt.

Mr. Cavallo describes an easy and expeditious method of purifying ether, though a very expensive one; as out of a pound of the common kind scarce three or four ounces will remain of that which is purified. The method of purifying it, he says, was communicated to him by Mr. Winch chemist in London, and is to be performed in the following manner. "Fill about a quarter of a strong bottle with common ether, and pour upon it twice as much water; then stop the bottle and give it a shake, so as to mix the ether for some time with the water. This done, keep the bottle for some time without motion, and the mouth of it downwards, till the ether be separated from the water, and swims above it; which it will do in three or four minutes. Then opening the bottle with the mouth still inverted, let the greatest part of the water run out very gently; after this, turn the bottle with the mouth upwards; pour more water upon the ether, shaking and separating the water as before. Repeat this operation three or four times; after which the ether will be exceedingly pure, and capable of dissolving elastic gum, though it could not do so before."

As great part of the ether undoubtedly remains nitrous mixed with the water after this process, our author remarks, that it might be worth while to put the water into a retort and distil the ether from it, which will come sufficiently pure for common use. He observes also, that "it is commonly believed that water combines with the purest part of the ether when the two fluids are kept together; though the contrary seems to be established by this process. According to Mr. Waferumb, we may obtain from the residuum of vitriolic ether a resin containing vitriolic acid, vinegar, Glauber's salt, selenite, calcareous earth, silicium, iron, and phosphoric acid.

§ 2. Of the Nitrous Acid and its Combinations.

This acid is far from being so plentiful as the vitriolic. It has been thought to exist in the air; and the experiments of Mr. Cavendish have shown, that it may be artificially composed, by taking the electric spark in a mixture of dephlogisticated and phlogisticated air. See Astrology, n° 77.

With regard to the preparation of nitre, Dr. Black ob-Of the preserves, that it is made in great plenty in the more northern parts of Europe; likewise in the southern parts of nitre, Persia, in China, the East Indies, and in North America. We have had no accounts of the manner in which it is prepared in the East Indies, nor person on the spot having taken particular notice of the manufacture. The general account is, that it is obtained from the soil of certain districts which are called saltpetre grounds; where the soil is very cold, barren, and unhealthy. The salt is there ready formed by nature. It is only necessary to gather large quantities of the earth, and to put it into a cavity through which a great quantity of water is poured, which dissolves the nitre; and the lixivium runs into an adjacent pit, out of which it is lifted in order to be evaporated and obtained in the form of crystals. This account, however, has been thought unsatisfactory; because there is hardly any part of Europe in which it is found in this manner. It is discovered indeed in some very large districts in Poland, particularly in Podolia, where in some country is flat and fertile, and had been once very populous, but is now in a great measure deserted. It is there obtained from tumuli or hillocks, which are the remains of former habitations; but these are the only places in which it is found in any considerable quantity. In Spain, it is said that the inhabitants extract it from the soil after a crop of corn. It has been found in America in lime-stone grounds, in the floors of pigeon-houses, tobacco-houses, or the ruins of old stables, where a number of putrefying vegetables were once collected. In general, however, it is extracted from artificial compounds or accidental mixtures, where animal and vegetable substances have been fully putrefied by being exposed to the air with any spongey or loose earth, especially of the calcareous kind, and open to the north or north-east wind, and more or less covered from the heat or rains. This last particular is for its formation absolutely necessary to its formation in any quantity; nation, for the heat, by evaporating the moisture too much, prevents it from being produced, and the rains wash it away after it is already made. Cramer, an author of compendious credit, informs us in his Docimastics, that for making be made a little hut exposed to the fresh air of the nitre, country. Nitrous Acid and its Combinations.

Country, with windows to admit the winds. In this he put a mixture of garden mold, the rubbish of lime, and putrid animal and vegetable substances. This he frequently moistened with urine; and in a month or two found his composition very rich in nitre, yielding at least one-eighth part of its weight.

It is manufactured in Europe by making artificial compounds with less trouble. In Hanover it is got by collecting the raking of the streets; which are built up into mud-walls that are allowed to remain a certain time, when the surface is found covered with a white saline efflorescence. A person is employed to scrape this off; and putting it into a vessel, it is washed with water to dissolve the nitre, and the remaining earthy matter is again plastered on the mud-walls, and fresh matter brought from the streets to renew them occasionally; and by this simple method a considerable quantity is obtained. In Germany the peasants are directed by law to build mud-walls of this kind with the dung and urine of animals, and some straw. After they have stood for some time, and the vegetable and animal substances are rotten, they afford a considerable quantity of nitre. In France it is obtained from accidental collections of this kind; as where loose earth has been long exposed to the contact of animal substances, as the ruins of old stables, pigeon-houses, &c. Sometimes from the mould upon the ground where dunghills have been lying. A particular set of people go about in search of these materials; and when, by making a small essay, they find that they will turn to account, they put the materials into a large tub with a perforated bottom, and another which is water-proof put below it. Some straw is interposed betwixt the two; and on pouring water upon the materials, it soaks through them, undergoes a kind of filtration in passing through the straw, and is then drawn off by a cock placed in the under-tub, and boiled to a proper consistence for crystallization. The crystals are at first brown and very impure, but by repeated dissolution and crystallization become pure and white.

From these particulars relating to the history of saltpetre, Dr Black concludes, that it is not properly a fossil, being produced at the surface of the ground. Mmgraeef discovered a small quantity of it in the analysis of some of the waters about Berlin, and others have found it in the wells about some great cities; but no true nitre has ever been found in springs; so that this nitrous salt may be supposed to have derived its origin from the quantity of putrid matters with which all cities abound. All rich and fertile soils are found to contain it; and in the hot countries, where the products of nature are numerous, and putrefaction carried on very fast, they are often very rich in nitre. This may happen in some places from the confluence of waters; which remaining for some time on the surface, and afterwards exhaling, left the saline particles behind.

On the whole, Dr Black concludes, that neither nitre nor its acid does exist in the air, because it might easily be detected there; though many have embraced this opinion from its being usually found at the surface of the ground. He is of opinion, that it is the effect of the last stage of putrefaction of animal and vegetable substances; and it is never to be found except where these or their effluvia are present, and never till the putrefaction is complete. It has been a matter of dispute, whether it existed in those matters before the process of putrefaction, or was produced by it. But it is pretty certain, says the Doctor, that it originated in them; for the sunflower, tobacco, and other plants, are found to contain it before putrefaction; and some have even affirmed, that plants placed in the earth, deprived of all its saline substances, will yield it. The compositions recommended by Cramer are the fittest for producing a complete degree of putrefaction, provided they contain a moderate degree of humidity, and that the quantity exposed to the air be defended from too great a heat by the sun, which would dry up its moisture; and likewise from too great a degree of cold, which likewise checks fermentation. The importance of the calcareous earth in such a composition would likewise favour the conclusions just now drawn; for the most remarkable effect of this earth is to promote and perfect the putrefaction of these substances. It would seem, therefore, that the true secret of the production of nitre is to mix properly together animal and vegetable substances with earth, particularly of the calcareous kind; exposing them to the air with a moderate degree of humidity, sufficient to promote their putrefaction in the most effectual manner; and when the putrefaction is carried to the utmost height, we may then expect that nitre will be produced.

The distinguishing characteristic of the nitrous acid Difficult is its great disposition to unite with the phlogiston; and, when so united, first to become exceedingly volatile, and at last to be dissipated in a very white bright nitrous flame: this is called its detonation or deflagration. In the fluid state in which this acid is procurable in a liquid form, it is of a reddish yellow colour, and continually exhales in dense, red, and very noxious fumes; and in this state is called smoking, or, from its inventor, Glauert's spirit of nitre.

I. To extract the Nitrous Acid by means of the Vitriolic.

Into a glass retort put two pounds of good salt-spirit of petre, and pour upon it 18 ounces of concentrated oil nitre of vitriol; let the retort in a fand heat, and late on a large receiver with the composition already recommended, for resisting acid fumes; the mixture will grow very warm, and the retort and receiver will be filled with red vapours. A small fire is then to be kindled, and cautiously raised till no more drops will fall from the nose of the retort. What comes over will be a very strong and smoking spirit of nitre.

In this process, the nitrous acid is generally mixed with part of the vitriolic which comes over along with it, and from which it must be freed if designed for nice purposes. This is most effectually done by dissolving in it a small quantity of nitre, and redistilling the mixture. The vitriolic acid which came over in the first distillation is kept back by the nitre in the second, combining with its alkaline basis, and expelling a proportionable quantity of the nitrous acid.

We have here directed the pure vitriolic acid to be different used, in order to expel the nitrous one; but for this purpose any combination of the vitriolic acid with a chilling-metallic or earthy basis may be used, though not with equal advantage. If calcined vitriol is made use of, Nitrous Acid and its Combinations.

As much phlogiston is communicated by the calx of iron contained in that salt as makes the nitrous acid exceedingly volatile, so that great part of it is lost. If calcined alum, or selenite, is made use of, the vitriolic acid in these substances immediately leaves the earth with which it was combined, in order to unite with the alkaline basis of the nitre, and expels its acid; but the moment the nitrous acid is expelled from the alkali, it combines with the earth which the vitriolic acid had left; from which it cannot be driven without a violent fire; and part of it remains obstinately fixed, so as not to be expelled by any degree of heat. Hence the produce of spirit, when nitre is distilled with such substances, always turns out considerably less than when the pure vitriolic acid is used. Alum is preferable to selenite, for the purpose of distilling spirit of nitre; because the acid does not adhere so strongly to argillaceous as to calcareous earth.

According to Weigle, the nitrous acid may be expelled not only by clay, gypsum, and other substances containing the vitriolic acid, but even by various kinds of vitrifiable earth. Clean pebbles, quartz in the form of sand, pieces of broken china and stone ware, powdered glass, &c., mixed with nitre in the proportion of six to one, always expel the acid, though imperfectly. In France the acid is always extracted by means of clay.

The reason of these decompositions is, that the alkaline basis of the nitre attracts the siliceous earth, whose fixedness in a vehement fire gives it an advantage over the volatile nitrous acid, in the same manner that the weak acid of phosphorus or arsenic will also expel it by reason of their fixedness in the fire.

Even spirit of salt, according to Margraaff's experiments, may be used for distilling the spirit of nitre. That celebrated chemist informs us, that on distilling nitre with eight or nine times its quantity of strong marine acid, a spirit comes over which consists chiefly of the nitrous acid, but has also some portion of that of sea-salt. The reason of this is shown in Mr Kirwan's experiments on chemical attractions*. In the present case, however, the decomposition may be facilitated by the strong attraction of the nitrous acid for phlogiston; for it is well known, that on mixing the nitrous and marine acids together, the latter is always dephlogisticated. It seems therefore that in this case a double decomposition takes place, the nitrous acid uniting itself to the phlogiston of the marine, and the latter attaching itself to the alkali of the nitre.

Spirit of nitre is very useful in the arts of dyeing and refining, where it is known by the name of aqua fortis; and therefore an easy and cheap method of procuring it is a valuable piece of knowledge. Many difficulties, however, occur in this process, as well as that for the vitriolic acid. Oil of vitriol, indeed, always expels the nitrous acid with certainty; and on distilling the mixture, a spirit of nitre arises; but if a glass retort is used for the purpose of distilling this acid, the quantity of residuum left in distillation is so great, and so insoluble in water, being no other than vitriolated tartar, that the retort must always be broken in order to get it out; and the produce of spirit will scarce afford the breaking a retort. If earthen retorts are made use of, they must certainly be of that kind called stone-ware, and the price of them will be very little if at all inferior to that of glass. Iron pots Nitrous are said to be made use of in the distillation of common acid and its aquafortis in large quantities; but they have the great inconvenience of making a quantity of the acid too volatile, that it not only will not condense, but spreads its suffocating vapours all around in such a manner as to prove very dangerous to those who are near it. If an iron vessel, therefore, is thought of for the purpose of distilling aquafortis, it will be proper at least to attempt luting over the inside with a mixture of gypseous earth and sand, to prevent as much as possible the acid from attacking the metal.

Dephlogisticated spirit of nitre is obtained by distilling the smoking kind with a gentle heat, until what remains is as colourless as water. It is distinguished by emitting white and not red fumes like the other kind, when set in a warm place. It must be kept constantly in the dark, otherwise it will again become phlogisticated, and emit red vapours by the action of the light; the same thing will also take place if it be heated with too violent a fire.

II. To procure the Nitrous Acid by means of Arsenic.

Pulverise equal quantities of dried nitre and white blue aqua-crytalline arsenic; mix them well together, and distil tortis. In a glass retort with a fire very cautiously applied; for the arsenic acts on the nitre with such a violence, and the fumes are here so volatile, that unless great care is taken, a most dangerous explosion will almost certainly happen. As, in this case, the nitrous fumes arise in a perfectly dry state, some water must be put into the receiver, with which they may unite and condense. The aquafortis so produced will have a blue colour, owing to the inflammable principle separated from the arsenic, by which its extreme volatility is likewise occasioned. If this blue aquafortis is exposed to the air, its colour soon flies off. If instead of the white arsenic we employ the pure arsenic acid, the distilled liquor will have no blue colour.

Nitrous Acid combined,

I. With Vegetable fixed Alkali. This salt, combined with the nitrous acid to the point of saturation, regenerates nitre. It is observable, however, according to Neumann, that there is always some dissimilarity between the original and regenerated nitre, unless quicklime is added. The regenerated salt, he says, always corrodes tin, which the original nitre does not; owing probably to a quantity of phlogisticated acid remaining in it. Boiling with quicklime deprives it of this quality, and makes it exactly the same with original nitre.

II. With Fossil alkali. The neutral salt arising from a combination of the nitrous acid and fossil alkali is somewhat different from common nitre; being more difficult to crystallize, inclining to deliquesce in the air, and shooting into crystals of a cubical form, whence it gets the name of cubic nitre. Its qualities are found somewhat inferior to the common nitre; and therefore it is never made, unless by accident, or for experiments.

Nitre is one of the most fusible salts. It is liquefied fusibility, in a heat much less than what is necessary to make it red; and thus remain in tranquil fusion, without swelling. If nitre thus melted be left to cool and fix, whe- whether it has been made red hot or not in the fusion, it coagulates into a white, semi-transparent, solid mass called mineral crystal, having all the properties of nitre itself. By this fusion, Mr Beaume observes that nitre loses very little, if any, of the water contained in its crystals, since the weight of mineral crystal is nearly the same with that of the nitre employed.

When nitre is kept in fusion with a moderate heat, and at the same time does not touch any inflammable matter, nor even flame, it remains in that state without suffering any very sensible alteration; but if it is long kept in fusion with a strong fire, part of the acid is destroyed by the phlogiston which penetrates the crucible; and hence the nitre becomes more and more alkaline.

Nitre is of very extensive use in different arts; being the principal ingredient in gunpowder; and serving as an excellent flux to other matters; whence its use in glass making. (See Glass.) It is also possessed of a considerable antiseptic power; whence its use in preserving meat, to which it communicates a red colour. In medicine, nitre is used as a diuretic, sedative, and cooler; but very often fits uneasy on the stomach. The resemblance of the crystals of nitre to those of Glauber's salt has sometimes been the occasion of dangerous mistakes. Dr Alexander mentions a swelling over the whole body of a woman, occasioned by her taking a solution of nitre instead of Glauber's salt. Two mistakes of the same kind we have also known. In one an ounce, and in the other upwards of two ounces, of nitre were swallowed. The symptoms occasioned were universal coldness and shivering, extreme debility and sickness at stomach, cold sweats, and faintings. Neither of the cases proved mortal. The cure was effected by cordials and corroborants.

A process has obtained a place in the distillatories for a supposed purification of nitre by means of flower of brimstone. A pound of saltpetre is to be melted in a crucible, or small iron vessel; and an ounce of flowers of sulphur thrown upon it, by small quantities at a time: a violent deflagration ensues on each addition; and after the whole is put in, the salt is poured out in moulds, and then called sal prunella. It has been disputed whether the nitre was at all depurated by this process; Dr Lewis thinks it is not. From our own experience, however, we can affirm, that by this means a sediment falls to the bottom, which carries with it any impurities that may have been in the nitre, and leaves the fluid salt clear and transparent as water. This precipitate is probably no other than a vitriolated tartar formed by the union of the sulphurous acid and alkali of the nitre, which being less fusible than the nitre, sublimes in a solid form and clarifies it.

III. With Volatile Alkali. The nitrous acid seems peculiarly adapted to an union with volatile alkali; saturating as much, or rather more of it than the strongest vitriolic acid is capable of doing. The product is a very beautiful salt, called volatile nitre, or nitrous sal ammoniac. It very readily dissolves, not only in water, but in spirit of wine, which distinguishes it from the vitriolic and common kind of sal ammoniac. It also requires less heat for its sublimation: indeed care must be taken not to apply too great a heat for this purpose, as the nitrous sal ammoniac has the property of degrading by itself without any addition of inflammable matter; and this it does more or less readily, as the volatile alkali with which it was made was more or less impure and oily.

The medical virtues of this kind of nitre have not been inquired into. It seems to have made the principal ingredient in the famous Dr Ward's white drop, which was celebrated as an antifebrifuge; with what justice, those who have tried it must determine.

IV. With Calcareous Earths. These the nitrous acid decomposes into a transparent colourless liquor; but for this purpose it must be very much diluted, or the solution will have a gelatinous consistence. This compound is not applicable to any useful purpose. It has a very acrid taste; and, if inspissated, attracts moisture from the air. If it is totally dried, it then resembles an earthy matter, which deflagrates very weakly. By distillation in a retort, almost all the acid may be expelled, and what little remains flies off in an open fire.

Mr Pott, who has particularly examined the combination of nitrous acid with quicklime, says that the decomposition suffered remarkable alterations by distillation from quicklime, and repeated cohabitations upon it. By these experiments he obtained a salt more sensibly susceptible of crystallization and detonation, than what can be obtained by a single combination. From his experiments it would seem, that nitrous acid, by this treatment with quicklime, was capable of being entirely decomposed.

If a solution of chalk in the nitrous acid be evaporated to dryness, and then gently calcined, it acquires the property of shining in the dark, after having been exposed to the sun's rays, or even to the light of a candle. This substance, from its inventor, is called phosphorus; or, from its being necessary to keep it in a glass hermetically sealed, phosphorus hermeticus. (See Earths.)

V. With Argillaceous Earths and Magnesia. All that is known concerning the combinations of nitrous acid with these earths is, that the first produce astringent, and the second purgative, compounds, similar to alum and Epsom salt, and which are not susceptible of crystallization.

VI. With Gold.—Till very lately, it has been the opinion of chemists, that the nitrous acid by itself was incapable of acting upon this metal.—Dr Brandt, however, produced before the Swedish academy of sciences, a solution of gold in the nitrous acid, obtained in parting, by that acid, a mixture of gold and silver. The mixed metal was boiled with aquafortis in a glass body fitted with a head and receiver, the liquor poured off, and the coction repeated with fresh parcels of stronger and stronger nitrous spirits, till all the silver was judged to be extracted. The last parcel was boiled down till the matter at the bottom looked like a dry salt; on boiling this in fresh aquafortis in close vessels, as before, a part of the gold was dissolved, and the liquor tinged yellow. But though gold is by this means truly soluble in the nitrous acid, the union is extremely slight; the gold being not only precipitated on the addition of silver, but likewise spontaneously on exposure to the air.—Dr Lewis very justly observes, that this solution may have been often made unknown. unknown to the chemists who did so; and probably occasioned the mistakes which some have fallen into, who thought that they were in possession of aquafortis capable of transmuting silver into gold. Notwithstanding these authorities, Mr Kirwan is of opinion that the nitrous acid is in no case able to dissolve gold; the metal being only intimately mixed or diffused through it.

II. With Silver.—Pure spirit of nitre will dissolve its own weight of silver; and floats with it into fine white crystals of a triangular form, consisting of very thin plates joined closely one upon another. These crystals are somewhat deliquescent; of an extremely bitter, pungent, and nauseous taste; and, if taken internally, are highly corrosive and poisonous. They melt in a small heat, and form, on cooling, a dark-coloured mass still more corrosive, called lunar caustic or lapsis infernalis. They readily dissolve in water; and, by the assiduity of warmth, in spirit of wine. In the Acta Naturae Curiosorum, tom. vi. there is a remarkable history of silver being volatilized by its combination with the nitrous acid. Four ounces of silver being dissolved in aquafortis, and the solution set to distil in an earthen retort, a white transparent butter arose into the neck, and nothing remaining behind; by degrees the butter liquefied, and palled down into the phlegm in the receiver. The whole being now poured back into the retort, the silver arose again along with the acid. The volatilization being attributed to the liquor having stood in a laboratory where charcoal was bringing in, the experiment was repeated with a fresh solution of silver, and a little powdered charcoal, with the same event.

Solution of silver in the nitrous acid stains hair, bones, and other solid parts of animals, and different kinds of wood, of all the intermediate shades from a light brown to a deep and lasting black. The liquors commonly used for staining hair brown or black, are no other than solutions of silver in aquafortis, so far diluted in water as not sensibly to corrode the hair.

It gives a permanent stain likewise to sundry stones; not only to those of the softer kind, as marble, but to some of considerable hardness, as agates and jaspers. The solution for this purpose should be fully saturated with the metal; and the stone, after the liquor has been applied, exposed for some time to the sun. M. du Fay observes (in a paper on this subject in the French memoirs for 1728), that if the solution be repeatedly applied, it will penetrate in the whitest agate, or chalcedony, about one-twelfth of an inch; that the tincture does not prove uniform, on account of the veins in the stone; that the colours, thus communicated by art, are readily distinguishable from the natural, by disappearing on laying the stone for a night in aquafortis: that, on exposing it to the sun afterwards for some days, the colour returns; that the solution gave somewhat different tinctures to different stones; to oriental agate, a deeper black than to the common chalcedony; to an agate spotted with yellow, a purple; to the jade stone, a pale brownish; to the common emerald, an opaque black; to common granite, a violet unequally deep; to serpentine stone, an olive; to marble, a reddish, which changed to purple, and fixed in a brown; that on slates, talcs, and amianthus, it had no effect.

Vol. IV. Part II.

If a solution of silver be diluted with pure water, a considerable quantity of pure mercury added, and the whole set by in a cold place; there will form by degrees a precipitation and crystallization resembling a little tree, with its root, trunk, and branches, called Arbor Diane or the philosophic silver tree. Another kind of artificial vegetation may be produced by spreading a few drops of solution of silver upon a glass plate, and placing in the middle a small bit of any of the metals that precipitate silver, particularly iron. The silver quickly concretizes into curious ramifications all over the plate.

Like other metallic solutions, this combination of Solution of nitrous acid with silver is decomposed by fixed and silver volatile alkalies, calcareous earths, and several metals, composed, (see the Table of Affinities;) but with several peculiar circumstances attending the precipitation. With metals, the silver is readily and copiously thrown down at first, but slowly and difficultly towards the end. The menstruum generally retains some portion of the silver, as the silver almost always does of the metal which precipitated it. For recovering the silver from aquafortis after parting, the refiners employ copper. The solution, diluted with water, is put into a copper vessel, or into a glass one with thin plates of copper, and set in a gentle warmth. The silver begins immediately to separate from the liquor in form of fine grey scales, or powder; a part of the copper being dissolved in its place, so as to tinge the fluid more or less of a bluish green colour. The plates are now and then shaken, that such part of the silver as is deposited upon them may fall off, and settle to the bottom. The digestion is continued till a fresh bright plate, kept for some time in the warm liquor, is no longer observed to contract any powdery matter on the surface; when the liquor is poured off, and the precipitate washed with fresh parcels of boiling water. It is observable, that though the acid in this process saturates itself with the copper, in proportion as it lets go the silver, yet the quantity of copper which it takes up is not near so great as that of silver which it deposits. One drachm of copper will precipitate three of silver, and saturate all the acid that held the three drachms dissolved.

Calcareous earths, as chalk or quicklime, throw down a part of the silver, but leave a very considerable part suspended in the liquor. If the earth be moistened with the solution into the confluence of a glass paste, and exposed to the sun, it changes its white by means of a dark purple black; distinct characters of the sun's may be exhibited on the matter, by intercepting a part of the sun's light by threads, slit paper, &c., placed on the outside of the glass. Culinary fire does not affect its colour: after the mass has been excrated by this, it changes as before, on exposure to the sun.

Mild volatile alkaline spirits, added to a solution of silver, precipitate but little, and caustic volatile alkalies none. Pure fixed alkalies, and alkalies rendered caustic by quicklime, throw down the whole. Fixed alkalies inpregnated with inflammable matter by calcination with animal coals, occasion at first a considerable precipitation; but if added to a larger quantity, take up great part of the metal again. Mr Margraff relates, that edulcorated calces of silver totally dissolve, both in a lixivium of these alkalies and in vo- Nitrous Acid and its Combinations.

latile spirits; and that the marine acid precipitates the silver from the volatile, but not from the fixed, alkaline solution. Kunckel reports, that the calx precipitated by volatile spirits made with quicklime, fulminates or explodes in the fire; and that by infusillating a solution of pure silver, melting the dry residuum, pouring it on spirit of urine super saturated with salt, and setting the mixture in a gentle warmth, a blood-red mass is produced, so tough as to admit of being wound about the fingers.

III. With Copper. The nitrous acid very readily dissolves this metal into a green-coloured and very caustic liquor. The solution, if properly evaporated, will crystallize; but the crystals are deliquescent, and therefore difficult to be preserved. The only use of this combination is for the preparation of the pigment called verditer. Of this there are two kinds, the blue and green. The blue is by far the brightest colour, and consequently the most valuable. It has been said that this is obtained by precipitating a solution of copper by any calcareous earth; and therefore is sold by the refiners, who have large quantities of solution of copper accidentally made. The solution is said to be precipitated by chalk, or whiting; and that the precipitate is the beautiful blue colour called verditer. By this method, however, only the green kind can be obtained. The blue we have found to be of a quite different nature, and formed by precipitation with a gentle heat from a solution of copper in volatile alkali. See the article Colour-making.

IV. With Iron. On this metal the concentrated nitrous acid acts very violently, and plentifullly corrodes, but does not dissolve it; the calx falling almost as fast as dissolved; and when it is once let fall, fresh acid will not take it up again. If the acid was diluted at first, it takes up a considerable proportion, provided the metal be leisurely added. If the solution is performed with extreme slowness, the colour will be green; but if otherwise, of a dark red. It does not crystallize; and, if infusillated to dryness, deliquesces in the air.

V. With Tin. Concentrated nitrous acid acts upon tin with great force, but only corrodes the metal into a white indissoluble mass. In order to obtain a perfect solution of tin in the nitrous acid, the metal must be put in by very little at a time, and a diluted aquafortis made use of. This solution has been considerably used in dyeing, and is remarkable for heightening red colours of all kinds; but the solution made with aqua-regia is preferable.

VI. With Lead. Proof aquafortis, lowered with an equal quantity of water, dissolves about half its weight of lead. On diluting the solution with a large quantity of water, it turns milky, and deposits great part of the metal. The solution shoots, upon exhaling part of the menstruum, into small pyramidal crystals with square bases, of an aulterie sweet taste.

In the memoirs of the French academy for 1733, there is a particular account of an experiment, in which mercury is said to have been extracted from lead by dissolving it in the nitrous acid. During the dissolution, there fell a precipitate, which is plainly proved to be mercury, and was looked upon to be one of the constituent parts of the lead separated by this simple process; it seems probable, however, that the mercury in this case had been contained in the aquafortis; for nitrous pure lead dissolved in pure aquafortis gives no such precipitate.

The crystals of lead in the nitrous acid, when thrown into the fire, do not deslagrate as other combinations of this acid with metallic or saline bases; but crackle violently, and fly around, with great danger to the bystanders. If they are rubbed into very fine powder, they may then be melted without any danger. By repeated dissolutions in fresh aquafortis, they at last form a thick fluid like oil, which cannot be dried without great difficulty. This composition is not adapted to any particular use, and is a violent poison.

VII. With Quicksilver. Aquafortis, of such a degree quickfill of strength as to take up half its weight of silver, dissolves with ease above equal its weight of mercury into a limpid liquor, intensely corrosive and poisonous, which spontaneously flows into white crystals. These crystals, or the solution effused, and moderately calcined, assume a sparkling red colour; and are used in medicine as an elixir, under the name of red precipitate. The precipitate has sometimes been given internally, it is said, in very large quantities; even a whole drachm at one dose. But this would seem incredible; and the present practice does not countenance the taking of red precipitate inwardly. This solution seems to have been what gave the efficacy to Ward's white drop.

When red precipitate is prepared in quantity, it is proper to distil the mercurial solution; because most of the aquafortis may then be saved. It is exceedingly pure, if by purity we mean its being free of any admixture of vitriolic or marine acid; but is considerably tainted with the inflammable principle of the mercury extricated during the dissolution. In consequence of this, it is very volatile and smoking; which has generally, though improperly, been taken as a sign of strength in the nitrous acid.

VIII. With Bismuth. This semimetal is very readily acted upon by the nitrous acid. Proof aquafortis dissolves about half its weight of bismuth. If the metal was hastily added, the solution proves of a greenish colour; if otherwise, it is colourless and transparent. Unless the acid was diluted with about an equal quantity of water, a part of the bismuth crystallizes almost as fast as it dissolves. The metal is totally precipitated both by fixed and volatile alkalies. The last, added in greater quantities than are sufficient for precipitation, take it up again. The liquor generally appears greenish; by alternate additions of the alkaline spirit and solution, it becomes bluish or purple. Fixed alkalies calcined with inflammable matter likewise dissolve the bismuth after they have precipitated it.

The only use of this compound is for the precipitate, which is used as a cosmetic, under the name of bismuth magnesia. The common way of preparing this is by diluting the solution very largely with water, upon which it turns milky, and a fine white precipitate falls, which is to be well edulcorated with water, and is then employed as a cosmetic both in washes and pomatums.

Concerning the preparation of this cosmetic, Neumann observes, that there are foundry variations.—"Some (says he) take aqua-regia for the menstruum; and for the precipitant a solution of sea-salt, alkalies, spirit of wine, &c. Some mix with the solution of bismuth a solution of benzoin in spirit of wine, and thus obtain a magifery compounded of bismuth and benzoin. Others add a solution of chalk to the metallic solution, and precipitate both together by alkalies. I have made trial with a good number of different precipitants; and found, that with common fixed alkali and caustic alkali, with watery and vinous alkaline spirits, the magifery was white, and in considerable quantity; the liquor, after the precipitation with volatile spirits, appearing blue. That oil of vitriol threw down a white precipitate very copiously; but that with spirit of salt, or spirit of vitriol, the precipitate was in very small quantity, in colour like the foregoing; distilled vinegar making no precipitation at all. Common rectified spirit of wine, and tartrated spirit, common water, and lime-water, gave white precipitates. Solutions of nitre, vitriolated tartar, sal mirabile, alum, borax, common salt, sal ammoniac, the combination of marine acid with calcareous earth, and terra foliata tartari, all precipitated the bismuth white. With a solution of gold in aqua-regia the magifery proved grey; with a solution of the same metal in aqua-regia made with spirit of salt, the precipitate was likewise grey, and in small quantity; with solution of copper in aquafortis, white, and in very small quantity, the liquor continuing blue; with solution of vitriol of copper, white; with solution of mercury sublimate, white and plentiful; with solution of iron in aquafortis, yellowish; with solution of lead in aquafortis, and of sugar of lead, white; with solution of zinc in aquafortis there was little precipitate; and with solutions of silver, tin, regulus of antimony, and of mercury, in the same acid, none at all.

IX. With Zinc. Upon this semimetal the nitrous acid acts with greater violence than any other, and will forfeit any other metallic substance for it. The whole is very soon dissolved into a transparent colourless liquor. The calces of flowers of zinc are likewise soluble in the nitrous acid; but neither the solution of the flowers, nor of the metal itself, has been yet found applicable to any useful purpose. Neumann remarks, that on extracting with nitrous acid the soluble parts of calamine, which is an ore of zinc, the solution, infusoriated to dryness, left a reddish brown mass, which on digestion with spirit of wine exploded and burst the vessel.

X. With Regulus of Antimony. The nitrous acid rather corrodes than dissolves this semimetal. The corroded powder forms a medicine formerly used under the name of bezoar mineral, but now disfavored.

XI. With Regulus of Cobalt. This semimetal dissolves readily in the nitrous acid, both in its metallic form and when reduced to a calx. The solution is of a red colour. Hence the nitrous acid furnishes means of discovering this semimetal in ores after strong calcination; very few other calces being soluble in the nitrous acid, and those that are not influencing the colour.

XII. With Nickel. This semimetal is easily dissolved by the nitrous acid into a deep green liquor; but neither this solution, nor indeed the semimetal of which it is made, has hitherto been found of any use.

XIII. With Arsenic. This substance is readily dissolved by the nitrous acid; which abstracts the phlogiston, and leaves the pure arsenical acid behind. See below Nitrous Acid and its Combinations.

Acid of Arsenic.

XIV. With Exprefled Oils. These, as well as all other fatty or unctuous substances, are considerably thickened and hardened by their union with the nitrous acid. There is only one preparation where this combination is applied to any use. It is the Unguentum citrinum of the shops. This is made by adding to some quantity of melted hog's-lard a solution of quicksilver in the nitrous acid. The acid, though in a diluted state, and combined with mercury, nevertheless acts with such force on the lard, as to render the ointment almost of the consistence of tallow.

XV. With Vinous Spirits. If highly rectified spirit of wine and strong spirit of nitre are suddenly mixed to wine together, the acid instantly becomes volatile, and is diffused with great heat and effervescence in highly noxious red fumes. If the acid is cautiously poured into the spirit, in the proportion of five, fix, or even ten parts of spirit to one of acid, and the mixture distilled in a glass retort set in a water-bath, an exceedingly fragrant and volatile spirit comes over, used in medicine as a diuretic and cooler, under the name of Spiritus nitri dulcis. This liquor is not acid; nor has Spiritus nitre dulcis what remains in the retort any more the characteristics of nitrous acid, which seems to be entirely decomposed in this process. (See the following article.)

With the nitrous acid and spirit of wine, may also Nitrous ether be made an exceedingly volatile liquor, called nitrous ether, to distinguish it from the vitriolic above mentioned. The proportions of nitrous acid and spirit of wine to each other for nitrous ether, are two of the acid by weight to three of the spirit. Dr Black's process for making it is as follows. Take four ounces of strong phlogisticated nitrous acid; and having cooled it by putting it into a mixture of salt and snow, or into water cooled very near the freezing point, by putting pieces of ice into it, he puts it into a phial, and pours upon it an equal quantity of water, likewise cooled very low, in such a manner that the water may float as much as possible on the surface of the spirit. Six ounces of strong spirit of wine are then put in, so as to float in like manner on the surface of the water; the phial is placed in a vessel containing cold water; and so great is the power of cold in restraining the action of bodies, that if the mixture was too cold, no ether would be produced; but at the temperature just mentioned, the ether begins to be formed in a few hours, with some little effervescence, and an expulsion of a small quantity of nitrous air. We must provide for the escape of this elastic fluid, by having an hole in the cork, or the vessel would be broken. The whole of the ether will be formed in a few days, and may be separated from the rest of the liquor by means of a funnel, shaped as in the margin.

To procure the nitrous ether in large quantities, Woulfe's Mr Woulfe recommends the following process. Put procfs for into a retort four pounds of nitre, then mix together four pounds of vitriolic acid, and three pounds five ounces of spirit of wine. These are poured on the nitre by adding only two ounces at a time: the vitriolic acid acting on the nitre, produces a sufficient degree of heat; and the acid of the nitre uniting with the spirit, forms a nitrous ether, which flies off from the mixture, and is condensed in a number of vessels placed in cold water.—To obtain good nitrous ether readily, and at one distillation, Mr Dollfus advises to dilute four parts of nitre of manganese, four of vitriolic acid, and eight parts of spirit of wine.

Macquer supposes that ether is the most oily part or quintessence of spirit of wine. But it cannot be proved that ether contains any oil. And, besides, if this were the case, those acids which have the strongest attraction for water would produce the greatest quantity of ether; which is found not to be the case: and it is most probable that ether is produced by a combination of some part of the acid with a portion, particularly the inflammable part, of the spirit of wine; and it has been shown by chemical experiments, that every kind of ether contains a part of the acid employed. Dr Black himself has formed ether without any spirit at all, by exposing nitrous acid highly phlogisticated for some months to the light of the sun. This was owing to the attraction of the principle of inflammability; which it is well known that light has the power of affording to bodies that attract it with force.

Nitrous Acid decomposed,

I. By Essential Oils. If equal quantities of strong nitre, by spirit of nitrous acid and oil of cloves are poured into the same vessel, the mixture instantly takes fire; both acid and oil burning with great fury till only a light spongy coal remains. Dr Lewis observes, that this experiment does not always succeed, and that there are but few oils which can be fired with certainty, without attending to a particular circumstance first discovered by M. Rouelle, and communicated in the French Memoirs for the year 1747. "On letting fall into the oil equal its quantity of acid, the mixture effervesces, swells, and a light fungous coal arises; a little more of the acid poured upon this coal sets it instantly on fire. By this method almost all the distilled oils may be fired by spirit of nitre of moderate strength. Expressed oils also may be set on fire by a mixture of the nitrous acid and oil of vitriol; the use of which last seems to be to absorb the aqueous humidity of the spirit of nitre.

II. By Charcoal. By this substance the nitrous acid cannot be conveniently decomposed, unless it is combined with an alkaline or metallic base. For the purpose of decomposing the acid, common saltpetre is most convenient. The proportions recommended by Dr Lewis for alkaliating nitre, are four ounces of the salt to five drachms of powdered charcoal. If these are carefully mixed, and injected by little and little into a tubulated retort made red hot, and fitted with a large receiver and a number of adopters, a violent deflagration will ensue on every addition, attended with a great quantity of air, and some vapours which will circulate for some time, and then condense in the vessels. This liquor is called clystus of nitre. If sulphur is used instead of nitre, the clystus is of a different kind, consisting of a mixture of the nitrous and vitriolic acids. The residuum, when charcoal is used, is a very strong and pure alkali; with sulphur it is vitriolated tartar. To prevent the loss occasioned by the violent deflagration, when this operation is performed in open vessels, Dr Black recommends to have the materials somewhat moist.

III. By Vinous Spirits. In the process already mentioned for making spiritus nitri dulcis, a total decomposition of the acid seems to take place: for neither the acid nor dulcified spirit itself, nor the acid matter left in the retort, show any signs of deflagration with inflammable matters, which is the peculiar characteristic of nitrous acid.

Mr Pott has given an analysis of the oleaginous residue of the distillation. Distilled by a stronger fire, of spirits it gave over a yellow, acid, slightly empyreumatic spirit; which being saturated with fixed alkali, the analyzed liquor evaporated, and the dry neutral salt laid on burning coals, did not deflagrate. After this spirit a red empyreumatic oil; and in the bottom of the retort was left a shining black mass like pitch; which, burnt in a crucible, left a white fixed earth, convertible by a vehement fire into glaigs. Another parcel of the above residuum was evaporated to the consistence of pitch. In this state it gave a yellow tincture to spirit of wine, flamed vividly and quietly on burning coals, and at last swelled up like bitumen. Another portion was saturated with alkaline ley, with which it immediately effervesced, and then evaporated as the former. It gave, as before, a yellow colour to rectified spirit of wine, and a much deeper yellow to dulcified spirit of nitre; and in the fire discovered no footprint of detonation. M. Macquer supposes this acid to have been not the nitrous, but the acetic, which enters into the composition of the spirit of wine; and his conjecture is now confirmed by late experiments.

§ 3. Of the Marine Acid and its Combinations.

This acid is never, at least very rarely, found but in a state of saturation with the mineral alkali; in acid, which case it forms the common salt used in food. Almost the only exception to this is human urine, and perhaps that of some other animals; for there the marine acid is found saturated, not with the mineral, but the common vegetable, fixed alkali. From being found in such plenty in the waters of the ocean, it has the name of marine acid.

It is commonly thought that this acid is no other than the vitriolic, somehow or other disguised by the inflammable principle; to which some have added another, called by them a mercurial earth.

The reasons given for this supposition, however, are but very slight, consisting chiefly in the resemblance between the volatile vitriolic acid and the marine, both in the white colour of their vapours, and the vitriolic-like great volatility of both. As to the existence of that principle called a mercurial earth, it hath never been proved; and, till that time, can never be allowed to be an ingredient in the composition of any substance whatever. As we do not remember to have read of any experiments where the marine acid was directly produced from that of vitriol, we shall content ourselves with relating one very remarkable fact, which happened to fall under our own observation.

As vitriolated tartar, or Glauber's salt, when fused with charcoal-dust, is converted into an hepatic fulgurite, attempts have been made on this principle to separate the pure alkali from the residuum of Glauber's spirit of nitre and spirit of salt. In an attempt of this kind, which, by the bye, proved unsuccessful, as all others of the same kind must do, 30 or 40 pounds pounds of the mass for Glauber's salt were fused in a strong iron pot, with a sufficient quantity of common coal powdered and sifted. As the quantity of powdered coal was pretty large, the mass was thereby hindered from flowing into thin fusion; and, that the whole might be perfectly alkalisated, it was frequently stirred up with an iron ladle, and kept very intensely heated for some hours. The mass was now taken out by means of an iron ladle, and laid on a flat stone; and, as it was but half fluid, every ladleful concreted into a black irregular saline mass, which had the appearance of a cinder; but which, however, consisted of an heap sulphur mixed with some coal-dust. As there was a considerable quantity of this matter, and the ladlefuls were thrown at random above one another, it so happened, that between two or three of the pieces, a kind of chimney was formed, so that there being a small draught of air through the interstices, and the masses containing a quantity of coal-dust, the internal parts were in a state of ignition, while the external were quite cold. From these ignited places a white fume arose; which being collected on the colder masses, assumed the form of white flowers. These were found to be genuine sal ammoniac, composed of a volatile alkali and marine acid; both of which we have the greatest reason to think were produced at that very time, and that a double transmutation took place; namely, of the vitriolic acid into the marine, and of the fixed alkali into the volatile. Our reasons for being of this opinion are, 1. That the matter had been subjected to such an extreme and long continued heat, that, had any sal ammoniac been present in the mixture, it must have certainly been dissipated, as this salt always sublimes with a degree of heat below ignition. 2. Though the matter was taken out of the pot of a very intense red heat, so that the saline part was evidently melted, yet no ammoniacal fume issued from it at that time, nor till the masses had been for some time exposed to the air, and were become cool, excepting only those interstices where the air kept up a burning heat, by a small draught being formed from the situation of the saline masses. 3. In those ignited places, when cool, the fixed salt was entirely decomposed, neither alkaline salt, Glauber's salt, fixed alkali, nor sulphur remaining; but the whole was consumed to a kind of ferruginous ashes. We are therefore of opinion, that the marine acid and volatile alkali are, in some cases, mere creatures of the fire, and most commonly produced at the same time, from the slow combustion of mineral substances. Hence, where heaps of hot cinders are thrown out, small quantities of the true sal ammoniac are always formed, when the ignited ones happen to fall in such a manner as to occasion a small draught of air through them.

The marine acid, or spirit of salt, is weaker than either the vitriolic or nitrous; though Dr Priestley has observed, that, when concentrated to the utmost degree, in which state it was perfectly invisible and elastic as air, it was then able to separate the nitrous acid from an alkali. In some other cases, too, it appears not only stronger than the nitrous, but even than the vitriolic; of which we shall take notice in course.

—Mr Berthollet says, that he has been able also to procure the marine acid in a solid state, by distilling it in Mr Woulfe's apparatus, kept perfectly cool with ice.

The yellow colour of the marine acid is sometimes owing to iron, which may be precipitated from it by means of an alkali. In certain cases, however, it is observed to have a much darker and nearly a brown colour, without containing the smallest particle of this metal.—Mr Dollfus is of opinion, that the yellow colour of the marine acid is owing to a portion of dephlogisticated air which it generally contains. A pretty strong proof that it emits this kind of air indeed is, that a candle will burn longer in a bottle containing marine acid, than it will in an equal quantity of common air.

I. To procure the Marine Acid by means of the Vitriolic.

Put any quantity of sea-salt into a tubulated glass retort, to which a large receiver is firmly fitted, having a quantity of water in it, more or less as you want your spirit of salt to be more or less strong. Having placed your retort in a sand-bath, take of concentrated oil of vitriol half as much as you put salt into the retort. Through the aperture in the upper part of the retort, pour a small quantity of the vitriolic acid; a violent effervescence will immediately arise, and white vapours will ascend, and come over into the receiver. These vapours are the marine acid in its most concentrated state; and, as they are very greedy of moisture, they will unite with the water in a very short time, unless too much oil of vitriol is put in at once; in which case, part of them will be diffused through the small hole in the receiver. When you perceive the first fumes condensed, add a little more oil of vitriol, taking care to stop the aperture of the retort as soon as you drop in the vitriolic acid, that the marine acid may not escape. Continue this by intervals, till your acid is all put in; and then make a very gentle fire, that the retort may be no warmer than the hand can bear. This degree of heat must be continued a long time, otherwise very much of the acid will be lost. To perform this operation perfectly, no more acid should be forced over, than what the water in the receiver can take up; and by this means the operator's patience will be rewarded with a vastly larger produce of acid than can be procured by hasty distillation. When the vapours become a little more fixed, a greater heat is necessary, but nothing equal to what the nitrous acid requires. For distilling spirit of salt, Mr Wiegleb recommends four pounds of oil of vitriol to five of common salt.—It may also be obtained from the bittern remaining after the crystallization of common salt, by adding one pound of oil of vitriol to five of bittern. It may even be obtained from this liquid by simple distillation without any additional acid; but a violent fire will then be necessary, and it is almost impossible to prevent the liquor from swelling and running over the neck of the retort in the beginning of the process.

The marine acid cannot be procured by means of why distillations of the vitriolic acid with metallic and earthy bases, as the nitrous is; for though, by means of calcined vitriol, for instance, the marine acid is effectually expelled from its alkaline basis, yet it immediately combines with the calx of iron left by the vitriolic acid, and not only adheres obstinately, but even sublimes the metal; so that what little spirit can be obtained, is never pure. This inconvenience is not so great when uncalcined copperas is made use of; for the marine acid has a very strong attraction to water; which partly dissolves its union with the metallic calx. If gypsum is used, instead of calcined vitriol, not a drop of spirit will be obtained. Alum and sal catharticus amarus answer better.

II. To procure the Marine Acid by means of the Nitrous.

Take equal quantities of sea-salt and Glauber's spirit of nitre; put the salt into a retort, and pour on it the nitrous acid; let them stand for 10 or 12 hours; then distil with a gentle heat; an acid liquor will come over, which is a compound of the nitrous and marine acids, called aqua-regis. When the distillation is finished, and the vessels cooled, pour back the distilled liquor on the mass which is left on the retort, and distil again; the second produce will be more of the nature of spirit of sea-salt than the former. Continue to do this, pouring the distilled liquor either on the mass left in the retort, or upon fresh sea-salt, till you observe that no nitrous acid arises. No experiments have been made on this spirit of salt, by which we can judge whether it is different from that procured by the vitriolic acid or not.

III. To procure the Marine Acid, by distilling Salt per se.

Put into a retort any quantity of common salt which has not been dried, and distil in a sand heat till nothing more will come over. In the receiver you will have a liquor considerably more acid than vinegar, in weight about the fourth part of the salt employed. On the dry salt left in the retort, pour some water, somewhat less in quantity than the liquor which came over. Let it stand till the salt has thoroughly imbibed the moisture, and then distil again. You will again have an acid, but weaker than the former. Repeat this five or seven times; after which you will obtain no more marine acid in this way. It has been thought that sea-salt was capable of total decomposition by means of moisture alone; but that is found to be a mistake. The reason of any acid being procurable in this way, is the impurity of the common salt, which is always mixed with a quantity of sal catharticus amarus, and of marine acid combined with magnesia, from which last it is separable by moisture. If a pure salt be formed by combining marine acid with salt of soda, no spirit will be obtained.

IV. To dephlogisticate the Marine Acid.

The marine acid, when mixed either with that of nitre or with manganese, loses that peculiar smell by which it is usually distinguished, and acquires one much more volatile and suffocating. When mixed with the former, the compound is called aqua-regia; when subjected to the action of manganese, the product is called dephtlogisticated spirit of salt. The method of procuring this acid recommended by Mr Scheele is as follows: Mix common muriatic acid in any quantity with levi-gated manganese in a glass retort; to which lute, on blotting paper a receiver capable of containing about 12 ounces of water. Put about two drachms of liquid into it; and in about a quarter of an hour, or somewhat more, a quantity of elastic fluid, which is the true dephtlogisticated spirit of salt, will pass over, and Marine Acid and its Combinations.

Marine acid dephlogisticated by that of nitre or by manganese.

Scheele's method of dephtlogisticating it by manganese.

A new salt has been produced by Mr Bertholet from the union of dephtlogisticated spirit of salt with vegetable alkali. This appears to be of the nitrous kind, more by having a cool taste and detonating strongly in the fire. The compound was in very small quantity, and seemed to require more pure air for its composition than an equal bulk of acid. The greatest part of the salt produced was the common salt of Sylvius, or defective salt, formed by a combination of the phlogisticated marine Marine Acid combined.

I. With Vegetable Fixed Alkali. This combination is accidentally formed after the distillation of volatile salts, by means of salt of tartar (see Alkaline Salts). It was formerly known by the name of sal digestivus Sylvii; and a process for making it was inserted in the dispensatories, under the name of spiritus salis marini coagulatus; but as it has been found to possess no virtues superior, or even equal, to common salt, it is fallen into disuse.

The crystals of this kind of salt are not cubical, like those of common salt, but parallelopipeds, and if thrown into the fire crack and leap about with violence. They are soluble in greater quantity by hot water than cold; and therefore are crystallized by evaporating the solution to a pellicle, and then letting it cool.—It is very remarkable, that though by a direct combination of vitriolic acid with vegetable fixed alkali, the salt called vitriolated tartar is formed; yet if this alkali is once saturated with spirit of salt, so as to form a sal digestivus, upon the decomposition of this salt by means of oil of vitriol, the residuum of the distillation will not be a vitriolated tartar, but a salt easily soluble in water, and which bears a strong resemblance to Glauber's salt. Whether, by means of spirit of sea-salt, the vegetable alkali could be converted into the mineral, or salt of soda, is a question well worthy of being solved.

II. With Mineral Alkali. This combination is the common alimentary salt, and is never made but for experiment's sake; as the marine acid cannot be had but from sea-salt. For the extraction of this salt from seawater, see the article Salt.

III. With Volatile Alkali. The produce of this combination is the common sal ammoniac, which is used nice, in different arts, and which has the property of making tin unite very readily with iron and copper, so is much used by copper-smiths and in the manufactory of tinned iron.

Sal ammoniac is usually sold in large semi-transparent cakes, which are again capable of being sublimed into masses of the like kind. If they are dissolved in water, the salt very easily shoots into small crystals like feathers. Exposed to a moist air, it deliquesces. It is one of the salts which produces the most cold by its solution; so as to sink the thermometer 18 or 20 degrees, or more, according to the temperature of the atmosphere. According to Mr Gellert, a solution of sal ammoniac has the property of dissolving resins. According to Neumann, the volatility of sal ammoniac is so much diminished by repeated sublimations, that at last it remains half fluid in the bottom of the subliming vessel. In its natural state, it sublimes with a degree of heat necessary to melt lead. Pott says, that a small quantity of sal ammoniac may be produced by distilling sea-salt with charcoal, or with alum, or by distilling marine acid with Armenian bole. The same author affirms, that the inflammability of sulphur is destroyed by subliming it with twice its quantity of sal ammoniac.

The method of making this salt was long unknown; and it was imported from Egypt, where it was said to be prepared by sublimation from foot alone, or from a mixture of sea-salt, urine, and foot. That it should be produced from foot alone is very improbable; and the other method, from the known principles of chemistry, is absolutely impossible. The composition of this salt, however, being once known, there remained no other defideratum than a method of procuring those component parts of sal ammoniac sufficiently cheap, so as to afford sal ammoniac made in Britain at a price equally low with what was imported. The volatile alkali is to be procured in plenty from animal substances or from foot; and the low price of the vitriolic acid made from sulphur affords an easy method of decomposing sea-salt, and obtaining its acid at a low rate. A sal-ammoniac work has, accordingly, been established for several years past in Edinburgh: the principal material made choice of for procuring the volatile alkali is foot; and though no persons are admitted to see the work, the large quantities of oil of vitriol brought into it, and the quantities of genuine sal mirabile which are there made, evidently show that the process for making sal ammoniac allows making Glauber's salt, by the decomposition of common salt by means of vitriolic acid. The method of conducting the process is unknown; but it is plain that there can be no other difficulty than what arises from the volatility of the vapours of the alkali and of the marine acid. In the common way of distilling those substances, a great part of both is lost; and if it is attempted to make sal ammoniac by combining these two when distilled by the common apparatus, the pro- duce will not pay the cost; a little ingenuity, however, will easily suggest different forms and materials for distilling-vessels, by which the marine acid and volatile alkali may be united without losing a particle of either.

If a solution of vitriolic or Glauber's secret sal ammoniac is mixed with sea-salt, the vitriolic acid seizes the alkaline basis of the sea-salt, and expels the marine acid; which immediately unites with the volatile alkali left by the vitriolic acid, and forms a true sal ammoniac. If this solution is now evaporated to dryness, and the saline mass sublimed, the sal ammoniac rises, and leaves a combination of vitriolic acid and mineral alkali at the bottom. This fixed mass being dissolved, filtered, and evaporated, affords Glauber's salts. This has sometimes been thought a preferable method of making sal ammoniac, as the trouble of distilling the marine acid was thereby prevented; but it is found vastly inconvenient on another account, namely, that when sal ammoniac is mixed with any fixed salt, it is always more difficult of sublimation, and a part of it even remains entirely fixed, or is destroyed. The mass of Glauber's salt also, by reason of the inflammable and oily matter contained in impure volatile alkalies, is partly changed into a sulphurous mass, so that the solution refuses to crystallize; at least the operation is attended with intolerable trouble.

IV. With Earths. The combinations of this acid with earths of any kind have never been found applicable to any purpose, and therefore they are seldom made or inquired into. The combination with calcareous earth is indeed pretty frequently made accidentally, in the distillation of volatile alkali from sal ammoniac by means of chalk or quicklime. When melted in a crucible and cooled, it appears luminous when struck, and has been called phosphorus scintillans. See Earths.

V. With Gold. The marine acid has no action on gold in its metallic state, in whatever manner the acid be applied; but if the metal is previously attenuated, or reduced to a calx, either by precipitation from aqua regis or by calcination in mixture with calcinable metals, this acid will then perfectly dissolve, and keep it permanently suspended. Gold, precipitated from aqua regis by fixed alkalies, and dulcorated by repeated ablutions, may be dissolved even in a very weak spirit of salt by moderate digestion. This solution appears of the same yellow colour as that made in aqua-regis; gives the same purple stain to the skin, feathers, bones, and other solid parts of animals; the same violet stain to marble; and strikes the same red colour with tin. Even when common aqua-regia is made use of for the menstruum, it seems to be chiefly by the marine acid in that compound liquor that the gold is held in solution. In distillation the nitrous acid arises, and the marine acid remains combined with the gold in a blood-red mass, soluble, like most of the combinations of metallic bodies with this acid, in spirit of wine. If, towards the end of the distillation, the fire is hastily raised, part of the gold distills in a high saffron-coloured liquor; and part sublimes into the neck of the retort in clutters of long slender crystals of a deep red colour, fusible in a small heat, deliquating in the air, and easily soluble in water. By repetitions of this process the whole of the gold may be elevated, except a small quantity of white powder whose nature is not known. Marine —This red sublimate of gold is said to be easily fusible Acid and with the heat of one's hand, and to be shown by its Combi- Papists for the blood of St Januarius; the sublimate contained in a phial, being warmed by the hands of the priests who hold it, constitutes the miracle of that Blood of St Januarius's blood melting on his birth-day.

VI. With Silver. Strong spirit of salt corrodes leaf-silver into a white powder, but has no effect on filings or larger masses of the metal. If applied in the form of vapour to masses of silver, and strongly heated at the same time, it readily corrodes them. Thus, if filings, grains, or plates, of silver are mixed with about twice their weight of mercury sublimate, and exposed to a moderate fire, in a retort, or other distilling vessel, a part of the marine acid in the sublimate will be separated and unite with the silver, leaving the mercury to arise in the form of mercurius dulcis. Marine acid is commonly supposed to be incapable of dissolving silver into a liquid state; but Henckel relates, that if red silver ore, which consists of silver intimately mixed with red arsenic, be digested in spirit of salt, the silver will be extracted and kept permanently dissolved.

The combination of marine acid with silver is called Luna corona. The most ready way of preparing it is by dissolving silver in the nitrous acid, and then adding spirit of salt, or a solution of sea-salt, when a precipitation instantly ensues; the marine acid expels the nitrous, and, uniting with the silver, falls to the bottom in form of a white powder. The same precipitation would take place, if a solution of silver was made in the vitriolic acid.

Luna corona weighs one-fourth more than the silver employed; yet, when perfectly washed, it is quite inert to the taste. It does not dissolve in water, spirit of wine, aquafortis, or aqua-regis; but is in some small degree acted upon by the vitriolic acid. It melts in the fire as soon as it grows red-hot; and, on cooling, forms a ponderous brownish mass, which being cast into thin plates, becomes semi-transparent, and somewhat flexible, like horn; whence its name luna corona. A stronger fire does not expel the acid from the metal, the whole concrete either subliming entire, or passing through the crucible. It totally dissolves in volatile alkaline spirits without any separation of the metal. Exposed to the fire in a close copper vessel, it penetrates the copper, and tinges it throughout of a silver colour. Kunckel observes, that when carefully prepared, melted in a glass vessel, and suffered to cool slowly, to prevent its cracking, it proves clear and transparent; and may be turned into a lathe and formed into elegant figures. He supposes this to be the preparation which gave rise to the notion of malleable glass.

VII. With Copper. In the marine acid, copper dissolves but slowly. The solution, if made without heat, appears at first brown; but, on standing for some time, deposits a white sediment, and becomes green. On adding fresh copper, it becomes brown again, and now recovers its greenness more slowly than before. The white sediment, on being barely melted, proves pure and perfect copper of the same colour as at first. Copper calcined by fire communicates a reddish colour to this acid.

VIII. With Iron. The marine acid acts upon iron les vehemently than the nitrous, and does not dissolve so much; nevertheless, it attacks the metal briskly, so as to raise considerable heat and effervescence, and dissolve it into a yellow liquor. During the solution, an inflammable vapour arises as in the solution of this metal by vitriolic acid. This solution of iron does not crystallize. If it is evaporated, it leaves a greenish saline mass, which is soluble in spirit of wine, and runs into the air into an astringent yellow liquor. On distillation, some of the acid separates, and towards the end of the operation the spirit becomes yellow. This is followed by a yellowish, or deep reddish sublimate, which glitters like the scales of fishes, leaving behind a substance which consists of thin, glossy plates, like talc.

The solution of iron in spirit of salt, with the addition of some spirit of wine, is used in medicine as a corroboration, under the name of tinctura maris. The sublimate of iron is also used for the same purpose, and called ens veneris, or flores maritimes. It is commonly directed to be prepared by subliming iron filings and sal ammoniac together. In the process, the sal ammoniac is partly decomposed, and a caustic alkaline liquor dittis. Then the undecomposed sal ammoniac, and the martial sublimate above mentioned, arise together. The sublimate has a deeper or lighter yellow colour, according as it contains more or less iron. The name ens veneris is improper. It was given by Mr Boyle, who discovered this medicine. He imagined it to be a preparation of copper, having made use of a colo- thar of vitriol containing both iron and copper. A medicine of this kind was lately sold with great reputation on the Continent, under the name of Befuchet's nervous tincture. It was introduced by M. Befuchet Field Marshal in the Russian service; but not long after it came into vogue in Prussia and other northern kingdoms of Europe; it made its appearance also in France, under the name of General de la Motte's golden drops. This happened through the infidelity of Befuchet's operator, who, for a sum of money, violated the oath of secrecy he had taken to Befuchet, and discovered the secret to de la Motte. To the latter it proved a very valuable acquisition; for he not only procured a patent for it from the king of France in 1730, with the exclusive privilege of selling it, but had a handsome pension settled upon him; selling his medicine besides a half a Louis d'or per phial.

The attention of the public was particularly drawn to these drops, by their remarkable property of losing their yellow colour in the sun, and regaining it in the shade, which induced many to believe that they contained gold; and in which opinion they were encouraged by de la Motte. Even chemists of no little reputation were deceived by this appearance; and M. Beaumé, imagining he had discovered the secret, published a preparation to the world as the true arcanum of de la Motte's drops. It consisted of a calx of gold precipitated from aqua-regia by means of fixed alkali, and redissolved in nitrous acid, to which was added a large quantity of spirit of wine. Others, however, who could find nothing but iron by an analysis of the drops, refused their assent; and at length, in 1780, M. Beaumé's mistake was made evident by the publication of the process at the desire of the empress of Russia, who gave 3000 rubles for the receipt. The original recipe is perplexed, tedious, and expensive; but when deprived of its superfluous parts, is nearly as follows. Six pounds of common pyrites and twelve pounds of corrosive sublimate are to be triturated together, and then sublimed six or eight times till all the mercury is expelled. The residuum is to be boiled three times with thrice its quantity of water, and as often filtered, and lastly, distilled to dryness. By increasing the fire, a martial salt is at last sublimed into the neck of the retort; to three drachms of which are to be added 12 ounces of highly rectified spirit of wine, and the whole exposed to the rays of the sun. This is the yellow tincture; but there was also a white one, which, however, seems to be but of little value. It is made by pouring on the residuum of the last sublimation twelve pounds of highly rectified spirit of wine, and drawing it off by a gentle distillation after a few days digestion.—Mr Klaproth imagines, from the following experiment, that Befuchet's tincture absorbs a phlogiston from the rays of the sun. He poured a few drops of a solution of tartar into two ounces of sun's rays, distilled water, and divided this into two parts. Into one glass having poured a few drops of the tincture that had not been exposed to the sun, the iron was precipitated in the usual form of a yellow ochre; but on treating in the same manner a portion of the tincture that had been exposed to the solar rays, the precipitate fell of a bluish green colour.

IX. With Tin. Though the concentrated marine acid Solution of tin has a greater attraction for tin than any other acid, it tin, does not readily dissolve this metal while the acid is in its liquid state; but may be made to dissolve it perfectly by the addition of a small quantity of spirit of nitre. Neumann observes, that an ounce of spirit of salt, with only a scruple of spirit of nitre, dissolved tin perfectly; but on inverting the proportions, and taking a scruple of marine acid to an ounce of the nitrous, four scruples, or four and an half, of tin, were dissolved into a thick paps; some more of the marine acid being gradually added, the whole was dissolved into a clear liquor. In making these solutions, a small quantity of black matter usually subsides.

The solution of tin is sometimes colourless; sometimes of a bluish, or yellow colour, according to different circumstances of the process. It is of the greatest consequence in dyeing, by not only heightening the colours, but making them more durable (See Dyeing). It shoots into small crystals; and, if impregnated, deliquesces in the air.

Marine acid in its concentrated state volatilizes tin, smoking liquor, and forms with it a thick liquor, which, from its inventor, is called smoking liquor of Libavus. To prepare this smoking liquor, an amalgam must be made of four parts of tin and five of mercury. This amalgam is to be mixed with an equal weight of corrosive mercury, by triturating the whole together in a glass mortar. The mixture is then to be put into a glass retort, and the distillation performed with a fire gradually increased. A very smoking liquor passes into the receiver; and towards the end of the distillation, a thick, and even concrete matter. When the operation is finished, the liquor is to be poured quickly into a crystal glass-bottle, with a glass stopper. When this bottle is opened, a white, copious, thick, and poignant fume issues, which remains long in the air without disappearing.

The acid in this liquor is far from being saturated, and is capable of still dissolving much tin in the ordinary way. From this imperfect saturation, together with its concentration, proceeds partly its property of smoking so considerably; nevertheless, some other cause probably concurs to give it this property; for though it smokes infinitely more than the most concentrated spirit of salt, its vapors are, notwithstanding, much less elastic. It has all the other properties of concentrated marine acid when imperfectly saturated with tin. If it is diluted with much water, most of the metal separates in light white flocks. In dyeing, it produces the same effects as solution of tin made in the common way. If the distillation is continued after the smoking liquor of Libavius has come over, the mercury of the corrosive sublimate will then arise in its proper form.

X. With Lead. Marine acid, whether in its concentrated or diluted state, has little effect upon lead, unless assisted by heat. If spirit of salt is poured on filings of lead, and the heat is increased so as to make the liquor boil and distill, a part of the acid will be retained by the metal, which will be corroded into a saline mass; and thus, by a repetition of the process, may be distilled into a limpid liquor. If lead is distilled in aquafortis, and spirit of sea-salt, or sea-salt itself, added, a precipitation of the metal ensues; but if some aqua-regia is added, the precipitate is redissolved.

The combination of lead with marine acid, has, when melted, some degree of transparency and flexibility like horn; whence, and from its resemblance to luna cornea, it is called plumbum cornu. This substance is used in preparing phosphorus, according to Mr Margraaff's method.

XI. With Quicksilver. Marine acid in its limpid state, whether concentrated or diluted, has no effect upon quicksilver, even when assisted by a boiling heat; but if mercury is distilled in the vitriolic or nitrous acids, and sea-salt, or its spirit, is added to the solution, it immediately precipitates the quicksilver in the same manner as it does silver or lead. If concentrated marine acid, in the form of vapor, and strongly heated, meets with mercury in the same state, a very intimate union takes place; and the produce is a most violent corrosive and poisonous salt, called corrosive sublimate mercury. This salt is soluble, though sparingly, in water; but is far from being perfectly saturated with mercury; for it will readily unite with almost its own weight of fresh quicksilver, and sublime with it into a solid white mass (which, when leached, assumes a yellowish color) called mercurius dulcis, aqua alba, or calomel.

There have been many different ways of preparing corrosive mercury, recommended by different chemists. Neumann mentions no fewer than ten:

1. From mercury, common salt, nitre, and vitriol. 2. From mercury, common salt, and vitriol. 3. Mercury, common salt, and spirit of nitre. 4. Solution of mercury in aquafortis and salt. 5. Solution of mercury in aquafortis, and spirit of salt, or the white precipitate. 6. Mercury, common salt, nitre, and oil of vitriol. 7. Edulcorated turbith mineral, and common salt. 8. Red precipitate, common salt, and oil of vitriol. 9. Edulcorated turbith mineral, and spirit of salt. 10. Mercury, sal ammoniac, and oil of vitriol.

From a view of these different methods, it is evident, that the intention of them all is to combine the marine acid with quicksilver; and as this combination can be effected without making use of the nitrous acid, the greatest chemists have imagined that this acid, which is by far the most expensive of the three, might be thrown out of the process altogether, and the sublimate be more conveniently made by directly combining marine acid and mercury in a process similar to the distillation of spirit of salt. This method was formerly recommended by Kunckel; then published in the memoirs of the Academy of Sciences for 1730; and has been adopted and recommended by Dr Lewis.

The process consists in dissolving mercury in the vitriolic acid, as directed for making turbith mineral. The white mass remaining on the evaporation of this solution is to be triturated with an equal weight of dried salt, and the mixture is then to be sublimed in a land-heat; gradually increasing the fire till nothing more arises.

Neumann observes, that there is a considerable difference in the quality of sublimes made by the different methods he mentions; particularly in those made with or without nitre. This we have also found to be the case; and that sublimate made without the nitrous acid is never so corrosive, or soluble in water, as that which is made with it; nor will it afterwards take up so large a quantity of crude mercury as it otherwise would, when it is to be formed into calomel. The above process, therefore, tho' very convenient and easy, is to be rejected; and some other in which the nitrous acid is used, substituted in its stead. The reason of these differences is, that the spirit of salt must by some means or other be dephlogisticated before it can unite in sufficient quantity with the metal, into the compound desired, which is accomplished by the addition of nitrous acid.

From Tachenius, Neumann gives us the following process, which he says was the method of making sublimate at London, Venice, and Amsterdam. Two hundred and eighty pounds of quicksilver, 400 pounds of calcined vitriol, 200 pounds of nitre, the same quantity of common salt, and 50 pounds of the caput mortuum remaining after a former sublimation, or (in want of it) of the caput mortuum of aquafortis, making, in all, 1130 pounds, are well ground, and mixed together; then set to sublimate in proper glasses placed in warm ashes; the fire is increased by degrees, and continued for five days and nights. In the making such large quantities, he says, some precautions are necessary, and which those constantly employed here-in are best acquainted with. The principal are, the due mixture of the ingredients, which in some places is performed in the same manner as that of the ingredients for gun-powder; that a head and receiver be adapted to the subliming glass, to save some spirit of nitre which will come over. (Here a bent tube of glass will answer the purpose, as already mentioned.) The fire must not be raised too hastily. When the sublimate begins to form, the ashes must be removed a little from the sides of the glass, or the glass cautiously raised up a little from the ashes. (This last, we think, is highly imprudent.) Lastly, the laboratory must have a good chimney, capable of carrying off the noxious fumes. The above-mentioned quantities commonly yield 360 pounds of sublimate; the 280 pounds of quicksilver gaining 80 from the 200 pounds of sea-salt. The makers of sublimate The above processes, particularly the last, are unexceptionable as to the production of a sublimate perfectly corrosive; but the operation, it is evident, must be attended with considerable difficulty, by reason of the large quantity of matter put into the glass at once. We must remember, that always on mixing a volatile salt with a quantity of fixed matter, the sublimation of it becomes more difficult than it would have been had no such matter been mixed with it. It is of considerable consequence, therefore, in all sublimations, to make the quantity of matter put into the glass as little as possible. It would seem more proper, instead of the calcined vitriol used in the process last mentioned, to dissolve the mercury in the vitriolic acid, as directed for turpith mineral, and sublime the dry mass mixed with nitre and sea-salt.

It has been said, that corrosive sublimate mercury was frequently adulterated with arsenic; and means have even been pointed out for detecting this supposed adulteration. These means are, to dissolve a little of the suspected salt in water, and add an alkaline lixivium to precipitate the mercury. If the precipitate was of a black colour, it was said to be a certain sign of arsenic. This, however, shows nothing at all, but that either the alkali contains some inflammable matter, which, joining with the precipitate, makes it appear black; or that the sublimate is not perfectly corrosive; for if a volatile alkali is poured on levigated mercurius dulcis, the place it touches is instantly turned black.

Mercurius dulcis, or calomel, is prepared by mixing equal parts, or at least three of quicksilver with four of sublimate; after being thoroughly ground together in a glass or stone mortar, they are to be poured through a long funnel into a bolt-head, and then sublimed. The medicine has been thought to be improved by repeated sublimations, but this is found to be a mistake. Mr Beaumé has found that mercurius dulcis cannot be united with corrosive sublimate in the way of sublimation; the former, by reason of its superior volatility, always rises to the top of the vessel.

XII. With Zinc. This semimetal dissolves readily in the marine acid into a transparent colourless liquor. It is volatilized, as well as most other metallic substances, by this combination, as appears from the following process delivered by Neumann.

"Equal parts of filings of zinc and powdered sal ammoniac being mixed together, and urged with a gradual fire in a retort; at first arose, in a very gentle heat, an excessively penetrating volatile spirit, so strong as to strike a man down who should inadvertently receive its vapour freely into the nose. This came over in subtile vapours, and was followed by a spirit of salt in dense white fumes. In an open fire, white flowers succeeded; and at length a reddish and a black butter. In the bottom of the retort was found a portion of the zinc in its metallic form, with a little ponderous and fixed butyraceous matter, which liquefied in the air."

The lump was far more brittle than zinc ordinarily is; of a reddish colour on the outside, and blackish within. The bottom of the retort was variegated with yellow and red colours, and looked extremely beautiful. The remaining zinc was mixed afresh with equal its weight of sal ammoniac, and the process repeated. A volatile alkaline spirit and marine acid were obtained as at first; and in the retort was found only a little black matter. When the zinc was taken at first in twice the quantity of the sal ammoniac, the part that preserved its metallic form proved less brittle than in the foregoing experiment, and the retort appeared variegated in the same manner. On endeavouring to rectify the butter, the retort parted in two by the time that one half had distilled." The nature of this combination is unknown.

XIII. With Regulus of Antimony. This semimetal cannot be united with the marine acid unless the latter is antimonial in its most concentrated state. The produce is an excessively caustic thick liquid, called butter of antimony. The process for obtaining this butter is similar to that for distilling the smoking spirit of Libavius. Either crude antimony, or its regulus, may be used; for the spirit of salt will attack the reguline part of this mineral without touching the sulphurous. Three parts of corrosive sublimate are to be mixed with one of crude antimony; the mixture to be digested in a retort set in a fand heat; the marine acid in the sublimate will unite with the reguline part of the antimony. Upon increasing the fire, the regulus arises, dissolved in the concentrated acid, not into a liquid form, but that of a thick unctuous substance like butter, from whence it takes its name. This substance liquefies by heat, and requires the cautious application of a live coal to melt it down from the neck of the retort. By rectification, or exposure to the air, it becomes fluid like oil, but still retains the name of butter. If water is added to butter of antimony, either when in a butyraceous form, or when become fluid by rectification, the antimony is precipitated in a white powder called powder of alguroth, and improperly mercurius vita. This powder is a violent and very unsafe emetic. The butter itself was formerly used as a caustic; but it was totally neglected in the present practice, until lately that it has been recommended as the most proper material for preparing emetic tartar. (See below.) Mr Dolfus recommends the following method as the best for making butter of antimony; viz. two ounces and a quarter of the grey calx of antimony, eight ounces of common salt, and six of acid of vitriol. By distilling this mixture, ten ounces of the antimonial caustic were obtained; and in order to determine the quantity of metal contained in it, he mixed two ounces of the caustic with four ounces of water; but thus such a strong coagulum was formed, that he was not able to pour off any of the water even after standing 24 hours. The precipitate, when carefully dried, weighed 50 grains. The result was much the same when glass of antimony was used, only that the precipitate was much more considerable; half an ounce of the caustic then yielding 60 grains, though at another time only 50 grains were obtained. In the re- Marine Acid and its Combinations.

When the mercurius vitæ precipitates, the union between the marine acid and regulus is totally dissolved; so that the powder, by frequent washings, becomes perfectly free from every particle of acid, which unites with the water made use of, and is then called, very improperly, *philosophic spirit of vitriol*.

**XIV. With Regulus of Cobalt.** Pure spirit of salt dissolves this semimetal into a reddish yellow liquor, which immediately becomes green from a very gentle warmth. On saturating the solution with urinous spirits, the precipitate appears at first white, but afterwards becomes blue, and at length yellow. If the nitrous acid is added to solutions of regulus of cobalt, they assume a deep emerald green when moderately heated, and on cooling become red as at first. Duly evaporated, they yield rose-coloured crystals, which change their colour by heat in the same manner. This solution makes a curious sympathetic ink, the invention of which is commonly ascribed to M. Hellot, though he himself acknowledges that he received the first hint of it from a German chemist in 1736. Any thing wrote with this solution is invisible when dry and cold; but assumes a fine green colour when warm, and will again disappear on being cooled; but if the heat has been too violent, the writing still appears. M. Hellot observes, that if nitre or borax be added to the nitrous solution, the characters wrote with it become rose-coloured when heated; and if sea-salt is afterwards passed over them, they become blue; that with alkali sufficient to saturate the acid, they change purple and red with heat.—A blue sympathetic ink may be made from cobalt in the following manner. Take of an earthy ore of cobalt, as free from iron as possible, one ounce. Bruise it, but not to too fine a powder. Then put it into a cylindrical glass, with 16 ounces of distilled vinegar, and let the mixture in hot sand for the space of five days, stirring it frequently; or else boil it directly till there remain but four ounces. Filter and evaporate it to one half. If your solution be of a rose colour, you may be certain that your cobalt is of the right sort. A red brown colour is a sign of the solution containing iron; in which case the process fails. To two ounces of the solution thus reduced, add two drachms of common salt.—Set the whole in a warm place to dissolve, and the ink is made.

**XV. With Regulus of Arsenic.** This substance is soluble in all acids; but the nature of the compounds formed by such an union is little known. If half a pound of regulus is distilled with one pound of corrosive sublimate, a thin smoking liquor and a butyraeous substance will be obtained, as in making the smoking liquor of Libavius. By repeated rectifications, this butter may be almost all converted into spirit. If equal parts of the arsenic and sublimate are used, a ponderous black oil comes over along with the spirit, which cannot be mixed with it. By rectification in a clean retort, they will become clear, but still will not incorporate. If they are now returned upon the red mats remaining in the first retort, and again distilled, a much more ponderous oil than the former will be obtained.

**XVI. With Inflammable Substances.** The acid of sea-fall is very little disposed to contract any union with the phlogiston, while in a liquid state; and much less acid and fo, even in its most concentrated state, than either the Combinations.

Mr Beaumé, however, has found, that a small quantity of ether, similar to that prepared with the vitriolic and nitrous acids, may be obtained by causing the fumes of the marine acid unite with those of spirit of wine. Others, and particularly some German chemists, attempted to make this liquor, by employing a marine acid previously combined with metallic substances, such as butter of antimony. The smoking liquor of Libavius succeeds best. If equal parts of this liquor and highly rectified spirit of wine are distilled together, a considerable quantity of true ether is produced; but which, like the vitriolic and nitrous ether, must be rectified in order to its greater purity. The tin contained in the smoking liquor is separated and precipitated in white powder. In this process, the acid is probably more disposed to unite with the spirit of wine, by having already begun to combine with the inflammable principle of the metal.—For marine ether, Mr Dollfus recommends to put into a retort four ounces of digestive salt previously well dried and powdered, and two ounces of manganese; pouring upon this a mixture of five ounces of spirit of wine and two of oil of vitriol; the first five ounces and a half of the distilled liquor being poured back on the residue, and the whole afterwards drawn off by a gentle heat. The spirit of fall thus obtained had a very penetrating agreeable odour, somewhat like that of nitrous ether; and at first swam upon the top of water, but at length mixed with it on being agitated for a long time. Towards the end of the distillation a little oil was obtained, which did not mix with the water; and by the addition of four ounces more of spirit of wine, more of the dulcified acid was obtained. With regard to this kind of ether, however, Mr Weltrumb denies that it can be made by any method hitherto known; and insists, that all the liquids as yet produced under the name of marine ether are in reality dulcified spirit of salt, and not true ether, which will float on the top of water.

Dr Priestley has observed, that the pure marine acid, when reduced to an invisibly aerial state, has a strong for phlogistic affinity with phlogiston; so that it decomposes many substances that contain it, and forms with them an air permanently inflammable. By giving it more time, it will extract phlogiston from dry wood, crusts of bread not burnt, dry flesh; and, what is still more extraordinary, from flints. From what has been above related, it appears that the dephlogisticated spirit of fall has a very strong attraction for phlogiston.

Essential oil of mint absorbed the marine acid air pretty fast, and presently became of a deep brown colour. When taken out of this air, it was of the consistence of treacle, and funk in water, smelling differently from what it did before; but still the smell of the mint was predominant. Oil of turpentine was also much thickened; and became of a deep brown colour, by being saturated with acid air. Ether absorbed the air very fast; and became first of a turbid white, and then of a yellow and brown colour. In one night a considerable quantity of strongly inflammable air was produced.

Having once saturated a quantity of ether with acid air, air, he admitted bubbles of common air to it, through the quicksilver by which it was confined, and observed that white fumes were made in it, at the entrance of every bubble, for a considerable time. Having, at another time, saturated a small quantity of ether with this kind of air, and the phial which contained it happening to be overturned, the whole room was instantly filled with a white cloud, which had very much the smell of ether, but peculiarly offensive. Opening the door and window of the room, this light cloud filled a long passage and another room. The ether, in the mean time, was seemingly all vanished; but, sometime after, the surface of the quicksilver in which the experiment had been made was covered with a very acid liquor, arising probably from the moisture in the atmosphere, attracted by the acid vapour with which the ether had been impregnated. This seems to show, that, however much dilposed the marine acid may be to unite with phlogistic matters when in its aerial state, the attraction it has for them is but very slight, and still inferior to what it has for water.

Camphor was presently reduced into a fluid state by imbibing this acid air; but there seemed to be something of a whitish sediment in it. After continuing two days in this situation, water was admitted to it, upon which the camphor immediately resumed its former solid state; and to appearance was the same substance that it had been before.

Strong concentrated oil of vitriol, being put to marine acid air, was not at all affected by it in a day and a night. In order to try whether it would not have more power in a condensed state, it was compressed with an additional atmosphere; but, on taking off this, the air expanded again, and was not in the least diminished. A quantity of strong spirit of nitre was also put to it without any sensible effect. From these last experiments it appears, that the marine acid is not able to dislodge the other acids from their union with water.

Besides the acids already mentioned, Mr Humberg describes an artificial one generated by mixing two ounces and a half of luna cornea, with an ounce and a half of tin calcined alone and without addition, by means of fire. The mixture is to be exposed to a naked fire in a coated retort, of which two thirds ought to be left empty; when a brownish matter, an ounce and a half in weight, will adhere to the neck of the retort. This matter is tin combined with the marine acid, and the residuum is silver deprived of the same acid, which may therefore now be melted together without any loss. The sublimate, well powdered and dried, is to be equally divided into two phials, and sublimed; by repeating which operation two or three times, a volatile salt, of an acid nature, very white and transparent, is obtained. The residuum of these sublimations is always calx of tin.

§ 4. Of the Fluor Acid.

This acid was discovered some time ago by Mr Margraf, and more fully investigated by Mr Scheele. The experiments by which it was originally produced, and its properties ascertained, are as follows:

1. Two ounces of concentrated vitriolic acid were poured upon an equal quantity of fluor, which had been previously pounded in a glass mortar, and then put into a retort, to which a receiver was adapted, and the juncture cloed with grey blotting paper. On the application of heat, the mists began to effervescence and swell, invisible vapours penetrated everywhere through the joining of the vessels, and towards the end of the process white vapours arose, which covered all the internal parts of the receiver with a white powder. The mass remaining in the retort was as hard as a stone, and could not be taken out without breaking the vessel. The lute was quite corroded and friable.

II. The process was repeated exactly in the same manner, excepting only that a quantity of distilled water was put into the receiver. A white spot soon began to form on the surface of the water, just in the white centre, and immediately under the mouth of the retort. This spot continually increased, till at last it covered the whole surface of the water, forming a pretty thick crust, which prevented the communication of the water with new vapours that came over. On gently agitating the receiver, the crust broke, and fell to the bottom; soon after which a new crust like the former was produced. At last the receiver, and soon after the retort also, became white in the inside. The vessels, when cooled, were found much corroded internally. In the receiver was an acid liquor mixed with much white matter, separable by filtration.

III. This white matter when edulcorated and dried, showed itself to be siliceous earth, by the following properties:

1. It was rare, friable, and white. 2. It was not sensibly soluble in acids. 3. It did not make a tough paste with water, but was loose and incoherent after being dried. 4. It dissolved by boiling in lixivium tartari, and the solution in cooling assumed a gelatinous consistence. 5. In its pure state it suffered no change in the strongest heat; but when mixed with alkali, it boiled, frothed up, and formed a glaas in a melting heat. 6. It dissolved in borax without swelling.

IV. To determine whether this earth was formed during the process, he poured vitriolic acid upon powdered fluor contained in a cylinder of brass which was to be closed exactly with a cover, after having suspended the mixture an iron nail and a bit of charcoal. On opening the vessel two hours afterwards, he found the nail and charcoal unchanged; but on moistening them, he found both covered with a white powder in a short time. This powder had all the properties of siliceous earth; and as in the experiment he had made no use of glass vessels, he concluded that it did not proceed from the glass vessels, as might have been suspected from their being too much corroded, but was generated in some other way.

V. Having recomposed fluor by saturating the acid with calcareous earth, he treated the compound in flour yields the same manner as the natural fluor, with a similar result; and repeating the experiment five times over, he constantly found the siliceous earth and acid diminish considerably, so that at last scarce any mark of acidity was left. Thence he concluded, that all the fluor acid united itself by degrees with the vapours of the water, and thus formed the siliceous earth. "It may be objected (says Mr Scheele), that the fluor acid is perhaps already united by nature with a fine siliceous powder," Fluor Acid and its Combinations.

Mr Scheele's conclusion that the earth proceeds from an union of the acid with water.

This opinion of Mr Scheele did not meet with general approbation. Mr Boullanger endeavoured to show, that the fluor acid is no other than the muriatic acid intimately combined with some earthly substance; and Mr Monnet maintained that it is the same with that of vitriol volatilized by some extraordinary connection with the fluor; which opinion was also maintained by Dr Priestley. Mr Scheele contested these opinions, but found much greater difficulty in supporting his own opinions than in overthrowing those of his adversaries. Boullanger insisted that fluor acid precipitates the solutions of silver and quicksilver, producing luna cornea with the former, and mercurius dulcis with the latter. Mr Scheele owns that fluor acid precipitates both these metals, but the precipitate obtained is in very small quantity, and the little that is produced arises only from a small quantity of sea-salt with which the fluor, as well as all other calcareous substances, is generally mixed. The greatest part of the acid, therefore, will not precipitate the solutions of these metals, which it ought to do upon Mr Boullanger's hypothesis. Mr Scheele then proceeds to show a method of separating this small quantity of marine acid from that of fluor. A solution of silver made with nitrous acid is to be precipitated with alkali of tartar, and as much acid of fluor poured upon the educulated powder as is sufficient to give an excess of acid; after which the solution is to be filtered. This solution of silver in fluor acid is then to be dropped into that acid we desire to purify, till no more precipitation ensues; after which the acid is filtered through grey paper, and distilled to dryness in a glass retort. The aqueous part comes over first, but is soon followed by fluor acid, which covers the inside of both the vessels, together with the surface of the water in the receiver, with a thick siliceous crust. The acid, thus rectified, does not precipitate solution of silver in the least, nor otherwise show the smallest sign of muriatic acid.

That the fluor acid is different from that of vitriol, Mr Scheele proved by the following experiment. Up Fluor Acid on one ounce of pure levigated fluor with alcohol, he and its companions three ounces of concentrated oil of vitriol, and condensed the mixture in a sand-bath, having previously put 12 ounces of distilled water into the receiver. He then took another three ounces of the same acid diluted and with 24 ounces of water, to which he afterwards added that of vitriolic acid tartar previously weighed, till he attained the exact point of saturation. After the distillation he weighed the remaining lixivium; having kept up such a degree of heat for eight hours as was not sufficient to raise the vitriolic acid. On breaking the retort, and reducing the mass to powder, he boiled it in a glass vessel with 24 ounces of water for some minutes; after which he added just as much lixivium tartar as he had found before to be requisite for the saturation of three ounces of the vitriolic acid, and continued the boiling for a few minutes longer. On examining the solution, it was found to contain a vitriolated tartar perfectly neutralized, neither acid nor alkaline prevailing in any degree; which showed that no vitriolic acid had passed into the receiver. The saline matter being then extracted with hot water, the remaining earth was found to weigh 9½ drachms. Two drachms of this dissolved in muriatic acid, excepting only a small quantity of matter which seemed to be fluor undecomposed, and which on being dried weighed only nine grains. Into one part of this solution he poured some acid of sugar, and into another vitriolic acid. The former produced saccharated lime, and the latter gypsum. A third part was evaporated to dryness, and left a deliquescent salt; and the remaining part of the earth burned in a crucible, produced a real quicklime.

Thus it appeared that the real basis of fluor is quicklime, and likewise that the fluor acid is different from the basis of that of vitriol, as appears further from the following considerations: 1. Pure fluor acid does not precipitate terra ponderosa, nor solution of lead in nitrous acid. 2. The same acid, when saturated with alkali of tartar, evaporated to dryness, and afterwards melted with powdered charcoal, does not produce any hepatic fulphuris.

Mr Monnet, in order to support his hypothesis, denies that fluor contains any calcareous earth. In proof of which he adduces the following experiment: Equal quantities of alkali and fluor were melted together, with little or no change on the mineral; for, after having taken away by lixiviation the alkali employed, he dissolved the fluor remaining on the filter in nitrous acid, adding vitriolic acid to the solution; and because he obtained no precipitate, concluded at once, that fluor contains no calcareous earth. Mr Scheele, on the contrary, affirms that all solutions of fluor yield a precipitate of gypsum whenever vitriolic acid is added to them. He explains Mr Monnet's failure, by supposing that he had diluted his solution with too great a quantity of water.

Mr Wiegleb, dissatisfied with the hypothesis of Scheele, as well as others, concerning the fluor acid, began a new set of experiments on the mineral. Having first accurately repeated those made by Mr Scheele, he proceeded to inquire into the origin of the siliceous earth, in the following manner: Having first weighed the retort destined for the experiment in an accurate manner, and found that its weight was two ounces and five drachms; he put into it two ounces of calcined fluor in powder, adding, by means of a glass tube, 2½ ounces of oil of vitriol. The retort was then placed on the furnace; and a receiver, which when empty weighed two ounces, two drachms, and 30 grains, and now contained two ounces of distilled water, was luted to it. The distillation was conducted with all possible care, and at last pushed till the retort grew red hot; but it was found impossible to prevent a few vapours from penetrating through the lute. Next day the retort, separated from the receiver, was found to weigh, together with its contents, five ounces, five drachms, and 30 grains; and consequently had lost in weight one ounce, three drachms, and 30 grains. The receiver, which, with the water, had originally weighed four ounces, two drachms, and 30 grains, now weighed five ounces and three drachms, and had therefore gained one ounce and 30 grains. This gain, compared with the loss of the retort, shows that the retort lost more by three drachms than the receiver gained; so that these must have undoubtedly passed through the luting in form of vapour.

To determine the point in question, the empty vessels, with what had been put into them, were accurately weighed; when the weights and losses upon the whole were found to be as follows:

| oz. dr. gr. | |-------------| | The empty retort | 2 5 0 | | Calcined fluor | 2 0 0 | | Oil of vitriol | 2 4 0 |

Total weight before distillation | 7 1 0 | After it | 5 5 30 |

Loss of retort | 1 3 30 |

The empty receiver weighed | 2 2 30 | The water put into it | 2 0 0 |

Total weight before distillation | 4 2 30 | Total weight after distillation | 5 3 0 |

Gain of receiver | 1 0 30 |

Deducing this gain of weight in the receiver from the loss of weight in the retort, we find, that three drachms were wanting on the whole, which must undoubtedly, as already observed, have been distipated in vapour. The retort being now broken, and the dry earth both in its neck and arch separated as accurately as possible, it was found to weigh three drachms; the residuum in the retort weighed three ounces, two drachms, and 40 grains. Now, as the mass in the retort had originally weighed four ounces and four drachms, it appeared, by deducting the residuum, to have suffered, on the whole, a loss of one ounce, one drachm, and 20 grains. To determine the loss more accurately, the following calculations were made:

| oz. dr. gr. | |-------------| | The white earth separated from the neck and arch of the retort | 0 3 0 | | Gain of the receiver | 1 0 30 | | Loss in vapour | 0 3 0 |

Total | 1 6 30 |

Here Mr Wiegleb was surprised to find, that the matter which came from the retort amounted to more fluor acid by five drachms ten grains than the mass in the retort had lost of its original weight; to illustrate which it was necessary to weigh the retort and receiver by themselves. The pieces of the retort now weighed only one ounce seven drachms and 50 grains; whereas, before the process, the weight of the retort was two ounces five drachms. It appeared, therefore, that it had lost five drachms ten grains, the very quantity which had been gained by the receiver. This last had lost nothing of its original weight.

The fluid in the receiver was next diluted with four ounces of distilled water, and the whole poured out on a filter, in order to separate the earthy matter with which it was mixed, and fresh water poured upon it to take out all the acid; after which the earth was dried, and found to weigh 57 grains. The clear liquor was then diluted with more distilled water, and afterwards precipitated with spirit of sal ammoniac prepared with fixed alkali. A brisk effervescence took place before any precipitate began to fall, but ceased soon after the precipitation took place. The whole mixture became gelatinous; and the precipitate, when dry, weighed two drachms. The whole quantity of earth, therefore, obtained in this process amounted to five drachms 47 grains, which is forty-seven grains more than the retort had lost in weight. This excess is, by our author, attributed to part of the acid still adhering to it, and to the accession of some moisture from the air; to determine which he heated each of the parcels of earth red hot separately, and thus reduced them to four drachms 52 grains, which is less by 18 grains than the loss of the retort, and which, he is of opinion, must have escaped in the three drachms of vapour.

From this experiment Mr Wiegleb concludes, that the earthy matter produced in the distillation of fluor proceeds partly from the spar nor from a combination of the seeds from the solution acid with water, but from the solution of the glaas of the sparry acid. To his opinion also Dr Crell accedes. "In distilling fluor (says he) with oil of vitriol, I have found the retort as well as the receiver very much corroded. I poured the acid obtained by the process into a phial furnished with a glass stopper, and observed after some time a considerable deposition. I then poured the liquor into another phial like the former; and that it might neither on the one hand attack the glaas, nor on the other, compose filaceous earth with the particles of water, according to Mr Scheele's hypothesis, I added highly rectified spirit of wine. I saw, however, after some time, another considerable deposition. This seemed also to proceed from the glaas that had been before dissolved, which the acid let fall in consequence of the gradual combination with the spirit of wine; otherwise we must suppose, what to me appears incredible, that the acid decomposes the spirit, attracts the water, and forms the earth."

This singular acid has been still further examined by Mr Meyer. He informs us, that among Mr Scheele's experiments, he was particularly struck by one in which no earthly crust was obtained, after putting spirit of wine into the receiver. Mr Meyer repeated this experiment, hoping, that when but little spirit was put into the receiver, he might be able to procure a new kind of ether. An ounce of finely powdered fluor, which had been previously heated red hot, was put into a Fluor Acid and its Combinations.

glafs retort, to which was fitted a receiver containing three ounces of highly rectified French brandy. The distillation was continued for three hours with a gentle heat; when the acid, having made its way through the bottom, put an end to the process. No crust could be perceived on the surface of the spirit; but in the place where it had been in contact with the receiver there was a thin ring of transparent jelly. The same mixture of oil of vitriol and flour was therefore again put into a retort of very strong glass, and the same spirit put into the receiver. The distillation was conducted two hours with a gentle, and afterwards with a stronger, heat. When it was half over, the spirit began to change into a thin jelly; and at the end of the process some firmer pieces were found at the bottom. These were washed with spirit of wine; and in order to obtain the spirit together with the acid in a pure state, it was put into a large retort, and again subjected to distillation. As the retort grew warm, the opal-coloured spirit became clear and swollen, what remained becoming again gelatinous; a good deal of earth remained behind, but did not adhere firmly to the retort, which was smooth in the inside, though full of shallow excoriations. It was also evident, that the glass was actually corroded, and that the earthy matter is not a mere crust adhering to the inside. The jelly being thoroughly educolourated, as well as the earth that remained in the retort after the rectification, and that which was dissolved in the water precipitated by spirit of sal ammoniac, the whole quantity amounted to two drachms. That which had separated spontaneously was semitransparent. "As this earth (says he) showed the properties of siliceous earth, and the glass, which was so much corroded, consists in great measure of it, the greatest part of it might come from the glass, and the rest of it perhaps be a constituent part of the fluor itself." In order to ascertain this, it was necessary to obtain the fluor acid quite free from siliceous earth. I therefore exposed the ley, which I had procured by the precipitation of the earth with sal ammoniac, to a gentle evaporation in a slightly covered glass vessel. The product was one drachm 56 grains of an ammoniacal salt; the glass did not appear to have been attacked. Half a drachm of this salt was sublimed in a small retort, which, towards the end of the operation, was laid on the bare fire. No crust appeared on the surface of the water in the receiver. At the bottom of the retort lay a little flocculent earth of a light grey colour, above which the internal surface was covered with a white pellicle that reflected various colours; and in the neck there was a sublimate. The thin pellicle easily separated in many places from the glass, which was smooth beneath, though not without some small furrows. I poured water both upon the ammoniacal salt and crust; in consequence of which it acquired a very sour taste, and coloured the tincture of turpentine red. The white crust that was left behind undissolved weighed five grains, and melted into a green glass without addition. This was nothing but the glass that had been corroded by the fluor acid; but as this acid can be set loose only by strong heat, it had done no more than corrode the glass, without passing over along with it in the form of vapour, and then depositing it again on the water. For, upon pouring two drachms of oil of vitriol upon half a drachm of this ammoniacal salt,

No. 73.

a little moistened, and placed in a glass retort, a great Fluor Acid foam arose, and the thick vapours that ascended covered and insulated the water in the receiver with a white crust. A fragment of the salt on solution, left behind a grain of earth, which, as I conjecture, it had taken up during the evaporation in the glass vessel."

To prevent this, our author distilled half an ounce of fluor with an ounce of oil of vitriol for five hours. The crusts were separated from the water; they weighed, after being well washed and dried, eleven grains; they were white and very flocculent; thirty-two grains of siliceous earth were precipitated from the filtered water; the ley was then evaporated in a leaden vessel, and yielded 80 grains of salt. As glass vessels were no longer to be trusted, a piece of a gun-barrel furnished with a cover, and terminated by a bent tube, intended to serve instead of the neck of a retort, was afterwards used; and with this apparatus the following experiments were made:

1. Half a drachm of the newly prepared sal-ammoniac was distilled for two hours with two drachms of oil of vitriol, into a glass receiver containing an ounce of water. No vestige of a crust could be perceived on the water, but some earth was perceived in the receiver, where the vapours having ascended through the tube, came into contact with the wet glass; and here the surface was become sensibly rough. On the addition of volatile alkali, a few flocculi of siliceous earth, amounting only to one-fourth of a grain, were thrown down out of the water.

2. A drachm of oil of vitriol was added to a drachm and an half of the salt; but a leaden receiver was now used, containing an ounce of water as before. The water acquired an unpleasant smell, but showed no signs of a crust. On the addition of spirit of sal ammoniac, a little grey earth weighing half a grain fell to the bottom.

3. A ferule of this salt, mixed with an equal quantity of white sand in fine powder, and distilled with a formed by drachm and an half of oil of vitriol, into an ounce of mixing water in the leaden receiver, showed no sign of a crust. Sand with a The water had a putrid smell, and left on the filter containing two grains and an half of grey earth, which ran under fluor acid, the blow-pipe into a grain of lead. Volatile alkali precipitated five grains of grey earth, which melted on the addition of a little salt of tartar into a black globule, though the blow-pipe alone made no change in it.

4. To 13 grains of the same ammoniacal salt a drachm But a great of oil of vitriol and two scruples of green glass, broken or cut into small pieces, were added. The iron tube had using powders become warm, when a great crust of siliceous earth was perceived on the surface of the water, and the same appearance on the moist sides of the vessel. It did not, however, seem to increase during the remainder of the distillation. A grain and a quarter of earthy matter remained on the filter, consisting partly of white films, which ran under the blow-pipe into a greenish glass.

5. To ascertain this matter still more clearly, a different species of mineral fluor was used, which being distilled with a double quantity of oil of vitriol, and with a drachm of water in the receiver, yielded a thin pellicle of the appearance of lead, but no siliceous crust. Volatile alkali threw down 2½ grains of grey earth. Fluor Acid earth.—A drachm mixed with the same quantity of pulverized sand afforded a pellicle of lead interspersed with a few particles of white crust, which ran into glaas under the blow-pipe. Volatile alkali precipitated eight grains.—A drachm, mixed with an equal quantity of green glaas reduced to powder, swelled a good deal, and yielded a thick filaceous crust.

6. To a drachm of green fluor that had been heated and powdered were added two drachms of oil of vitriol, still employing the iron tube. A piece of wet charcoal was also suspended in the inside, a cover fixed on the tube, and the latter was heated for about 15 minutes in a sand bath. Observing now that the charcoal was dry, and had no earth upon it, a scruple of sand in fine powder was added, the charcoal was wetted and replaced, but nothing appeared. Some bits of green glaas were then thrown into the mixture, which instantly foamed up and ran over. The charcoal was not replaced in the tube, nor was it any longer necessary, as it gained a covering of white powder by being held a very few moments over the orifice.

Mr Scheele, in one of his experiments, observes, that he observed the white powder on a piece of charcoal that had been moistened and suspended over fluor to which vitriolic acid was added. As this experiment was made in metallic vessels, Mr Meyer conjectures, that the mortar used for reducing the fluor to powder was of soft glaas, and that the phenomenon was occasioned by the abrasion of some particles of glaas.

7. To determine whether the acid can carry up much more of the filaceous earth than is sufficient to saturate it, an ounce and an half of pure oil of vitriol was added in a retort of glaas, and three ounces of water put into the receiver. The retort was corroded through in an hour's time, and the crust on the water weighed ten grains. The liquid being then filtered and divided into two equal parts, one was precipitated with caustic volatile, and the other with mild fixed vegetable, alkali. The former yielded 25 grains of filaceous earth, and the latter 68 grains of a precipitate, which flowed under the blow-pipe, ran into the pores of charcoal, and gave out strong vapours of fluor acid. The reason of this difference shall be explained when we come to treat of filaceous earth.

8. To a mixture of half an ounce of fluor and the same quantity of glaas, in powder, 12 drachms of oil of vitriol were put in a small retort, half filled with the mixture. The ingredients acted upon each other so violently that they rose up into the neck of the retort; and the operation being intermitted on account of the noxious vapour they emitted, the retort was found next day covered with fasciculated crystals like hoarfrost.—The experiment being repeated in a more capacious retort, and the mixture thoroughly blended by agitation, it became a thick mass, and swelled like dough in fermentation; the bottom of the retort grew very hot, and the filaceous crust appeared on three ounces of water in the receiver. The distillation being continued for three hours, 16 grains of filaceous earth were found on the surface, and the precipitate by volatile alkali weighed 56 grains; the retort was much less corroded than usual.

9. Thirty grains of this precipitate, distilled in a glaas retort with a drachm and an half of oil of vitriol, produced no filaceous earth on the water in the receiver, or that with which the earth was edulcorated. The ley of fluorated volatile alkali was mixed with a solution of chalk in nitrous acid till no more precipitation took place. The mixture was passed through nitrous acid, and the precipitate adulcorated. It weighed, when dry, two drachms and 36 grains.

10. Two drachms of oil of vitriol being added to a drachm of this precipitate contained in a glaas retort, the precipitate was attacked in the cold, but no crust appeared; the heat, however, was scarce applied, when the whole surface of the water was covered, and the same phenomena exhibited which are produced by the natural fluor.

11. Mr Scheele having observed that a mixture of farther fluor as transparent as mountain crystal, and oil of proofs that vitriol in a metallic cylinder, produced no appearance of the earthy crusts present on a wet sponge suspended in the inside, seeds from at Mr Meyer's request he made a new experiment, the glaas transparent kind placed in two tin cylinders; some filaceous earth was put into one, and a wet sponge suspended in both. The next morning the sponge that was suspended over the cylinder which held the filaceous earth, was covered with the white powder, but no appearance of it was seen on the other. The experiment was repeated by Mr Meyer with the same result, but the white crust did not appear till after a night's standing.

12. A drachm of fluor, mixed with two of oil of vitriol, afforded, after a distillation of two hours, a thin film of lead on the surface of the water in the receiver, but no filaceous earth. The same mixture was afterwards distilled with the use only of a glaas receiver instead of a lead one. In the beginning of the distillation a small spot appeared under the neck of the retort, and the neck itself was covered with white powder, but it soon disappeared; and though the empty part of the receiver was corroded, yet no more than half a grain of earth was procured.

These experiments so clearly point out the origin of the filaceous crust on the surface of the fluor acid, that its existence as a distinct acid is now universally allowed, even by those who formerly contended for its being only the vitriolic or some other acid dignified.

Experiments of a similar kind were made by Mr Wen-Mr Wenzel, who performed his distillation in a leaden retort, zel's experiments furnished with a glaas receiver. The water was covered in a leaden retort, with a variegated crust, and yielded a gelatinous precipitate, with fixed alkali. On examining the receiver, he found its internal surface corroded, so that it appeared as if it had been rubbed with coarse sand. By substituting a leaden receiver, however, instead of a glaas one, he obtained the acid entirely free from filaceous matter, and containing only a small quantity of iron and aluminous earth.

The fluor acid may also be procured by the nitrous, Fluor acid muriatic, and phosphoric acids.—Mr Scheele distilled procurable one part of the mineral with two of concentrated nitrous acid. One part went over into the receiver along with the fluor acid, and a thick crust was formed on the water of the receiver. The mass remaining in the retort was calcareous earth saturated with nitrous acid. With an equal quantity of marine acid, that of fluor passed over into the receiver with a large quantity of the muriatic; the internal surface of the receiver, as well as of the water contained in it, being covered with a white crust. The residuum was fixed sal ammoniac.

Phosphoric acid digested with powdered fluor, dissolved a good deal of it; and on distilling this solution, the fluor acid went over together with the watery particles of the mixture; the remaining mass in the retort had the properties of the ashes of bones.

The fluor acid procured in any of these ways is not distinguishable by the smell from that of sea-salt; in some cases it acts as muriatic acid, in others like that of tartar; but in most cases it shows properties peculiar to itself.

With fixed alkali the fluor acid forms a gelatinous and almost insipid matter, which refuses to crystallize. By evaporation a saline mass was obtained, which was in weight only the fifth part of the fixed alkali dissolved; it did not change the colour of syrup of violets, but precipitated water and likewise the solutions of gypsum and Epson salt. With mineral alkali the same phenomena were produced as with the vegetable.

Volatile alkali with fluor acid formed likewise a jelly, which when separated from the liquor appeared to be siliceous earth. The clear liquid tasted like vitriolic ammonia, and shot into very small crystals, which by sublimation yielded first a volatile alkali, and then a kind of acid sal ammoniac. By distillation with chalk and water, all the volatile alkali quickly came over. Lime water instantly threw down a regenerated fluor, which was the case also with solutions of lime in the nitrous and muriatic acids.—Solution of silver let fall a powder, which, before the blow-pipe, resumed its metallic form, the acid being dissipated, and forming a white spot on the charcoal round the reduced silver. Solution of quicksilver in nitrous acid was precipitated, and the powder was entirely volatile in the fire; but a solution of corrosive sublimate remained unchanged. Lead was totally precipitated from nitrous acid; and a solution of Epson salt was rendered turbid. Oil of vitriol produced a fluor acid by distillation, which formed at the same time a thick crust on the water of the receiver. The regenerated fluor procured either by means of lime water or solutions of the earth in acids, was decomposed by fixed, but not by volatile alkali.

With lime, magnesia, and earth of alum, this acid became gelatinous. Part of the two last were dissolved.

Gold was not touched by the fluor acid either alone or mixed with that of nitre. Silver, in its metallic state, underwent no change. Its calx, precipitated by an alkali, was partly dissolved; but the remainder formed an insoluble mass at the bottom. Vitriolic acid expelled the fluor acid in its usual form. Quicksilver was not dissolved, but its calx precipitated from the nitrous solution was partially so. The remaining insoluble part of the calx united with the acid, and formed a white powder, from which the fluor acid was expelled by the vitriolic. The same powder formed, by means of the blow-pipe, a yellowish glass; which, however, evaporated by degrees, leaving a small globule of fixed glass behind. Lead was not dissolved, Fluor Acid but the acid formed a sweet solution with its calx, and its acids of vitriol, and sea-salt, as also by sal ammoniac.

On digesting a quantity of acid with calx of lead, which had been previously digested in the same, a spontaneous precipitation took place. The precipitate melted easily before the blow-pipe, and ran into metal; but part of the glass remained fixed in the fire. Copper was partially dissolved, as appeared by the blue colour assumed by the liquid on the addition of volatile alkali. The calx of copper was easily soluble; and the liquor, though gelatinous, yielded blue crystals, partly of a cubic and partly of an oblong form, from which the acid could not be separated but by heat. Iron was violently attacked, and gave out inflammable vapours during the solution. The liquor refused to crystallize; but, by evaporation, congealed into a hard mass after the moisture was dissipated; and from this mass the fluor acid might be expelled as usual by oil of vitriol. The same effect was also produced by heat alone; the acid rising in vapours, and leaving a red ochre behind. Calx of iron was also dissolved, and the solution tasted like alum; but it could not be reduced to crystals. Tin, bismuth, and regulus of cobalt, were not attacked in their metallic state; but the calces of all of them were soluble. Regulus of antimony and powdered antimony were not sensibly acted upon. Zinc produced the same effects as iron, excepting that the solution seemed more inclined to crystallize.

The most remarkable property of this acid, however, is its readily dissolving glass, and carrying it off in the form of vapour. This singular property belongs not this acid, only to the pure acid, but also to the ammoniacal salt as well as the formed by combining it with the volatile alkali. Mr. Wieglich informs us, that on evaporating to dryness, in a cup of Münster porcelain, a solution of this kind of volatile alkali, the glazing of the inside was entirely corroded, and the bottom left as rough as a file. During the evaporation the cup was covered with white paper, which when dry appeared full of small crystals of an acid taste, easily distinguishable by the naked eye. These, as well as the ammoniacal salt, powerfully attracted the moisture of the air.

This property of the fluor acid renders it extremely difficult to be kept. Mr. Meyer informs us, that difficult having kept some upwards of a year in a glass phial, he kept it corroded the glass in many points surrounded with concentric circles, depositing a powder which adhered to the bottom. He is of opinion that golden vessels would be most proper for keeping this acid, as also for making experiments on the fluor itself. A phial proper for storing in the inside with wax and oil has been recommended for the same purpose.

This acid, as well as those of vitriol, nitre, and sea-salt, has been exhibited by Dr. Priestley in an aerially experiment. Having put some pounded spar into a phial, rimmed on and poured oil of vitriol upon it, adopting at the same time the usual apparatus for obtaining air, he observed to a kind of that a permanent cloud was formed by the vapour arising out from the mouth of the tube, which he attributed to the attachment of the acid to the aqueous moisture of the atmosphere. The moment that water came came in contact with this air, its surface became opaque and white by a stony film, which retarded the ascent of the water, till the air infusing itself through the pores and cracks of the crust, the water necessarily rose as the air diminished; and breaking the crust, presented a new surface to the air, which was immediately covered with another crust. Thus one stony incrustation was formed after another till every particle of the air was united to the water; and the different films being collected and dried, formed a white powdery substance, generally a little acid to the taste; but when washed in much pure water, perfectly insipid. The property of corroding glass he found to belong to the fluor acid air only when hot. From former experiments he concluded, that the fluor acid air was the same with what he had formerly obtained from vitriolic acid: but the experiments made since that time by various chemists, have now convinced him that it is an acid of a nature entirely different from all others.

By means of the fluor acid, a new art has been discovered, viz. that of engraving upon glass. For this purpose a looking-glass plate is to be covered with melted wax or mastic; and when the coating becomes hard, it is to be engraved upon by a very sharp-pointed needle or other instrument of that kind. A mixture of oil of vitriol and fluor acid are then to be put upon the plate, and the whole covered with an inverted China vessel, to prevent the evaporation of the fluor acid. In two days the glass plate may be cleared of its coating, when all the traces of the needle will be found upon it.

§ 5. Of the Sal Sedativus, or Acid of Borax.

This is a saline substance of a very singular nature, and till lately found nowhere but in borax itself. Its origin in different parts of the world is related under the article Borax; but since that article was printed, we have accounts of its being discovered in a mineral of a peculiar kind found at Lunenburg near Hartz. This is frequently transparent, but sometimes also a little opaque, and strikes fire slightly with steel. It has hitherto been found only in small crystals enveloped in a gypseous matter. These generally affect the cubical form, though they are sometimes irregular, and from the truncatures frequently appear to be of different kinds. One of them had fourteen faces, six small square planes, and eight hexahedral; though all these are modifications of cubes. Mr Weitbrunn analyzed it with some difficulty; but at last found that 100 parts of the mineral contained 60 of sedative salt, ten of magnesia, and ten of calcareous earth; of clay and flint five parts; sometimes ten of iron, though frequently but five. The same acid has also been discovered in Peru, and a little in Hungary from an analysis of petroleum. This bitumen arises from a rock between Pecklenicza and Moscowina. It seems at first to be white, but soon grows black by exposure to the air. It was analyzed by professor Winterl, who found it to contain a transparent oil in a butyraeous form, and a true sedative salt, united with the oil by means of an excess of phlogiston. The sedative salt was first discovered by Becher, and afterwards more accurately described by Homberg; but its nature was at first very much misunderstood, being named the narcotic salt of vitriol, on account of the vitriolic acid used in separating it from the borax. From this it is separable either by sublimation or crystallization. The method by sublimation is that recommended by Homberg. His process consists in mixing green vitriol with borax, dissolving them in water, filtering the solution, and evaporating till a pellicle appears: the liquor is then to be put into a small glass alembic, and the sublimation promoted till only a dry matter remains in the cucurbit. During this operation, the liquor passes into the receiver; but the internal surface of the capital is covered with a saline matter forming very small, thin, laminated crystals, very shining, and very light. This is the sedative salt. The capital is then to be unluted, and the adhering salt swept off with a feather; the part of the liquor which passed last into the receiver, is to be poured on the dry matter in the cucurbit; and a new sublimation is to be promoted as before, by distilling till the matter in the cucurbit is dry. These operations are to be frequently repeated in the same manner, till no more sedative salt can be obtained.

To obtain the sedative salt by crystallization, borax is to be dissolved in hot water; and to this solution any one of the three mineral acids is to be gradually added, by a little at a time, till the liquor be saturated, and even have an excess of acid, according to Mr Beaume's process. The liquor is then to be left in a cold place; and a great number of small, shining, laminated crystals will be formed: these must be washed with a little very cold water, and drained upon brown paper. The sedative salt obtained by this process is somewhat denser than that obtained by sublimation; the latter being so light that 72 grains are sufficient to fill a large phial.

Sedative salt, though thus capable of being once fixed in sublimed, is not, however, volatile; for it arises only by means of the water of its crystallization; and when it has once lost its water by drying, it cannot be raised into vapors by the most violent fire, but remains fixed, and melts into a vitreous matter like borax itself. This glass is soluble in water, and then becomes sedative salt again. A great quantity of water is required to dissolve the sedative salt, and much more of cold than of boiling water; whence it is crystallizable by cold, as it also is by evaporation; a singular property, which scarce belongs to any other known salt.

This substance has not an acid, but a somewhat bitterish taste, accompanied with a slight impression of tics. It nevertheless unites with alkaline salts as acids do, and forms with them neutral salts. It is soluble in spirit of wine, to which it communicates the property of burning with a green flame. It makes no change on the blue colour of vegetables, as other acids do. It expels the other acids from their bases, when distilled with a strong heat; though these are all capable of expelling it in the cold, the acid of vinegar not excepted.

The composition of sedative salt is very much unknown, as no means sufficient for its decomposition have hitherto been found out. Mr Bourdelin, who made many experiments on this salt, found that it was unalterable by treatment with inflammable matters, with sulphur, with mineral acids disengaged, or united with metallic substances, and with spirit of wine. He could only perceive some marks of an inflammable matter, and a little marine acid. The former discovered itself by its communicating a sulphurous smell to the vitriolic acid employed; and the latter by a white precipitate formed in a solution of mercury in the nitrous acid, by the liquor which came over on distilling the salt with powdered charcoal.

Mr Cadet's experiments. Mr Cadet, in the Memoirs of the Royal Academy of Sciences for 1766, has given an account of some experiments made by him on borax and its acid: from which he infers (1) That the acid contained in borax itself is the marine, and not sedative, salt. (2.) That it is the marine, he proves by having made a corrosive sublimate with this acid and mercurius precipitatus per se. That sedative salt does not enter the composition of borax itself, he proves, by the impossibility of recomposing borax from uniting the sedative salt with foible alkali. The salt so produced, he owns, is very like borax, but unfit for the purposes of soldering metals as borax is. He therefore thinks, that, in the decomposition of borax, the principles of the salt are somewhat changed, by the addition of that acid which extricates the sedative salt; and that this salt is composed of the marine acid originally existing in the borax, of the vitriolic acid employed in the operation, and of a vitreous earth. (If this is true, then sedative salt either cannot be procured by any other acid than the vitriolic, or it must have different properties according to the acid which procures it.) The vitreous earth, he says, is that which separates from borax during its solution in water, and which abounds more in the unrefined than refined borax, and which he thinks consists of a calx of copper, having obtained a regulus of copper from it. As he has never been able, however, to compose borax by the union of these ingredients, his experiments are by no means decisive. Mr Beaumé has asserted that it is always produced by rancid oils; but Dr Black thinks his proofs by no means satisfactory.

Sedative Salt combined.

I. With Vegetable Alkali. This salt forms a compound very much resembling borax itself in quality; but in what respects it differs from, or how far it is applicable to, the purposes of borax, hath not yet been determined.

II. With Mineral Alkali. This salt has generally been thought to recompose borax; and though Mr Cadet has denied this, yet as his experiments are hitherto imperfect and unsupported, we shall here give the history of that salt, as far as it is yet known.

This salt is prepared in the East Indies. It is said, that from certain hills in these countries there runs a green saline liquor, which is received in pits lined with clay, and suffered to evaporate with the sun's heat; that a bluish mud which the liquor brings along with it is frequently stirred up, and a bituminous matter, which floats upon the surface, taken off; that when the whole is reduced to a thick consistence, some melted fat is mixed, the matter covered with vegetable substances and a thin coat of clay; and that when the salt has crystallized, it is separated from the earth by a sieve. In the same countries is found native the mineral alkali in considerable quantity; sometimes tolerably pure, at other times blended with heterogeneous matters of various kinds. This alkali appears to exist in borax, as a Glauber's salt may be formed from a combination of borax with vitriolic acid. For a further account see Borax.

Borax, when imported from the East Indies, consists of small, yellow, and glutinous crystals. It is refined, some say, by dissolving it in lime-water; others, in alkaline lixivia, or in a lixivium of caustic alkali; and by others, in alum-water. Refined borax consists of large eight-sided crystals, each of which is composed of small, soft, and bitterish scales. It has been said that crystals of this size can by no means be obtained by dissolving unrefined borax in common water; that the crystals obtained in this way are extremely small, and differ considerably from the refined borax of the shops; inasmuch that Cramer calls the large crystals, not a purified, but an adulterated borax. When dissolved in lime-water, the borax shoots into larger crystals; and largest of all, when the vessel is covered, and a gentle warmth continued during the crystallization. All this, however, is denied by Dr Black; who says, that in order to accomplish the purification, we have only to dissolve the impure borax in hot water; to separate the impurities by filtration, after which the salt shoots into the crystals we commonly see. During the dissolution, borax appears glutinous, and adheres in part to the bottom of the vessel. From this glutinous quality, peculiar to borax among the salts, it is used by dyers for giving a gloss to silks.

All acids dissolve borax slowly, and without effervescence. It precipitates from them most, but not all, metallic substances; along with which a considerable part of the borax is generally deposited. It does not absorb the marine acid of luna cornea, or of mercury sublimate. It melts upon the surface of the former without uniting, and suffers the latter to rise unchanged; the borax in both cases becomes coloured; in the first, milky with red streaks; in the latter, amethyst or purple. Mixed with sal ammoniac, it extricates the volatile alkali, and retains the acid; but mixed with a combination of the marine acid with calcareous earths, it unites with the earth, and extricates the acid. It extricates the acid of nitre without seeming to unite with the alkaline basis of that salt; nor does it mingle in fusion with the common fixed alkaline salts, the borax flowing distinct upon their surface. A mixture of borax with twice its weight of tartar, dissolves in one fifth of the quantity of water that would be necessary to dissolve them separately: the liquor yields, on inspissation, a viscous, tenacious mass like glue; which refuses to crystallize, and which deliquesces in the air. Borax affords likewise a glutinous compound with the other acids, except the vitriolic; whence this salt is generally preferred for making the sedative salt. It proves most glutinous with the vegetable, and least with the marine. With oils, both expressed and distilled, it forms a milky, semi-saponaceous compound. It partially dissolves in spirit of wine. In conjunction with any acid, it tinges the flame of burning matters green; the precipitate thrown down by it from metallic solutions has this effect. It does not deflagrate with nitre. Fused with inflammable matters, it yields nothing sulphurous, as those salts do which Acetous Acid which contain vitriolic acid. By repeatedly moistening it when considerably heated, it may be entirely sublimed.

Borax retains a good quantity of water in its crystals; by which it melts and swells up in a heat insufficient to vitrify it. It is then spongy and light, like calcined alum; but, on increasing the fire, it flows like water.

§ 6. Of the Acetous Acid and its Combinations.

This acid is plentifully obtained from all vinous liquors, by a fermentation of a particular kind, (see Fermentation, and Vinegar.) It appears first in the form of an acid liquor, more or less deeply coloured, as the vinegar is more or less pure. By distillation in a common copper-till, with a pewter head and worm, this acid may be separated from many of its oily and impure parts. Distilled vinegar is a purer but not a stronger acid than the vinegar itself; for the acid is originally less volatile than water, though, by certain operations, it becomes more so. After vinegar has been distilled to about \( \frac{1}{2} \) of its original bulk, it is still very acid, but thick and black. This matter continues to yield, by distillation, a strong acid spirit, but tainted with an empyreumatic oil. If the distillation is continued, a thick black oil continues to come over; and at last some volatile alkali, as in the distillation of animal substances. The caput mortuum left in the distilling vessel, being calcined in an open fire, and afterwards lixiviated, yields some fixed alkaline salt.

Acetous Acid combined,

I. With Vegetable Alkali. The produce of this combination is the terra foliata tartari, or sal diureticus of the shops; but to prepare this salt of a fine white flaky appearance, which is necessary for sale, is a matter of some difficulty. The best method of performing this operation is, after having saturated the alkali with the vinegar, which requires about 15 parts of common distilled vinegar to one of alkali, to evaporate the liquor to dryness; then melt the false mass which remains with a gentle heat; after which it is to be dissolved in water, then filtered, and again evaporated to dryness. If it is now dissolved in spirit of wine, and the liquid abstracted by distillation, the remaining mass being melted a second time, will, on cooling, have the flaky appearance desired.

A good deal of caution is necessary in the first melting; for the acetous acid is easily diffusible, even when combined with fixed alkali, by fire. It is proper, therefore, that, when the salt is melted, a little should be occasionally taken out, and put into water; and, when it readily parts with its blackness to the water, must then be removed from the fire. The salt, when made, has a very strong attraction for water, inasmuch that it is not easily preserved, even when put into glass bottles. To keep it from deliquescing, Dr Black, therefore, recommends the corks to be covered with some bituminous matter; otherwise they would transmit moisture enough to make the salt deliquescent.

II. With Fulgile Alkali. This alkali, combined with the acetous acid, forms a salt whose properties are not well known. Dr Lewis affirms, that it is nearly similar to the terra foliata tartari. The author of the Chemical Dictionary, again, maintains it to be quite different; particularly that it crystallizes well, and is not deliquescent in the air; whereas the former cannot be crystallized; and even when obtained in a dry form, unless great care is taken to exclude the air, will presently deliquesce.

III. With Volatile Alkali. This combination produces Vegetable a salt so exceedingly deliquescent, that it cannot be procured in a dry form without the greatest difficulty. In a liquid state, it is well known in medicine, as a fudorific, by the name of spiritus minderer. It may, however, be procured in a dry form, by mixing equal parts of vitriolic sal ammoniac and terra foliata tartari, and subliming the mixture with a very gentle heat. When the salt is once procured, the utmost care is requisite to preserve it from the air.

IV. With Earths. Combinations of this kind are but little known. With the calcareous and argillaceous earths compounds of an astringent nature are formed. According to the author of the Chemical Dictionary, the salt resulting from a combination of vinegar with calcareous earth easily crystallizes, and does not deliquesce. With magnesia the acetous acid does not crystallize; but, when inspissated, forms a tough mass, of which two drachms, or two and a half, are a brisk purgative.

V. With Copper. Upon this metal the acid of vinegar does not act briskly, until it is partly at least calcivered. If the copper is previously dissolved in a mineral acid, and then precipitated, the calx will be readily dissolved by the acetous acid. The solution is of a green colour, and beautiful green crystals may be obtained from it. The solution, however, is much more easily effected, by employing verdigris, which is copper already united with a kind of acetous or tartarous acid, and very readily dissolves in vinegar. The crystals obtained by this process are used in painting, under the name of distilled verdigris.

The most ready, and in all probability the cheapest, method of preparing the crystals of verdigris is that proposed by Mr Wenzel, by mixing together the solutions of sugar of lead and blue vitriol, when an exchange of bases takes place; the lead being instantly precipitated by the vitriolic acid, and the acetous acid uniting with the copper. From 15 ounces and two drachms of sugar of lead with twelve ounces of blue vitriol, five ounces of the crystals were obtained. The precipitate of lead, though washed several times with water, never lost its green colour. It may either be used, he says, in this state, as a green pigment, or it may be made perfectly white by digestion in dilute nitrous acid.

VI. With Iron. Vinegar acts very readily upon iron, and dissolves it into a very brown and almost black liquor, which does not easily crystallize, but, if inspissated, runs per deliquium. This liquor is employed in the printing of linens, calicoes, &c., being found to strike a finer black with madder, and to injure the cloth less, than solutions of iron in the other acids.

VII. With Lead. The acetous acid dissolves lead in its metallic state very sparingly; but if the metal is calcined, it acts upon it very strongly. Even after lead is melted into glass, the acetous acid will receive a strong impregnation from it; and hence it is dangerous to Acetous Acid—To put vinegar into such earthen vessels as are glazed with lead. In the metallic state, only a drachm of lead can be dissolved in eight ounces of distilled vinegar.

If lead is exposed to the vapors of warm vinegar, it is corroded into a kind of calx, which is used in great quantities in painting, and is known by the name of cerus, or white lead. The preparation of this pigment has become a distinct trade, and is practiced in some places of this kingdom where lead is procurable at the lowest price. The process for making cerus is thus given by the author of the Chemical Dictionary.

"To make cerus, leaden plates rolled spirally, so that the space of an inch shall be left between each circumvolution, must be placed vertically in earthen pots of a proper size, containing some good vinegar. These leaden rolls ought to be so supported in the pots that they do not touch the vinegar, but that the acid vapor may circulate freely betwixt the circumvolutions. The pots are to be covered, and placed in a bed of dung, or in a sand-bath, by which a gentle heat may be applied. The acid of vinegar being thus reduced into vapor, easily attaches itself to the surface of these plates, penetrates them, and is impregnated with the metal, which it reduces to a beautiful white powder, called cerus. When a sufficient quantity of it is collected on the plates, the rolls are taken out of the pots, and unfolded; the cerus is then taken off, and they are again rolled up, that the operation may be repeated.

"In this operation, the acid being overcharged with lead, this metal is not properly in a saline state; hence cerus is not in crystals, nor is soluble in water; but a saline property would render it unfit for painting, in which it is chiefly employed."

Though this process may in general be just, yet there are certainly some particulars necessary to make cerus of a proper color, which this author has omitted; for though we have carefully treated thin plates of lead in the manner he directs, yet the calx always turned out of a dirty grey color. It is probable, therefore, that after the lead has been corroded by the steam of vinegar, it may be washed with water slightly impregnated with the vitriolic and nitrous acids.

This preparation is the only white hitherto found fit for painting in oil; but the discovery of another would be very desirable, not only from the faults of cerus as a paint, but also from its injuring the health of persons employed in its manufacture, by affecting them with a feverish colic; which lead, and all its preparations, frequently occasion.

If distilled vinegar is poured on white lead, it will dissolve it in much greater quantity than either the lead in its metallic form, or any of its calces. This solution filtered and evaporated, flows into small crystals of an austerely sweetish taste, called sugar of lead. These are used in dyeing, and externally in medicines. They have been even given internally for spitting of blood. This they will very certainly cure; but at the same time they as certainly kill the patient by bringing on other diseases. If these crystals are repeatedly dissolved in fresh acids, and the solutions evaporated, an oily kind of substance will at last be obtained, which can scarcely be dried.

From all the metallic combinations of the acetous acid, it may be recovered in an exceedingly concentrated form, by simple distillation, sugar of lead only excepted. If this substance is distilled in a retort with inflammable spirit, and not an acid, comes over; but this is denied of lead by Dr. Black.

VIII. With Tin. The combination of acetous acid with tin is so little known, that many have doubted whether distilled vinegar is capable of dissolving tin or not. Dr. Lewis observes, "That plates of pure tin put into Dr. Lewis's common vinegar begun in a few hours to be corroded, experiment without the application of heat. By degrees a portion of the metal was taken up by the acid, but did not seem to be perfectly dissolved, the liquor appearing quite opaque and turbid, and depositing great part of the corroded tin to the bottom, in a whitish powder. A part of the tin, if not truly dissolved, is exquisitely divided in the liquor; for, after standing many days, and after passing through a filter, so much remained suspended as to give a whitishness and opacity to the fluid. Acid juices of fruits, substituted to the vinegar, exhibited the same phenomena. These experiments are not fully conclusive for the real solubility of tin in these acids, with regard to the purposes for which chemists have wanted such a solution; but they prove what is more important; that tin, or tinned vessels, however pure the tin be, will give a metallic impregnation to light vegetable acids suffered to stand in them for a few hours."

With regard to other metallic substances, neither the degree of attraction which the acetous acid has for them, nor the nature of the compounds formed by the union of it with such substances, are known; only, that as much of the reguline part of antimony is dissolved in this acid as to give it a violent emetic quality. See Regulus of Antimony.

Concentration of the Acetous Acid.

Common vinegar, as any other weak acid, may be advantageously concentrated by frost; as also may its spirit or the distilled vinegar of the shops: but as the cold, in this country, is seldom or never so intense as to freeze vinegar, this method of concentration cannot be made use of here. If distilled vinegar be set in a water-bath, the most aqueous part will arise, and leave the more concentrated acid behind. This method, however, is tedious, and no great degree of concentration can be produced, even when the operation is carried to its utmost length. A much more concentrated acid may be obtained by distilling in a retort the crystals of copper, mentioned (no 872.) under the name of distilled verdigris. A very strong acid may thus be obtained, which has a very pungent smell, almost as suffocating as volatile sulphurous acid. The Count de Lauraguais discovered that this spirit, if heated in a wide-mouthed pan, would take fire on the contact of flaming substances, and burn entirely away, like spirit of wine, without any residuum. The same nobleman also observed, that this spirit, when well concentrated, easily crystallizes without ad- This may seem to be the most proper method of obtaining the acetic acid in its greatest degree of strength and purity; but as the process requires a very strong heat to be used towards the end of the operation, it is probable that part of the acetic acid may be by that means entirely decomposed. It would seem preferable, therefore, to decompose pure terra foliata tartari by means of the vitriolic acid, in the same manner as nitre or sea-salt are decomposed for obtaining their acids. In this case, indeed, the acetic acid might be a little mixed with the vitriolic; but that could easily be separated by a second distillation. A still better method of preparing this acid seems to be by distilling sugar of lead with oil of vitriol. The proportion used by M. Lorenzen of Copenhagen, is three ounces of vitriolic acid to eight of the sugar of lead. Mr Dollfus recommends two parts of sugar of lead to one of vitriolic acid.

Dr Priestley, who gives us several experiments on the vegetable acid when reduced to the form of air, mentions his being easily able to expel it from some exceedingly strong concentrated vinegar, by means of heat alone. This seems somewhat contrary to the count de Lauragnais's observation of the deposition of the spirit of verdigris, as it is commonly called, to crystallize; but a still greater difference is, that the vegetable acid air extinguished a candle, when, according to the Count's observation, it ought to have been inflammable. The most curious property observed by Dr Priestley is, that the vegetable acid air being imbued by oil olive, the oil was rendered less viscous, and clearer, almost like an essential oil. This is a useful hint; and, if pursued, might lead to important discoveries.

Acetous acid combined with Inflammable Matter.

The only method yet known, of combining acetous acid with the principle of inflammability, is by mixing together equal parts of the strongly concentrated acid called spirit of verdigris, and spirit of wine. The result is, a new kind of ether, similar to the vitriolic, nitrous, and marine. This ether, however, retains some of the acidity and peculiar smell of the vinegar. By rectification with fixed alkali, it may be freed from this acidity, and then smells more like true ether, but still retaining something of the smell, not of the acid, but the inflammable part of the vinegar.

In this process a greater quantity of ether is obtained than by employing the vitriolic acid; which shows that the vegetable acid is essentially fitter to produce ether than the vitriolic. For making the acetous ether readily, Mr Dollfus recommends eight ounces of sugar of lead dried by a very gentle heat, until it loses the water of crystallization, when it will weigh five ounces and six drachms. It is then to be put into a glass retort, and a mixture of five ounces of vitriolic acid, with eight of spirit of wine, poured upon it, and the whole distilled with a very gentle fire. The first ounce that passes over will be dulcified acetous acid, the next almost all ether, and the third ether in its purest state.

An ether may also be obtained from vinegar of wood. To make it, the most concentrated acid of this kind is to be made use of. For this purpose an empyreumatic acid must first be distilled from beech-wood, and then rectified by a second distillation. Three pounds of this require for their saturation five ounces of purified alkali, which by evaporation and fusion affords three ounces and a quarter of terra foliata tartari. From this, one ounce fix drachms of concentrated acid are obtained; and this, on being mixed with an equal quantity of alcohol, yields two ounces one drachm and a half of genuine ether.

§ 7. Of the Acid of Tartar.

Tartar is a substance thrown off from wine, after it is put into casks to depurate. The more tartar that is separated, the more smooth and palatable the wine is. This substance forms a thick hard crust on the sides of the casks; and, as part of the fine dregs of the wine adhere to it, the tartar of the white wines is of a greyish white colour, called white tartar; and that of red wine has a red colour, and is called red tartar.

When separated from the casks on which it is formed, tartar is mixed with much heterogeneous matter; from which, for the purposes of medicine and chemistry, it requires to be purified. This purification is performed at Montpelier; and consists first in boiling the tartar in water, filtrating the solution, and allowing the salt to crystallize, which it very soon does; as tartar requires nearly twenty times its weight of water to dissolve it.

The crystals of tartar obtained by this operation are far from being perfectly pure; and therefore they are again boiled in water, with an addition of clay, which absorbs the colouring matter; and thus, on a second crystallization, a very pure and white salt is obtained. These crystals are called cream, or crystals, of tartar; and are commonly sold under these names.

Dr Black observes, that in the purification of tartar, it is necessary to add some earthy substances, in order to absorb or carry down the colour. Macquer thinks that these substances unite in part with the tartar, and render it more soluble, but they have little disposition to unite with acids; they are the purer kinds of clay, and promote the complete deposition of its impurities: so that in the management of wines it is necessary to add certain powdery substances which have some weight, and fall to the bottom readily; and which, in falling, carry down a number of particles that would otherwise float in the liquor for a long time, being so light that they could hardly be made to subside; but the particles of clay adhering to them increase their gravity; and probably it answers the same purpose in the refinement of tartar.

To obtain the pure Acid of Tartar.

For a long time the cream or crystals of tartar Scheele's were considered as the purest acid which could be obtained from this substance; but, in the year 1770, an analysis of tartar was published in the Swedish transactions, by Mr Scheele. His method of decomposing the salt was, to dissolve it in a sufficient quantity of boiling water, then to add chalk in fine powder till the effervescence ceased. A copious precipitation ensued; and the remaining liquor being evaporated, porated, afforded a soluble tartar. This proved, that cream of tartar is not, as was commonly supposed, an acid of a peculiar kind, joined with a great deal of earthy impurities; but really a compound salt, containing an alkali joined with an acid; and that the alkali produced from burnt tartar is not generated in the fire, but pre-existent in the salt.

The whole sediment obtained in this experiment, is the calcareous earth combined with the acid of tartar, which may justly be called selenites tartareus. If some diluted vitriolic acid is poured upon this selenites tartareus, the vitriolic acid expels the acid of tartar, forming a true selenite with the earth, while the liquor contains the pure acid of tartar. By infusion this acid may be made stronger, and even formed into small white crystals, which do not deliquesce in the air. A particular species of tartar extracted from sorrel hath been sold for taking spots out of cloths, under the name of essential salt of lemons, and which is now discovered to be the same with the acid of sugar.

This experiment was soon after confirmed by Dr Black; who farther observed, that if quicklime was used instead of chalk, the whole acid would be absorbed by the lime, and the remaining liquor, instead of being a solution of soluble tartar, would be a caustic lixivium. The most ready method, however, of procuring the pure acid of tartar seems to be that recommended by Mr Schiller in the Chemical Annals for 1787. One pound of cream of tartar is to be boiled in five or six pounds of water, and a quarter of a pound of oil of vitriol added by little and little, by which means a perfect solution will be obtained. By continuing the boiling, all the vitriolated tartar is precipitated. When the liquor is evaporated to one half, it must be filtered; and if, on the renewal of the boiling, anything farther is precipitated, the filtration is to be repeated. The clear liquor is then to be reduced to the consistence of a syrup, and set in a temperate, or rather a warm place, when very fine crystals will be formed, and as much acid obtained as is equal in weight to half the cream of tartar employed. If too small a quantity of vitriolic acid has been employed, the undecomposed cream of tartar falls along with the vitriolated tartar.

Acid of Tartar combined,

I. With Vegetable Alkali. If the pure acid of tartar be combined with this alkali to the point of saturation, a neutral salt is produced, which deliquesces in the air, and is not easily crystallized, unless the liquor be kept warm, and likewise be somewhat alkaline. This salt, called soluble tartar, is used in medicine as a purgative; but as its deliquescence does not admit of its being kept in a crystalline form, it is always sold in powder. Hence those who prepare soluble tartar, take no further trouble than merely to rub one part of fixed alkaline salt with three of cream of tartar, which renders the compound sufficiently neutral, and answers all the purposes of medicine. Dr Black informs us, that in medical prescriptions, where soluble tartar is ordered as a purgative along with a decoction of tamarinds, the acid of the latter will decompose the soluble tartar, and thus the prescription may perhaps be rendered ineffectual. The saline mixture used in fevers is nothing but a tartarus solubilis in solution.

According to Mr Scheele, cream of tartar may be recomposed from the pure acid and alkali in the following manner: "Upon fixed vegetable alkali pour its Combination. Continue this till the nations. effervescence is over; the fluid will then be transparent; but if more of the acid is added, it will become turbid and white, and small crystals like white sand will be formed in it. These crystals are a perfect cream of tartar."

Upon these principles, another method of decomposing cream of tartar might be tried; namely, adding to it as much oil of vitriol as would saturate the alkali, then dissolving and crystallizing the salt: but, by this method, there would be danger of the acid being adulterated with vitriolated tartar.

II. With Fossil Alkali. The salt produced from an Seignette's union of cream of tartar with fossil alkali, has been or Rochelle long known under the names of Seignette's salt, sal Ru-pellensia, or Rochelle salt; but as the cream of tartar is now discovered to be not a pure acid, but adulterated with a portion of soluble tartar, possibly some differences might be observed if the pure acid was used.

This salt was first invented and brought into vogue by one Seignette, an apothecary at Rochelle, who kept the composition a secret as long as he could. Messrs Boydouc and Geoffroy afterwards discovered and published its composition.

To prepare this salt, crystals of mineral alkali are to be dissolved in hot water, and powdered cream of tartar thrown in as long as any effervescence arises. For the better crystallization of the salt, the alkali ought to prevail. The liquor must then be filtered and evaporated, and very fine large crystals may be obtained by cold, each of which is the half of a polygonous prism cut in the direction of its axis. This section, which forms a face much larger than the rest, is, like them, a regular rectangle, indistinguishable from the others, not only by its breadth, but also by two distinct diagonal lines which intersect each other in the middle. The following method of preparing Seignette's salt, recommended by Mr Scheele, seems preferable to any other on account of its ease and cheapness. Thirty six ounces of crystals of tartar are to be saturated with potash, and eleven ounces of common salt dissolved in the ley. When it is grown cold, and the vitriolated tartar has subsided to the bottom, it is filtered and evaporated till a pellicle appears; the two first crystallizations yield a fine Seignette's salt; the third contains some digestive salt; and the fourth is entirely composed of it. The reason of this formation of Seignette's salt is, that the vegetable alkali has a greater attraction for acids than the mineral, and therefore decomposes the sea-salt, whose basis is then at liberty to combine with the acid of tartar; while the stronger marine acid takes the vegetable alkali.—A salt of the same kind will be produced by adding Glauber's salt instead of common sea-salt.

III. With Volatile Alkali. With regard to this combination, all we know as yet is, that if the alkali is tartrate, over-saturated with acid, a cream of tartar, almost as difficult of solution as that of fixed alkali, will be obtained. When the saturation has been pretty exact, a beautiful salt, composed of four sided pyramids, and which does not deliquesce in the air, is produced. It is instantly decomposed, and emits a pungent volatile smell on being mixed with fixed alkali. IV. With Earths. All that is as yet known concerning these combinations, is, that with the calcareous earth a compound not easily soluble in water is formed. The other properties of this substance, and the nature of combinations of tartarous acid with other earths, are entirely unknown.

V. With Copper. In its metallic state, cream of tartar acts but weakly on this metal, but dissolves verdigris much more perfectly than distilled vinegar can. The solution with cream of tartar, being evaporated, does not crystallize, but runs into a gummy kind of matter; which, however, does not attract the moisture of the air. It readily diffuses in water, and makes a beautiful bluish green on paper, which has the property of always shining, as if covered with varnish. The effects of the pure acid on this metal have not yet been tried.

VI. With Iron. The effects of a combination of iron with the pure acid have not hitherto been tried. Cream of tartar dissolves this metal into a green liquor, which being evaporated runs per deliquium. It has been attempted to substitute a solution of this kind to the liquor used in printing calicoes formed of iron and four beer; but this gave a very dull brownish colour with madder. Possibly, if the pure acid was used, the colour might be improved. In medicine, a combination of cream of tartar with iron is used, and probably may be an useful chalybeate.

VII. With Regulus of Antimony. See Sect. III.

§ 8. Of the Acid of Sugar.

That sugar contains an acid, which on distillation by a strong fire arises in a liquid form, in common with that of most other vegetable substances, has been generally known; but how to obtain this acid in a concrete form, and to appearance as pure and crystallizable as the acid of tartar, we were entirely ignorant, till the appearance of a treatise intitled, Differetia Chemicas, de acido Sacchari, autore Johanne Afzelio Arvidsson, 4to, Upsalia.

Of the method of procuring, and the properties of, this new acid, we have the following account in the Edinburgh Medical Commentaries, vol. iv.

1. To an ounce of the finest white sugar in powder, in a tubulated retort, add three ounces of strong spirit of nitre.

2. The solution being finished, and the phlogiston of the spirit of nitre mostly exhaled, let a receiver be properly fitted to the retort and luted, and the liquor then made to boil gently.

3. When the solution has obtained a brownish colour, add three ounces more of spirit of nitre, and let the ebullition be continued till the fumes of the acid are almost gone.

4. The liquor being at length emptied into a larger vessel, and exposed to a proper degree of cold, quadrangular prismatic crystals are observed to form; which being collected, and dried on soft paper, are found to weigh about 109 grains.

5. The remaining liquor being again boiled in the same retort, with two ounces of fresh spirit of nitre, till the red vapours begin to disappear, and being then in the same manner exposed to crystallize, about 43 grains of saline spicule are obtained.

Vol. IV. Part II. Acid of Sugar: The acid appears in form of a white powder, soluble neither in water nor spirit of wine, unless the acid prevails. It has a stronger affinity with magnesia than any of the alkaline salts. With earth of alum, no crystals are obtained; but a yellow pellucid mass, of a sweetish and somewhat astringent taste; which, in moist air, liquefies, and increases two-thirds in weight.

This acid acts upon all metals, gold, silver, platinum, and quicksilver, not excepted, if they have been previously dissolved in an acid, and then precipitated. Iron in its metallic state is dissolved in very large quantity by the saccharine acid; 45 parts of iron being soluble in 55 of acid. By evaporation, the liquor shoots into yellow prismatic crystals, which are easily soluble in water. With cobalt, a quantity of yellow-colored crystals are obtained, which being dissolved in water, and sea-salt added to the solution, form a sympathetic ink. The elective attractions of this singular acid are, first, lime, then the terra ponderosa, magnesia, vegetable alkali, mineral alkali, and lastly clays. With spirit of wine an ether was obtained, which cannot easily be set on fire unless previously heated, and burns with a blue instead of a white flame.

Towards the conclusion of his dissertation the author observes, that some may imagine that the acid of nitre, made use of in these experiments, may have a considerable share in the production of what he has termed acid of sugar. But though he acknowledges that this acid cannot in any way be obtained but by the affluence of spirit of nitre, he is thoroughly convinced that it does not, in any degree, enter into its composition.

What occurs to us on this subject is, that if the acid really pre-exists in the sugar, it must give some tokens of its existence by mixing the sugar with other substances besides spirit of nitre. The author himself thinks that lime acts upon the acid part of the sugar: from whence we are apt to conclude, that by mixing lime, in a certain proportion, with sugar, a compound should be obtained somewhat similar to what was formed by a direct combination of lime with the pure acid. In this case, we might conclude that the nitrous acid produces this salt, by combining with the inflammable part of the sugar, becoming thereby volatile, and flying entirely off, so as to leave the acid of the sugar pure. In the distillation of dulcified spirit of nitre, however, we have an instance of the nitrous acid itself being very much altered. This must therefore suggest a doubt, that the acid salt obtained in the present case is only the nitrous acid deprived of its phlogiston, and united with some earthy particles.

In a treatise lately published by Mr Rigby, however, we are informed that sugar itself may be recomposed by uniting the acid of sugar with phlogiston; which assertion, if well founded, undoubtedly decides the dispute in favour of the saccharine acid being originally contained in the sugar. Late experiments have determined it to be the same with that of forrel; for which, as well as many other valuable acquisitions, the science of chemistry is indebted to Mr Scheele. Having dissolved as much acid of sugar in cold water as the liquor could take up, he added to this solution some lixivium of tartar drop by drop, waiting a little after each drop and found the mixture, during the phosphorus effervescence, full of small crystals, which were genuine Combination of wood-foerel. M. Klaproth having precipitated a nitrous solution of quicksilver with salt of wood-foerel, perfectly neutralized by vegetable alkali, obtained a white precipitate; which, when edulcorated and fulminated, dried, and gently heated in a tea-spoon, fulminated quickly with a noise not inferior to that of fulminating gold, silver. Acid of sugar perfectly neutralized with vegetable alkali, afforded the same precipitate, and fulminated in the same manner.

§ 9. Of the Acid of Phosphorus.

This acid was first discovered by Homberg in phlogistic urine; afterwards by Margraaf in mustard and cruciferous plants: M. Bochante discovered it in wheat; and lastly, M. Haffenfratz has traced it in the mineral kingdom with great attention.—He has found that phosphorated iron is contained in all the Prussian blues, when not purified; but that this acid is produced by the coals employed in the process, and is no constituent part of the tinged matter. According to him it occurs almost universally in the minerals of iron which are found in the flinty strata of the earth, as well as those which are undoubtedly modern, whether primary or secondary; unless the iron be so far of a metallic nature as to be attracted by the magnet, or very near that state. It is afforded by the ochre strata, and those which contain haematites as well as the flinty kind. Into these it is supposed to have come by the decomposition of vegetables; and to investigate this matter he examined the hibiscus palustris, foliago, virga aurea, antirrhinum, lunaria, solanum nigrum, vulgatum, flachys palustris, artemisia Zeylandica, ruta graveolens, lycopus Europaeus, carex aceta, vinca major, nepeta Pannonica, and noa Abyssina. All these plants afforded the acid of wood-foerel and the phosphoric acid. The quantity of the former varied from two ounces two drachms 18 grains of acid salt containing some calcareous earth, to two drachms 24 grains in a pound of each plant; the quantity of calcareous phosphoric salt being from one ounce five drachms 48 grains, to one drachm 12 grains.—M. Haffenfratz also observes, that the phosphoric acid is procurable from all kinds of iron; though in some it seems to proceed from that contained in the earth, and in others from the coals employed in the reduction.

The phosphoric acid is also found by Dr Marquart to be contained in the gastric juice of animals. One pound four ounces of the gastric juice of oxen gave 10 grains of a lymphatic matter, exactly like the blood in its qualities; 16 grains and six-sevenths of phosphoric acid, which with a blow-pipe was changed into a very pure and deliquescent glass of phosphorus; five grains of phosphorated lime, two grains of resin, 14 grains of sal ammoniac, 29 grains of common salt, a very small quantity of an extract whose nature was difficult to ascertain; one pound three ounces five drachms and 67½ grains of water; so that the solid contents were only 166th part of the bulk.

In sheep, the quantity of gastric juice was about eight ounces in quantity, of a deeper and brighter green Acid of green than that of oxen or calves; but affording the same ingredients, though in a different proportion; though no other acid than that of phosphorus could be discovered. It was also more disposed to putrefaction. Calves furnished from four to six ounces of gastric juice, which contained very little lymph, but afforded some quantity of dry jelly, though the whole was not equal to the proper proportion of lymph. The phosphorated lime was in the usual quantity, but the disengaged phosphoric acid in a very small proportion. The lacteal acid was found in great quantity; to which, along with that of phosphorus, our author supposes the property of curdling the milk in the animal's stomach to be owing.

The phosphoric acid has also been found in very large quantity in the calcareous stones of Andalusia; and Mr Klaproth has found the same combined with calcareous earth in a kind of beryl, crystallized in hexahedral prisms, called by M. Verner aquit. Formerly the best method of obtaining it was from urine, where it is contained in very considerable quantity in combination with the volatile alkali, and forming a salt called the microcosmic, or essential salt of urine.

To procure this, a large quantity of urine is to be evaporated to the consistence of a thin syrup; which, being set in a cold place, will yield, in three or four weeks, foul brown-coloured crystals, which are the microcosmic salt, mixed with the marine, and other salts of urine. These crystals are to be dissolved in hot water; the solution filtered whilst it continues hot, and set to crystallize again; and the solution, filtration, and crystallization, repeated till the salt becomes pure and white. In all the crystallizations the microcosmic salt floats first, and is easily distinguished and separated from the others. If the urine which remains after the first crystallization be further evaporated, and again set in the cold, it will yield more crystals; but browner and more impure than the former; and therefore requiring to be purified by themselves. From 20 gallons of urine may be obtained four ounces of pure salt; a considerable part being still left in the residuum.

In these operations the heat ought to be gentle, and the vessels either of glass or compact stone-ware. Urine being evaporated in a copper vessel, afforded only a green solution of that metal.

Concerning the nature of the microcosmic salt obtained by the above process, Mr Margraff gives the following account in the Berlin memoirs for 1746.

"Sixteen ounces of the salt, distilled in a glass retort, in a heat gradually raised, gave over eight ounces of a volatile unuous spirit, resembling that made from sal ammoniac by quicklime. The residuum was a porous brittle mass, weighing eight ounces. This, urged with a stronger fire in a crucible, bubbled and frothed much, and at length sunk down into the appearance of glass, without seeming to suffer any further diminution of its weight in the most vehement heat.

The vitreous matter dissolved in twice or thrice its quantity of water, into a clear, transparent, acid liquor, somewhat thick, not ill resembling in consistence concentrated oil of vitriol. This liquor totally corroded zinc into a white powder, which, being diluted with water, appeared in great part to dissolve, fixed Acid of alkalies occasioning a plentiful precipitation. It acted Phosphorus powerfully upon iron, with some effervescence; and its Combining the metal into a kind of muddy substance in solutions. Clinging to bluish, in part soluble in water like the preceding. It dissolved likewise a portion of regulus of antimony, and extracted a red tincture from cobalt. On lead and tin it had very little action. Copper it corroded but slightly. On bismuth, silver, and gold, it had no effect at all, either by strong digestion, or a boiling heat. Nor did the adding of a considerable portion of nitrous acid enable it to act upon gold.

"The vitreous salt in its dry form, melted with metallic bodies with a strong fire, acts upon them more powerfully. In each of the following experiments, two drachms of the salt were taken to two scruples of the metal reduced to small parts. (1.) Gold communicated a purple colour to the vitreous salt; on weighing the metal, however, its diminution was not considerable. (2.) Silver lost four grains, or \( \frac{1}{5} \) oz.; and rendered the salt yellowish, and moderately opaque. (3.) Copper lost only two grains, or \( \frac{1}{5} \) oz., though the salt was tinged of a deep green colour. It seemed as if a portion of the salt had been retained by the metal, which, after the fusion, was found to be whiter and more brittle than before. (4.) During the fusion with iron, flashes like lightning were continually thrown out; a phosphorus being generated from the combination of the acid with the inflammable principle of the iron. Great part of the mixture rises up in froth; which, when cold, appears a vitreous scoria, covered on the surface with a kind of metallic skin, which, on being rubbed, changes its green colour to a yellowish. The rest of the iron remains at the bottom of the crucible, half melted, half vitrified, and spongy. (5.) Tin lost 18 grains, or nearly one-half its weight, and rendered the salt whitish; the remaining metal being at the same time remarkably changed. It was all over leafy and brilliant, very brittle, internally like zinc. Laid on burning coals, it first began to melt, then burnt like zinc, or phosphorus. (6.) Lead lost 16 grains, and gave the same whitish colour to the scoria that tin does. The remaining lead was in like manner inflammable, but burnt less vehemently than the tin; from which it differed also in retaining its malleability. (7.) Mercury precipitated from aquafortis, and well edulcorated, being treated with the salt in a glass retort, with a fire raised to the utmost, only 12 grains of mercury sublimed; 28 remaining united with the acid, in a whitish, semi-opaque mass. A solution of this mixed in distilled water, deposited a quantity of a yellowish powder; which, by distillation in a glass retort, was in great part revived into running mercury. A part also remained dissolved in the clear liquor; for a drop let fall on polished copper instantly whitened it. (8.) Regulus of antimony melted with the vitreous salt, lost eight or nine grains, (about \( \frac{1}{5} \)) the regulus assumed a fine, brilliant, striated appearance; the scoriae were somewhat opaque. (9.) Bismuth lost eight grains; the scoriae were like the preceding, but the bismuth itself suffered little change. (10.) Zinc, mixed with the salt, and distilled in a glass retort, yielded a true phosphorus, which arose in a very moderate heat. The residuum was of a grey colour, a little melted at

Practice.

Acid of Phosphorus and its Combinations.

The bottom, in weight not exceeding two drachms; so that two scruples had sublimed. This residuum, urged further in a small Hessian crucible to perfect fusion, emitted an infinity of phosphorine flashes, with a kind of detonation. The matter, grown cold, looked like the scoriae of melted glass. (11.) White arsenic, mixed with this salt, separated in the fire, greatest part of it subliming, and only as much remaining behind as incresced the weight of the salt eight or nine grains. This compound appeared at first transparent; but, on being exposed to the air, became moist, and of an opaque whiteness, much resembling crystalline arsenic. (12.) Cinnabar totally sublimed; suffering no change itself, and occasioning none in the salt. Sulphur did the same. (13.) One part of the salt, mixed with ten of manganese, and melted in a close vessel, gave a semitransparent mass, some parts of which were bluish. The crucible was lined with a fine purple glazing, and the edges of the mass itself appeared of the same colour.

"The vitreous salt dissolved also, in fusion, metallic calces and earths. Chalk, with one third its weight of the salt, formed a semitransparent vitreous mass: calcined marble, with the same proportion, flowed so thin as to run all through the crucible; gypsum, likewise, ran mostly through the crucible; what remained was semitransparent. Lapis specularis ran entirely through the vessel. Spanish chalk gave a semitransparent mass, which sparkled on breaking; and fine white clay, a similar one. Saxon topaz and flint were changed into beautiful opal-coloured masses; the earth of alum into a semitransparent mass, and quicklime into an opaque white one. The masses with flints imbibed moisture from the air; the others not.

"Oil of vitriol, poured upon one-fourth its weight of this salt in a retort, raised an effervescence, acquired a brownish colour, and afterwards became turbid and white. On raising the fire, the oil of vitriol distilled, and the matter in the bottom of the retort melted. In the neck was found a little sublimate, which grew moist in the air; as did likewise the remaining salt, which was opaque and whitish. Concentrated spirit of nitre, distilled with this salt in the above proportion, came over unchanged; no sublimate appeared; the residuum looked like glass of borax. The distilled spirit did not act in the least upon gold, even by coction. Strong spirit of sea-salt being distilled in the same manner, no sensible change was made either in the spirit or the salt.

"Equal parts of the vitrified microcomic salt and salt of tartar being urged with the strongest fire that a glass retort could bear, nothing sensible came over, nor did the mixture appear in thin fusion. Dissolved in water, filtered, and duly evaporated, it afforded, very difficultly, oblong crystals, somewhat alkaline; the quantity of alkali having been more than enough to saturate the acid. A whitish matter remained on the filter, amounting to seven or eight grains, from two drachms of the mixture; this, after being washed and dried, melted before a blow-pipe, as did likewise the crystals.

"This salt seems to extricate, in part, the acids of vitriolated tartar, nitre, and sea-salt. (1.) On distilling a mixture of it with an equal quantity of vitriolated tartar, there came over some ponderous acid drops, which, saturated with fixed alkali, formed a neutral salt Acid of greatly resembling the vitriolated tartar. The residuum readily dissolved in water, and difficulty crystallized. (2.) Nitre, treated with the same proportion of the salt, began to emit red vapours. The residuum was of a peach-blossom colour, appeared to have melted less perfectly than the preceding, and dissolved more difficulty in water. The solution deposited a little earthy matter; and, on being slowly evaporated, shot into crystals, which did not deflagrate in the fire. (3.) Sea-salt, distilled in the same manner, manifestly parted with its acid; the residuum was whitish, readily dissolved in water, and afforded some cubical crystals. (4.) Sal ammoniac suffered no change. (5.) Borax, with an equal quantity of vitreous salt, run all through the crucibles.

"Solutions of this salt precipitated the earthy part of lime-water, of solution of alum, of flint dissolved in fixed alkali, and the combination of marine acid with chalk or quicklime. The precipitate from this last liquor is tenacious like glue, and does not dissolve even in boiling water; exposed to a strong fire, it froths prodigiously, and at last melts into a thick scoria.

"Solutions of this salt precipitate also fusty metallic solutions; as butter of antimony, solutions of silver, copper, lead, iron, mercury, and bismuth, in the nitrous acid; and of tin in aqua regis. The precipitate of iron from spirit of salt is a tenacious mass; that of silver from aquafortis, sometimes a white powder, sometimes tenacious. Copper from aquafortis is sometimes thrown down in form of a white powder, and sometimes in that of a green oil, according to the proportions and diluteness of the liquor. Silver is not precipitated at all by this acid from its solution in vinegar, nor gold from aqua regis.

"An ounce of the vitreous salt, well mixed with half an ounce of foot, and committed to distillation, yielded a drachm of fine phosphorus. The black residuum, being eluated with boiling water, and the liquor passed through a filter, there remained upon the filter eight scruples of a black matter; and, on evaporating and crystallizing the liquor, about seven drachms were obtained of oblong crystals, which did not delicate in a moist air, but became powdery in a warm one. These crystals, treated fresh with inflammable matter, yielded no phosphorus. Before a blowpipe they melted into a transparent globular mass, which, on cooling, became turbid and opaque. Dissolved in water, they precipitated solutions of silver, mercury, copper, and of chalk; though they did not act upon the latter so powerfully, nor produce with it a gluey mass, as before they had been deprived of their phosphorine acid."

Mr Wiegleb informs us, that the phosphoric acid exhibits less affinity with calcareous earth, in the moist way, than the vitriolic; though it cannot be separated from the ultimate residuum of the calcareous earth by that acid. It expels, however, all the liquid acids from their basis in the dry way. It precipitates iron from a solution in vitriolic acid, of a perfectly white colour. For the uses of this acid as a flux, see the article Blow-pipe.

§ ro. Of the Acid of Ants.

The acid may be obtained from these insects either How pro- by distillation, or simple infusion in water. From twenty-four ounces of ants, Neumann obtained eleven ounces and an half of acid as strong as good vinegar, by distillation in balneo mariae. Of this acid, Mr Margraff gives the following account in the Berlin Memoirs for 1749.

"The acid of ants effervesces with alkaline salts, both fixed and volatile. With volatile alkalies it forms a neutral liquor, which, like that composed of the same alkalies and vinegar, yields no concrete salt on distillation. With fixed alkalies it concretes, upon proper exhalation, into oblong crystals, which deliquesce in the air. The crystals, or the saturated neutral liquor uncryallized, on being distilled with a fire increased till the retort began to melt, yielded a liquor scarce sensibly acid, and afterwards a small quantity of an urinous and partly ammoniacal liquor. The remaining black matter, dissolved in distilled water, filtered and evaporated, shot into large crystals which did not deliquesce in the air, though they were in taste strongly alkaline, effervesced with acids, and had all the other properties by which fixed alkalies are distinguished.

"This acid dissolves, with great effervescence, coral, chalk, and quicklime; and concretes with them all into crystals which do not deliquesce in the air.

"It does not precipitate silver, lead, or mercury, from the nitrous acid; nor quicklime from the marine. Hence it appears to have no analogy to the marine or vitriolic acids; the first of which constantly precipitates the metallic solutions, and the other the earthy.

"It does not act upon filings of silver; but (like vegetable acids), it totally dissolves, by the assistance of heat, the calx of silver precipitated from aquafortis by salt of tartar.

"It does not dissolve calces of mercury (as vegetable acids do); but revives them into running quicksilver.

"It acts very weakly upon filings of copper; but perfectly dissolves copper that has been calcined. The solution yields beautiful compact green crystals.

"It dissolves iron-filings with violence; the solution, duly evaporated, shoots into crystals more readily than that made in distilled vinegar. It scarcely acts at all upon filings of tin.

"It does not, according to Mr Margraff, corrode filings of lead; but dissolves, by the affluence of heat, the red calx of lead. The solution cryallizes into a saccharum saturni. In Mr Ray's philosophical letters, it is said, that lead put into the acid spirit, or fair water, together with the animals themselves, makes a good saccharum saturni; and that this saccharum, on being distilled, will afford the same acid spirit again, which the saccharum saturni made with vinegar will not do, but returns an inflammable oil with water, but nothing that is acid: and saccharum saturni made with spirit of verdigris doth the same in this respect with spirit of pimires.

"It dissolves zinc with vehemence, and shoots, upon due evaporation, into inelegant crystals, not at all like those produced with distilled vinegar. On bismuth, or regulus of antimony, it has little effect, either when calcined or in their metallic state."

The nature of this acid is as yet but little known, and Mr Pott is the only chemist who seems to have examined it with accuracy. We shall therefore give an abstract of the principal observations and experiments he has made on this salt.

"Salt of amber requires a large quantity of water for its solution. In the first cryallization (being much impregnated with the oil, which rises from the amber along with it), it shoots into spongy flakes, in colour resembling brown sugar-candy; the crystals which succeed prove darker and darker coloured. On repeating the depuration, the crystals appear at top of a clear yellow or whitish colour, in form of long needles or feathers; at bottom, darker, and more irregular, as are likewise the crystals which shoot afterwards. The crystals neither liquefy nor become powdery in the air; rubbed, they emit a pungent smell like that of radishes, especially if warmed a little; their taste is acid, not in the least corrosive, but with a kind of oily pungency.

"This salt, kept in the heat of boiling water, loses nothing of its weight, and suffers no alteration. In a great heat it melts like oil; after which a little oily acid arises, then oily strix appear in the lower part of the retort, and the salt sublimes into the neck, partly in the form of a dark yellow butter, and partly in that of feathers, a black coaly matter remaining at bottom; so that, by this process, a part of the salt is destroyed.

"Oil of turpentine has no action on this salt. Highly rectified spirit of wine gains from it a yellow colour in the cold; and, on the application of heat, dissolves a considerable quantity, but deposits great part of it on cooling. The salt thus deposited is somewhat whiter than before, but still continues sensibly yellow. The dulcified spirit of sal ammoniac dissolves it readily, without effervescence, into a yellow liquor; if the salt was foul, the solution proves of a red colour; on burning of the vinous spirit, a neutral liquor remains.

"A solution of salt of amber in water, saturated with a pure alkaline lixivium, yielded, on infusification, a saline matter, which would not cryallize, and which, when excised by heat, deliquescent in the air, leaving a considerable proportion of an earthy, unctuous matter. Being again gently infusified, it left a brownish salt, very soluble, weighing one half more than the salt of amber employed. This salt effervesced with the vitriolic and nitrous acids: the vapour, which exhale, was not acid, but oily and sulphureous. On repeating the experiment, and fully saturating the alkali with the salt of amber, the neutral salt made no effervescence with these acids. This salt did not perfectly melt before a blow-pipe; continued in the fire for some time, it effervesced with aquafortis. In distillation it yielded a bitter, oily, alkaline spirit, much resembling the spirit of tartar; and towards the end, an empyreumatic oil. The residuum elixited, yielded the alkaline salt again of a brown colour.

"Salt of amber effervesces strongly with volatile alkalies; and, on saturation, forms with them an oily am- Ammoniacal liquor, which, in distillation, totally arises in a fluid form, except that a small portion of a penetrating, oily, saline matter, concretes towards the end.

On distilling salt of amber with an equal quantity of common sal ammoniac, a marine acid spirit came over, of a strong smell, and a brown colour; afterwards, a little white sal ammoniac sublimed; at length arose suddenly a large quantity of a fuliginous or bituminous matter, leaving behind a small portion of a like shining black substance. The coaly matter was considerably more in quantity than the salt of amber employed. On treating it with nitre, red vapours arose, and the mixture detonated with violence. A mixture of it with borax, frothed and swelled up much more than borax by itself; and, on raising the fire, yielded only some oily drops; the acid being destroyed by this salt, as by fixed alkalies and quicklime.

Spirit of sea salt, poured upon one-fourth its weight of salt of amber, made scarce any solution in the cold: on the application of heat, nearly the whole coagulated into the consistence of a jelly. In distillation, the spirit of salt arose first; then almost the whole of the salt of amber, partly like firm butter, partly like long striated plumous alum, very pure, and of a fine white colour, its oily matter being changed into a coal at the bottom. The salt, thus purified, makes no precipitation in the solution of silver, and consequently retains nothing of the marine acid; nor does it precipitate solution of quicklime made in spirit of salt, and consequently contains nothing vitriolic. If any of the mineral acids was contained in this salt, it could not here escape discovery; the oil, which in the rough salt is supposed to conceal the acid, being in this process separated.

Aquafortis being poured upon one-fourth its weight of salt of amber, extracted a yellowish colour from it in the cold, but dissolved little: on the application of heat, the whole dissolves into a clear liquor, without any coagulation: if the salt is very oily, the solution proves red. In distillation, the greatest part arises in a liquid form, with only a very small quantity of concrete salt. The spirit does not act upon gold, but dissolves silver, and quicksilver, as at first; a proof that it has received no marine acid from the salt of amber.

Oil of vitriol being added to twice its weight of salt of amber diluted with a little water, a moderate fire elevated an acidulous liquor, which appeared to proceed from the salt of amber; for its making no change in solution of fixed sal ammoniac, showed it not to be vitriolic. On continuing the distillation by a stronger fire, greatest part of the salt arises undestroyed, and the oil of vitriol along with it; a black, light, porous earth remaining.

Equal parts of quicklime and salt of amber gave over in distillation only an acidulous phlegm; the residuum, elixited with water, yielded a solution of the lime in the acid of amber, resembling a solution of the same earth in vegetable acids, precipitable by alkaline salts, and by the vitriolic acid. Lime, added to a watery solution of salt of amber, dissolves with some effervescence; after which, the whole coagulates into the consistence of a jelly: this, diluted with water, proves similar to the foregoing solution.

Solution of salt of amber makes no precipitation in solutions of silver or quicksilver. It dissolves zinc, as all acids do: fixed alkalies precipitate the zinc; the volatile do not; and when a sufficient quantity of the volatile has been added, the fixed make no precipitation. It acts exceedingly slowly and difficultly upon copper; but corrodes calcined copper in a shorter time. It soon corrodes iron, by coccion, into a crocus, and dissolves a part into a liquid form: the solution has little colour; but alkaline salts readily discover that it holds iron, by rendering it turbid and whitish, and throwing down a considerable quantity of a greenish calx.”

§ 12. Of the Acid of Arsenic.

Mr Scheele first perceived, from some experiments on manganese, that arsenic contained phlogiston: from which he was led to an analysis of this substance, which produced an acid of a very singular kind; by uniting of which with phlogiston in certain proportions, either white arsenic or its regulus may be composed at pleasure.

White arsenic may be decompounded in two ways. Two ways:

1. Put two ounces of it reduced to fine powder in a mortar into a retort of the same material; pour pounding upon it seven ounces of pure muriatic acid, whose specific gravity is to that of water as 10 to 8; and lute on a receiver. The arsenic is quickly dissolved in a boiling heat, which must be brought on as quickly as possible. After the solution is accomplished, while the liquor is still warm, three ounces and a half of nitrous acid, of the same specific gravity with the muriatic acid above-mentioned, is to be added, and the liquid which had already gone over into the receiver poured back. The receiver is then to be put on again, but not luted; the mixture soon begins to effervescence, and red vapours go over into the receiver. The distillation is to be continued till these vapours cease; when an ounce of finely powdered arsenic is again to be added, the receiver applied as before, and a gentle ebullition continued until the second quantity of arsenic be dissolved. An ounce and an half of nitrous acid is then to be added, and the mixture distilled to dryness, increasing the fire towards the end, so as to make the retort red hot. The acid which comes over into the receiver may serve again several times. The white mass which remains in the retort is the dry acid of arsenic. It may be reduced to a liquid form by pouring upon it, in coarse powder, twice its weight of distilled water, and boiling for a few minutes, pouring back the liquor which comes over, and afterwards filtering the solution through blotting paper, which has been previously washed in hot water.

In this process the nitrous acid attacks the phlogiston of the arsenic, is volatilized in consequence of its union with it, and leaves the more fixed but less powerful acid of arsenic behind. The nitrous acid would alone be sufficient for this purpose, could it accurately come into contact with the particles of arsenic; but this cannot be done without solution, and the nitrous acid is capable of dissolving arsenic only in The other method of decomposing arsenic is by means of the dephlogisticated spirit of salt. For this purpose, take one part of powdered manganese, and mix it with three of the muriatic acid above-mentioned. Put it into a retort, of which it may fill one-fourth; a receiver containing one-fourth of powdered arsenic, with one-eighth of distilled water, is to be fitted on, and the retort put into a sand-bath. The dephlogisticated muriatic acid, going over into the receiver, is instantly absorbed by the arsenic; which some hours afterwards will be dissolved, and two different liquid strata, which cannot be mixed together, will be perceived in the receiver. This solution is now to be put into a clean glass retort, and distilled to dryness; increasing the fire at last to such a degree as to make the whole red hot: and in this process also two different liquids pass over into the receiver which do not unite together.

Here the manganese attracts the phlogiston of the muriatic acid; and as this dephlogisticated acid has a very strong attraction for phlogiston, it deprives the arsenic of its phlogiston, and thus recomposes the ordinary phlogisticated muriatic acid. This portion of recomposed acid dissolves part of the arsenic, forming with it what is called butter of arsenic. The other part of the arsenic which has been decomposed, dissolves in the water, and forms a liquid specifically lighter than the butter, and therefore swims above it. On rectifying the two liquids, the undecomposed portion of the arsenic arises along with the muriatic acid, and goes over into the receiver in form of an heavy oil, while the acid of arsenic remains behind in the retort. The acid obtained in this way is precisely the same with the former, and one would hardly believe that it is an acid, because it has no acid taste; but after some days it grows moist in the air, and at last deliquesces, assuming the appearance of oil of vitriol. As the deliquescence, however, is very slow, it is proper to dissolve it in a certain quantity of water, when a small quantity of white powder remains undissolved, after preparing it by the first process, which is fibrous earth derived from the retort. This ought to be carefully separated from the acid by filtration; and in order to prevent the glue of the blotting-paper from mixing with the acid, it was directed to wash the filter with hot water previous to the operation.

The first experiment M. Scheele tried on this acid after he had obtained it, was to discover if it was as noxious to animals as when combined with phlogiston. Having mixed a little with honey, the flies that eat of it died in an hour; and eight grains reduced a cat to the point of death in two hours. Some milk, however, being then given to the animal, it vomited violently, and ran away.

2. An ounce of dry acid of arsenic, heated in a small phial to near the point of ignition, melts into a clear liquid, which congeals when cold; but if the heat be increased till the vessel begins to melt, the acid begins to boil, reforms its phlogiston, and arsenic sublimes in greater quantity as the heat is longer continued. After subjecting the acid to this violent heat in a retort for an hour, the vessel melted, and the acid had risen up as high as the neck.

3. In a crucible the arsenic attracts phlogiston in greater quantity, and is entirely dissipated in arsenical vapours; a little clear and difficultly fusible glass, consisting of clay and the acid of arsenic, remaining in the crucible.

4. The arsenical acid, after some days digestion with oil of turpentine, unctuous oil, and sugar, becomes black and thick. If some muriatic acid be distilled from this, a little nitrous acid added, and the distillation repeated, some acid of arsenic is left behind. Spirit of wine undergoes no change either by digestion or distillation with arsenical acid.

5. Six parts of acid digested with one of sulphur with fufufer no change; but when the mixture is evaporated to dryness, and then subjected to distillation in a glass retort, the two unite with great violence at that degree of heat in which sulphur melts; and the whole mass rises almost in the same instant, in form of a red sublimate; a little sulphureous acid in the mean time going over into the receiver.

6. Acid of arsenic, saturated with vegetable fixed alkali, forms a deliquescent salt which does not crystallize, but turns syrup of violets green, though it produces no change on the tincture of lacmus. On the addition of a little more acid, however, when it reddens lacmus, but makes no alteration on the syrup of violets, the liquor will afford fine crystals like Mr Macquer's neutral salt of arsenic. On keeping this salt for an hour in fusion in a crucible covered with another luted upon it, the inside of the vessel was found covered with a white glazing, and a salt remained, which was still the same arsenicated salt with excess of acid.

7. On distilling this salt in a retort with an eighth-part of charcoal-dust, it began to boil very violently as soon as the retort became red-hot, and a very fine regulus of arsenic sublimed. The black residuum contained the alkali entirely separated from the arsenical acid.

8. With mineral alkali the acid of arsenic forms crystals when perfectly neutralized, but not if added to excess. In that case, the mass becomes deliquescent like the former when neutral.

9. With volatile alkali a salt much resembling the With volatile alkali... Acid of Arsenic and its Combinations

929. Expels the acid of vitriolated tartar by dry distillation.

930. Acid of nitre; Of common salt.

931. Phenomena with sal ammoniac.

932. Decomposes spathum ponderosum and gypsum.

933. Cannot expel the fluor acid.

934. Precipitates lime water.

935. Phenomena with chalk acid diluted with water, the earth is at first dissolved, but by adding more chalk the whole is coagulated into small crystals.

936. With magnesia.

937. Earth of alum precipitated by alkali of tartar acid of Arsenic is easily soluble in arsenical acid, and coagulates as soon as it arrives at the point of saturation. Evaporated to dryness, mixed with some charcoal powder, and then subjected to strong distillation, a little yellow sublimate rises into the neck of the retort, as likewise with earth some shining regulus, while a volatile sulphureous acid of alum passes over into the receiver. The residuum dissolves with difficulty in the vitriolic acid, though some crystals of alum will form in the space of two months.

938. Four parts of arsenical acid mixed with one of powdered white clay, did not dissolve any part by digestion for a fortnight. By distillation in a retort till the vessel began to melt, it was converted into a thick flux, and a little arsenic sublimed. By mixing the residuum with a little powdered charcoal, a shining regulus was sublimed.

939. Terra ponderosa dissolves readily in the acid of arsenic, but precipitates again as soon as it has attained ponderosa, the point of saturation. The solution is precipitated by acid of vitriol, and forms regenerated ponderous spar.

940. Gold is not acted upon by acid of arsenic, either with gold by digestion or otherwise; nor is its solution precipitated, though the retorts used in the operation were stained with red and yellow spots, which could not be taken off; nor is its action increased by mixture with muriatic or with nitrous acid.

941. Pura platina is not acted upon. Its solution Platina is not precipitated by the pure arsenical acid, but readily by the arsenical fats. The precipitate is yellow, and dissolves in a large quantity of water, but contains no mark of arsenical acid. Addition of muriatic or of nitrous acid makes no change in its effects.

942. Pure silver is not acted upon by the arsenical Silver acid in digestion. On augmenting the fire till the acid melted, and keeping up this degree of heat for half an hour, the metal dissolved, and on breaking the retort, a colourless glassy mass, nearly transparent, was found in it; the retort being covered with a flame-coloured glazing, which could not be separated from it. By a great degree of heat the silver was reduced without addition. Solution of silver is precipitated by pure acid of arsenic, but more effectually by the neutral arsenical fats: the precipitate is of a brown colour, and by digestion in muriatic acid is changed into luna cornea; it is also soluble in spirit of sal ammoniac prepared with quicklime. The action of the arsenical acid upon silver is considerably increased by mixing it with spirit of sea-salt; the former attacking the phlogiston of the metal, while the latter attacks its earthy basis.

943. Quicksilver is not acted upon by digestion with Quick-arsenical acid. On putting the mixture into a retort, silver distilling to dryness, and then increasing the fire, the mass becomes yellow, quicksilver rises into the neck of the retort, with a little arsenic, and some yellow sublimate; but though the fire was augmented till the retort began to melt, the mass could not be fused. Three drachms and an half of quicksilver were obtained out of six employed in the experiment; the arsenical acid, therefore, contained two and an half. The mass was somewhat yellow: it dissolved very readily in muriatic acid, but scarcely at all in the nitrous or vitriolic; on evaporation to dryness and distillation, some corrosive sublimate Acid of Arsenic and its Combinations.

26. Acid of arsenic distilled with corrosive sublimate undergoes no change; but by sublimation with mercurius dulcis, a corrosive sublimate is obtained. Some have asserted, that by subliming arsenic with corrosive sublimate, a butter of arsenic is obtained; but Mr Scheele informs us that this is a mistake; and that, by distilling this mixture, he constantly obtained corrosive sublimate at first, and arsenic afterwards. With regulus of arsenic, however, a smoking butter of arsenic, mercurius dulcis, and some quicksilver, are obtained. The same thing happens with a mixture of orpiment and corrosive sublimate.

27. Arsenical acid dissolves copper by a digesting heat. The solution is of a green colour; a quantity of light blue powder is deposited, and attaches itself to the copper. This powder consists of the acid of arsenic and calcined copper. On mixing two parts of dry acid of arsenic, in fine powder, with one of filings of copper, and distilling the mixture, some arsenic rose into the neck, and the mass melted and turned blue. On boiling it with water, the solution was similar to one made directly from acid of arsenic and copper. A little copper remained in the bottom of the retort, which was tinged with brown, red, and yellow spots, insoluble in any menstruum. The solutions of this metal are not precipitated by arsenical acid, but the acetous solution is. Neutral arsenical salts throw down a blue precipitate, which by exposure to a strong fire, turns brown and covers the inside of the containing vessel with a yellow enamel. On mixing the leonora in fine powder with a little lampblack, some fine regulus of arsenic sublimed, and the copper in the residuum was reduced.

28. With iron the acid of arsenic forms a gelatinous solution, which by exposure to the air grows so thick that in two hours' time it will not flow out at the mouth of a phial. With alkali of tartar a whitish green powder is thrown down; which being edulcorated and distilled in a glass retort, yields some arsenic, and leaves a red ochre behind. On distilling four parts of arsenical acid with one of iron filings, the mass effervesced strongly towards the end; and when it became dry, took fire in the retort upon increasing the heat, when both arsenic and regulus of arsenic were sublimed. The residuum was black, friable, and contained but little acid of arsenic; the retort was covered with yellowish brown spots. Solutions of iron in mineral acids are not precipitated by acid of arsenic, but the acetous solution lets fall a dark brown powder. All the solutions are precipitated by the arsenical neutral salts, the precipitates by a strong fire, converted into black scoriae; which mixed with powdered charcoal, and calcined, yield copious vapours of arsenic, and are afterwards attracted by the magnet.

29. Lead digested with arsenical acid turns black at first, but in a few days is surrounded with a light greyish powder, containing some arsenic which may be separated by sublimation. On distilling one part of shavings of lead with two of dry acid of arsenic, the lead was dissolved, the mass flowed clear, and a little arsenic rose into the neck of the retort. A milky glass was found in the bottom, which by boiling in distilled water, let fall a quantity of white powder, the superfluous acid being dissolved in the water; the edulcorated powder yielded regulus of arsenic by distillation with charcoal. Solutions of lead in nitrous and muriatic acids are precipitated by arsenical acid.

30. Tin digested with acid of arsenic becomes first with tin, black, then is covered with a white powder, and afterwards becomes gelatinous. One part of tin filings distilled with two of acid of arsenic, took fire as soon as the retort became red-hot, and immediately after both arsenic and a little regulus were sublimed. The tin was distilled into a limpid liquor, which became milky when cold.—By washing in water, a quantity of white powder was separated, insoluble in any acid, and containing very little of that of arsenic.

31. Arsenical acid dissolves zinc with effervescence. With zinc, the metal grows black, and the transparency of the acid is destroyed by a quantity of black powder. This powder edulcorated, dried, and put on an iron plate heated nearly red hot, emits a blue flame and white arsenical smoke in the dark, leaving behind a white powder; thus manifesting itself to be mostly regulus of arsenic. One part of filings of zinc distilled with two of acid of arsenic, took fire in the retort with a very bright flame, and burnt the vessel with an explosion. Some regulus of arsenic and flowers of zinc were found in the neck.

32. Bismuth digested with acid of arsenic is covered with a white powder; water precipitates the solution, and the precipitate consists of calcined bismuth and acid of arsenic. On distilling one part of bismuth with three of arsenical acid, the mass melted, the metal was calcined, but remained undissolved in the bottom of the vessel; a little arsenic rose into the neck; and after the retort became cool, water was poured on the residuum, which dissolved the acid, but the calx of bismuth remained unchanged. Solution of this semifinal in the acid of nitre was precipitated by arsenical acid. This precipitate, as well as the calx, are very difficult of fusion, but on adding a little powdered charcoal, the mixture instantly melts, the arsenic goes off in vapours, and the bismuth is reduced.

33. With regulus of antimony a quantity of white Regulus of powder is produced by digestion, and the clear solution is likewise precipitated by dropping it into pure water. This powder is soluble only by muriatic acid, and may be precipitated again by the addition of water. One part of regulus of antimony distilled with three parts of arsenical acid, took fire as soon as the mass melted, and regulus of arsenic with a red matter were sublimed; a little volatile sulphureous acid came over into the receiver. On boiling the residuum in water, the acid was dissolved, a white shining powder remained behind, which on being mixed with charcoal powder and distilled, an ebullition took place, some regulus of arsenic rose into the neck of the retort, and the antimony was reduced. Butter of antimony was not precipitated by the pure acid, but very readily by the arsenical salts. Acetous and tartraceous solutions of glaas of antimony are precipitated by arsenical acid. 34. Cobalt is partially dissolved, and the solution assumes a rose-colour; on putting the whole mass into a retort, distilling off the liquid, and then augmenting the fire, the mass melted, and a little arsenic was fulminated. The residuum when cold had a semi-transparent violet colour. On pouring water upon it, and putting it on hot sand, the acid was dissolved, the violet colour disappeared, and the solution assumed a dark-red colour. The bottom of the retort had a blue tinge, which could not be taken off. Solutions of cobalt in mineral acids are readily precipitated by the arsenical neutral salts. The precipitate is of a rose-colour, but melts with difficulty into a dark blue scoria.

35. Nickel, with acid of arsenic, assumes a dark green colour, and lets fall a green powder containing arsenic in substance, which may be separated from it by a gentle heat. One part of nickel distilled with two of dry arsenical acid, melted with some appearance of inflammation, yielding some arsenic at the same time. The mass was yellow, with a number of grey elevated streaks upon it, which appeared like vegetation, and were formed during the distillation. On boiling the yellow mass in water, the acid was dissolved, leaving a yellow powder behind; which, when treated with charcoal-powder, yielded regulus of arsenic, but was not reduced itself. The solutions of nickel in acids are not precipitated by arsenical acid, nor even that in vinegar, but the neutral arsenical salts throw down a whitish green powder.

36. Manganese in its natural state is dissolved only in small part; but when phlogisticated it dissolves readily and totally; though, whenever the acid arrives at the point of saturation, the solution coagulates into small crystals.

37. Regulus of arsenic digested with its own acid soon becomes covered with a white powder, which is arsenic in substance. On distilling one part of the regulus with two of the acid, the former sublimed, and the latter melted. If small pieces of regulus of arsenic be gradually added to the acid of arsenic in fusion, an inflammation takes place, and arsenic is sublimed.

On distilling a mixture of equal parts of terra foliata tartari and arsenic, a limpid liquor like water first came over, smelling strongly of garlic; on changing the receiver, a liquor of a brownish red colour was collected, which filled the receiver with a thick cloud, emitting an intolerable smell of arsenic. On pouring this upon a filter, hardly a few drops had passed when a very thick flanking smoke suddenly arose as high as the ceiling of the room; an ebullition ensued towards the edge of the filtering-paper, and a fine rose-coloured flame broke out, that lasted for some moments.

§ 13. Of the Acid of Molybdæna.

We owe this, as well as the succeeding acids, to the industry of the late Mr Scheele. The substance from which he extracted it is named by Cronstedt molybdæna membranacea nitens.—As this substance is of a flaky nature, and incapable of pulverization by itself, our author mixed some pieces of vitriolated tartar along with it in a glass mortar; by the attrition of which it was at last reduced to a fine powder, and which was afterwards freed from the vitriolated tartar by washing with hot water. He then treated this acid of molybdæna with all the known acids, but found none of them to have any effect upon it excepting those of arsenic combined and nitre. No sensible effect was perceived from the addition of arsenic until the water was evaporated; after which, by increasing the fire, a little yellow ornament was sublimed in the neck of the retort, and some fulvous acid passed over into the receiver. On pouring two parts of concentrated nitrous acid upon one part of powdered molybdæna, the mixture was scarce warm in the retort, when it palled all, together into violent red vapours. Had the quantity been larger, he had no doubt that it would have taken fire; for which reason the experiment was repeated with diluted nitrous acid. Six ounces of diluted nitrous acid being poured on an ounce and a half of powdered molybdæna, no effect was perceptible till the liquor began to boil; after which a great number of red elastic vapours began to appear, and the mixture swelled considerably. The distillation being continued to dryness, the residuum appeared of a grey colour; the same quantity of nitrous acid was poured on, and the process repeated, when the residuum was whiter; and on still repeating the operation a fourth and fifth time, the remaining powder became at last as white as chalk. This residuum, after being edulcorated with hot water, was quite tasteless and insipid when dry. The limpid liquor which ran from it, being evaporated to half an ounce, first assumed a fine blue colour, and then grew thick. On being examined, it was found to contain some iron, and was otherwise chiefly acid of vitriol. The colour disappeared on diluting the acid with water.

The white powder just mentioned is the true acid of molybdæna, and may be obtained by the help of molybdæna exposed on a silver plate to the blow-pipe, makes a beautiful appearance, when the white vapours attach themselves to the plate in the form of small shining scales, in the direction of the flame. This white sublimate becomes blue whenever it is in contact with the blue flame; but changes to white whenever the point of the flame is directed against it. An ounce of powdered molybdæna was mixed with four ounces of purified nitre, and detonated in a crucible heated thoroughly red hot. The mass thus obtained was of a reddish colour. On dissolving it in water, the solution was clear and colourless. A small quantity of red powder fell to the bottom of the vessel; which, when dry, weighed 11 grains, and showed itself to be an iron ochre. By evaporation vitriolated tartar and nitre were obtained; but a good deal of lixivium remained, which refused to crystallize, though no mark of superfluous alkali remained. It was then mixed with some water, to which diluted acid of vitriol was added, until no more precipitate fell. The white powder which precipitated weighed three drachms; but if too much acid be added, the precipitate will be redissolved, and the water itself retains a part of it in solution. A precipitate is likewise obtained by means of nitrous or muriatic acid.

The precipitate thus obtained, like those which result from the two former processes, is the true acid of cal proper molybdæna, and has the following chemical properties. 1. The solution reddens lacmus, coagulates a solution of soap, and precipitates hepar sulphuris. 2. If this solution be boiled with the filings of any of the imperfect metals, it affumes a bluish colour. 3. By the addition of a little alkali of tartar, the earth becomes soluble in greater quantity in water; and after evaporation shoots into small confused crystals. 4. Under the blow-pipe this earth is soon absorbed by charcoal; but when placed on a silver plate it melts, and evaporates with the same phenomena as molybdæa itself. 5. By the addition of alkali, the earth is deprived of its property of being volatilized in the fire. 6. The solution, whilst hot, shows its acid power more evidently than when cold, and tinges lacmus of a deeper colour. It effervescences with chalk, with magnesia, and with earth of alum; with all of which it forms farts very difficult of solution in water. 7. It precipitates, from the nitrous acid, silver, quicksilver, and lead, as also lead dissolved in marine acid. These precipitates are reduced on burning charcoal, and the melted metal runs into the pores. Corrosive sublimate is not precipitated; neither are the solutions of the other metals. 8. Terra ponderosa is also precipitated from the nitrous and marine acids; and the precipitate is soluble in a large quantity of cold water. None of the solutions of the other earths are precipitated. 9. Fixed air is also expelled by this acid from the fixed and volatile alkalies, and forms with them neutral salts which precipitate all other metallic solutions. Gold, corrosive sublimate, zinc, and manganese, are precipitated in form of a white powder; iron and tin, from their solution in marine acid, of a brown colour; cobalt of a rose colour; copper of a blue; the solutions of alum and quicklime, white; and if the ammoniacal salt formed by the earth of molybdæa and volatile alkali be distilled, the earth parts with its alkali in a gentle heat, and remains in the retort in form of a grey powder. 10. Concentrated vitriolic acid dissolves a great quantity of this earth by means of heat. The solution acquires a fine blue colour; which, however, disappears on being heated, or by diluting the acid with water. In a stronger heat the acid flies off, leaving the earth unaltered behind. This solution becomes thick on cooling. 11. The nitrous acid has no effect upon the earth of molybdæa. 12. Boiled with the muriatic acid it dissolves in considerable quantity; and, on distilling the mixture to dryness, a dark-blue residuum remains. On increasing the heat, white flowers arise, with a little blue sublimate, and a smoking muriatic acid is found in the receiver. The residuum is of a grey colour. These flowers are only the earth of molybdæa volatilized by means of the muriatic acid, and therefore manifests the same properties. 13. If one part of this earth be distilled with two parts of vitriolated tartar, a little vitriolic acid passes over, at least when the heat is very strong; and the remaining earth is more soluble in water than before. 14. With two parts of nitre it expels, by means of distillation, a strong nitrous acid; the residuum dissolved in water is a neutral salt which precipitates all metallic solutions, and is similar to that formed by a direct union of the acid and fixed alkali. 15. Distilled with two parts of pure common salt, the acid is expelled in a smoking state, and white, yellow, and violet-coloured flowers arise, which become moist in the air, and when sprinkled on metals give them a blue colour. These flowers, as has been already remarked, are only the acid of molybdæa volatilized by that of sea-salt.

The blue colour acquired by this earth on the contact of flame, also in the moist way in some cases, shows that it is capable of contracting an union with the phlogiston. To reduce this to certainty, Mr Scheele distilled some of the earth of molybdæa in boiling water, with the addition of a little alkali. Into this solution he poured some drops of muriatic acid, and divided it into several parts, into each of which he put filings of several metals. The solutions soon acquired a bluish colour, which grew deeper and deeper; and in an hour's time, during which the bottle was now and then shaken, the liquor assumed a fine dark blue. That this colour depends on phlogiston, he infers from the following circumstances: 1. If, instead of the metals themselves, you take their calces, no blue colour is produced. 2. If there be dropped into the blue solution a few drops of acid of nitre, and the solution be then put into a warm place, the colour disappears. It is therefore no matter of surprise, that both silver and quicksilver should be attacked, since a double elective attraction takes place; the muriatic acid uniting with the metallic calx, and the earth of molybdæa with the phlogiston of the metals. Gold, however, is not attacked in this way. 3. Too great a quantity of muriatic acid produces not a blue but a yellowish colour, which at last turns brown if the mixture be digested; but on adding this solution to a solution of the earth of molybdæa, a blue colour as usual is produced. 4. Lixivium sanguinis, in which the acid prevails, throws down the earth of a brown colour, and the infusion of galls of a dark brown.

The acid of molybdæa, treated with various fluxes, and with charcoal, shows no signs of containing any sign of metallic matter. Moistened with oil-olive, and containing any metal, but remained in the retort in form of a black powder; which, on being calcined in a crucible, sublimed in white flowers as usual. On inverting another crucible into the former, and luting the juncture, the earth remained unchanged and of a black colour, without any sign of fusion. This black powder did not dissolve in boiling water, nor even with alkali, which on other occasions so readily dissolves it; but when mixed with a triple quantity of salt of tartar, a great effervescence ensued; the produce was a neutral salt resembling that formed by the direct union of the acid and alkali.

The earth of molybdæa, procured by nitre, requires much less water for its solution; it does not expel the acid from vitriolated tartar; is more easily obtained by nitre, and does not sublime in an open crucible. When fused with charcoal-powder, it affords a solution with water, containing a neutral salt, which precipitates all others. The reason of these differences is, that it contains a portion of alkali, though it be ever so frequently purified by solution and crystallization. That this is the case we know from the following experiments: 1. If to a solution of the nitrous earth of molybdæa we add some nitrous acid, the latter attacks the alkali, and the greatest part of the dissolved earth is precipitated. This, however, does not happen, except by long boiling. 2. The neutral salt obtained by fusion proves the same. This neutral salt is produced in the following manner. The earth which con- Acid of Molybdæna and its Combinations.

Tains only a small quantity of alkali operates as an acid, as appears from its changing the colour of lacmus to red; but the alkali prevents as much earth from entering into it as is necessary to its saturation with phlogiston; for the acid of molybdæna has a greater attraction for alkali than for phlogiston. The charcoal which remains after lixiviating the compound of acid of molybdæna and charcoal, yields vapours in an open crucible, and gives a sublimate containing the phlogisticated earth of manganese. This alkali fixes the earth in the open air; and hence we see also the reason why this earth does not expel the acid from vitriolated tartar; for its attraction for the alkali must diminish in proportion as it comes nearer the point of saturation; and as the pure earth contains no alkali, it attracts a little from the vitriolated tartar; and consequently there can appear but a slight vestige of vitriolic acid. This small quantity of acid likewise occasions its more easy solubility in water.

The pure acid of molybdæna recomposes that substance by being combined with sulphur. Mr Scheele having mixed some very fine powder of this earth with three parts of sulphur, and committed the mixture to distillation in a glass retort, the receiver was filled with the superfluous sulphureous vapours, which had also the fetid smell of volatile spirit of sulphur. In the retort a black powder remained; which on every chemical trial was found to be a true molybdæna; so that there is now no doubt of this substance being composed of a particular kind of acid united to sulphur.

§ 14. Of the Acid of Lapis Ponderosus, Tungsten, or Wolfram.

This substance has been analysed both by Mr Scheele and Mr Bergman, though the former has the merit of discovering the acid contained in it; which the latter considers, as well as the earth of molybdæna, not as truly acid, but as metallic earths. Mr Scheele's experiments for analysing this substance were as follow:

1. On one part of finely powdered tungsten were poured two parts of concentrated acid of vitriol. By distillation the acid passed over unchanged; the residuum, which was of a bluish colour, after being boiled for a short time, and the liquor filtered off, deposited some vitriolated lime or gypsum by standing.

2. Twelve scruples of common nitrous acid, or pure aquafortis, being poured on two of finely powdered tungsten, no effervescence ensued; but on exposing the mixture to a strong digesting heat, it assumed a citron yellow colour. The acid was then poured off into another phial, and the yellow powder edulcorated with water.

3. On this yellow powder eight scruples of caustic volatile alkali were poured, and the phial exposed to heat; on which the yellow colour instantly vanished, and the powder became white. This solution was in like manner put into a separate phial, and the powder edulcorated; and as the matter was sensibly diminished by these operations, they were alternately repeated, till at length the whole was dissolved, excepting three grains, which seemed to be siliceous earth. The same effects ensued on treating this substance with muriatic acid, only the solution was of a deeper yellow colour.

4. The solutions made in the foregoing manner with nitrous acid being all mixed together, some drops of phlogisticated alkali were added; by which about three grains of Prussian blue were precipitated. 5. The Lapis Pon- mixture was then saturated with caustic volatile Combi- alkali; but as no precipitate appeared, a solution of fixed alkali was added, which threw down two feruples and five grains of white earth of a mild calcareous kind. On adding some nitrous acid to the extracts made by volatile alkali, a white powder was precipitated, which, on edulcoration, proved to be the true acid of tungsten.

On treating tungsten with a strong heat in the dry way, the following appearances took place: 1. One eat upon part of tungsten mixed with four of alkali of tartar was melted in an iron crucible, and then poured out on an iron plate. Twelve times its weight of boiling water being then poured upon it, a white powder subsided to the bottom, which diffused in a great measure in nitrous acid. 2. The undissolved part of the powder was tried; and being again mixed with four parts of alkali, was melted as before; and the mass being also diffused in water, and nitrous acid poured on the residuum, only a very small portion of grey powder was left undissolved. 3. The ley being saturated with nitrous acid, grew thick by the precipitation of a white powder; which was afterwards washed with cold water and dried, and then proved to be the same acid of tungsten with that already described. The solution in nitrous acid precipitated with fixed alkali gave a white precipitate, which was found to be calcareous earth.

The properties of the acid of tungsten are, 1. Units chemi- der the blow-pipe it became first of a reddish yellow proper- colour, then brown, and at last black. It neither ties, smoked nor gave any lumps of fusion. 2. With borax it produced a blue, and with microcosmic salt, a fag- green glass. 3. Boiled with a small portion of the nitrous or marine acids, the powder becomes yellow, and with the acid of vitriol bluish. 4. On saturating a solution of the acid with fixed alkali, a neutral salt in very small crystals is obtained. 5. With volatile alkali this acid forms an ammoniacal salt shaped like the points of small pins. On distillation the alkali separates in a caustic state, the acid remaining behind in the retort in form of a dry yellow powder. On mixture with a solution of lime in spirit of nitre, a double elective attraction takes place, the acid of tungsten uniting itself with the lime, and that of nitre with the volatile alkali. 6. With magnesia the acid of tung- sten forms a salt very difficult of solution. 7. It produces no change on solutions of alum or lime, but decomposes a solution of terra ponderosa in acetic acid, and the compound is totally insoluble in water. 8. It precipitates of a white colour solutions of iron, zinc, and copper, in the vitriolic acid; silver, quicksilver, and lead, in that of nitre; and lead in the acid of fea- falt. Tin combined with the same acid is thrown down of a blue colour; but corrosive sublimate and solutions of gold undergo no change. 9. On cal- cining the acid of tungsten in a crucible, it loses its solubility in water. 10. It turns black by calcination with inflammable matters and with sulphur, but in other respects continues unaltered. 11. Solution of hepatic sulphur is precipitated of a green colour by this acid, and the phlogisticated alkali white; the latter precipitate being soluble in water. On the addition of a few drops of muriatic acid to a solution of the acid Acid of tungsten in water, and spreading the liquor on polished iron, zinc, or even tin, it acquires a beautiful blue colour; and the same thing happens when these metals are put into the acid. It differs from the acid of molybdena in not being volatile in the fire; in having little attraction for phlogiston or sulphur; in turning lime yellow, and forming an insoluble compound with it, as well as with ponderous earth. It has also a stronger attraction for lime than the acid of molybdena; for if a combination of lime and acid of molybdena be digested in a solution of the ammoniacal salt formed by uniting the acid of tungsten with volatile alkali, the latter expels the former, and produces regenerated tungsten.

Mr Bergman observes, that the acid earth of tungsten is nearly allied to that of molybdena; and both are in a state much resembling that of white arsenic. "It is well known (says he) that arsenic, in its semimetallic state, is nothing but a peculiar acid saturated with phlogiston; and that the white calc is an intermediate state between acid and metal, containing just phlogiston enough to coagulate the acid, but remaining still soluble in water, and showing signs of acidity. If a conclusion from analogy be admissible, all the other metals should consist in a combination of the same nature of the different radical acids, which with a certain quantity of phlogiston are coagulated to a dry earthly substance; and on full saturation are reduced to the state of complete metals."

The reasons which induced Mr Bergman to suppose that the acids in question are metallic earths, are as follows: 1. They both show a striking resemblance to white arsenic in form, in producing effects like acids, and in their difficult solubility in water. 2. Their specific gravity; that of arsenic being 3750, the earth of molybdena 3460, and the acid of tungsten 3000. 3. Their precipitation with phlogisticated alkali; a property hitherto deemed peculiar to metallic calces. Arsenic also, properly dissolved in nitric acid, gives, with the phlogisticated alkali, a precipitate soluble in water, in the same manner as the acid of tungsten. 4. From their property of tingeing vitreous matters; which, as well as that of precipitating with the phlogisticated alkali, is reckoned to be a peculiar property of metals. The acid of tungsten produces by itself some effervescence with mineral alkali. With microcosmic salt it produces a globule at first of a light blue; more of the acid makes it a dark blue; but still it remains free from redness by refraction. A further addition makes it brown. Borax acquires a slight tinge of blue, and with more of the acid becomes of a yellowish brown colour; but remains transparent, provided no further addition be made. This ultimate brown colour cannot be driven off either by nitre or the point of the flame urged by a blow-pipe. Acid of molybdena is no less powerful; for with microcosmic salt it produces a beautiful green colour: borax well saturated with it appears grey when viewed by the reflected rays, but of a dark violet by the refracted.

§ 15. Of the Acid of Milk.

It is universally known, that in the summer-time milk grows sour and thick in a few days, and that this acid of sourness continues for some time to increase. It is combined after a fortnight has elapsed; after which, if the whey be filtered and evaporated to one half the quantity, a few curds will fill kettle to the bottom.

By saturating the whey with volatile alkali, a small milk most quantity of animal earth precipitates; and the same thing takes place on the addition of lime-water. On taking the addition of a small quantity of acid of tartar, the former latter foam becomes partially saturated with vegetable alkali, and is converted into tartar. Thus the acid of milk, besides its proper acid part, contains animal earth principles and vegetable alkali in a looie state, and which is attracted by the acid of tartar; besides all these, it has also a small quantity of the same alkali saturated with muriatic acid. It is no easy matter to separate these substances from one another; because the acid is not sufficiently volatile to rise in distillation by a gentle heat, nor are its principles sufficiently fixed to bear the action of a strong fire. With the one therefore it remains almost entirely in the retort, and with the other it is destroyed. Mr Scheele therefore used the following process.

He evaporated four whey till only one-eighth part Scheele's remained; when the cheesy part being totally separated, he strained the acid; and in order to obtain the pure animal earth, saturated the liquor with lime, diluting the solution with a triple quantity of water. In order to separate the lime, he employed the acid of sugar, which has a stronger attraction than any other for lime. This earth therefore being separated, the matter was evaporated to the consistence of honey, and highly rectified spirit of wine poured upon it to dissolve the acid part; which being accomplished, the other saline substances were left by themselves; and, lastly, the acid solution being diluted with pure water, and the spirit separated by distillation, the pure acid remained in the retort.

The properties of the acid of milk are, 1. Evaporated to the consistence of a syrup, it yields no crystals; this acid, and when evaporated to dryness, it deliquesces. 2. By distillation it yields first water, then a weak acid like spirit of tartar; afterwards some empyreumatic oil, with more of the same acid, fixed air, and inflammable air; in the retort was left a fixed coal. 3. By saturation with fixed vegetable alkali it yields a deliquescent salt, soluble in spirit of wine. 4. A salt of a similar kind is obtained by combining it with mineral alkali. 5. With volatile alkali a deliquescent salt is produced, which by distillation yields a great deal of its alkali before the acid is destroyed by heat. 6. It forms deliquescent salts with terra ponderosa, lime, and clay; but with magnesia it forms small crystals, which, however, are again deliquescent. 7. It has no effect either by digestion or boiling on bismuth, cobalt, regulus of antimony, tin, quicksilver, or gold. However, after digestion with tin, it precipitated gold from its solution in aqua-regia, in the form of a black powder. 8. It dissolves iron and zinc, producing inflammable air during the solution. The liquor produced by the dissolution of iron was brown, and yielded no crystals; but the solution of zinc crystallizes. 9. Copper dissolved in this acid communicates to the liquor first a blue, then a green, and then a dark blue colour, without crystallizing. 10. Lead was dissolved after some some days digestion; the solution had a sweet astrin- gent taste, and would not crystallize. A small quan- tity of white matter fell to the bottom, which on exa- mination was found to be vitriol of lead.

"From these experiments (says Mr Scheele) it ap- pears, that the acid of milk is of a peculiar kind; and though it expels the vinegar from the acetated vegeta- ble alkali, yet it seems destined, if I may so speak, to be vinegar; but from the want of such substances as, during fermentation, produce some spirituous matter, it seems not to be volatilized, though a portion of it in- deed arrives at this point, and really becomes vinegar; for without a previous spirituous fermentation, or with- out brandy, there never arises any vinegar. But that the milk enters into a complete fermentation though there be no sign of brandy present, appears from the following experiment: If a bottle full of fresh milk be inverted into a vessel containing so much of the same liquor that the mouth of the bottle reaches below the surface of the latter, and if you expose this bottle to a degree of heat a little greater than our summer, you will find, in the space of 24 hours, that the milk is not only coagulated, but in part expelled out of the bottle; and that in a couple of days afterwards, the aerial acid extricated from the milk will have expelled the greater part of it. It was said above, that the acid of milk cannot be converted into vinegar, from the want of such substances as during fermentation produce brandy; which appears to be evident from this: If to a kanne of milk you add five spoonfuls of good brandy, and ex- pose the vessel, well corked, in such a manner, however, that you now and then give vent to the air developed during fermentation, you will find in a month, sooner or later, that the whey will be changed into good vi- negar, which, strained through a cloth, may be kept in bottles."

The acid of sugar of milk is considerably different from that just now described. To procure it, Mr Scheele poured 12 ounces of diluted nitrous acid on four ounces of finely powdered sugar of milk con- tained in a glass retort, to which a receiver was adapted. The retort was placed in a sand-bath, and as soon as the mixture acquired a certain degree of heat, it began to effervescence violently; for which rea- son, the retort and receiver were taken away from the fire. The mixture, however, continued to grow hotter and hotter, with a great emission of dark red vapours continually inclosing, for half an hour. A considerable quantity of nitrous air and aerial acid were extricated during that time. Care must be ta- ken, therefore, to have the retort and receiver both of a sufficient size, and not to make the luting too tight. When the effervescence had subsided, the retort was again placed in the sand bath, and the nitrous acid thus distilled off till the mass acquired a yellowish colour; on which the retort was immediately taken away from the fire. In two days time the solution seemed to have undergone no remarkable change, nor was there any appearance of crystals. Eight ounces more of the same nitrous acid were therefore added, and the whole exposed to the same degree of heat as before. When the mass grew warm, another effervescence, though weaker than the former, ensued; the yellow colour disappeared, and the nitrous acid was again ab- stracted, till the solution, which had been rendered opaque by the appearance of a white powder in it, Acid of assumed a yellowish colour, on which the retort was a- gain removed from the sand. After it was grown cool, the mass in the retort was found to be impregnated; it was redissolved in eight ounces of water, and filtered. Seven and a half drachms of white powder remained on the filter; the solution which passed through the filter was very acid. It was evaporated to the con- sistence of a syrup, four ounces more nitrous acid poured upon it, and the evaporation repeated in a sand heat. After the whole was cool, some small long ac- id crystals were found, together with a small quanti- ty of white powder which was separated from it, and some more nitrous acid poured on the remaining mass, and on evaporation, more such crystals made their ap- pearance. The same process was repeated several times; by which means the whole mass was at last changed into such crystals, and weighed about five drachms, showing in every respect the same pheno- mena produced by acid of sugar. The white powder, weighing seven and a half drachms, was the true acid of sugar of milk; and its properties are,

1. It burns in a red hot crucible like oil, without p leaving behind it any mark or ashes. 2. It dissolves of this acid in boiling water in the proportion of one of salt to 60 of the liquid. 3. One fourth part of the disso- ved powder separates from the liquid on cooling, in form of very small crystals. 4. Half an ounce of the salt was dissolved in a glass vessel in 30 ounces of boil- ing water, and the solution filtered when cold. It had a sourish taste, reddened the tincture of lacmus, and effervesced with chalk. 5. Two drachms of the salt exposed to an open fire in a glass retort, melted, grew black, and frothed very much; a brown salt was found sublimed into the neck of the retort, which smelled like a mixture of salt of benzoin and salt of amber, eleven grains of coal remaining in the retort. The receiver contained a brown liquid without any mark of oil, smelling like the sublimed salt. It contained also some of the salt dissolved, which was separated from it by a gentle evaporation. The sublimed salt weighed 35 grains, had a sour taste, and was easily soluble in spirit of wine, but with more difficulty in water, and burned in the fire with a flame. 6. Con- centrated vitriolic acid, distilled with this salt, became very black, frothed much, and decomposed the salt entirely. 7. Acid of sugar of milk, gradually added to a hot solution of alkali, occasioned an effervescence and coagulation in consequence of the formation of a vast number of crystals, which require eight times their weight of water to dissolve them, and separate again in a great measure from the liquid on cooling. The same phenomena took place with the mineral alkali, only the salt was somewhat more soluble, requiring only five times its weight of water for solution. If to a solution of it a solution of alkali of tartar be added, a number of small crystals will soon be formed at the bottom of the vessel, on account of the greater attraction of this acid with the vegetable alkali. 8. With volatile alkali it forms a kind of sal am- moniac, which, after being gently dried, has a sourish taste. By distillation, the volatile alkali is first separated, the lime-water precipitates, and the residuum yields the same products by distillation as the pure acid. 9. With all the earths, acid of sugar of milk forms insoluble salts. If a solution of ponderous earth in muriatic or nitrous acid be dropped into a solution of acid of sugar of milk, the former is instantly decomposed, and the earth falls to the bottom in combination with the acid of saccharum lactis. The same phenomena take place with solutions of lime in the nitrous and marine acids; but solution of gypsum is not decomposed. The same also takes place with solutions of magnesia in vegetable or mineral acids, and with earth of alum; all of which are decomposed by the neutral salts above mentioned.

The solution of this acid, by reason of the small quantity dissolvable in water, has no sensible effects on metals in their perfect state; but when they are reduced to calces, it then acts upon them, and forms salts, very little or not at all soluble in water. Silver, mercury, and lead are precipitated in form of a white powder; blue, green, and white vitriol, as well as manganese combined with acid of vitriol, are not precipitated; but all metallic solutions are precipitated by the neutral salts.

§ 16. Of the Lithiasic Acid, or Acid of the human Calculus.

The calculi examined by Mr Scheele, with a view to discover their constituent parts, were, as he informs us, all of the same nature, whether flat and polished, or rough and angular. A small quantity of calculus in powder was put into a retort, and some diluted vitriolic acid poured upon it. The powder was not affected by a digesting heat; however, it was dissolved when the humidity was abstracted by distillation. After the distillation of the acid, a black coal was left in the retort, and the vitriolic acid which had passed into the receiver was become sulphureous. The marine acid, whether diluted or concentrated, had no effect upon the calculus, not even when boiled with it. The nitrous acid diluted, or aquafortis, had some effect on the calculus, even in the cold. On the application of heat, an effervescence ensued with red vapours, and the calculus was dissolved. Repeating the experiment in a retort with lime-water, the latter was precipitated. The solution of calculus is acid, though the menstruum be boiled with a superabundant quantity of powder, so that there may remain a portion of it undissolved. It produces deep red spots on the skin in half an hour after it is applied; and if the saturated solution be a little more evaporated, it affumes of itself a blood-red colour, which, however, disappears on dropping in a single drop of nitrous acid. Terra ponderosa is not precipitated by it from the muriatic acid; nor are metallic solutions sensibly changed. With alkalies it becomes somewhat more yellow when the alkali is superabundant. The mixture, in a strong digesting heat, affumes a rose colour, and stains the skin in the same manner, without any sensation of burning. The mixture likewise precipitates metals of different colours; vitriol of iron, black; of copper, green; solution of silver, grey; corrosive sublimate, zinc, and lead, of a white colour. Lime water precipitates a white powder soluble in muriatic and nitrous acids without effervescence; and though there be an excess of precipitated powder, the solution will be acid. This white powder, therefore, is the acid of the calculus itself, the existence of which is also confirmed by Mr Bergman's experiments. The further analysis Flowers of this is related under the article Calculus, below.

§ 17. Of the Flowers of Benzoin, Acid of Lemons, with other anomalous vegetable acids, and the resemblance which the vegetable acids in general bear to one another.

It has long been known, that the resinous substance, Flowers of improperly called gum benzoin, yields by sublimation benzoin obtained by a gentle heat a quantity of fine saline matter called the flowers of benzoin. Another method of obtaining this substance is by lixiviating the gum with water, and crystallizing the salt. Mr Scheele, determined to try what quantity of the flowers could be obtained from the resin, found that, by sublimation, he was able obtained by to obtain from one pound of benzoin between nine and twelve drachms of flowers. By lixiviation the quantity obtained was considerably less than the former, owing to the saline particles being so much covered by the resin, that the water could not have sufficient access to dissolve them all. It was next attempted to procure all the flowers which the benzoin was capable of yielding. This was first done by boiling the powdered chalk and benzoin in water, and then filtering the decoction; but no crystals appeared. On pouring some drops of vitriolic acid into the liquor, the salt of benzoin soon afterwards precipitated (for this salt, which is an acid, was united to the chalk); but the quantity of salt was no greater than that obtained by lixiviation. Alkaline ley was next tried, and the solution saturated with an acid. Thus the salt of benzoin was obtained by precipitation; but here this inconvenience was met with, that the powder of benzoin ran together during the boiling, and floated on the surface like a tenacious resin. One only method, therefore, remained to be tried, and that was to boil the lime benzoin with quick-lime; and as the particles of lime, the best by interfering themselves betwixt those of the benzoin, would prevent their running together, and lime has likewise the property of acting upon the resinous particles, this seems to be the best method of procuring the flowers of benzoin in the greatest quantity, and also of the best quality; and thus we may obtain from 12 to 14 drachms of flowers from a pound of benzoin. Mr Scheele's receipt for preparing them after Scheele's new method, is as follows: "Pour 12 ounces of receipt for water upon four of unflaked lime, and after the ebullition is over, add eight pounds (of 12 ounces each) of water; put then a pound of finely powdered resin zoin by of benzoin into a tinned pan, pour upon it first about this mix ounces of the lime-water above mentioned; mix them well together, and thus add all the rest of the lime-water in succession. The reason of adding the lime-water thus by portions, is, that if it be poured in all at once, it will not mix with the benzoin, which will likewise coagulate and run together into a mass. This mixture must be boiled over a gentle fire for half an hour, agitating it constantly; then taking it from the fire, let it stand quiet for some time to settle, after which the clear liquor is to be poured off into a glass vessel. Pour then eight pounds of water more upon the lime in the vessel, and use this lime-water as before, repeating this process twice more, making four times... Flowers of Benzoin, &c.

in all; and lastly, putting all the residues together on a filter, pour hot water upon them. During this process, the calcareous earth of the lime-water combines with the acid of benzoin, and separates it from the resinous particles of this substance; but a small quantity of resin is dissolved by the lime-water, and gives it a yellow colour.

"All these liquors being mixed together and boiled down to two pounds, are then to be strained into another glass vessel. They are infusoried so far, because the superfluous water would hold a great quantity of the salt in solution; and a little of the resin being soluble in a large quantity of lime-water, but not in a small, falls to the bottom on the liquor being infusoried. When the liquor has become cold, after being strained the last time, add muriatic acid till the flowers be totally precipitated, which happens by reason of the stronger attraction of the marine acid for the calcareous earth. The precipitated coagulum is then to be put upon a filter; and, after being well dried, to be calcinated sufficiently, by repeatedly pouring cold water upon it, when it must be dried with a gentle heat. As the water made use of for this purpose, however, is capable of dissolving a little of the salt of benzoin, it ought to be evaporated, and afterwards set to crystallize. In order to give this salt a shining appearance, let it be dissolved in a sufficient quantity, six ounces, for instance, of water by gentle boiling; then strain it immediately, while yet warm, through a cloth, into a glass vessel which has been heated before; and thus a number of fine crystals will shoot as soon as the solution is grown cold. The water is then to be strained from the crystals, and the rest of the salt suspended in the water may be obtained by repeated evaporation and crystallization. In this method, however, a great quantity of the flowers are lost by reason of their volatility; it will therefore be more convenient to keep them in the form of their original precipitate, which is always in fine powder. Cloth answers best for the filtration of the hot solution: when blotting paper is used, the salt sometimes crystallizes in the filter, and obstructs it. The filtration itself might be omitted, were it not that about two grains of resin of benzoin remain united to the liquor, from whence it cannot be separated but by the operation just mentioned."

The properties of this salt as an acid are but little known. It has a most agreeable flavour; which, however, ceases as soon as it unites with calcareous earth, but is recovered again on being separated by any other acid.

With regard to the other vegetable acids, they may be divided into the essential, the fermented, and empyreumatic. The essential acids are pure, as exemplified in those of lemons, forrel, and forrel-docks; or but little altered by the admixture of other matters, as those of cherries, barberries, tamarinds, &c. In sweet fruits, they are generally so much covered when ripe as scarce to be distinguished; however, these latent acids become more evident, partly in fermentation, and partly by dry distillation. By the former method, all flowers, excepting a few which bear cruciform flowers, are made to yield vinegar; and by dry distillation only a very few yield a volatile alkali.

The acid which passes over in dry distillation is scarcely perceptible while the subject retains its natural form; but when once produced, has the same essential flowers of qualities with the other; whence it was naturally sup-

posed, that all vegetable acids are at bottom the same.

Chemists, however, have been divided in their opinions on this subject; some supposing that the acid of sugar or whether of tartar is the basis, and others that vinegar is the basis of all of them all. In proof of this latter hypothesis, it has been urged, that the acid of lemons may be crystallized; of which we have the following account in Scheele's Essays.

"The juice will not shoot into crystals by mere evaporation, even when thickened to the consistence of a syrup. This our author supposed to proceed from the great quantity of mucilaginous matter with which the juice abounds; for which reason he mixed the infusoried juice with strong spirit of wine, which coagulated the whole: but even thus he could obtain no crystals by evaporation. He therefore employed the method used for procuring the pure acid of tartar, and which is formerly described. The lemon juice, while boiling, was saturated with pulverized chalk, and the compound immediately fell to the bottom in a form nearly resembling tartarized lime. To separate the acid, a quantity of oil of vitriol, equal in weight to the chalk employed, but diluted with ten times its weight of water was necessary. This mixture must be boiled in a glass vessel for a few minutes; and when grown cold, the acid is to be separated from the gypsum by filtration. In order to crystallize it, we must evaporate the whole to the consistence of a thin syrup; but great care is to be taken lest any of the calcareous earth remain in the evaporated liquor; to determine which, a little of it is to be tried with fresh oil of vitriol, which will throw down the remainder: and in this case some more must be added to the whole quantity; for the least particle of lime remaining prevents the crystallization, while the superfluous quantity of acid remains in the liquor. The crystals shoot equally well in a hot as in a cold temperature, which is very unusual."

It is very remarkable that this crystallized salt of lemons cannot be converted into acid of sugar by means of that of nitre, though the extract of the juice itself may. Sour cherries afford acid of sugar, and yet another salt supposed to be tartar; and a kind of sugar may be obtained not only from roots of various kinds, but from pine raisins, and, as Dr Crell thinks, from expressed must; but whether the saccharine acid can be procured from this kind of sugar in equal quantity as from the common, or even whether it yields the same products with common sugar by dry distillation, is still a matter of doubt.

Pure acid of tartar yields on distillation per se an empyreumatic acid, and a coal consisting of oily par-acid of tartar by dry distillation. May not the acetous acid be mere acid of tartar, which did not meet with alkaline salt and earth enough with which it might combine and become more fixed; but, on the contrary, attracted more fugitive oily particles, and thus became more volatile? In distilling terra fo-Acetata tartari in the dry way, the acid of vinegar which acid almost enters its composition is almost entirely destroyed, only a fourth of pure acid being obtained, the residuum by fire in the retort, as well as the rest of that which comes over into the receiver, being entirely alkaline; and the same Identity of same thing happens to the acid of tartar, the empyreumatic acid above mentioned being extremely weak. Mr Beaumé likewise informs us, that if any calcareous earth, egg-shells, for instance, be dissolved in vinegar, and the crystallized salt be distilled, we obtain \( \frac{3}{4} \) of a red and very fiery inflammable fluid, smelling like empyreumatic acetous ether, which reddens tincture of turpentine. Malt, distilled before fermentation, yields only an empyreumatic acid resembling spirit of tartar.

The conjecture therefore seems reasonable, that vinegar and tartar have for their basis the same species of acid, which in the case of vinegar is combined with a greater proportion of oil, and in tartar with more earth. To bring vinegar therefore nearer the state of tartar, we must deprive it of its fine volatilizing phlogiston, combine it with more fixed matter, and restore its grosser oil. All this, however, is extremely difficult to be effected. Mr Weftrumb, who attempted it, added nitrous acid in various proportions, but could only produce a phlogistication of the latter, and dephtogistication of the vinegar; but as he could not think of any method of separating the two acids from one another, he was unable to investigate the properties of vinegar thus dephtogisticated. Dr Crell's opinion is of opinion, that this might have been done by vegetable alkali, lime, and terra ponderosa. The nitrous acid, with vegetable alkali, would have shot into the ordinary hexangular crystals of nitre: the acetous acid would have formed a compound not easily crystallized, provided it had remained unchanged; and though it had approached the nature of saccharine acid, would still have formed a compound difficultly crystallizable. The effects of these acids, indeed, on lime, are directly opposite to what they are on terra ponderosa. With the former, nitrous acid forms a liquor which can scarce be crystallized; with the latter, it produces salts difficult to be dissolved; while the acetous acid, with terra ponderosa, forms deliquescent salts; with lime, such as effloresce in the air. But if the vinegar, by means of the operation already mentioned, had been made to approach towards the nature of acid of sugar, transparent crystals would immediately have fallen, by reason of the strong attraction of this acid for lime. Dr Crell therefore recommends the following method. Let nitrous acid be several times distilled off from vinegar; and when the former, upon being newly added, produces no more red vapours, saturate the liquor with lime or terra ponderosa, separating the ley, which will not shoot, from the crystals. The nature of the salt which does not contain nitrous acid, may be determined from the figure of its crystals, or from the effects of other salts in consequence of a double elective attraction. We might likewise add fresh nitrous acid to the separated salt, or to the whole mixture, without any separation of the nitrous salt, till the earthy salt, which does not contain any nitrous acid, be saturated. The vinegar, if unaltered by the operation, would rise on distilling the liquor; and if converted into saccharine acid, would not be dislodged from lime by spirit of nitre. In like manner, distilled vinegar should be saturated with chalk, the compound reduced to crystals, and then exposed to as strong a fire as it can bear without expelling the acid, in order to displace some phlogistic particles. Let it then be distilled, filtered, and crystallized again; after which it may be treated with nitrous acid as above directed.

Perhaps (says Dr Crell), the acetous acid may by this combination acquire more fixity; so that the nitrous acid shall be able to produce a greater change. Should it pass over again in the form of acetous acid unchanged, let it be combined once more with calcareous earth; and let the foregoing experiment be repeated, in order to try whether some sensible change will not ensue. Should this method fail, try the opposite; that is, endeavour to add more gross phlogistic matter to the vinegar. Try to combine strong vinegar, and that which has been distilled, with unctuous oils. Thus we might perhaps bring it nearer to tartar; and, again, by means of nitrous acid, convert it into acid of sugar.

In another dissertation on this subject, Dr Crell undertakes to show, that all the vegetable acids may be converted into one, and that this is contained in the purest spirit of wine. The following are adduced as proofs.

1. If the residuum of dulcified spirit of nitre be boiled with a large quantity of nitrous acid, care being taken at the same time to condense the vapours by a proper apparatus; and if the liquid which has passed over be saturated with vegetable alkali, nitre and dulcified terra soliata tartari will be obtained; and on separating the latter by means of spirit of wine, the vinegar may be had in the ordinary way of decomposing the salt.

2. On boiling the residuum over again with nitrous acid, the same products are obtained; and the more frequently this process is repeated, the less acid of sugar is procured, until at length no vestige of it is to be met with.

3. Pure acid of sugar, boiled with 12 or 14 times its quantity of nitrous acid, is entirely decomposed, and the receiver is found to contain phlogisticated nitrous acid of sugar, vinegar, fixed air, and phlogisticated air, while a little calcareous earth remains in the retort.

4. Acid of sugar is likewise decomposed by boiling with six times its quantity of vitriolic acid. In the receiver we find vinegar, phlogisticated vitriolic acid, aerial acid; while pure vitriolic acid remains in the retort.

5. By saturating the residuum of dulcified spirit of nitre with chalk, there is formed an insoluble salt, which by treatment with vitriolic acid yields a real acid of tartar, constituting a cream of tartar with vegetable alkali.

6. On evaporating the liquor from which the tartarous felsite was obtained, a dark-coloured matter remains, yielding on distillation an empyreumatic acid of tartar, and a fleshy coal. Hence it would seem, that spirit of wine consists of acid of tartar, water, and phlogiston; so that it is a native dulcified acid: and nitrous acid, on being mixed with it in moderate quantity, dislodges the acid of tartar. On the addition of more nitrous acid, the acid of tartar is resolved into acid of sugar and phlogiston; and by a still greater addition, the saccharine acid is changed into vinegar.

7. On boiling one part of acid of sugar with one and an half of manganese and a sufficient quantity of nitrous acid and acid of sugar. Acid of Fat. Nitrous acid, the manganese will be almost entirely dissolved, and phlogisticated nitrous acid along with vinegar will pass over into the receiver.

8. On boiling together acid of tartar, manganese, and nitrous acid, we obtain a solution of the manganese, with phlogisticated nitrous acid and vinegar as before.

9. If acid of tartar be boiled along with vitriolic acid and manganese, the latter will be dissolved, and vinegar with vitriolic acid will pass over into the receiver.

10. On digesting acid of tartar and spirit of wine for several months, the whole is converted into vinegar; the air in the vessel being partly converted into acetaceous acid, and partly into phlogisticated air.

11. On boiling spirit of wine with vitriolic acid and manganese, it will be converted into vinegar and phlogisticated air.

12. By distilling spirit of wine upwards of 20 times from caustic alkali, it was changed into vinegar, and a considerable quantity of water was obtained.

Hence it appears, says Dr Crell, that the acids of tartar, sugar, and vinegar, are modifications of the same acid, as it contains more or less phlogiston. The acid of tartar has the greatest quantity, the acid of sugar somewhat less, and vinegar the least of all. In these experiments, however, care must be taken that neither the nitrous acid nor fixed alkali employed contain any marine acid, otherwise the results will be uncertain.

§ 18. Of the Acid of Fat.

This may be obtained from fuel by means of many repeated distillations. A small quantity is separated at each distillation; but by distilling the empyreumatic oil into which the fuel is thus converted over and over, a fresh quantity is always obtained. The acid of fat in some respects has a resemblance to that of sea-salt; but in others is much more like the vegetable kind, as being destructible in a strong fire, forming compounds which do not deliquesce with calcareous earth, and uniting intimately with oily substances. With alkalies it forms salts entirely different from those yielded by the other acids; with the volatile alkali, particularly, it produces a concrete volatile salt. When saturated with calcareous earth, it yields brown crystals; and a salt of the same kind was obtained by Dr Crell from a mixture of quicklime and fuel distilled to dryness, and boiling up the residue with water. The crystals were hexagonal, and terminated by a plane surface; their taste was acid and saltish; they did not deliquesce in the air, and were easily and copiously dissolved in water. With magnesia and earth of alum a gummy mass is obtained, which refuses to crystallize.

With regard to the metals, Dr Crell informs us, that the acid of fat copiously dissolves manganese into a clear and limpid liquor. It dissolves the precipitate of cobalt, but not the regulus. White arsenic is acted upon but sparingly, and nickel not at all, though it forms a green solution with the precipitate from nitrous acid. Regulus of antimony, by the affluence of heat, is dissolved into a clear liquor, which became milky in the cold; it crystallized on evaporation, and did not deliquesce in the air. Zinc readily dissolved, and imparted a peculiar metallic taste, falling line salts to the bottom in the form of a white powder on the combination of an alkali. Bismuth in the metallic state was not dissolved; but the precipitate was. It acted upon mercury after being twice distilled from it, and poured afresh upon the metal. The mercury could not be entirely precipitated by common salt. It acted more vigorously upon a precipitate from corrosive sublimate; from the solution of which a white sublimate was obtained after the liquor had been drawn off by distillation. A gold-coloured solution was obtained from platinum by distilling the acid from it to dryness, and then pouring it back again; the precipitate of this metal from aqua-regia by spirit of wine was dissolved in great abundance. Iron was very easily dissolved in it, and exhibited a liquor of an astringent taste, which shot into needle-like crystals that did not deliquesce in the air. Lead was corroded, and rendered the acid turbid. Minium was converted into a white powder, and then dissolved with greater ease. The solution has a sweet taste, and cannot be precipitated by sea-salt. Tin was corroded into a yellow calx, and dissolved but in very small quantity. Copper was dissolved, even in the cold, into a green liquor; but, the solution was greatly promoted by heat. On evaporation it showed some disposition to crystallize, but again attracted moisture from the air. Silver-leaf was attacked only in a very small degree; however, some was precipitated by means of copper, and the marine acid rendered the liquor turbid. The calx precipitated from aquafortis was dissolved more copiously. Silver was precipitated of a white colour from aquafortis by the pure acid itself, as well as by its ammoniacal salt. Half an ounce of the acid distilled four times almost to dryness from some gold leaves, and at length poured back upon them, the precipitate of a dilute solution of tin obtained by it, gained only a faint colour, rather inclining to red; but a mixture of two parts of acid with one of aquafortis, dissolved gold very readily.

§ 19. Of Fixed Alkaline Salts.

Of these there are two kinds; the vegetable and how pro-mineral. The former is never found by itself, and but rarely in combination with any acid; but is always prepared from the ashes of burnt vegetables. It is got in the greatest quantity from crude tartar; from which, if burned with proper care and attention, we may obtain one pound of alkali out of 2½ of the tartar. The latter is found native in some parts of the earth. It is likewise found in very large quantities combined with the marine acid, in the waters of the ocean, and in the bowels of the earth; thus forming the common alimentary salt. It is also produced from the ashes of certain sea-plants, and of the plant called kalli; from whence both the mineral and vegetable alkalies have taken their name.

The vegetable alkali difficulty affinities a crystalline vegetable form; nevertheless, it may be partially united with alkali crys-tome acids in such a manner as to crystallize, and lose its property of deliquating in the air, without, at the same time, ceasing to be an alkali. Of this we have an example in the acid of ants above mentioned. Something Fixed Alkali—thing of the same kind we have observed in treating vegetable fixed alkali with spirit of wine. A gallon of pretty strong spirit of wine being drawn over from a pound of salt of tartar, a black unctuous liquor was left, which shot into crystals very much resembling vitriolated tartar, and which did not deliquesce in the air, but were nevertheless strongly alkaline. Dr Black, however, informs us, that the vegetable alkali may be shot into fine crystals; but which cannot be preserved, on account of their great attraction for moisture, unless closely shut up from the air. They have not such a quantity of water as to undergo the aqueous fusion.

The mineral alkali in its natural state always assumes a crystalline form, somewhat resembling that of sal mirabile. It does not deliquesce in the air, nor does it seem to have so strong an attraction for water, even when in its most caustic state, as the vegetable alkali: hence mineral alkali is preferable to it in making soap, which is always of a firmer consistence with mineral than with vegetable alkali. If vegetable alkali is combined with spirit of salt, some change seems to be thereby induced upon it; as the salt produced by expelling the marine acid by means of the vitriolic, and then crystallizing the mass, crystallizes differently from vitriolated tartar. Whether the vegetable alkali might by this means be entirely converted into the mineral, deserves a further inquiry.

Both mineral and vegetable alkalies, when applied to the tongue, have a very sharp, pungent, and urinous taste; but the vegetable considerably more so than the mineral. They both unite with acids, and form different neutral salts with them: but the vegetable alkali seems to have rather a greater attraction for acids than the other; although this difference is not so great as that a neutral salt, formed by the union of mineral alkali with any acid, can be perfectly decomposed by an addition of the vegetable alkali, unless in considerable excess.

Both vegetable and mineral alkali appear to be composed of an exceedingly caustic salt united with a salt and fixed air. This may be increased so far, as to make the vegetable alkali assume a crystalline form, and lose great part of its alkaline properties: but as the adhesion of great part of this air is very slight, it easily separates by a gentle heat. Some part, however, is obstinately retained; and the alkali cannot be deprived of it by the most violent calcination per se. The only method of depriving it entirely of its fixed air is, by mixing an alkaline solution with quicklime.

Fixed Alkalies combined,

1. With Sulphur. The produce of this is the red fetid compound called hepar sulphuris, or liver of sulphur. It may be made by melting sulphur with a gentle heat, and stirring into it, while melted, four times its weight of dry alkaline salt. The whole readily melts and forms a red mass of a very fetid smell, and which deliquesces in the air. If sulphur is boiled in a solution of fixed alkaline salt, a like combination will take place.

In this process, when the hepar is made either in the dry or the moist way, the fixed air of the alkali is discharged, according to Dr Priestley's observation. Neither does a fixed alkali, when combined with fixed air, seem capable of uniting with sulphur; nor will the union be accomplished without heat, unless the alkali is already in a caustic state. Hence a cold solution of hepar sulphuris may be decomposed, partly at least, by fixed air. On adding an acid, however, the decomposition takes place much more rapidly; and the sulphur is precipitated at the bottom, in form of a white powder.

During the precipitation of the sulphur from an alkali, by means of acids, a thick white smoke arises, of a most fetid smell and suffocating nature. It burns quietly, without explosion, on a candle's being held in it. Cales of silver, lead, iron, or bismuth, are rendered black by it. Hence, if any thing is wrote with a solution of lead, and a solution of hepar sulphuris isable vapour passed over it when dry, the writing, formerly invisible, will immediately appear of a blackish brown colour.

Silver, in its metallic state, is prodigiously blackened either by the contact of this vapour, or by being immersed in a solution of the hepar sulphuris itself. Litharge is instantly restored to its metallic state, on being immersed even in a cold solution of hepar sulphuris.

By being united with an alkali, the acid of sulphur Phlogiston seems very much disposed to quit the phlogiston. If a solution of hepar sulphuris is exposed to the air for some time, it is spontaneously decomposed; the phlogiston of the sulphur flying off, and the acid remaining united with the alkali into a vitriolated tartar. This decomposition takes place so remarkably, when liver of sulphur is dissolved in water, that, by a single evaporation to dryness, it will be almost totally changed into vitriolated tartar. If this substance, in a dry state, be exposed to a moderate degree of heat, and the mass kept constantly stirring, a like decomposition will follow; the phlogiston of the sulphur will fly off, and the acid unite with the alkali.

Liver of sulphur is a great solvent of metallic matters; all of which, except zinc, it attacks, particularly in fusion. It seems to dissolve gold more effectually than other metals. This compound also dissolves vegetable coals, even by the humid way; and these solutions, if suffered to stand in the open air, always precipitate a black powder, no other than the coal they had dissolved, in proportion to the quantity of hepar sulphuris decomposed. When vegetable coal is thus dissolved by liver of sulphur in fusion, it is of a much deeper red than in its natural state. The solution in water is of a green colour.

II. With Expressive Oils. The result of this combination is soap; for the preparation of which in large quantities in the way of trade, see Soap. The soap which is used in medicine is prepared without heat, in the following manner, according to the author of the Chemical Dictionary.

"One part of quicklime, and two parts of good Spanish soda (the salt prepared from the ashes of the herb kali), are boiled together during a short time in an iron caldron. This lixivium is to be filtered, and evaporated by heat, till a phial, capable of containing an ounce of water, shall contain an ounce and 216 grains of this lixivium. One part of this lixivium is to be mixed with two parts of oil of olives, or of sweet almonds, in a glass or stone-ware vessel. The mixture soon becomes thick and white; and must be stirred from time to time with an iron spatula. The combi- Fixed Alkali—nation is gradually completed, and in seven or eight days a very white and firm soap is obtained."

In attempting combinations of this kind, it is absolutely necessary that the alkali be deprived of its fixed air as much as possible; otherwise the soap will be quite unctuous and soft: for fixed alkalis have a greater attraction for fixed air than for oil, and hence soap is decomposed by blowing fixed air into a solution of it in water. It may be made either with tallow, wax, spermaceti, butter of cocoa, the coarser resinous substances, or animal oils.

III. With Essential Oils. The volatility of these oils in a great measure hinders them from being acted upon by alkalis: nevertheless, combinations of this kind have been attempted; and the compounds so produced have been called Starkey's soap, from one Starkey a chemist, who endeavoured to volatilize salt of tartar by combining it with oil of turpentine. His method was to put dry salt of tartar into a matras, and pour upon it essential oil of turpentine to the height of two or three fingers breadth. In five or six months, a part of the alkali and oil were combined into a white faponaceous compound. This must be separated from the mixture, and more of it will afterwards be formed by the same method.

Chemists, imagining this soap to be possessed of considerable medical virtues, have endeavoured by various methods to shorten this tedious process. Of these one of the most expeditious is that recommended by Mr Beaumé; which consists in triturating, for a long time, alkaline salt upon a porphyry, and adding oil of turpentine during the trituration. According to him, the thick resinous part of the oil only can combine with the salt; and, during the time this combination is effected, the more subtile and attenuated parts will fly off. Hence he finds that the operation is considerably abridged by the addition of a little turpentine or common soap. The most expeditious of all, however, is that mentioned by Dr Lewis; which consists in heating the alkali red hot, and then throwing it into oil of turpentine, stirring them well together; on which they immediately unite into a faponaceous mass.

This kind of soap is subject to great alterations from keeping; particularly the loss of its colour, and a kind of decomposition occasioned by the extraction of an acid from the oil of turpentine, which unites with the alkali, and crystallizes not only all over the surface, but in the very substance of the soap. The nature of this salt is unknown, but certainly deserves consideration.

IV. With Phlogiston. This combination is effected by calcining them with the charcoal either of vegetable or animal matters. The consequence is, that they are greatly altered in their properties; sometimes so much as to be enabled to precipitate calcareous earths from their solutions in acids. Metallic solutions precipitated by them in this state, assume different colours.

Differences observed between Fixed Alkalies obtained from different Vegetables.

These differences we must conceive to arise from some proportion of the oily and phlogistic matter of the vegetable remaining in the ashes from whence the salts are extracted; for when reduced to their utmost purity, by repeated calcinations in a strong fire, and deliquations in the air, all of them, the marine alkali excepted, appear to be the very same.

On this subject Mr Gradlin has given a great number of experiments in the fifth volume of the Commentaria Petropolitana; and found very considerable differences, not only between the alkaline salts, but likewise the pure vegetable earths obtained from different vegetables by burning. The salts of the several plants examined were prepared with great care, and all of them exactly in the same manner; each vegetable being burnt in a separate crucible, with the same degree of fire, till no remains of coaly matter could any longer be perceived; and the ashes eluted in glaas vessels with cold distilled water. The salts, thus obtained, were found to produce different colours on mixture with certain liquors, and to effervesce in very different degrees with acids: certain metallic solutions were by some precipitated, by others only rendered thicker, by others both precipitated and rendered thick; whilst some occasioned neither the one nor the other of these changes, but left the fluid clear and transparent. Thus, with the vitriolic acid, the salts of southernwood and sage struck a pale brown colour; those of pine-tops and rue, a yellow; that of fern, a reddish yellow; and that of fanicle, a dark leek-green: that of dill yielded a leek-green precipitate, with elegant green flakes floating in the liquor. This last salt also gave a greenish precipitate with the marine acid, and a red one with the nitrous. Solution of corrosive sublimate was changed yellow by salt of southernwood; of a brownish colour, by that of colt's-foot; of a deep red, by that of wormwood; and of a pitch-colour, by that of dill. That of fern threw down an opal-colour; of sage, a sulphur-yellow; of elder flowers, a citron yellow; of fanicle, a saffron colour; and of milfoil, a deep-red precipitate. From solution of silver, salt of carduus benedictus threw down a white; of camomile, a grey; of hyssop, a brownish; of dill, a blackish brown; of scabious, a yellowish; and that of pine-tree tops, a sulphur yellow precipitate. Solution of vitriol of copper was changed by salt of southernwood to a bright sea-green; by that of dill, to an unfrightly green; of agrimony, to a greenish blue; and by that of milfoil, to a bright sky-blue: the salt of penny-royal made the liquor thick as well as blue, and that of feverfew made it thick and green: the salt of hyssop threw down a green precipitate, that of fever-grass a blue one, and that of fumitory a greenish blue: whilst the salt of fern made scarcely any change either in the colour or consistency of the liquor.

§ 19. Of Volatile Alkali.

This is a kind of salt obtained from all animal, some vegetable, substances, from root by distillation with a strong heat, and from all vegetable substances by putrefaction. Though a volatile alkali is procurable from all putrid animal substances by distillation, yet the putrefactive process does not seem to prepare volatile alkali in all of these. Putrid urine, indeed, contains a great quantity of alkali ready formed, whence its use in scouring, &c., but the case is not so with putrid blood or flesh. These afford no alkali till after the phlegm has arisen; and this they would. would do, though they had not been putrefied. According to Mr. Wiegleb, volatile alkali is found in limestone, lapis fulvas, chalk, marble, coals, turf, loam, clay, and many other kinds of earth. Its existence in these substances may be discovered merely by distilling them with a brisk fire, but still better by the addition of some quantity of fixed alkali or quicklime before the distillation.—It has even been found in all mineral salts and their acids, as vitriol, nitre, common salt, and the acid liquors drawn from these substances, also in gypsum and sulphur; from all which it may be separated by means of quicklime.—In the vegetable kingdom it is produced by dry distillation from mustard-seed, elder flowers and leaves; the leaves of the wild cherry tree, white water-lilies, tobacco, and sage; as well as from many other plants. According to our author, the simplest proof of its existing almost universally in the vegetable kingdom, is, that the foot of our chimneys affords a volatile alkali by distillation, either with or without quicklime.

Volatile alkali, when pure, appears of a snowy whiteness; has a very pungent smell, without any disagreeable empyreuma; is very easily evaporable, without leaving any residuum; effervesces with acids much more strongly than fixed alkali; and forms with them neutral compounds called ammoniacal salts, which we have already described, and which are different according to the nature of the acid made use of; for all volatile alkalies, when perfectly purified, appear to be the very same, without the smallest difference.

Like fixed alkalies, these salts contain a great quantity of fixed air, on which their solidity depends; and which may be so increased as perfectly to neutralize, and deprive them of their peculiar taste and smell. When neutralized by fixed air, they have a very agreeable pungent taste, somewhat resembling that of weak fermenting liquors. When totally deprived of fixed air, by means of lime, they cannot be reduced to a solid form; but are dissipated in an invisible and exceedingly pungent vapour, called by Dr. Priestley alkaline air. When volatile alkaline salt is dissolved in water, the solution is called a volatile alkaline spirit.

**Distillation and Purification of Volatile Alkalies**

The materials most commonly used for preparing volatile alkalies are the solid parts of animals, as bones, horns, &c. These are to be put into an iron pot of the shape recommended for solution; to this must be fitted a flat head, having a hole in the middle about two inches diameter. From this a tube of plate-iron must issue, which is to be bent in such a manner that the extremity of it may enter an oil jar, through a hole made in its upper part, and dip about half an inch under some water placed in the lower part. The mouth of the jar is to be fitted with a cover, fitted on very exactly; and having a small hole, which may be occasionally stopped with a wooden peg. The junctures are to be all fitted as close as possible, with a mixture of clay, sand, and some oil; and those which are not exposed to a burning heat, may be further secured by quicklime and the white of an egg, or by means of glue. A fire being now kindled, the air contained in the distilling vessel is first expelled, which is known by the bubbling of the water; and to this vent must be given by pulling out the wooden peg. A considerable quantity of phlegm will then come over, along with some volatile alkali, a great quantity of fixable air, and some oil. The alkali will unite with the water, and likewise some part of the fixed air, the oil swimming above. A great many incenseable vapours, however, will come over, to which vent must be given from time to time, by pulling out the peg. The distillation is to be continued till all is come over; which may be known by the cessation, or very slow bubbling of the water. The iron-pipe must then be separated from the cover of the distilling vessel, lest the liquid in the jar should return into it, on the air being condensed by its cooling. In the jar will be a volatile spirit, more or less strong according as there was less or more water put in, with an exceedingly fetid black oil floating upon it.

The rectification of the volatile alkali is most commodiously performed at once by combining it with an acid; and, as spirit of salt has the least affinity with inflammable matter, it is to be chosen for this purpose, in preference to the vitriolic or nitrous. As the spirit is excessively oily, though already much weakened by the admixture of the water in the jar, if a very large quantity was not originally put in, an equal quantity of water may still be added, on drawing off the spirit. That as little may be lost as possible, the spirit should be received in a stone bottle; and the marine acid, likewise in a distilled state, added by little and little, till the effervescence ceases. The liquor, which is now an impure solution of sal ammoniac, is to be left for some time, that the oil may separate itself; it is then to be filtered, evaporated, and crystallized in a leaden vessel. If the crystals are not sufficiently pure at the first, they will easily become so on a second distillation.

From sal ammoniac thus obtained pure, the volatile alkali may be extricated by distillation with chalk, alkaline salts, or quicklime. Alkaline salts act more briskly than chalk, and give a much stronger volatile alkali. The strength of this, however, we know may be altered at pleasure, by adding to, or depriving it of, its natural quantity of fixed air. Hence, perhaps, the best method would be, to prepare volatile alkalies altogether in a fluid state, by means of quicklime; and then add fixed air to them, by means of an apparatus similar to that directed by Dr. Priestley for impregnating water with fixed air. To prevent lime from adhering to the distilling vessels in which it is put, the translator of Wiegleb's chemistry recommends the putting in three or four ounces of common salt along with the other ingredients.

**Volatile alkalies combined**

I. **With Metals.** There are only three metals, viz., copper, iron, and lead, upon which, while in their metallic form, volatile alkalies are capable of acting. Copper-salts are dissolved by volatile alkali, especially in its caustic state, into a liquor of a most admirable blue colour. It is remarkable, that this colour depends entirely upon the air having access to the solution: for if the bottle containing it is closed (lopt), the liquor becomes colourless; but, however, resumes its blue colour on being exposed to the air. On evaporation, a blue saline mass is obtained, which, mixed with fats, or other inflammable matters, tinges their flame green, leaving a red calx of copper, soluble again in volatile spirits as at first. This saline sub- flance has been received into the last edition of the Edinburgh Dispensatory, under the name of caprum ammoniacum, as an antiepileptic.

The blue mixture of solution of copper in aquafortis with volatile spirits, yields sapphire-coloured crystals, which dissolve in spirit of wine, and impart their colour to it. If, instead of crystallization, the liquor be totally evaporated, the remaining dry matter explodes, in a moderate heat, like aurum fulminans. This is given as a fact by Dr Lewis; but hath not succeeded upon trial by Dr Black. Various phenomena, says Mr Wieglet, occur in the dissolution of copper by the volatile alkali.—On saturating dilute spirit of sal ammoniac with copper-filings, crystals are formed of a dark-blue colour, but which, by exposure to the air, fall to pieces and become green. Vivous spirit of sal ammoniac impregnated with copper, loses in an instant its blue colour, on the addition of an equal quantity of saturated solution of fixed alkaline salt. The copper is then taken up by the fixed alkaline solution, which of consequence acquires a blue colour, while the spirit of wine, deprived of the metal, floats clear on the top. When filings of copper are put into a bottle, and that bottle quite filled with caustic volatile alkali, and is immediately stoppered up, no solution takes place: but when the bottle is left open, only for a short time, or an empty space is left in it, a colourless solution is obtained, which in the air obtains a blue colour; but which may be deprived of this colour as often as we please, by shutting it up exactly from the air, and letting it stand, in this situation, on fresh filings of copper.—From these phenomena Mr Wieglet concludes, that copper does not dissolve in volatile alkali until it has lost part of its phlogiston, to which the air, by the attraction it exerts upon it, contributes its share. If this has taken place only in a small proportion, and the farther access of air be prevented, the remainder will be dissolved without any colour; which, however, appears in the instant that, by a fresh accession of air, the phlogiston still remaining finds means to escape. The dissolved copper is always precipitated when the solution meets with phlogisticated copper. The colourless solution is precipitated by zinc and vitriolic acid, but not by iron. It tastes rather sweet, and does not smell very strong of volatile alkali; while, on the contrary, the blue solution has a pungent smell, and is precipitated by distilled water.

On the other two metals the action of volatile alkali is by no means so evident; it dissolves iron very slowly into a liquor, the nature of which is not known; and lead is corroded by it into a mucilaginous substance.

II. With Inflammable Substances. With expressed oils, the caustic volatile alkali unites into a soft unctuous mass, of a very white colour, imperfectly soluble in water, and which is soon decomposed spontaneously. Compositions of this kind are frequently used for removing pains, and sometimes with success. With essential oils, volatile alkalies may be united, either in their dry or liquid form, by means of distillation. The produce is called sal volatile oleofum; it is much more frequently used in a liquid than in a dry form. The general method of preparation is by distilling volatile alkali along with essential oils and spirit of wine, or the aromatic substances from whence the essential oils are drawn. These compositions are volatile variable at pleasure; but certain forms are laid down Alkali and in the dispensatories, with which it is expected that all nations, the chemists should comply in the preparation of these medicines.

III. Eau de Luce. This is the name given to an Spiritus exceedingly volatile spirit, which some years ago was laudis fuscus, pretty much in vogue; and indeed seems very well natus, calculated to answer all the purposes for which volatile alkalies can be used. It was of a thick white colour, and smelled somewhat of oil of amber. A receipt appeared in Lewis's Dispensatory for the preparation of this fluid, under the name of spiritus volatilis fuscus. The method there directed, however, did not succeed; because, though the alkaline spirit is capable of keeping a small quantity of oil of amber suspended, the colour is greatly more dilute than that of genuine eau de luce. In the Chemical Dictionary we have the following receipt: "Take four ounces of rectified spirit of wine, and in it dissolve 10 or 12 grains of white soap; filter this solution; then dissolve in it a drachm of rectified oil of amber, and filter again. Mix as much of this solution with the strongest volatile spirit of sal ammoniac, as will be sufficient, when thoroughly shaken, to give it a beautiful milky appearance. If upon its surface be formed a cream, some more of the oily spirit must be added."

This receipt likewise seems insufficient. For the oil of amber does not dissolve in spirit of wine: neither is it probable that the small quantity of soap made use of could be of any service; for the soap would dissolve perfectly in the alkaline spirit, without suffering any decomposition. The only method which we have found to answer is the following. Take an ounce, or any quantity at pleasure, of balsamum Canadense; place it in a small china basin, in a pan of boiling water, and keep it there till a drop of it taken out appears of a resinous consistence when cold. Extract a tincture from this resin with good spirit of wine; and having impregnated your volatile spirit with oil of amber, lavender, or any other essential oil, drop in as much of the spirituous tincture as will give it the desired colour. If the volatile spirit is very strong, the eau de luce will be thick and white, like the cream of new milk; nor is it subject to turn brown with keeping.

IV. With Volatile Tincture of Sulphur. This is a combination of the caustic volatile alkali, or spiritus kalmi of sal ammoniac, with sulphur. It is usually divided with respect to be made by grinding lime with the sulphur, and afterwards with the sal ammoniac, and distilling the whole in a retort; but the produce is by this method very small, and even the success uncertain. A preferable method seems to be, to impregnate the strongest caustic volatile spirit with the vapour which arises in the decomposition of hepar fulphuris by means of an acid, in the same manner as directed for impregnating water with fixed air.

This preparation has a most nauseous fetid smell, which spreads to a considerable distance; and the effluvia will blacken silver or copper, if barely placed in the neighbourhood of the stoppered bottle. This property renders it capable of forming a curious kind of sympathetic ink; for if paper is wrote upon with a solution of saccharum saturni, the writing, which disappears when dry, will appear legible, and of a brownish Practice.

Phenomena brownish black, by barely holding it near the mouth of the bottle containing volatile tincture of sulphur. The vapours of this tincture are so exceedingly penetrating, that it is said they will even penetrate through a wall, so as to make a writing with saccharum saturni appear legible on the other side; but this is much to be doubted. It is even said that it cannot penetrate through the substance of paper, but only infuses itself between the leaves; and hence if the edges of the leaves are glued together no black colour will appear.

§ 20. Of the PHENOMENA resulting from different mixtures of the Acid, Neutral, and Alkaline Salts, already treated of.

1. If concentrated oil of vitriol is mixed with strong spirit of nitre, or spirit of salt, the weaker acid will become exceedingly volatile, and emit very elastic fumes; so that if a mixture of this kind is put into a close stopp'd bottle, it will almost certainly burst it. The same effect follows upon mixing spirit of salt and spirit of nitre together. In this case, both acids become surprisingly volatile; and much of the liquor will be dissipated in fumes, if the mixture is suffered to stand for any considerable time. Such mixtures ought therefore to be made only at the time they are to be used.

2. If vitriolated tartar is dissolved in an equal quantity of strong spirit of nitre, by heating them together in a matras, the stronger vitriolic acid will be displaced by the weaker nitrous acid, and the liquor, on cooling, will shoot into crystals of nitre. The same thing happens also upon dissolving vitriolated tartar, or Glauber's salt, in spirit of salt. This observation we owe to Mons. Reaumur, and the reason of it has been already explained. See n° 285.

3. If vitriolated tartar, or Glauber's salt, is dissolved in water, and this solution mixed with another consisting of calcareous earth, silver, mercury, lead, or tin, dissolved in the nitrous or marine acids, the vitriolic acid will leave the fixed alkali with which it was combined, and, uniting with the calcareous earth or metal, fall with it to the bottom of the vessel. This decomposition takes place only when the vitriolic acid meets with such bodies as it cannot easily dissolve into a liquid, such as those we have just now mentioned; for though vitriolated tartar is mixed with a solution of iron, copper, &c., in the nitrous or marine acids, no decomposition takes place. The case is not altered, whatever acid is made use of; for the marine acid will effectually separate silver, mercury, or lead, from the vitriolic or nitrous acids.

4. According to Dr Lewis, if a solution of vitriolated tartar is dropped into lime-water, the acid will unite with the lime, and precipitate with it in an indissoluble selenite, the alkali remaining in the water in a pure and caustic state.

5. If green vitriol is mixed with any solution containing substances which cannot be dissolved into a liquid by the vitriolic acid, the vitriol will be immediately decomposed, and the liquor will become a solution of iron only. Thus, if green vitriol is mixed with a solution of saccharum saturni, the vitriolic acid immediately quits the iron for the lead, and falls to the bottom with the latter, leaving the vegetable acid of saccharum saturni to combine with the iron.

6. If solution of tin in aqua regia is mixed with solution of saccharum saturni, the marine acid quits the salts-tin for the lead contained in the saccharum; at the same time, the acetic acid, which was combined with the lead, is unable to dissolve the tin which was before kept suspended by the marine acid. Hence, both saccharum saturni, and solution of tin, are very effectually decomposed, and the mixture becomes entirely useless. Dyers and calico-printers ought to attend to this, who are very apt to mix these two solutions together; and no doubt many of the faults of colours dyed or printed in particular places, arise from injudicious mixtures of a similar kind. See Dyeing.

7. If mild volatile alkali, that is, such as remains in a concrete form, by being united with a large quantity of fixed air, is poured into a solution of chalk in the nitrous or marine acids, the earth will be precipitated, and a true sal ammoniac formed. If the whole is evaporated to dryness, and a considerable heat applied, the acid will again part with the alkali, and combine with the chalk. Thus, in the purification of volatile alkalies by means of spirit of salt, the same quantity of acid may be made to serve a number of times. This will not hold in volatile spirits prepared with quicklime.

8. If equal parts of sal ammoniac and corrosive sublimate mercury are mixed together and sublimed, they both unite in such a manner as never to be separable from one another without decomposition. The compound is called sal alembricus; which is said to be a very powerful solvent of metallic substances, gold itself not excepted. Its powers in this, or any other respect, are at present but little known. By repeated sublimations, it is said this salt becomes entirely fluid, and refuses to arise in the strongest heat.

9. If vitriolic acid is poured upon any salt difficult to dissolve in water, it becomes then very easily soluble. By this means, vitriolated tartar, or cream of tartar, may be dissolved in a very small quantity of water.

Sect. II. Earths.

The general divisions and characters of these substances we have already given; and most of their combinations with saline substances have been mentioned, excepting only those of the terra ponderosa; a substance whose properties have been but lately inquired into, and are not yet sufficiently investigated. In this section, therefore, we have to take notice only of their various combinations with one another, with inflammable, or metallic substances, &c. As they do not, however, act upon one another till subjected to a vitrifying heat, the changes then induced upon them come more properly to be treated of under the article Glass. Upon metallic and inflammable substances (fulphur alone excepted), they have very little effect; and therefore what relates to these combinations shall be taken notice of in the following sections. We shall here confine ourselves to some remarkable alterations in the nature of particular earths by combination with certain substances, and to the phosphoric quality of others. § 1. The Terra Ponderosa.

This earth is of the true calcareous kind, and capable of being converted into a very acid lime; but in other respects is very different. It is most commonly met with in the veins of rocks, united with the vitriolic acid in a mass somewhat resembling gypsum, but much heavier and more opaque; and from the great weight of this substance the earth itself has its name, though when freed from the acid it is by no means remarkable for this property. Its properties were first taken notice of by foreign chemists; but they have been more accurately investigated by Dr. Withering, who has published his observations in the 74th volume of the Philosophical Transactions. His experiments were not made on the gypseous substance above mentioned; but on a combination of the earth with fixed air, which is much more uncommon, and like the other possesses a very considerable degree of specific gravity. Both these combinations have the general name of *spar*; the former being also called *barofelenite*, &c.

The spar used by Dr. Withering was got out of a lead mine at Alston Moor in Cumberland. Its appearance was not unlike that of a lump of alum; but on closer inspection it appeared to be composed of slender spicules in close contact, more or less diverging, and so fine that it might be cut by a knife; its specific gravity from 4.300 to 4.338. It effervesced with acids, and melted, though not very readily, under the blowpipe. In a common fire it lost its transparency; and on being urged with a stronger heat in a melting furnace, it adhered to the crucible, and showed signs of fusion; but did not appear to have lost any of its fixed air, either by diminution in weight, becoming caustic, or losing its power of effervescence with acids.

Five hundred grains of this spar, by solution in muriatic acid, lost 104 grains in weight, and left an insoluble residuum of three grains. In another experiment, 100 grains of spar lost 21; and there remained only 0.6 of a grain of insoluble matter.

On dissolving another hundred grains in dilute muriatic acid, 25 ounce-measures of air were obtained, which by proper trials appeared to be pure aerial acid; and, on precipitating the solution with mineral alkali, 100 grains of earth were again obtained; but on dissolving the precipitate in fresh muriatic acid, only 20 ounce-measures of air were produced.

Mild vegetable alkali precipitated a saturated solution of this spar in marine acid, with the escape of a quantity of fixed air; and the same effect took place on the addition of fossil alkali; but with caustic alkalies there was no appearance of effervescence, though a precipitate likewise fell.

Fifty parts of spar, dissolved in marine acid, lost 10½; and with caustic vegetable alkali, a precipitate weighing 45½ was obtained. Phlogiticated alkali precipitated the whole of the earth, as appeared by the addition of mild fixed alkali afterwards, which occasioned no further precipitation.

Part of the precipitate thrown down by the mild alkali was exposed to a strong heat in a crucible, and then put into water. The liquid was instantly converted into a very acid lime-water, which had the following remarkable properties: 1. The smallest portion of vitriolic acid, added to this water, occasioned an immediate and copious precipitation, which appeared even after the liquid was diluted with 200 times its bulk of pure water. 2. A single drop let fall into a solution of Glauber's salt, vitriolated tartar, alum, vitriolic ammoniac, Epsom salt, or selenite, occasioned an immediate and copious precipitate in all of them; the reason of which was the superior attraction of the ponderous earth for the acid of these salts, which forming with it an indissoluble concrete, instantly fell to the bottom.

The precipitate thrown down by the caustic vegetable alkali was put into water, but exhibited no such precipitate appearances as the other; even the mixture was boiled; thrown nor had it any acrimonious taste. On adding the caustic alkali three mineral acids to separate portions of the precipitate itself, neither effervescence, nor any sign of solution, appeared. After standing an hour, water was added, and the acids were suffered to remain another hour on the powder; but on decanting them afterwards, and adding fossil alkali to the point of saturation, no precipitate appeared.

The precipitate thrown down by the phlogisticated alkali, mixed with nitre and borax, and melted with a blow-pipe on charcoal, formed a black glass; on flint-glass, a white one; and on a tobacco-pipe, a yellowish white one. Another portion, melted with soap and borax in a crucible, formed a black glass.

The small quantity of insoluble residuum formerly mentioned, appeared to be the combination of ponderous earth with vitriolic acid, called heavy gypsum, marmor metallicum, barofelenite, &c.

From these experiments the Doctor concludes, that Analysis 100 parts of this spar contain 78.6 of pure ponderous and pro-earth, 7½ of a grain of marmor metallicum, and 20.8 heretic grains of fixed air. 2. The quantity of mild alkali ponderous necessary to saturate any given portion of acid, contains a greater quantity of fixed air than can be absorbed by that quantity of terra ponderosa which the acid is able to dissolve. 3. The terra ponderosa, when precipitated by means of a mild alkali, readily burns to lime; and this lime-water proves a very nice test of the presence of vitriolic acid. 4. In its native state the terra ponderosa will not burn to lime; when urged with a strong fire, it melts and unites with the crucible, without becoming caustic; nor can it be made to part with its fixed air by any addition of phlogiston. He conjectures, therefore, that as caustic lime cannot unite to fixed air without moisture, and as this spar seems to contain no water in its composition, it is the want of water which prevents the fixed air assuming its elastic aerial state. "This supposition (says he) becomes still more probable, if we observe, that when the solution of the spar in an acid is precipitated by a mild alkali, some water enters into the composition of the precipitate; for it has the same weight as before it was dissolved, and yet produces only 20 ounce-measures of fixed air, while the native spar contains 25 of the same measures: so that there is an addition of weight equal to five ounce-measures of air, or three one-half grains, to be accounted for; and this can only arise from the water.

The precipitate formed by the caustic alkali, taking some of the latter down with it, forms a substance neither soluble in acids nor water. This insoluble compound is also formed by adding the lime-water already Dr Withering having exposed 100 grains of the Terra Ponderosa metalicum to a red heat for an hour, in a black crucible, found that it had lost five grains of its weight; but as a fulphurous smell was perceptible, he suspected that a decomposition had taken place, and therefore exposed another portion to a similar heat in a tobacco-pipe, which had no smell of sulphur, nor was it diminished in weight. It melted with borax into a white opaque glass, but was barely fusible by itself under the blow pipe. It did not seem to dissolve in water, nor in any of the acids, except the vitriolic, dilluted in very concentrated form and almost red hot. It then appeared perfectly diffused; but separated again unchanged on the addition of water. On exposing the vitriolic solution to the atmosphere for some days, beautiful radiated crystals were formed in it.

On adding a solution of mild vegetable alkali to this precipitated vitriolic solution, a precipitate appeared; but it consisted of marmor metalicum unchanged. An ounce of it in fine powder was then fused with two of tartar until it ran thin, when six drachms of a residue, insoluble in water was left. On the addition of nitrous acid, only 52 grains were left, which appeared to be marmor metalicum unchanged. On saturating in the dry alkaline solution with distilled vinegar, and washing away by salt the precipitate, the liquor was found to contain terra foliata tartar, formed by the union of the acetic acid with part of the alkali; and of vitriolated tartar, formed by that of the alkali with the native acid of the marmor metalicum.

The salt formed by the nitrous acid shot readily into beautiful permanent crystals of a rough bitterish taste. Some of the salt deflagrated with nitre and charcoal, leaving behind it a white, capable of being burnt into lime, and again forming an insoluble compound with vitriolic acid. An hundred grains of aerated terra ponderosa, dissolved in marine acid, and precipitated by the vitriolic, were augmented 17 grains in weight. Hence it appears,

1. That the marmor metalicum is composed of vitriolic acid and terra ponderosa. 2. That this compound has very little solubility in water. 3. That it can only be dissolved in highly concentrated oil of vitriol, from which it separates unchanged on the addition of water. 4. That it cannot be decomposed in the moist way, by mild fixed alkali, though it may be so in the dry. 5. That it may be decomposed by the union of inflammable matter to its acid, by which sulphur is formed, though the acid cannot be dissipated by mere heat. 6. An hundred parts of this substance contain 32.8 of pure vitriolic acid, and 67.2 of terra ponderosa. The marmor metalicum, our author remarks, may possibly be useful in some cases where a powerful flux is wanted; for having mixed some of it with the black flux, and given the mixture a strong heat in a crucible, it ran entirely through the pores of the vessel.

Dr Withering describes two other kinds of this substance, known by the name of caulk, and found in substances of the mines of Derbyshire, and other places. These differ from the other only in containing a small proportion of iron. On the whole, he concludes, that "the terra ponderosa seems to lay claim to a middle place between the earths and metallic calces." Like the former... Transmutation of Flints into an Earth Soluble in Acids.

This is effected by mixing powdered flints with alkaline salt, and melting the mixture by a strong fire. The melted mass deliquesces in the air, like alkaline salts; and if the flint is then precipitated, it becomes soluble in acids, which it entirely resists before.

In this process the alkali, by its union with the flint, is deprived of its fixed air, and becomes caustic. To this causticity its solvent power is owing; and therefore the flint may be precipitated from the alkali, not only by acids, but by any substance capable of furnishing fixed air; such as magnesia alba or volatile alkali. The precipitate in both cases proves the same; but the nature of it hath not hitherto been determined. Some have conjectured that the vitriolic acid existed in the flint; in which case, the alkali made use of in this process ought to be partly converted into vitriolated tartar.

The above process is delivered on the authority of former chemists; but Mr Bergman, who has published a dissertation on this subject, affirms that it cannot be dissolved except by the fluor acid. The vitriolic, nitrous, or marine acids, have no effect upon it, even when newly precipitated from the liquor of flints washed and still wet, and though a thousand parts of acid be added to one of the earths, and boiled upon it for an hour: but when three parts of alkaline salt are melted in a crucible with one of quartz, the salt dissolves at the same time about seven hundredth parts of its own weight of the clay which composes the crucible; and the solubility of this has given occasion to the mistake above mentioned. If the fusion be performed in an iron vessel, no soluble part will be obtained, excepting the very small portion of clay which the quartz contains; and when this is once exhausted by an acid, no more can be procured, by any number of fusions with alkali.

The fluor acid, he observes, is never obtained entirely free from siliceous earth, and consequently its power as a menstruum must be weakened in proportion to the quantity it contains. In order to observe its solvent power, however, our author, in the year 1772, put some quartz, very finely powdered, into a bottle containing ½ of a kanne of fluor acid. The bottle was then slightly corked, and set by in the corner of a room. Two years afterwards it was examined; and on pouring out the liquor there were found concreted at the bottom of the vessel, besides innumerable small prismatic spicules, 13 crystals of the size of small peas, but mostly of an irregular form. Some of these resembled cubes, whose angles were all truncated, such as are often found in the cavities of flints. These were perfect siliceous crystals, and very hard, but not comparable with quartz, though they agreed with it in essential properties. "Possibly (says he) the length of a century may be necessary for them to acquire, by evaporation, a sufficient degree of hardness. The earth bottom itself, as far as the liquor had reached, was found covered with a very thin siliceous pellicle, which was scarcely visible, but separated on breaking the bottle. It was extremely pellucid, flexible, and showed prismatic colours. These phenomena show, that why the much siliceous matter is dissolved and suspended" (in fluor acid). "Whether any of the quartz was taken up in this experiment is uncertain; but it appears probable that little or none was dissolved; since, by the help of heat during the distillation, the acid had previously taken up so much siliceous earth, that upon slow evaporation it was unable to retain it. Hence appears the origin of the crystals and the pellicle; and hence appears the cause which impedes the action of fluor acid upon flint; namely, that the acid obtained in the ordinary way is already saturated with it.

The volatile alkali precipitates siliceous earth most completely from fluor acid: and thus we find, that one part of it is contained in 600 of the acid, diluted to such a degree, that its specific gravity is only 1.064. A triple fixed alkali does not afford a pure siliceous earth, but a peculiar kind of triple salt, formed of the earth, precipitated fluor acid, and fixed alkali, which dissolves, though with difficulty, in warm water, especially the earth procured by vegetable alkali, but is easily decomposed by lime-water, and lets fall the mineral fluor regenerated.

Fixed alkaline salts attack this earth by boiling, but siliceous earth unless it be reduced to very fine powder, and newly precipitated from the liquor. Oil of tartar percolated by liquor takes up about one-sixth of its weight, and the solution of liquor becomes gelatinous on cooling, though at first alkali, diluted with 16 times its weight of water. This solution is effected only by the caustic part; for when fully saturated with fixed air, it cannot enter into any union with it. Volatile alkali, even though caustic, has no effect.

The attraction betwixt siliceous earth and fixed alkali is much more remarkable in the dry way; for when it melts with one half its weight of alkali into an attraction hard, firm, and transparent glass, the aerial acid and water going off in a violent effervescence. In proportion as the alkali is increased, the glass becomes more soft and lax, until at last it dissolves totally in water, as has been already mentioned. The siliceous matter thus precipitated is of a very rare and spongy texture, and so much swelled by water, that its bulk when wet is at least twelve times greater than when dry; nor does it contract more though suffered to remain a long time in the water. Hence it is easy to reduce the liquor of flints to a jelly, by diluting it with four or eight times its weight of water, and adding a sufficient quantity of precipitate; but if an over-proportion of water be used, for instance, 24 times the weight, the liquor will then remain limpid, though why can we add as much acid as is sufficient for saturating the not fore-alkali. The reason of this Mr Bergman supposes to be, that the siliceous particles are removed to such a distance from one another, that they cannot overcome acid without the aid of heat.

Phosphoric the friction they must necessarily meet with in their passage downwards through the fluid; but if the liquor be boiled, which at once diminishes its quantity and tenacity, the siliceous matter is instantly separated.

Liquor of flints is also decomposed by too great a quantity of water; for by this the efficacy of the menstruum is weakened, and it is also partly saturated by the aerial acid contained in the water. A precipitate also falls when the fluor acid is made use of; the reason of which is the same as the precipitation by other acids: in this case, however, the alkali makes part of the precipitate, as has been already observed; and therefore the matter which falls is fusible before the blowpipe, and soluble in a sufficient quantity of water.

§ 3. Of Phosphoric Earths.

These are so called from their property of shining in the dark. The most celebrated and anciently known of this kind is that called the Bolognian stone, from Bologna, a city in Italy, near which it is found. The discovery, according to Lemery, was accidentally made by a shoe-maker called Vincenzo Caffiarolo, who used to make chemical experiments. This man, having been induced to think, from the great weight and lustre of these stones, that they contained silver, gathered some, and calcined them; when carrying them into a dark place, probably by accident, he observed them shining like hot coals.

Mr Margraff describes the Bolognian stone to be an heavy, soft, friable, and crystallized substance, incapable of effervescence with acids before calcination in contact with burning fuel. These properties seem to indicate this stone to be of a felsitic or gypseous nature.

When these stones are to be rendered phosphoric, such of them ought to be chosen as are the cleanest, best crystallized, most friable and heavy; which exfoliate when broken, and which contain no heterogeneous parts. They are to be made red hot in a crucible; and reduced to a very fine powder in a glass-mortar, or upon a porphyry. Being thus reduced to powder, they are to be formed into a paste with mucilage of gum tragacanth, and divided into thin cakes. These are to be dried with a heat, which at last is to be made pretty considerable. An ordinary reverberating furnace is to be filled to three quarters of its height with charcoal, and the fire is to be kindled. Upon this charcoal the flat surfaces of the cakes are to rest, and more charcoal to be placed above them, so as to fill the furnace. The furnace is then to be covered with its dome, the tube of which is to remain open; all the coal is to be consumed, and the furnace is to be left to cool; the cakes are then to be cleansed from the ashes by blowing with bellows upon them. When they have been exposed during some minutes to light, and afterwards carried to a dark place, they will seem to shine like hot coals; particularly if the person observing them has been some time in the dark, or have shut his eyes, that the pupils may be sufficiently expanded. After this calcination through the coals, if the stones be exposed to a stronger calcination, during a full half hour, under a muffle, their phosphoric quality will be rendered stronger.

From attending to the qualities of this stone, and the requisites for making this phosphorus, we are naturally led to think, that the Bolognian phosphorus is no other than a composition of sulphur and quicklime. Analysis of the stone itself, in its natural state, evidently contains the phosphoric acid, from its not effervescing with acids of any kind. This acid cannot be expelled from earthy substances by almost any degree of fire, unless inflammable matter is admitted to it. In this case, part of the acid becomes sulphureous, and flies off; while part is converted into sulphur, and combines with the earth. In the above mentioned process, the inflammable matter is furnished by the coals in contact with which the cakes are calcined, and by the mucilage of gum tragacanth with which the cakes are made up. A true sulphur must therefore be formed by the union of this inflammable matter with the vitriolic acid contained in the stone; and part of this sulphur must remain united to the earth left in a calcareous state, by the dissipation, or conversion into sulphur, of its acid.

In the year 1730, a memoir was published by Mr Allcarr du Fay; wherein he affirms, that all calcareous stones, whether they contain vitriolic acid or not, are capable of becoming luminous by calcination; with this difference only, that the pure calcareous stones require a stronger, or more frequently repeated, calcination to convert them into phosphorus; whereas those which contain an acid, as selenites, gypsum, spars, &c., become phosphoric by a lighter calcination. On the contrary, Mr Margraff affirms, that no other stones can be rendered phosphoric but those which are saturated with an acid; that purely calcareous stones, such as marble, chalk, limestone, stalactites, &c., cannot be rendered luminous, till saturated with an acid previously to their calcination.

We have already taken notice, that the compounds formed by uniting calcareous earths with the nitrous and marine acids become a kind of phosphorus; the former of which emits light in the dark, after having been exposed to the sun through the day; and the latter becomes luminous by being struck. Signior Beccaria found, that this phosphoric quality was capable of being given to almost all substances in nature, metals perhaps excepted. He found that it was widely diffused among animals, and that even his own hand and arm possessed it in a very considerable degree. In the year 1775, a treatise on this kind of phosphorus was published by B. Willon, F. R. S. and member of the Royal Academy at Upsal. In this treatise he shows, that oyster-shells, by calcination, acquire the phosphoric quality in a very great degree, either when combined with the nitrous acid or without it.

The first experiment made by our author was the pouring some aquafortis, previously impregnated with copper, on a quantity of calcined oyster-shells, so as to form them into a kind of paste; he put this paste into a crucible, which was kept in a pretty hot fire for about 40 minutes. Having taken out the mass, and waited till it was cool, he presented it to the external light. On bringing it back suddenly into the dark, he was surprised with the appearance of a variety of colours like those of the rainbow, but much more vivid. In consequence of this appearance of the prismatic colours, colours, he repeated the experiment in various ways, combining the calcined oyster-shells with different metals and metallic solutions, with the different acids, alkaline and neutral salts, as well as with sulphur, charcoal, and other inflammable substances; and by all of these he produced phosphor, which emitted variously coloured light.

What is more remarkable, he found that oyster-shells possessed the phosphoric quality in a surprising degree; and for this purpose, nothing more was requisite than putting them into a good tea-coal fire, and keeping them there for some time. On scaling off the internal yellowish surface of each shell, they become excellent phosphor, and exhibit the most vivid and beautiful colours. As we know that neither the vitriolic nor any other acid is contained in oyster-shells, we cannot as yet say anything satisfactory concerning the nature of this phosphorus.

§ 4. Of the VEGETABLE Earth.

This is produced from vegetables by burning, and, when perfectly pure, by lixiviating the ashes with water, to extract the salt; and then repeatedly calcining them, to burn out all the inflammable matter; and is perhaps the same from whatever substance it is obtained: in this state, according to Dr Lewis, it is of the same nature with magnesia. In the state, however, in which this earth is procurable by simply burning the plant, and lixiviating the ashes, it is considerably different, according to the different plants from which it is obtained. The ashes of mugwort, small centaury, chervil, and dill, are of a brownish grey; goat's beard and lungwort afford white ashes; those of fennel are whitish; those of Roman wormwood of a greenish grey; those of rue, agrimony, saxifrage, brown; those of tansey, of a dusky green; those of dodder, of a fine green; eyebright, southern-wood, common wormwood, and scabious, afford them grey; scurvy-grafts, of a whitish grey; hyssop, yarrow, and sowbane, of a dusky grey; melilot, and oak-leaves, as also plantain, colts-foot, pine-tops, and fumitory, of a dusky brown; penny-royal, of a pale brown, with some spots of white; elder-flowers, fage, and mother of thyme, afford yellow ashes; those of strawberry-leaves are of a pale brimstone colour; those of cat-mint, of a dusky red; of prunella, brick-coloured; of honey-suckle, blue; of fern, blackish; and those of St John's-wort, feverfew, origanum, and pimpernel, all of a deep black. The only use to which this kind of earth has yet been put, is that of glass-making and manure.

Sect. III.: Of Metallic Substances.

§ 1. Gold.

This metal is reckoned of all others the most perfect and indestructible. When in its greatest purity, it has very little elasticity, is not sonorous, its colour is yellow, it is exceedingly soft and flexible, and is more ductile than any other metal whatever. (See GOLD LEAF, and WIRE-DRAWING.) Of all bodies it is the most ponderous, except platinum; its gravity being to that of water, according to Dr Lewis, as 19,280, or 19,290, to one. For its fusion it requires a low degree of white heat, somewhat greater than that in which silver melts. Whilst fluid, it appears of a bluish green colour; when cold, its surface looks smooth, bright, and considerably concave; it seems to expand more in the act of fusion, and to shrink more in its return to solidity, than any of the other metals; whence the greater concavity of its surface. Before fusion it expands the least of all metals, except iron. By sudden cooling it becomes, as well as other metals, brittle; which effect has been erroneously attributed to the contact of fuel during fusion.

Gold amalgamates very readily with mercury, and unites readily with all the metals. It is remarkably disposed to unite with iron; of which it dissolves itself many times its own weight, in a heat not much greater than that in which gold itself melts; the mixture is of a silver colour, very brittle and hard. All the metals, except copper, debase the colour of gold; and, if their quantity is nearly equal to that of the gold, almost entirely conceal it.

The malleability of gold is impaired by all the metals, but less by copper and silver than any others. Its malleability respect; and it has been a received opinion among metallurgists, that the smallest quantity of this metal entirely destroys the ductility of gold; and Dr Lewis tells us, that "the most minute portion of tin or lead, and even the vapours which rise from them in the fire, though not sufficient to add to the gold any weight sensible on the tenderest balance, make it so brittle, that it flies to pieces under the hammer." On respectable an authority, this continued to be believed as an undoubted fact, until, in the year 1784, a paper appeared in the Philosophical Transactions by Mr Alchorne of the mint; in which it was clearly disproved by the following experiments:

1. Sixty Troy grains of pure tin were put into 12 ounces of pure gold in fusion; after which the mixture was cast into a mould of sand, producing a flat bar an inch wide, and an eighth of an inch thick. The bar appeared found and good, suffered flating under the hammer, drawing several times between a pair of steel-rollers, and cutting into circular pieces of near an inch diameter, which bore flamping in the money-pres by the usual stroke, without showing the least brittleness, or rather with much the same ductility as pure gold.

2. With 90 grains of tin the bar was scarce distinguishable from the former.

3. With 120 grains it was rather paler and harder; and on drawing between the rollers the edges were a little disposed to crack.

4. With 140 grains, the paleness, hardness, and disposition to crack, were evidently increased; nevertheless it bore every other operation, even stamping under the press, without any apparent injury.

5. With an ounce of tin the bar was lead-coloured and brittle, splitting into several pieces on the first passing between the rollers.

6. A small crucible filled with standard gold fine, was placed in a larger one, having in it an ounce of rendered melted tin. The whole was covered with a large crucible inverted, in order to direct the fumes of the tin downward upon the gold. The metals were kept in fusion. fusioh for half an hour, during which time a full quarter of the tin was calcined; yet the gold remained altogether unchanged.

7. The mixture of gold and tin produced in exp. 1. was melted a second time in a stronger fire than at first, and kept in fusion for half an hour; during which time five grains of weight were lost, but the gold remained equally perfect as before.

8. and 9. The mixtures of exp. 2. and 4. viz. 90 and 140 grains to 12 ounces of gold, were re-melted separately, and an ounce of copper added to each. On being cast as usual, they bore all the operations of manufacturing as before, though sensibly harder. The last cracked at the edges as it had done without the copper, but bore cutting rather better than in its former state.

10. and 11. A quarter of an ounce of the last mixture, being tin 140 grains, and copper an ounce, and gold 12 ounces, with as much of the bar from experiment 3. consisting of 140 grains of tin to 12 ounces of gold, were each melted by a jeweller in a common tea-coal fire, into small buttons, without any loss of weight. These buttons were afterwards forged into small bars, nealing them often with the flame of a lamp, and afterwards drawn each about twenty times through the apertures of a steel plate, into fine wire, with as much ease as coarse gold commonly passes the like operation.

12. Sixty grains of tin were added to 12 ounces of standard gold \( \frac{1}{5} \) fine; and the compound passed every one of the operations already described, without showing the least alteration from the tin.

Several other trials were made with different mixtures of copper, tin, and silver, with gold, even as low as two ounces and a half of copper, with half an ounce of tin, to twelve ounces of gold; all of which bore hammering and flating by rollers to the thinness of stiff paper, and afterwards working into watch-cases, cane-heads, &c. with great ease. They grew more hard and harsh indeed in proportion to the quantity of alloy; but not one of them had the appearance of what workmen call brittle gold. Mr Alchorne therefore is of opinion, that when brittleness has been occasioned by the addition of tin to gold, the former has been adulterated with arsenic; as he has found, that by adding 12 grains of regulus of arsenic to as many ounces of fine gold, the compound has been rendered altogether unamalleable.

When gold is struck during a certain time by a hammer, or when violently compressed, as by the wire-drawers, it becomes more hard, elastic, and less ductile; so that it is apt to be cracked and torn. Its ductility is, however, restored by the same means used with other metals, namely, heating it red hot, and letting it cool slowly. This is called annealing metals; and gold seems to be more affected by this operation than any other metal. The tenacity of the parts of gold is also very surprising; for a wire of \( \frac{1}{16} \) of an inch in diameter will support a weight of 500 pounds.

Gold is unalterable by air or water. It never contracts rust like other metals. The action of the fiercest furnace-fires occasions no alteration in it. Kuncel kept gold in a glass-house furnace for a month, and Boyle kept some exposed to a great heat for a still longer time, without the loss of a single grain.

It is said, however, to be dissipated in the focus of a large burning mirror.

Mr Boyle relates a very curious and extraordinary experiment, which he thought was sufficient to prove the total destructibility of gold. About an eighth part ments for of a grain of powder, communicated by a stranger, the detru- was projected upon two drachms of fine gold in fu- sion, and the matter kept melted for a quarter of an hour. During the fusion, it looked like ordinary gold; except only once, that his assistant observed it to look exactly of the colour of opal. When cold, it was of a dirty colour, and, as it were, overcast with a thin coat, almost like half-vitrified litharge; the bottom of the crucible was overlaid with a vitrified substance, partly yellow, and partly reddish brown; with a few small globules, more like impure silver than gold. The metal was brittle, internally like brass or bell-metal; on the touchstone more like silver than gold; its specific gravity was to that of water only as \( \frac{15}{16} \) to 1. There was no absolute loss of weight. By cupellation, 60 grains of this mass yielded 53 grains of pure gold, with seven grains of a ponderous, fixed, dark-coloured substance.

We have already mentioned, that in certain circumstances gold is soluble in the nitrous and marine aqua regia acids separately. It is, however, always soluble by the two united, but dissolves slowly even then. The most commodious method of obtaining this solution is, by putting the gold, either in leaves, or granulated, or cut into small thin pieces, into a proper quantity of aquafortis; then adding, by degrees, some powdered sal ammoniac, till the whole of the gold is dissolved. By this means a much smaller quantity of the menstruum proves sufficient, than if the sal ammoniac was previously dissolved in the aquafortis; the conflict, which each addition of the salt raises with the acid, greatly promoting the dissolution. Aquafortis of moderate strength will, in this way, take up about one-third of its weight of gold; whereas an aqua regis, ready prepared from the same aquafortis, will not take up above one-fifth its weight. Common salt answers better for the preparation of the aqua regis than sal ammoniac.

This solution, like all other metallic ones, is corrosive. It gives a violet colour to the fingers, or to any of the following animal matters. If the solution is evaporated and cooled, yellow transparent crystals will be formed; but, if the evaporation is carried too far, the acids with which the gold is combined may be driven from it by heat alone; and the gold will be left in the state of a yellow powder, called calx of gold.

Gold may be precipitated from its solution by those substances which commonly precipitate metals, such as alkaline salts and calcareous earths. It may also be precipitated in a fine purple powder, by tin or its solution.

When fixed alkalies are made use of, the precipitate weighs about one-fourth more than the gold employed. With volatile alkalies also, if they are added in no greater proportion than is sufficient to saturate the acid, the quantity of precipitate proves nearly the same; but if volatile spirit is added in an over-proportion, it redissolves part of the gold which it had before precipitated, and the liquor becomes again considerably yellow. The whole of the precipitate, how- ever, could not be redissolved, either by the mild or caustic alkali; nor did either of these spirits sensibly dissolve or extract any tinge from precipitates of gold which had been thoroughly edulcorated with boiling water.

All the metallic bodies which dissolve in aqua regia, precipitate gold from it. Mercury and copper throw down the gold in its bright metallic form; the others, in that of a calx or powder, which has no metallic aspect. Vitriol of iron, though it precipitates gold, yet has no effect upon any other metal; hence it affords an easy method of separating gold from all other metals. The precipitation with tin succeeds certainly only when the metal in substance is used, and the solution of gold largely diluted with water. It is observable, that though the gold is precipitated from the diluted solution by tin, yet, if the whole is suffered to stand till the water has in a great measure exhaled, the gold is taken up afresh, and only a white calx of tin remains.

Gold precipitated from its solution in aqua regia explodes by heat with much greater violence than any other substance in nature. This property was known in the 16th century; but whether the ancient alchemists knew anything of it or not, is a matter of uncertainty. Basil Valentine first gave any distinct account of it. He directs the gold to be dissolved in aqua regia made with sal ammoniac, and then precipitated by vegetable fixed alkali, to be twelve times washed with water, and lastly dried in the open air, where the sun's rays cannot reach it. He forbids it to be dried over a fire, as it explodes with a gentle heat, and flies off with inconceivable violence.

Succeeding chemists have performed this operation with some little differences; but the necessity of employing volatile alkali was but little regarded till the beginning of the present century.

The calx of gold is always somewhat increased in weight by being converted into aurum fulminans; but authors are not agreed about the quantity of augmentation. Becher makes it heavier by one-fifth part; Lemery by one fourth; and Juncker by one-fourth.

Lemery by one fourth; and Juncker by one-fourth.

All agree, however, that it explodes with a violence of gold by almost inconceivable. Crollius relates, that 20 grains of this powder explodes with more force than half a pound of gunpowder, and exerts its force downwards, though M. Teykmeyer frequently showed in his lectures that it would throw a florin upwards above six ells. A great number of experiments were made before the Royal Society at London, in order to determine the comparative forces of these two powders. Equal parts of gunpowder and aurum fulminans were included in iron globes placed among burning coals; those which contained the former burnt with great violence, but the globes containing the aurum fulminans remained perfectly silent. But though no explosion takes place in close vessels, the utmost caution is necessary in managing this substance in the open air, especially when it is subjected to friction, or to a slight degree of heat; for such is the nature of the calx we speak of, that it is not necessary, in order to cause it explode, to touch it with an ignited substance, or to make it red-hot. The heat requisite for this purpose is, according to Dr Lewis, intermediate between that of boiling water and the heat which makes metals of an obscure red. With friction, however, it seems still more dangerous; for in this case it explodes with what we should think scarce sufficient to communicate any degree of heat whatever. Orficial relates, that this powder ground in a jasper mortar, exploded with such violence as to burst the vessel in a thousand pieces; Dr Lewis gives an instance of a similar kind in England; and Dr Birch tells us of doors and windows torn to pieces by the violence of this explosive matter. Macquer relates the following accident to which he was witness. "A young man, who worked in a laboratory, had put a drachm of fulminating gold into a bottle, and had neglected to wipe the inner surface of the neck of the bottle, to which some of the powder adhered. When he endeavoured to close the bottle, by turning round the glass stopper, the friction occasioned an explosion of part of the powder. By this the young man was thrown some steps backward, his face and hands wounded by the fragments of the bottle, and his eyes put out; yet, notwithstanding this violent explosion, the whole drachm of fulminating gold certainly did not take fire, as much of it was afterwards found scattered about the laboratory."

It has already been mentioned, that some imagine the force of this explosion to be directed downwards; but explosion is Dr Lewis is of opinion that it is equally directed every way. Certain it is, that the quantity of from 10 to 12 grains of aurum fulminans, exploded on a metallic plate, lacerates it; a smaller quantity forms a cavity, and a still smaller only scratches the surface; effects which are never produced by gunpowder in even so large a quantity. A weight laid upon the powder is thrown upwards in the moment of explosion. If it be of silver or copper, this weight is marked with a yellowish spot, as the supports will also be, if made of either of these metals. A large grain, says Mr Bergman, brought near to the side of the flame of a candle, blows it out with great noise; and a few ounces exploding together by incautious drying, has been known to shatter the doors and windows of the apartment; hence it is evident, that aurum fulminans exerts its force in all directions; yet it cannot be denied, that it strikes bodies with which it is in contact more violently than those which are at a small distance, though in its vicinity; thus, if a small portion of it explodes in a paper box, it lacerates only the bottom, unless the top be pressed down close; in which case it perforates both the top and bottom. When carefully and gradually exploded in a glass phial or a paper box, it leaves a purple spot, in which are found many particles of shining gold; and if the quantity exploded be large, several grains remain totally unchanged, as it is only the lowermost stratum that is inflamed.

Aurum fulminans, when moist, does not explode at all; but as it dries, the grains go off in succession like moist air the decrepitation of common salt.—In glass vessels closed, or with their mouths immersed in water, it explodes, but with a very weak report. An elastic vapour, in the quantity of seven inches, from half a drachm of the powder, broke forth in the moment of explosion, which, by our author's account, seems to be phlogisticated air. In metallic vessels sufficiently strong, the gold is silently reduced when they are per- Practice.

Chemistry.

Gold.

Cause of this explosion attributed to a saline principle.

This opinion shown to be erroneous by Mr Bergman.

Aurum fulminans can be made without nitrous or marine acids.

Fixed air not the cause of the explosion.

feetly found; but if they have any very small chinks in them, the vapour makes its way through them with a hissing noise.

The cause of this extraordinary explosive force of gold has been attributed chiefly to a saline principle, viz., the combination of nitrous acid with volatile alkali; and this opinion has been supported by an affirmation, that the fulminating property is destroyed by treating the calx with vitriolic acid or with fixed alkali; the former expelling the nitrous acid, and the latter disengaging the volatile alkali.—Mr Bergman allows, that fixed alkali destroys the fulminating property; but affirms, that it acts only by separating the particles when the two are triturated together; and this might be done by many other substances as well as fixed alkali; but when the alkali, instead of being triturated in the dry way with the calx, was boiled in water along with it, the explosion not only took place, but was much more violent than usual. It must be observed, however, that heat alone destroys the fulminating property of this calx; and therefore, if the alkaline solution be made too strong, the additional heat which it then becomes capable of sustaining, is sufficient to deprive the calx of its fulminating property. The case is the same with the vitriolic acid; for this has no effect upon the calx, either by digestion in its concentrated state, or by boiling in its diluted state. If it be boiled in its concentrated state indeed with the fulminating calx, the heat conceived by the acid is sufficient to destroy the fulminating property of the former; and in like manner, unless the calx be in some measure destroyed, or reduced to its metallic state, it can never be deprived of its fulminating property.

It was further proved, that the fulminating property did not depend on the presence either of nitrous or marine acids, for it can be made without them. A calx of gold, not fulminating, dissolved in vitriolic acid, and precipitated by caustic volatile alkali, had acquired this property. A solution of the same calx in nitrous acid, let fall a precipitate by the addition of pure water; and this precipitate edulcorated, and digested with volatile alkali, fulminated as if it had been originally precipitated with that alkali: The experiment was repeated on other non-fulminating precipitates with the same success. Let any suspicion, however, should remain, that a small quantity of aqua-regia might still be left, which, by combining with the volatile alkali, would make a proportionable quantity of nitrum flammans, the precipitate was digested 24 hours in vitriolic acid, then washed in pure water, and immersed in aqueous and spirituous solutions of alkali, both mild and caustic; but the event was the same. Lastly, an inert calx of gold may always be made to fulminate by digesting it with volatile alkali; nor can this property be communicated to it by any means without the use of this alkali.

It has been supposed by some very eminent chemists, among whom we may number Dr Black, that fixed air is the cause of the fulmination of gold: but it is evident that this cannot be the case; because, 1. Gold fulminates as well when precipitated by the caustic volatile alkali, as by that which contains fixed air. 2. This metal does not combine, during precipitation, with fixed air. 3. Gold, when precipitated by mild fixed alkali, does not fulminate, unless the menstruum contain volatile alkali.

The fulminating calx of gold may be prepared either with a compound aqua-regia of pure nitrous and marine acids; or of pure nitrous acid and sal ammoniac; or of a compound of alum, nitre, and sea-salt. When Mentru this kind of liquor is made use of, the acid of the um fine alum expels the other two, and thus forms an aqua-regia. This was formerly called menstruum sine firepitu. By whatever method the gold is dissolved, it always affords a yellow calx with alkalies, but the volatile alkali most readily throws down the metal. Dephlogisticated spirit of salt very readily dissolves gold, and produces a fulminating precipitate as well as aqua-regia.

We shall conclude this account of aurum fulminans Mr Bergman's theory of the explosion. He observes, that volatile alkali contains phlogiston; an undoubted proof of which is given by Dr Priestley, by converting alkali into phlogisticated air. This phlogiston, says he, may be separated by means of a superior attraction; so that the volatile alkali is decomposed, and the residuum diffused in form of an elastic fluid, altogether similar to that which is extricated during the fulmination; the source then from whence the elastic fluid is derived must be obvious; and it only remains to examine the medium by which the volatile alkali is dephlogisticated.

"In those metals which are called perfect, so great is the firmness of texture, and so close the connection of the earthy principle with the phlogiston, that by means of fire alone these principles cannot be divided; but when dissolved by acid menstrua, they must necessarily lose a portion of their phlogiston; and therefore, when afterwards precipitated by alkalies which cannot supply the loss, they fall down in a calcined state, though they attract phlogiston so strongly, that they can be reduced to a metallic state, merely by an intense heat penetrating the vessels. It may therefore be laid down as a fundamental position, that gold is calcined by solution.

"Let us now consider the consequence of exposing the powder consisting of calx of gold and volatile alkali the alkali intimately united, to an heat gradually increased. The calx which is united with the volatile alkali, by the affluence of a gentle heat, feizes its phlogiston; and when this is taken away, the residuum of the salt is instantaneously expanded into the form of an elastic fluid, which is performed with so much violence, that the air must yield a very acute sound."

Our author proceeds to explain this phenomenon upon the principles assumed by him and Mr Scheele, kalz exhibits of heat being a composition of light, and the phlogiston or principle of inflammability; but as this hypothesis is by no means satisfactory, we shall omit his reasoning founded upon it: That the volatile alkali, however, is really capable of producing a flash is easily proved, because it exhibits one when thrown into a hot crucible. A single cubic inch of gun-powder generates about 244 of elastic fluid; but the same quantity of elastic fluid yields at least four times as much; and hence we may easily understand the difference in their explosive force.

"That careful calcination should destroy the fulmi..." minating property, is not to be wondered at, as the volatile alkali is the indispensible material cause; but, the peculiar alacrity which it acquires before the explosive force is totally extinguished, depends upon the nature of the materials, and of the operation. Thus the heat, fulminating when inferior to that necessary for fulmination, acts upon both the principles of the aurum fulminans, it prepares the metallic calx for a more violent attraction for phlogiston; it also acts upon the phlogiston of the volatile alkali, and loosens its connection; which two circumstances must tend to the union producing the explosion. But this effect has a maximum; and at this period the slightest friction supplies the defect of necessary heat, and produces the fulmination. The calcined gold also seems to collect and fix the matter of heat, though still insufficient by means of its phlogiston, in a certain degree; so that by means of friction, though but very slight, it becomes capable of exerting its force; but when the heating is often repeated without producing its effect, the volatile alkali is by degrees dissipated, and at length so much diminished that the calx becomes inert.

"But if aurum fulminans is capable of producing such a prodigious quantity of elastic fluid, how does it happen that it remains acute and inert when reduced in close vessels? Of this the reason may be, that every elastic fluid, in the act of breaking forth, requires a space to expand in; and if this be wanting, it remains fixed. Taking this for granted, a calx of gold cannot be reduced in close vessels either by heat or by the phlogiston of volatile alkali; for in either case it must evolve its elastic fluid, which by supposition it cannot do. Nothing remains to solve this difficulty but the ignition of the surrounding metal; by means of which the calx, in virtue of its superior attraction, seizes the phlogiston of the metal, which that substance here, as well as in other instances, is capable of losing without the eruption or absorption of any fluid whatever."

Several chemists have asserted, that the calces of copper or silver may be made to fulminate like that of the gold. But Mr Bergman informs us, that these experiments never succeeded with him; "so (says he) they have either been silent upon some circumstances necessary in the operation, or perhaps have been deceived by the detonation of nitrum flammans, or some other accidental occurrence. It is not sufficient for the volatile alkali to adhere to the precipitate; for platinum thrown down by this alkali retains a portion of it very obstinately, but yet does not fulminate on the exposure to fire.—Besides the presence of volatile alkali, it seems to be necessary that the metallic calx should be reducible by a gentle heat, in order to decompose it; but every explosion is not to be derived from the same causes; nay, in this respect, aurum fulminans, gun-powder, and pulvis fulminans, differ very much, though they agree in several particulars." Of late, however, it has been found that the calx of silver may be made to fulminate in a manner still more extraordinary than that of gold. See the next article.

If gold is melted with an hepatic sulphuris composed of equal parts of sulphur and fixed alkaline salt, the metal readily unites with it into an uniform mass, capable of dissolution in water without any separation of its parts. The solution, besides a nauseous taste from the sulphur, has a peculiar penetrating bitterness, not discoverable in any other metallic solution made by the same means.

Though the compositions of sulphur and alkali seem to unite more intimately with gold than any other metal, their affinity with it is but slight; copper, or iron, added to the matter in fusion, difusant, and precipitate the gold. The metal thus recovered, and purified by the common processes, prove remarkably paler-coloured than at first. In an experiment related by Dr Brandt, in the Swedish Memoirs, the purified gold turned out nearly as pale as silver, without any diminution of weight.

Gold has been thought to be possessed of many extraordinary virtues as a medicine; which, however, are long ago determined to be only imaginary. It is gold, not indeed very easy to prepare this metal in such a manner that it can be safely taken into the human body. The solution in aqua regia is poisonous; but if any essential oil is poured on this solution, the gold will be separated from the acid, and united to the essential oil; with which, however, it contracts no lasting union, but in a few hours separates in bright yellow film to the sides of the glass. Vitriolic ether diffuses the gold more readily and perfectly than the common essential oils; and keeps it permanently suspended, the acid liquor underneath appearing colourless. The yellow ethereal solution poured off, and kept for some time in a glass stopp'd with a cork, so that the spirit may slowly exhale, yields long, transparent, prismatic crystals, in shape like those of nitre, and yellow like topaz. What the nature of these crystals is, either as to medicinal effects, or other purposes, is as yet unknown.

Rectified spirit of wine mingles uniformly with the solution of gold made in acids: if the mixture is suffered to stand for some days in a glass slightly covered, the gold is by degrees revived, and arises in bright pellicles to the surface. Groser inflammable matters, wine, vinegar, solutions of tartar, throw down the gold, in its metallic form, to the bottom. Gold is the only metal which is thus separable from its solution in acids by these substances; and hence gold may be purified by these means from all admixtures, and small proportions of it in liquors readily discovered.

When the colour of gold is by any means rendered pale, it may be recovered again by melting it with gold-refined copper, and afterwards separating the copper; or by a mixture of verdigris and sal ammoniac with vitriol or nitre. The colour is also improved by fusion with nitre, injecting sal ammoniac upon it in the fusion, quenching it in urine, or boiling it in a solution of alum. When borax is used as a flux, it is customary to add a little nitre or sal ammoniac, to prevent its being made pale by the borax. Juncker reports, that by melting gold with four times its weight of copper, separating the copper by aquafortis unpurified, then melting the gold with the same quantity of fresh copper, and repeating this process eight or nine times, the gold becomes at length of a deep red colour, which sustains the action of lead, antimony, and aquafortis. This, next to gold, is the most perfect, fixed, and ductile of all the metals. Its specific gravity is to that of water nearly as 11 to 1. A single grain has been drawn into a wire three yards long, and flattened into a plate an inch broad. In common fire it suffers no diminution of its weight; and, kept in the vehement heat of a glass-house for a month, it loses no more than one sixty-fourth. In the focus of a large burning-glass, it smokes for a long while, then contracts a greyish ash on the surface, and at length is totally dissipated.

Silver is somewhat harder and more sonorous than gold, and is fusible with a less degree of heat. The tenacity of its parts also is nearly one half less than that of gold; a silver wire of \( \frac{1}{16} \) of an inch diameter being unable to bear more than 270 pounds.

Mercury unites very readily with silver-leaf, or with the calx of silver precipitated by copper; but does not touch the calces precipitated by alkaline salts. The vapours of sulphurous solutions stain silver yellow or black. Sulphur, melted with silver, debases its colour to a leaden hue, renders it more easily fusible than before, and makes it flow so thin as to be apt in a little time to penetrate the crucible: in a heat just below fusion, a part of the silver shoots up, all over the surface, into capillary efflorescence. Aquafortis does not act upon silver in this compound; but fixed alkaline salts will absorb the sulphur, and form a hepar sulphuris, which, however, is capable of again dissolving the metal. If the sulphurated silver is mixed with mercury sublimate, and exposed to the fire, the mercury of the sublimate will unite with the sulphur, and carry it up in the form of cinnabar, whilst the marine acid of the sublimate unites with the silver into a luna cornea, which remains at the bottom of the glass. Fire alone is sufficient, if continued for some time, to expel the sulphur from silver.

From the baser metals, silver is purified by cupellation with lead. (See Refining.) It always retains, however, after that operation, some small portion of copper, insufficient to give a blue colour to volatile spirits, which has been erroneously thought to proceed from the silver itself. It is purified from this admixture by melting it twice or thrice with nitre and borax. The loria, on the first fusion, is commonly blue; on the second, green; and on the third, white, which is a mark of the purification being completed.

The most effectual means, however, of purifying silver, is by reviving it from luna cornea; because spirit of salt will not precipitate copper as it does silver. The silver may be recovered from luna cornea, by fusion with alkaline and inflammable fluxes; but, in these operations, some loss is always occasioned by the dissipation of part of the volatile calx, before the alkali or metal can absorb its acid. Mr Margraff has discovered a method of recovering the silver with little or no loss; mercury assisted by volatile salts, imbibing it by trituration without heat. One part of luna cornea, and two of volatile salt, are to be ground together in a glass-mortar, with so much water as will reduce them to the consistence of a thin paste, for a quarter of an hour, or more; five parts of pure quicksilver are then to be added, with a little more water, and the trituration to be continued for some hours. A fine amalgam will thus be obtained; which is to be washed with fresh parcels of water, as long as any white powder separates. Nearly the whole of the silver is contained in the amalgam, and may be obtained perfectly pure by distilling off the mercury. The white powder holds a small proportion separable by gentle sublimation; the matter which sublimes is nearly similar to mercurius dulcis.

The colour of silver is debased by all the metals, and its malleability greatly injured by all but gold and copper. The English standard silver contains one part of copper to twelve and one third of pure silver. This metal discovers in some circumstances a great attraction for lead; though it does not retain any of that for lead metal in cupellation. If a mixture of silver and copper be melted with lead in certain proportions, and the compound afterwards exposed to a moderate fire, the lead and silver will melt out together, bringing very little of the copper with them; by this means silver is often separated from copper in large works. The effect does not wholly depend upon the different fusibility of the metals; for tin, which is still more fusible than lead, be treated in the same manner with a mixture of silver and copper, the three ingredients are found to attract one another so strongly as to come all into fusion together. Again, if silver be melted with iron, and lead added to the mixture, the silver will forsake the iron to unite with the lead, and the iron will float by itself on the surface.

Silver is purified and whitened externally by boiling in a solution of tartar and common salt. This is no external other than an extraction of the cuprous particles from the surface of the silver, by the acid of the tartar activated by the common salt.

M. Berthollet has lately discovered a method of imparting to the calx of silver a fulminating property, ting silver, and that much more terrible than fulminating gold itself. His receipt for making it is, "Take cupelled silver, and dissolve it in the nitrous acid; precipitate pared, the silver from the solution by lime-water, decant the clear liquor, and expose the precipitate three days to the open air. Mix this dried precipitate with the caustic volatile alkali, it will turn black; and when dried in the air, after decanting the clear liquor, is the fulminating powder required."

The properties of this powder are said to be so extraordinary, that it is impossible to imagine how any part of it can ever be separated from the rest after it is once prepared. To make this fulminate, it seems no sensible degree of heat is necessary, the contact of a cold body answering that purpose as well as any other, touch of a After it is once made, therefore, it must not be touched sub- ed, but remain in the vessel in which it is dried; and so violent is the explosion, that it is dangerous to at- tempt it in larger quantities than a grain at a time. For the same reason it undoubtedly follows, that no more than a grain ought to be made at a time, or at Dangerous least in one vessel, because no part of it could ever af- when more leaft in one vessel, because no part of it could ever af- terwards be separated from the rest. We are told, grain is ful- that, "the wind having turned over a paper containing ing some atoms of this powder," (we ought to have a time. been informed how the atoms came there, considering what we have just now related,) "the portion touched by the hand fulminated, and of course that which fell upon the ground. A drop of water which fell upon this powder caused it to fulminate. A single grain of fulminating silver, which was in a glass cup, reduced the glass to powder, and pierced several doubles of paper.

"If the volatile alkali, which has been employed with the above powder, be put into a thin glass matras and boiled, then, on standing in the cold, small crystals will be found fulminated on the interior sides of the vessel, and covering the liquor. On touching one of these crystals the matras will be burst with considerable explosion.

"The dangerous properties of this powder suggest the necessity of not preparing it but when the face is covered with a mask with glass eyes; and to avoid the rupture of the glass cups, it is prudent to dry the fulminating silver in small metallic vessels." To this we may add, that as the powder does not fulminate when wet, it may in that state be put up in very small quantities on paper, to be fulminated afterwards as occasion offers. This will perhaps account for the appearance of the few atoms above mentioned on the paper which the wind overturned.

With regard to the cause of this extraordinary fulmination we can say nothing satisfactory; the following curious reason is assigned by the antiphlogistons; which at once shows the futility of their theory, and sets in a very ridiculous light the hard words with which they would obscure the science of chemistry.

"The oxygenous principle* (say they) unites with the hydrogenous principle† of the volatile alkali, and form water in a vaporous state. This water (in a vaporous state) being instantaneously thrown into a state of vapour, possessing elasticity and expansive force, is the principal cause of this phenomenon, in which the azotic‡ air which is disengaged from the volatile alkali, with its whole expansive power, has a great share."

On this, as well as other theories, in which elastic fluids are alleged to be the cause of explosions, it is obvious to remark, that should we allow this to be the case, we are utterly at a loss to find a source of heat sufficient to rarefy the vapour to such a degree as is necessary for producing the effect ascribed to it. In the present case, we can scarcely suppose a grain weight of metallic calx, already dry, to contain as much either of fire or water as is necessary to produce the effect; nor can we explain why the touch of any cold body, and which may be supposed to contain less fire than the calx itself, should produce such an effect. As to the oxygenous and hydrogenous principles, they were there before the touch, and ought to have produced their effects, not to mention that the water produced by them could not have amounted to the thousandth part of a grain. It is much more probable, therefore, that the whole is to be considered as an effect of electricity, though we cannot tell how the fluid comes here to be excited in such a violent manner.

§ 3. Copper.

This is one of those metals which, from their destructibility by fire, and contracting rust in the air, are called imperfect. Of these, however, it is the most perfect and indestructible. It is of a reddish colour when pure; easily tarnishes in a moist air, and contracts a green rust. It is the most sonorous of all the metals, and the hardest and most elastic of all but iron. In some of its states, copper is as difficultly extended under the hammer as iron, but always proves softer to the file; and is never found hard enough to strike a spark with flint or other stones; whence its use for chisels, hammers, hoops, &c., in the gunpowder works. When broke by often bending backwards and forwards, it appears internally of a dull red colour without any brighttins, and of a fine granulated texture resembling some kinds of earthen ware. It is considerably ductile, though less so than either gold or silver; and may be drawn into wire as fine as hair, or beaten into leaves almost as thin as those of silver. The tenacity of its parts is very considerable; for a copper wire of \( \frac{1}{8} \) of an inch diameter will support a weight of 299\(\frac{1}{2}\) pounds without breaking. The specific gravity of this metal, according to Dr Lewis, is to that of water as 8.830 to 1.

Copper continues malleable when heated red; in which respect it agrees with iron; but is not, like iron, capable of being welded, or having two pieces joined into one. It requires for its fusion a stronger heat than either gold or silver, though less than that requisite to melt iron. When in fusion, it is remarkably impatient of moisture; the contact of a little water occasioning the melted copper to be thrown about with violence, to the great danger of the bystanders. It is, nevertheless, said to be granulated in the brass-works at Bristol, without explosion or danger, by letting it fall in little drops, into a large cistern of cold water covered with a brass-plate. In the middle of the plate is an aperture, in which is secured with Sturbridge clay a small vessel, whose capacity is not above a spoonful, perforated with a number of minute holes, through which the melted copper passes. A stream of cold water passes through the cistern. If suffered to grow hot, the copper falls liquid to the bottom, and runs into plates.

Copper, in fusion, appears of a bluish green colour, nearly like that of melted gold. Kept in fusion for a long time, it becomes gradually more and more brittle; but does not scorch considerably, nor lose much of its weight. It is much less destructible than any of the imperfect metals, being very difficultly subdued even by lead or bismuth. If kept in a heat below fusion, it contracts on the surface thin powdery scales; which, being rubbed off, are succeeded by others, till the whole quantity of the metal is thus changed into a scoria or calx, of a dark reddish colour. This calx does not melt in the strongest furnace fires; but, in the focus of a large burning mirror, runs easily into a deep red, and almost opaque, glass. A flaming fire, and strong draught of air over the surface of the metal, greatly promote its calcination. The flame being tinged of a green, bluish, or rainbow colour, is a mark that the copper burns.

This metal is very readily soluble by almost all alkaline substances; even common water, suffered to stand long in copper-vessels, extracts so much as to gain a coppery taste. It is observable, that water is much more impregnated with this taste, on being suffered to stand in the cold, than if boiled for a longer time in the vessel. The same thing happens in regard to the mild vegetable acids. The confectioners prepare the most acid syrups, even those of lemons and oranges, Copper by boiling in clean copper-vessels, without the preparations receiving any ill taste from the metal; whereas, either the juices themselves, or the syrups made from them, if kept cold in copper vessels, soon become impregnated with a disagreeable taste, and with the pernicious qualities of the copper.

By combination with vegetable acids, copper becomes in some respects remarkably altered. Verdigris, which is a combination of copper with a kind of acetic or tartaric acid, is partially soluble in distilled vinegar; the residuum, on being melted with borax and linseed oil, yields a brittle metallic substance, of a whitish colour, not unlike bell-metal. The copper also, when revived from the distilled verdigris, was found by Dr Lewis to be different from the metal before dissolution; but neither of these changes have yet been sufficiently examined.

Copper, in its metallic state, is very difficultly amalgamated with mercury; but unites with it more easily if divided by certain admixtures. If mercury and verdigris be triturated together with common salt, vinegar, and water, the copper in the verdigris will be imbibed by the mercury, and form with it, as Boyle observes, a curious amalgam, at first so soft as to receive any impression, and which, on standing, becomes hard like brittle metals. Brats leaf likewise gives out its copper to mercury, the other ingredient of the brats separating in the form of powder.

Easier methods of amalgamating copper are published by Dr Lewis in his notes on Wilson's Chemistry, p. 432. His receipts are—“Dissolve some fine copper in aquafortis: when the menstruum will take up no more of the metal, pour it into an iron mortar, and add six times the weight of the copper, of mercury, and a little common salt: grind the whole well together with an iron pestle; and, in a little time, the copper will be imbibed by the mercury, and an amalgam formed, which may be rendered bright by washing it well with repeated affusions of water.”

Another method. Take the muddy substance which is procured in the polishing of copper plates with a pumice stone, and grind it well with a suitable portion of mercury, a little common salt, and some vinegar, in an iron mortar, (a marble one will do, if you make use of an iron pestle), till you perceive the mercury has taken up the copper.” The copper recovered from these amalgams retains its original colour, without any tendency to yellow. Even when brats is made use of for making the amalgam, the recovered metal is perfect red copper; the ingredient from which the brats received its yellowness being, as above observed, separated in the amalgamation.

Copper is the basis of several metals for mechanic uses; as brats, prince’s metal, bell-metal, bath-metal, white copper, &c. Brats is prepared from copper and calamine, with the addition of powdered charcoal, cemented together, and at last brought into fusion. The calamine is to be previously prepared by cleansing it from adhering earth, stone, or other matters; by roasting, or calcining it; and by grinding it into a fine powder. The length of time, and degree of heat, requisite for the calcination of the calamine, are different according to the qualities of that mineral. The calamine, thus calcined, cleansed, and ground, is to be mixed with about a third or fourth part of charcoal dust, or powdered pit-coal, as is done in some parts of England. The malleability of the basis is diminished by the use of pit-coal, which is therefore only employed for the preparation of the coarser kinds. To this composition of calamine and coal, some manufacturers add common salt, by which the process of making brats is said to be hastened. In Goslar, where the cadmia adhering to the insides of the furnaces is used instead of the native calamine, a small quantity of alum is added, by which they pretend the colour of the brats is heightened. With this composition, and with thin plates or grains of copper, the crucibles are to be nearly filled. The proportion of the calamine to the copper varies according to the richness of the former, but is generally as three to two. The copper must be dispersed throughout the composition of calamine and coal; and the whole must be covered with more coal, till the crucibles are full. The crucibles, thus filled, are to be placed in a furnace sunk in the ground, the form of which is that of the frustum of a hollow cone. At the bottom of the furnace, or greater basis of the frustum, is a circular grate, or iron-plate. This plate is covered with a coat of clay and horse-dung, to defend it from the action of the fire; and pierced with holes, through which the air maintaining the fire passes. The crucibles stand upon the circular plate, forming a circular row, with one in the middle. The fuel is placed betwixt the crucibles, and is thrown into the furnace at the upper part of it, or the lesser basis of the frustum. To this upper part or mouth of the furnace is fitted a cover made of bricks or clay, kept together with bars of iron, and pierced with holes. This cover serves as a regester. When the heat is to be increased, the cover must be partly or entirely taken off, and a free draught is permitted to the external air, which passes along a vault under-ground to the ash-hole, through the holes in the circular grate or plate, betwixt the crucibles, and through the upper mouth, along with the smoke and flame, into an area where the workmen stand, which is covered with a large dome or chimney, through which the smoke and air ascend. When the heat is to be diminished, the mouth of the furnace is closed with the lid; through the holes of which the air, smoke, and flame pass. The crucibles are to be kept red-hot during eight or ten hours; and in some places much longer, even several days, according to the nature of the calamine. During this time, the zinc rises in vapour from the calamine, unites with the copper, and renders that metal considerably more fusible than it is by itself. To render the metal very fluid, that it may flow into one uniform mass at the bottom, the fire is to be increased a little before the crucibles are taken out, for pouring off the fluid metal into molds. From 60 pounds of good calamine, and 40 of copper, 60 pounds of brats may be obtained, notwithstanding a considerable quantity of the zinc is dissipated in the operation. The quantity of brats obtained has been considerably augmented since the introduction of the method now commonly practised, of granulating the copper; by which means a larger surface of this metal is exposed to the vapour of zinc, and consequently less of that vapour escapes. To make the finer and more malleable kinds of brats, besides the choice of pure calamine and pure copper, some manufacturers cement the brass a second time with calamine and charcoal; and sometimes add to it old brass, by which the new is said to be meliorated.

Brass is brittle when hot; but so ductile when cold, that it may be drawn into very fine wire, and beat into very thin leaves. Its beautiful colour, malleability, and its fusibility, by which it may be easily cast into moulds, together with its being less liable to rust than copper, render it fit for the fabrication of many utensils.

Although zinc be fixed to a certain degree in brass, by the adhesion which it contracts with the copper; yet when brass is melted, and exposed to a violent fire, during a certain time, the zinc dissipates in vapours, and even flames away, if the heat be strong enough; and if the fire is long enough continued, all the zinc will be evaporated and destroyed, so that what remains is copper.

Prince's metal is made by melting zinc in substance with copper; and all the yellow compound metals prepared in imitation of gold are nothing other than mixtures of copper with different proportions of that semimetal, taken either in its pure state, or in its natural ore calamine, with an addition sometimes of iron-flings, &c. Zinc itself unites most easily with the copper; but calamine makes the most ductile compound, and gives the most yellow colour. Dr Lewis observes, that a little of the calamine renders the copper pale; that when it has imbibed about one third of its own weight, the colour inclines to yellow; that the yellowness increases more and more, till the proportion comes to almost one half; that on further augmenting the calamine, the compound becomes paler and paler, and at last white. The crucibles, in which the fusion is performed in large works, are commonly tinged by the matter of a deep blue colour.

Bell-metal is a mixture of copper and tin; and though both these metals singly are malleable, the compound proves extremely brittle. Copper is dissolved by melted tin easily and intimately, far more so than by lead. A small portion of tin renders this metal dull-coloured, hard, and brittle. Bell-metal is composed of about ten parts of copper to one of tin, with the addition commonly of a little brass or zinc. A small proportion of copper, on the other hand, improves the colour and consistence of tin, without much injuring its ductility. Pewter is sometimes made from one part of copper and twenty or more of tin.

It has long been observed, that though tin is specifically much lighter than copper, yet the gravity of the compound, bell-metal, is greater than that of the copper itself. The same augmentation of gravity also takes place where the lighter metal is in the greatest proportion; a mixture even of one part of tin with two of copper, turning out specifically heavier than pure copper. Most metallic mixtures answer to the mean gravity of the ingredients, or such as would result from a bare apposition of parts. Of those tried by Dr Lewis, some exceeded the mean, but the greater number fell short of it; tin and copper were the only ones that formed a compound heavier than the heaviest of the metals separately.

White copper is prepared by mixing together equal parts of arsenic and nitre, injecting the mixture into a red-hot crucible, which is to be kept in a moderate fire, till they subside, and flow like wax. One part of this mixture is injected upon four parts of melted copper, and the metal, as soon as they appear thoroughly united together, immediately poured out. The copper, thus whitened, is commonly melted with a considerable proportion of silver, by which its colour is both improved and rendered more permanent. The white copper of China and Japan appears to be nothing other than a mixture of copper and arsenic. Geoffroy relates, that, on repeated fusions, it exhaled arsenical fumes, and became red copper, losing, with its whiteness, one seventh of its weight.

§ 4. IRON.

Iron is a metal of a greyish colour; soon tarnishing in the air into a dusky blackish hue; and in a short time contracting a yellowish, or reddish rust. It is the hardest of all metals; the most elastic; and, excepting platinum, the most difficult to fuse. Next to gold, iron has the greatest tenacity of parts; an iron wire, the diameter of which is the tenth part of an inch, being capable of sustaining 450 pounds. Next to tin, it is the lightest of all the metals, losing between a seventh and eighth part of its weight when immersed in water. When very pure, it may be drawn into wires as fine as horse-hair; but is much less capable of being beaten into thin leaves than the other metals, excepting only lead.

Iron grows red-hot much sooner than any other metal; and this, not only from the application of actual fire, but likewise from strong hammering, friction, or other mechanic violence. It nevertheless melts the most difficulty of all metals except manganese and platinum; requiring, in its most fusible state, an intense, bright, white heat. When perfectly malleable, it is not fusible at all by the heat of furnaces, without the addition or the immediate contact of burning fuel; and, when melted, loses its malleability: all the common operations which communicate one of these qualities deprive it at the same time of the other; as if fusibility and malleability were in this metal incompatible. When exposed to the focus of a large burning mirror, however, it quickly fused, boiled, and emitted an ardent flame, the lower part of which was a true flame. At length it was changed into a blackish vitrified scoria.

From the great waste occasioned by exposing iron to a red but especially to a white heat, this metal appears to be a combustible substance. This combustion is maintained, like that of all other combustible substances, by contact of air. Dr Hook, having heated a bar of iron to that degree called white heat, he placed it upon an anvil, and blew air upon it by means of bellows, by which it burnt brighter and hotter. Exposed to a white heat, it contracts a fenivitrous coat, which bursts at times, and flies off in sparkles. No other metallic body exhibits any such appearance. On continuing the fire, it changes by degrees into a dark red calx, which does not melt in the most vehement heat procurable by furnaces, and, if brought into fusion by additions, yields an opaque black glass. When strongly heated, it appears covered on the surface with a soft vitreous matter like varnish. In this state, pieces of it cohere; and, on being being hammered together, weld or unite, without discovering a juncture. As iron is the only metal which exhibits this appearance in the fire, so it is the only one capable of being welded. Those operations which prevent the superficial scorching, deprive it likewise of this valuable property; which may be restored again by suffering the iron to resume its vitreous aspect; and, in some measure, by the interposition of foreign vitreifiable matters; whilst none of the other metals will unite in the smallest degree, even with its own fecula.

Iron expands the least of all metals by heat. In the act of fusion, instead of continuing to expand, like the other metals, it shrinks; and thus becomes so much more dense, as to throw up such part as is unmelted to the surface; whilst pieces of gold, silver, copper, lead, or tin, put into the respective metals in fusion, sink freely to the bottom. In its return to a confluent state, instead of shrinking like the other metals, it expands; sensibly rising in the vessel, and affuming a convex surface, while the others become concave. This property, first observed by Reamur, excellently fits it for receiving impressions from moulds. By the increase of bulk which the metal receives in congelation, it is forced into the minutest cavities, so as to take the impression far more exactly than the other metals which shrink.

Iron is dissolved by all the metals made fluid, except lead; though none of them act so powerfully upon it as gold; but, as Cramer observes, if the iron contains any portion of sulphur, it can scarcely be made to unite at all with gold.

Among the semimetallic bodies, it is averse to an union with mercury; no method of amalgamating these two having yet been discovered; though quicksilver, in certain circumstances, seems in some small degree to act upon it. A plate of tough iron, kept immersed in mercury for some days, becomes brittle; and mercury will often adhere to and coat the ends of iron pebbles used in triturating certain amalgams with saline liquors. Mr Jones has also discovered, that by plunging iron, while heated to an intense white heat, into mercury, the latter will adhere to the surface of the iron, and completely silver it over.

Next to mercury, zinc is the most difficultly combined with iron; not from any natural indisposition to unite, but from the zinc being difficultly made to sustain the heat requisite. The mixture is hard, somewhat malleable, of a white colour approaching to that of silver. Regulus of antimony, as soon as it melts, begins to act on iron, and dissolves a considerable quantity. If the regulus be stirred with an iron rod, it will melt off a part of it. Arsenic likewise easily mingles with iron, and has a strong attraction for it; forsaking all the other metals to unite with this. It renders the iron white, very hard, and brittle.

This metal is the basis of the fine blue pigment, called, from the place where it was first discovered, Berlin or Prussian blue. This colour was accidentally discovered about the beginning of the present century, by a chemist of Berlin, who, having successively thrown upon the ground several liquors from his laboratory, was much surprized to see it suddenly stained with a beautiful blue colour. Recollecting what liquors he had thrown out, and observing the same effects from a similar mixture, he prepared the blue for the use of painters; who found that it might be substituted to ultramarine, and accordingly have used it ever since.

Several chemists immediately endeavoured to discover the composition of this pigment; and in the year 1724 Dr Woodward published the following process, except for the Philosophical Transactions, for making it. "Alkalize together four ounces of nitre, and as much tartar as is directed for charcoal (no 779). Mix this alkali well with four ounces of dried bullocks blood; and put the whole in a crucible covered with a lid, in which there is a small hole. Calcine with a moderate heat, till the blood be reduced to a perfect coal; that is, till it emits no more smoke or flame capable of blackening any white bodies that are exposed to it. Increase the fire towards the end, so that the whole matter contained in the crucible shall be moderately, but sensibly, red.

Throw into two pints of water the matter contained in the crucible, while yet red, and give it half an hour's boiling; decant this first water; and pour more upon the black charry coal, till it becomes almost insipid. Mix together all these waters; and reduce them by boiling, to about two pints.

Dissolve also two ounces of martial vitriol, and eight ounces of alum, in two pints of boiling water. Mix this solution when hot with the preceding lixivium also hot. A great effervescence will then be made; the liquors will be rendered turbid; and will become of a green colour, more or less blue; and a precipitate will be formed of the same colour. Filtrate, in order to separate this precipitate; upon which pour spirit of salt, and mix them well together; by which means the precipitate will become of a fine blue colour. It is necessary to add rather too much of the salt than too little, and till it no longer increases the beauty of the precipitate. The next day wash this blue, till the water comes off from it insipid; and then gently dry it."

Mr Geoffroy was the first who gave any plausible theory of this process, or any rational means of improving it. He observes, that the Prussian blue is not, other than the iron of the vitriol revived by the inflammable matter of the alkaline lixivium, and perhaps a little brightened by the earth of alum; that the green colour proceeds from a part of the yellow ferruginous ochre, or ochre, unreveled, mixing with the blue; and that the spirit of salt dissolves this ochre more readily than the blue part; though it will dissolve that also by long standing, or if used in too large quantity. From these principles, he was led to increase the quantity of inflammable matter; that there might be enough to revive the whole of the ferruginous ochre, and produce a blue colour at once, without the use of the acid spirit. In this he perfectly succeeded; and found, at the same time, that the colour might be rendered of any degree of deepness, or lightness, at pleasure. If the alkali is calcined with twice its weight of dried blood, and the lixivium obtained from it poured into a solution of one part of vitriol to six of alum, the liquor acquires a very pale blue colour, and deposits as pale a precipitate. On adding more and more of a fresh solution of vitriol, the colour becomes deeper and deeper, almost to blackness. He imagines with great probability, that the blue pigment, thus prepared, will prove more durable in the air, mingle more perfectly with other colours, and be... lefs apt to injure the luftre of such as are mixed with or applied in its neighbourhood, than that made in the common manner; the tarnish to which common Prussian blue is subject, seeming to proceed from the acid, which cannot be separated by any ablution.

He takes notice of an amusing phenomenon which happens upon mixture. When the liquors are well stirred together; and the circular motion, as soon as possible, stopped; some drops of solution of vitriol (depurated by long settling), let fall on different parts of the surface, divide, spread, and form curious representations of flowers, trees, shrubs, flying insects, &c., in great regularity and perfection. These continue 10 or 12 minutes: and on stirring the liquor again, and dropping in some more of the solution of vitriol, are succeeded by a new picture.

This theory is confirmed by Mr Macquer, in a Memoir printed in the year 1752. He observes, that the quantity of phlogiston communicated to the iron in this process is so great, as not only to cause the metal itself in a great measure the action of acids, and become totally unaffected by the magnet; but by a slight calcination it becomes entirely similar to other iron, and is at once deprived of its blue colour. He further observes, that fire is not the only means by which Prussian blue may be deprived of all the properties which distinguish it from ordinary iron. A very pure alkali produces the same effect. He has also discovered, that the alkali which has thus deprived the Prussian blue of all the properties which distinguish it from ordinary iron, becomes, by that operation, entirely similar to the phlogisticated alkali used for the preparation of Prussian blue.

By a more particular examination, he found, that the alkali might become perfectly saturated with the colouring matter; so that, when boiled on Prussian-blue, it extracted none of its colour. When the salt was thus perfectly saturated, it seemed no longer to possess any alkaline qualities. If poured into a solution of iron in any acid, a fling homogeneous, and perfect precipitate, was formed; not green, as in Dr Woodward's process, but a perfect Prussian blue; which needed no acid to brighten its colour. A pure acid added to the alkali was not in the least neutralized, nor in the least precipitated the colouring matter. From hence Mr Macquer concludes, that, in the making of Prussian blue, vitriol is decomposed; because the iron has a strong attraction for the colouring matter, as well as the acid for the alkali; and the sum of the attraction of the acid to the alkali, joined to that of the iron for the colouring matter, is greater than the fling attraction of the acid to the metal.

Another very important phenomenon is, that earths have not the same attraction for this colouring matter that metallic substances have. Hence, if an alkali saturated with this colouring matter be poured into a solution of alum, no decomposition is effected, nor any precipitate formed. The alum continues alum, and the alkali remains unchanged. From this experiment Mr Macquer concludes that alum does not directly contribute to the formation of the Prussian blue. The purpose he thinks it answers is as follows. Fixed alkaline salts can never be perfectly saturated with phlogistic matter by calcination; alkalies, therefore, though calcined with inflammable substances, so as to make a proper lixivium for Prussian blue, remain still alkaline. Hence, when mixed with a solution of green vitriol, they form, by their purely alkaline part, a yellow precipitate, so much more copious, as the alkali is less saturated with phlogiston. But nothing is more capable of spoiling the fine colour of the Prussian blue, than an admixture of this yellow precipitate: it is therefore necessary to add a quantity of alum, which will take up the greatest part of the purely alkaline salt; and of consequence the quantity of yellow ferruginous precipitate is much diminished. But the earth of alum, being of a fine shining white, does not in the least alter the purity of the blue colour, but is rather necessary to dilute it. From all this it follows, that it is a matter of indifference whether the green precipitate is to be again dissolved by an acid, or the alkaline part of the lixivium saturated with alum or with an acid, before the precipitate is formed. The latter indeed seems to be the most eligible method.

Most alkalis obtained from the ashes of vegetables, being combined, by their combustion, with a portion of inflammable matter, are capable of furnishing a other alkaline quantity of Prussian blue, proportionable to the quantity of colouring matter they contain, even without the necessity of mixing them with a solution of iron; because they always contain a little of this metal dissolved, some of which may be found in almost all vegetables; therefore it is sufficient to saturate them with an acid. Henckel observed the production of this blue in the saturation of the fossil alkali, and recommended to chemists to inquire into its nature.

The theories of Geoffroy, Macquer, &c., however, with respect to Prussian blue, have now given place to discoveries that of Mr Scheele; who has examined the substance the colouring matter, and found the colouring matter consisting of an extremely volatile substance, capable of uniting with and neutralizing alkalies, but easily expelled from them by any other acid, even by that of fixed air. He begins his dissertation on this subject by observing, that the solution of alkali calcined with dried blood, which he calls lixivium sanguinis, by exposure to the air, loses its property of precipitating the iron of a blue colour; and that the precipitate thus obtained is entirely soluble in the acid. In order to determine whether the air had thus undergone any change, he put some newly prepared lixivium into a glass vessel well sealed with rosin; but after some time finding no change on the lixivium or on the air contained in the vessel, he began to think that this might be occasioned by the absence of fixed air, which always abounds in the open atmosphere, though not in any confined portion of it, at least in an equal proportion. Having therefore filled a glass vessel with fixed air, he poured into it a little lixivium sanguinis; and next day found, that it threw down from green vitriol a precipitate entirely soluble in acids. With other acids he obtained no precipitate.

On inverting the experiment, and mixing some green vitriol with lixivium sanguinis, the mixture grew fixed by the yellow; and he found this addition capable of fixing addition of the colouring matter so, that neither the acid of fixed some green air nor any other could expel it from the alkali. For having poured the mixture above mentioned into a solution of green vitriol, and afterwards supersaturated the the lixivium with acid, he obtained a considerable quantity of blue. To the same lixivium fanguinis, in which a small quantity of green vitriol was dissolved, he afterwards added the other acids somewhat more than was necessary for its saturation; and though this was done, a considerable quantity of Prussian blue was afterwards obtained. Again, having precipitated a solution of green vitriol with alkali, and boiled the precipitate for some minutes in lixivium fanguinis, part of it was dissolved: the filtered lixivium underwent no change when exposed to the open air or to the aerial acid, and precipitated the solution of vitriol of a blue; and though the lixivium was supersaturated with acid, and some green vitriol added, a very beautiful Prussian blue was obtained. This, however, will not hold when a perfectly dephlogisticated calx of iron is employed, of which none can be dissolved by the lixivium fanguinis; nor will any Prussian blue be obtained by precipitating with lixivium fanguinis a perfectly dephlogisticated solution of iron in nitrous acid.

To determine what had become of the colouring matter in those experiments where it seemed to have been dissipated, some lixivium fanguinis was poured into a vessel filled with aerial acid. It was kept well corked during the night, and next day a piece of paper dipped in a solution of green vitriol was fixed to the cork, pencilling it over with two drops of a solution of alkali in water. The paper was thus soon covered with precipitated iron; and on being taken out two hours afterwards, and dipped in muriatic acid, became covered with most beautiful Prussian blue. The same thing happened when lixivium fanguinis supersaturated with vitriolic acid was employed; for in this case also the air was filled with the colouring matter, capable of being in like manner absorbed by the calx of iron. But though from these experiments it is plain that acids expel this colouring substance from the lixivium, a given quantity of air is only capable of receiving a certain quantity of it; for the same mixture removed into another vessel imparts the colouring property to the air it contains according to its quantity. On putting perfectly dephlogisticated calx of iron upon the papers, no Prussian blue was formed; but the muriatic acid dissolved the calx entirely.

Our author having now assured himself that acids really attract the alkali more than the colouring matter, proceeded to try the effects of distillation. Having therefore supersaturated some lixivium fanguinis with vitriolic acid, he distilled the mixture in a glass retort with a gentle fire. When about one-third had passed over, he changed the receiver, and continued the operation till one-half was distilled. The first product had a peculiar taste and smell; the air in the receiver was filled with colouring matter, and the aqueous fluid was also strongly impregnated with it, as appeared by its forming a fine Prussian blue with phlogisticated calx of iron. Part of it being exposed to the open air for some hours, entirely lost its power, and the product of the second operation was no other than water mixed with a little vitriolic acid.

The next step was to procure, if possible, the colouring matter by itself; and this he attempted to obtain from the Prussian blue, rather than the lixivium fanguinis, as he would thus not only avoid the troublesome calcination of the alkali and blood, but obtain the colouring matter in much larger quantity than could be done from the lixivium. On examining several kinds of this pigment, he found in them evident marks of sulphur, volatile alkali, vitriolic acid, and volatile sulphureous acid; all of which substances are to be found in the lixivium fanguinis, as well as in that of foot, and adhere to the precipitate in the preparation of Prussian blue. Finding, however, that he could not obtain his purpose by any kind of analysis of these by fire alone, he had recourse to a neutral salt used by chemists for discovering iron in mineral waters. This Neutral salt is formed by digesting caustic fixed alkali on Prussian salt for distillation, which effectually extracts the colour from it even in the cold, in a very short time, and being neutralized, may easily be reduced into a dry form. But it is not entirely to be depended upon for this purpose; for it always contains some iron, which indeed is the medium of its connection with the alkali. The lixivium fanguinis is preferable, though even this contains some iron, as well as the lixivium of foot; our author's experiments, however, were made with the neutral salt, for the reasons already mentioned.

1. An ounce of the salt was dissolved in a glass retort in four ounces of water, afterwards adding three drachms of concentrated vitriolic acid; and the mixture was distilled with a gentle fire. The mass grew vitriolic, thick as soon as it began to boil; from a great quantity of Prussian blue, a quantity of the colouring matter appeared by the smell to penetrate the lute; and part of it was absorbed by the air in the receiver, as in former experiments. The distillation was continued till about an ounce had passed into the receiver. The blue mass remaining in the retort was put into a strainer, and a piece of green vitriol put into the liquid which passed through; but by this last no Prussian blue was produced. The blue which remained in the filter was again treated with lixivium tartar; the solution freed from its ochre by filtration, and the clear liquor committed a second time to distillation with vitriolic acid. Prussian blue was again separated, though in smaller quantity than before, and the colouring matter came over into the receiver. After one third of the matter had passed over, that which had been obtained by the first distillation was added to it, the Prussian blue was separated from the lixivium in the retort, and extracted a third time. Some Prussian blue was formed again, though in much smaller quantity; whence it is apparent that Prussian blue may at last be totally decomposed by means of alkali. Lime, or terra ponderosa, likewise extract the blue colour, and show the same phenomena as alkali.

With volatile alkali a compound, consisting of the colouring matter united with volatile alkali, iron, and colouring matter, is formed, which shows the same phenomena with that formed with fixed alkali. By distillation per se after it has been dissolved in water, the liquor grows thick in consequence of a separation of Prussian blue, and volatile alkali passes over into the receiver. This volatile spirit is impregnated with the colouring matter; it is not precipitated by lime-water; but green vitriol is precipitated by it; and on adding an acid, Prussian blue is formed. If a piece of paper, dipped in a solution of green vitriol, be exposed to the vapour of this alkali, it is soon decomposed; and if the same be pencilled over with muriatic acid, it instantly becomes blue. blue. On exposing the liquor to the open air, it all evaporates, leaving pure water behind.

As in all the operations with vitriolic acid hitherto related, some small quantity of it passes into the receiver, our author shows how to deprive the colouring matter of that vitriolic taint. For this purpose nothing more is necessary than to put a little chalk into the matter, and redilute it with a very gentle heat; the acid unites with the chalk, and the colouring matter goes over in its greatest purity. In order to hinder, as much as possible, the escape of the volatile colouring matter through the lute, he makes use of a small receiver, putting into it a little distilled water, and placing it so that the greater part shall be immersed in cold water during the operation. The water impregnated with this colouring matter has a peculiar but not disagreeable smell, a taste somewhat approaching to sweet, and warm in the mouth, at the same time exciting cough. When rectified as above directed, it appears to be neither acid nor alkaline; for it neither reddens paper dyed with lacmus, nor does it restore the colour of such paper after it has been made red; but it renders turbid the solutions of soap and hepatic sulphuris. The same liquor mixed with fixed alkali, though it contains a superabundance of colouring matter, restores the blue colour of paper reddened by an acid. By distillation to dryness, there goes over a part of the colouring matter which disengages itself from the alkali; the residue is soluble in water, and has all the properties of the best lixivium falguinis; but, like the true lixivium, it is decomposed by all the acids, even by that of fixed air. With caustic volatile alkali it forms a kind of ammoniacal salt; which, however, always smells volatile, though the colouring matter be in ever so great proportion. By distillation the whole instantly rises, and nothing but pure water is left in the retort.

Magnesia precipitated from Epsom salt by caustic volatile alkali, was dissolved in the colouring matter by allowing them to stand together for several days in a warm close bottle. On exposure to the open air, the magnesia separated from it by its superior attraction for aerial acid, and formed on the surface of the water a pellicle like that of cream of tartar. This solution was likewise decomposed by alkalies and lime-water.

The colouring matter dissolves but a very small quantity of terra ponderosa, which may be afterwards precipitated by vitriolic and even by aerial acid.

Pure clay, or the basis of alum, is not attacked by it. Lime is dissolved in a certain quantity. The superabundant portion should be separated by filtration; and as the liquor contains, besides the combined lime, the portion which water itself is able to take up, in order to free it from this, precisely the same quantity of water impregnated with aerial acid is to be added as is requisite for precipitating an equal quantity of lime-water. The colouring matter, thus saturated with lime, is to be filtered again, and then to be preserved in a well closed bottle to prevent the access of fixed air. This solution is decomposed by all the acids, and by the pure or caustic alkalies. By distillation the colouring matter rises, and nothing but pure lime is left in the retort.—This solution of lime appears to our author to be so perfectly saturated, that he employed it in preference to any other in the experiments he made on metals, and which we are now about to relate.

From the trials made by Mr Scheele, it appears that the colouring matter has no effect upon any metal except for iron. Quicksilver, excepting those of silver and quicksilver in nitrous acid, and that of iron in fixed air. The first is precipitated in a white powder; the second in a black one; and the third assumes a sea-silver green colour, which afterwards turns to blue. With quicksilver, metallic calces it produces the following phenomena:

1. Gold precipitated by aerated alkali becomes white. 2. The fixed air is disengaged from a precipitate of flowing silver with a slight effervescence. 3. Calx of mercury matter is dissolved, and yields crystals by gentle evaporation. 4. The calx of copper precipitated by aerated alkali on metallic effervescences, and assumes a faint citron colour. 5. Calx of the calxes; iron precipitated from its solution in the vitriolic acid by the same alkali, effervesces, and assumes a dark blue colour. 6. Precipitated cobalt shows some signs of effervescence, and changes into a yellowish brown colour. The other calces are not acted upon.

The precipitating liquor above mentioned, poured into metallic solutions, produces the following appearances by means of double elective attraction.

1. Gold is precipitated of a white colour, but by adding a superabundant quantity of the precipitating liquor the calx is redissolved. The second solution is colourless as water. 2. Silver is precipitated in form of a white fulness of the confluence of cheese; by adding more of the liquor the precipitate is redissolved, and the solution is not decomposed either by sal-ammoniac or marine acid. 3. Corrosive sublimate apparently undergoes no change, though it is in reality decomposed; the calx being dissolved in the colouring matter. 4. Mercury dissolved in the nitrous acid without heat, is precipitated in form of a black powder. 5. The solutions of tin and bismuth are precipitated, but the calx is not acted upon by the colouring matter. 6. The same effects are produced on the solution of butter of antimony, as well as on that of well dephlogisticated calx of iron. 7. Blue vitriol is precipitated of a yellow citron colour; if more of the precipitating liquor be added, the precipitate is redissolved into a colourless liquor; and a colourless solution of the same calx is likewise obtained by volatile alkali. On adding more of the solution of blue vitriol, the solution likewise disappears, and the liquor assumes a green colour. Acids dissolve a portion of this precipitate, and the remainder is white. The muriatic acid dissolves the precipitate completely, but lets it fall again on the addition of water. 8. Green vitriol is precipitated, first of a yellowish brown colour, which soon changes to green, and then becomes blue on the surface. Some hours afterwards the precipitate subsides to the bottom of the vessels, and then the whole mixture turns blue; but on adding any acid the precipitate becomes instantly blue. If a very small quantity of green vitriol be put into the precipitating liquor, the precipitate is entirely dissolved, and the whole assumes a yellow colour. 7. Solution of cobalt lets fall a brownish yellow precipitate, which is not dissolved by adding more of the precipitating liquor, neither is it soluble in acids. By distillation the colouring matter goes over into the receiver.

Lastly, our author undertook an investigation of the constituent parts of the colouring matter itself; and in this he succeeded in such a manner as must do honour to his memory, at the same time that it promises to be a real and lasting improvement to science, by showing a method of preparing this valuable pigment without that nauseous and horrid ingredient, blood, which is now used in great quantities for that purpose.—His first hint concerning this matter seems to have been taken from an observation of the air in his receiver accidentally taking fire from the neighbourhood of a candle. It burned without any explosion, and he was able to inflame it several times successively. Wishing to know whether any fixed air was contained in the colouring matter, he filled a retort half full of the liquor containing the colouring matter, and applying a receiver immediately after, gave the retort a brisk heat. As soon as the receiver was filled with thick vapours of the colouring matter, he disjoined it, and, inflaming the vapour by a little burning sulphur introduced into the cavity, found that the air which remained threw down a precipitate from lime-water.

"Hence (says he) it may be concluded, that the aerial acid (A) and phlogiston exist in this colouring matter."

It has been affected by several chemists, that Prussian blue by distillation always yields volatile alkali.—To determine this, Mr Scheele prepared some exceedingly pure from the precipitating liquor above mentioned and green vitriol; distilling it afterwards in a glass retort, to which he adapted a receiver containing a little distilled water. The operation was continued till the retort became red-hot. In the receiver was found the colouring matter and volatile alkali, but no oil; the air in the receiver was impregnated with aerial acid, and the same colouring matter; the residuum was very black, and obeyed the magnet. On substituting, instead of the Prussian blue, the precipitates of other metallic substances precipitated by the Prussian alkali, the results were:

1. The yellowish brown precipitate of cobalt yielded the very same products with Prussian blue itself; the residuum in the retort was black. 2. The yellow precipitate of copper took fire, and emitted, from time to time, sparks during the distillation. It produced little colouring matter, but a greater quantity of aerial acid and volatile alkali than had been obtained by the former precipitates. A sublimate arose in the neck of the retort, but in too small a quantity to make any experiment; the residuum was reduced copper. 3. The precipitate of zinc yielded the same with Prussian blue. 4. That of silver yielded likewise volatile alkali and fixed air, but chiefly colouring matter; a sublimate containing some silver arose into the neck of the retort; the residuum was reduced.

Vol. IV. Part II.

(a) This reasoning seems not to be sufficiently conclusive; for late experiments have shown that inflammation is generally attended with the production of fixed air, which could not be proved to have an existence either in the materials or common atmosphere before. Iron, lation of Prussian blue, as well as in that of the other above mentioned metallic precipitates.—In the distillation of Prussian blue, for instance, the calx of iron attracts a portion of phlogiston from the colouring matter. The aerial acid being thus disengaged, must go over into the receiver with the volatile alkali, which is set free at the same instant; but as the calx of iron in the heat of this distillation cannot unite with more phlogiston, a portion of the colouring matter, not decomposed, must likewise arise. If the calx of iron could combine with the whole of the phlogiston, there would come nothing over into the receiver but aerial acid and volatile alkali. In order to prove this, I distilled a mixture of six parts of manganese finely powdered, and one part of pulverized Prussian blue, and obtained nothing but aerated volatile alkali, without the least mark of colouring matter.”

Mr Scheele further remarks, that this colouring matter may probably be obtained in an aerial form, though he had not been able to do so. It is also worth notice, that, excepting the solutions of silver and mercury in nitrous acid, the colouring matter of Prussian blue is not able to decompose any other by a single elective attraction. Now, as we know that Prussian blue is not soluble in acids, it naturally follows, that the colouring matter has a greater affinity with iron than acids have, notwithstanding there is no precipitation perceived when this matter is mixed with the solution of vitriol of iron. “It may not be easy (says Mr Scheele) to give a satisfactory explanation of this phenomenon.”

Iron desaggregates with nitre, and renders the salt alkaline and caustic. A part of the iron is thus rendered soluble, along with the alkalized salt. A mixture of equal parts of iron filings and nitre, injected into a strongly heated crucible, and, after the detonation, thrown into water, tinges the liquor of a violet or purplish blue colour. This solution, however, is not permanent. Though the liquor at first passes through a filter, without any separation of the iron; yet, on standing for a few hours, the metal falls to the bottom, in form of a brick-coloured powder. Volatile alkalies instantly precipitate the iron from this fixed alkaline solution.

Iron readily unites with sulphur; and when combined with it, proves much easier of fusion than by itself. A mixture of iron filings and sulphur, moistened with water, and pressed down close, in a few hours swells and grows hot; and, if the quantity is large, bursts into flame.

By cementation with inflammable matters, iron imbibes a larger quantity of phlogiston; and becomes much harder, less malleable, and more fusible. It is then called steel. See Metallurgy, and Steel.

§5. Lead.

Lead is a pale or livid-white metal, soon losing its brightness in the air, and contracting a blackish or greyish ash-colour. It is the softest and most flexible of all metallic bodies; but not ductile to any great degree, either in the form of wire or leaf; coming far short, in this respect, of all other metals. It has also the least tenacity of all metallic bodies; a leaden wire of \( \frac{1}{4} \) of an inch diameter being capable of supporting only \( \frac{1}{2} \) pounds. Lead has, however, a considerable specific gravity; losing, when immersed in water, between \( \frac{1}{4} \) and \( \frac{1}{2} \) of its weight. It is of all metals the most fusible, excepting only tin and bismuth. The sheet-lead plumbers cast thin sheets of lead upon a table or mould, covered with a woollen, and above this with a linen cloth, without burning or scorching the cloths. The melted lead is received in a wooden case without a bottom; which being drawn down the sloping table by a man on each side, leaves a sheet of its own width, and more or less thin according to the greater or less celerity of its descent. For thick plates, the table is covered over with moistened sand, and the liquid metal conducted evenly over it, by a wooden strike, which bears on a ledge at each side.

Some have preferred, for mechanic uses, the milled advanced lead, or flattened sheets, to the cast; as being more equal, of smoothness, and solid. But whatever advantage of this kind the milled fort may appear to have at first, they are not found to be very durable. When the lead is stretched between the rollers, its cavities must necessarily be enlarged. The particles of metal that may be squeezed into them can have no union or adhesion with the contiguous particles; and, of consequence, must be liable, from bending, blows, jars, &c., to start out again, and leave the mass spongy and porous.

Lead yields, the dullest and weakest found of all metallic bodies. Reaumur observes, that it is rendered porous by casting a small quantity into a spherical or elliptical segment, as in the bottom of an iron-ladle; from hence he conjectures, that the found of the porous metals might be improved for the bells of clocks, &c., by giving them a similar form.

Though this metal very soon loses its lustre, and tarnishes in the air, it resists much longer than iron or copper the combined action of air and water, before it is decomposed or destroyed; and hence it is exceedingly useful for many purposes to which these metals can by no means be applied. When just become fluid, calcined lead looks bright like quicksilver; but immediately contracts a variously coloured pellicle on the surface. If this is taken off, and the fire continued, a fresh pellicle will always be formed, till the metal is by degrees changed into a dusky powder or calx. The injection of a little fat, charcoal-powder, or other inflammable matter, prevents this change, and readily revives the calx into lead again. It is said, that lead, recovered from its calces, proves somewhat harder and whiter than at first, as well as less subject to tarnish in the air.

The blackish calx or ashes of lead become of a very different appearance if the calcination is continued with a fire too moderate as not to melt them, and particularly if exposed to flame. By this treatment it is said that they become first yellow; then they are called mossicot or yellow lead. This colour becomes gradually more and more intense, till at last the calx is of a deep red; and then is called minium or red lead; but it is certain, that by proper management this calx never becomes yellow, assuming a reddish colour from the beginning. Too great a heat makes it irrecoverably yellow. It can be more easily prepared without exposure. Lead exposure to the flame. The degree of heat necessary for converting it into minium is between 600 and 700 of Fahrenheit.

If, instead of keeping this calx in a continued moderate heat, it be suddenly fused, the matter then puts on a foliated appearance, changing to a dull kind of brick-colour when powdered, and is then called litharge. Most of this substance is produced by refining silver with lead (see Refining); and is of two kinds, white and red. These two are distinguished by the names of litharge of gold, and litharge of silver. The most perfect is that called litharge of gold: the pale fort contains a considerable proportion of lead in its metallic state; and even the highest coloured litharge is seldom free from a little metallic lead, discoverable and separable by melting the mass in a crucible; when the lead sublimes to the bottom.

Lead mingles in fusion with all the metals except iron, with which it refuses any degree of union as long as the lead preserves its metallic form. On continuing the fire, the lead, scorifying or calcining, absorbs the phlogistic principle of the iron, and consequently promotes the calcination of that metal; both being at length reduced to calces. The fusible calx of lead easily unites with the calx of iron, and both melt together into an opaque brown or blackish glass. Copper does not unite with melted lead till the fire is raised so high as to make the lead smoke and boil, and of a bright red heat. Pieces of copper, now thrown in, soon dissolve and disappear in the lead: the mixture, when cold, is brittle, and of a granulated texture. The union of these two metals is remarkably flight. If a mixture of copper and lead is exposed to a fire no greater than that in which lead melts, the lead almost entirely runs off by itself; a separation of which no other example is known. What little lead is retained in the pores of the copper, may be scorified, and melted out, by a fire considerably less than is sufficient to fuse copper. If any of the copper is carried off by the lead, it swims unmelted on the surface.

Gold and silver are both dissolved by lead in a flight red heat. They are both rendered extremely brittle by the minute quantity of this metal; though lead is rendered more ductile by a small quantity of either of them. In cupellation, a portion of lead is retained by gold, but silver parts with it all. On the other hand, in its eluation from copper, if the copper contains any of the precious metals, the silver will totally melt out with the lead, but the gold will not. The attraction of lead to copper, however flight, is greater than that of copper to iron: a mixture of copper and iron being boiled in melted lead, the copper is imbibed by the lead, and the iron thrown up to the top. Silver is in like manner imbibed from iron by lead; whilst tin, on the contrary, is imbibed from lead by iron. If two mixtures, one of lead and tin, and another of iron and silver, be melted together, the result will be two new combinations, one of the tin with the iron at the top, the other with the lead and silver at the bottom: how carefully forever the matter be stirred and mixed in fusion, the two compounds, when grown cold, are found distinct, so as to be parted with a blow.

This metal is soluble in alkaline lixivias and expressed oils. Plates of lead boiled in alkaline lixivias, have a small part dissolved, and a considerable quantity corroded: the solution stains hair black. Lead, fused with fixed alkaline salts, is in part corroded into a dark-colored scoria, which partially dissolves in water. Expelled oils dissolve the calces of lead, by boiling, in such large quantities as to become thick and consilient: hence plasters, cements for water-works, paint for preserving nets, &c. Acids have a greater affinity with leads than oils have. If the common plaster, composed of oil and litharge, be boiled in diluted vinegar, the litharge will be dissolved, and the oil thrown up to the top. The oil thus recovered, proves soluble like essential oils in spirit of wine; a phenomenon first taken notice of by Mr Geoffroy.

§ 6. Tin.

The colour of this metal resembles silver, but is somewhat darker. It is softer, less elastic, and porous, than any other metal except lead. When bent backwards and forwards, it occasions a crackling sound, as if torn asunder. It is the lightest of all the malleable metals, being little more than seven times specifically heavier than water. The tenacity of its parts also is not very considerable; a thin wire of 1/8 of an inch diameter being able to support only 49½ pounds.

Tin is commonly reckoned the least ductile of all metals except lead; and certainly is so, in regard to ductility into wire, but not in regard to extensibility into leaves. These two properties seem not to be so much connected with one another as is generally imagined. Iron and steel may be drawn into very fine wire, but cannot be beat into leaves. Tin, on the other hand, may be beat into very thin leaves, but cannot be drawn into wire: gold and silver possess both properties in a very eminent degree; whilst lead, notwithstanding its flexibility and softness, cannot be drawn into fine wire, or beat into thin leaves. It melts the most easily of all the metals; about the 430th degree of Fahrenheit's thermometer. Heated till almost ready to melt, it becomes so brittle that large blocks may be easily beat to pieces by a blow. The purer fort, from its facility of breaking into long shining pieces, is called grain-tin. Melted, and nimbly agitated at the instant of its beginning to congeal, it is reduced into small grains or powder.

With the heat necessary for fusion, it may also be calcined, calcined; or at least so far deprived of its phlogiston as to appear in the form of a grey calx, which may be entirely reduced to tin by the addition of inflammable matter. The calcination of tin, like that of lead, begins by the melted metal losing its brittleness, and contracting a pellicle on its surface. If the fire is raised to a cherry-red, the pellicle swells and bursts, discharging a small bright flame of an aromatic smell. By longer continuance in the fire, the metal is converted first into a greyish, and then into a perfectly white calx, called putty, which is used for polishing glasses and other hard bodies.

The calx of tin is the most refractory of all others. Even in the focus of a large burning mirror, it only softens a little, and forms crystalline filaments. With glafs of bismuth, and the simple and arsenicated glafes of lead, it forms opaque milky compounds. By this property it is fitted for making the basis of the imperfect glafes called enamels; (see Glass and Enamel). The author of the Chemical Dictionary relates, "that having exposed very pure tin, singly, to a fire as strong as that of a glass-house furnace, during two hours, under a muffle, in an uncovered teft, and having then examined it, the metal was found covered with an exceedingly white calx, which appeared to have formed a vegetation; under this matter was a reddish calx, and an hyacinthine glaf; and lastly, at the bottom was a piece of tin unaltered. The experiment was several times repeated with the same success."

Nitre deflagrates with tin, and hastens the calcination of this as well as of other imperfect metals. The vapours which rise from tin, by whatever method it is calcined, have generally an arsenical smell. Tin melted with arsenic falls in great part into a whitish calx: the part which remains uncalcined proves very brittle, appears of a white colour, and a sparkling plated texture, greatly resembling zinc. The arsenic is strongly retained by the tin, so as scarcely to be separable by any degree of fire; the tin always discovering, by its augmentation in weight, that it holds a portion of arsenic, though a very intense fire has been used. Hence, as the tin ores abound in arsenic, the common tin is found also to participate of that mineral.

Henckel discovered a method of separating actual arsenic from tin; namely, by slowly dissolving the tin in eight times its quantity of an aqua regia made with sal ammoniac, and setting the solution to evaporate in a gentle warmth: the arsenic begins to concrete whilst the liquor continues hot, and more plentifully on its growing cold, into white crystals. M. Margraaf, in the Berlin Memoirs for 1747, has given a more particular account of this process. He observes, that the white sediment which at first separates during the dissolution, is chiefly arsenical; that Malacca tin, which is accounted one of the purest sorts, yielded no less than ¼ th its weight of arsenical crystals; that some sorts yielded more; but that tin extracted from a particular kind of ore, which contained no arsenic, afforded none. That the crystals were truly arsenical, appeared from their being totally volatile; from their subliming (a little fixed alkaline salt being added to absorb the acid) into a colourless pellucid concrete; from the sublimate, laid on a heated copper-plate, exhaling in fumes of a garlic smell; from its staining the copper white; and from its forming, with sulphur, a compound similar to the yellow or sulphurated arsenic. He found that the arsenic was separable also by means of mercury; an amalgam of tin being long triturated with water, and the powder which was washed off committed to distillation, a little mercury came over, and bright arsenical flowers arose in the neck of the retort. Dr Lewis observes, that the crackling noise of tin in bending may possibly arise from its arsenic; as those operations which are said to separate arsenic from the metal, likewise deprives it of this property.

Tin may be alloyed, in any proportion, with all metals by fusion: but it absolutely destroys their ductility, and renders them brittle, as in hell-metal; whence this metal has obtained the name of diabolus metallorum.

Iron is dissolved by tin in a heat far less than that in which iron itself melts; the compound is white and brittle. Iron added to a mixture of lead and tin, takes up the tin, leaving the lead at the bottom; and, in like manner, if lead, tin, and silver, are melted together, the addition of iron will absorb all the tin, and the tin only. Hence an easy method of purifying silver from tin.

Tin, notwithstanding it is, like lead, soon deprived of its lustre by exposure to the air, is nevertheless much less liable to rust than either iron, copper, or lead; and hence is advantageously used for covering over the insides of other metallic vessels. The amalgam of mercury and tin is employed to cover one of the surfaces of looking-glasses; by which they are rendered capable of reflecting the rays of light. The amalgam also, mixed with sulphur and sal ammoniac, and let to sublime, yields a sparkling gold-coloured substance called aurum mofaicum; which is sometimes used as a pigment. This preparation is commonly made from quicksilver and tin, of each two parts, amalgamated together; and then thoroughly mixed with sulphur and sal ammoniac, of each one part and a half. The mercury and sulphur unite into a cinnabar, which sublimes along with the sal ammoniac; and, after sublimation, the aurum mofaicum remains at the bottom.

Sulphur may be united with tin by fusion; and forms with it a brittle mass, more difficultly fusible than pure tin. Sulphur has, in this respect, the same effect upon tin as upon lead. The alloy of tin lessens the fusibility of these very fusible metals; while it increases the fusibility of other difficultly fusible metals, as iron and copper.

§ 7. Mercury or Quicksilver.

Mercury is a fluid metallic substance, of a bright silver colour, resembling lead or tin when melted; entirely void of taste and smell; extremely divisible; and conglomerate only in a degree of cold very difficultly produced, in this country, by art (see Cold and Congelation). It is the most ponderous of all fluids, heavier in and of all known bodies, gold and platinum excepted; winter than its specific gravity being to that of water nearly as 14. in summer to 1. It is found to be specifically heavier in winter than in summer by 25 grains in 11 ounces.

Neither air nor water, nor the united action of these two, seem to make any impression upon mercury: nor is it more susceptible of rust than the perfect metals. Its surface, nevertheless, is more quickly tarnished than gold or silver; because the dust which floats in the air, quickly seizes on its surface. The watery vapours also, which float in the air, seem to be attracted by mercury.

From these extraneous matters, which only slightly adhere to it, mercury may be easily cleansed by purification through a clean new cloth, and afterwards heating it: but if mixed with any other metal, no separation can be effected without distillation. In this process, a small portion of some of the metals generally arise along with the mercury. Thus, quicksil- Practice.

Mercury or Quick-silver.

ver distilled from lead, bismuth, or tin, appears less bright than before; stains paper black; sometimes exhibits a skin upon the surface; and does not run freely, or into round globules. Mr Boyle relates, that he has observed the weight of mercury sensibly increased by distillation from lead, and this when even a very moderate fire was made use of. By amalgamation with stellated regulus of antimony, and then being distilled after a few hours digestion, mercury is said to become, by a few repetitions of the process, more ponderous, and more active. The animated, or philosophic mercuries of some of the alchemists, are supposed to have been mercury thus prepared. By the same, or similar processes, seem to have been obtained the curious mercuries which Boyle declared he was possessed of, and made himself; which were "considerably heavier in specie than common quicksilver,—dissolved gold more readily,—grew hot with gold, so as to be offensive to the hand, and elevated gold in distillation." When quicksilver is to be distilled, it is proper to mingle it with a quantity of iron-filings; which have the property of making it much brighter than it can be otherwise obtained, probably by furnishing phlogiston.

By digestion in a strong heat for several months, mercury undergoes a considerable alteration, changing into a powder, at first ash-coloured, afterwards yellow, at length of a bright red colour, and an acrid taste; and is then called mercurius precipitatus per fc. In this last state it proves similar to the red precipitate, prepared from a solution of mercury in nitrous acid. This calx proves less volatile in the fire than the mercury in its fluid state. It supports for some time even a degree of red heat. In the focus of a burning mirror, it is said to melt into glass when laid upon a piece of charcoal, and to revive into running mercury before it exhales. Evaporated by common fire, it leaves a small portion of a light brown powder; which, Boerhaave relates, bore a blast-heat; swelled into a spongy mass; formed with borax a viscous friable substance; but vanished in cupellation. By a long continued digestion in a gentle heat, mercury suffers little change. Boerhaave digested it in low degrees of heat, both in open and close vessels, for 15 years together, without obtaining any other reward for his labour than a small quantity of black powder; which, by trituration, was quickly revived into running mercury. Conitant triture, or agitation, produce a change similar to this in a short time. Both the black and red powders, by bare exposure to a fire sufficient to elevate them, return into fluid mercury. The red powder has been revived by simply grinding it in a glass mortar.

In like manner, quicksilver remains unchanged by distillation. Boerhaave had the patience to distil 18 ounces of mercury upwards of 500 times over, without observing any other change than that its fluidity and specific gravity were a little increased, and that some grains of a fixed matter remained. The vapours of mercury, like those of all other volatile bodies, cause violent explosions if confined. Mr Hellot gives an account of his being present at an experiment of this kind: a person pretending to fix mercury, had inclosed it in an iron box closely welded. When the mercury was heated, it burst the box, and dissipated in invisible vapours.

Mercury dissolves or unites with all metallic bodies, except three, viz. iron, arsenic, and nickel: in some cases it will absorb metals, particularly gold and silver, Amalgam from their solutions in acids or alkalies; but does not mate with act upon any metal when combined with sulphur, nor different substances on precipitates made by alkalies, nor on calces by fire. Whatever metal it is united with, it constantly preserves its own white colour. It unites with any proportion of those metallic substances with which it is capable of being combined; forming, with different quantities, amalgams of different degrees of consistence. From the fluid ones, greatest part of the quicksilver may be separated by colature. Bismuth is so far attenuated by mercury, as to pass through leather with it in considerable quantity. It also promotes the action of quicksilver upon lead to a great degree; so that mercury united with $\frac{1}{3}$, $\frac{1}{9}$, or $\frac{1}{27}$ its weight of bismuth, dissolves masses of lead in a gentle warmth, without the agitation, triture, comminution, or melting heat necessary to unite pure mercury with lead. From these properties, this solution of bismuth in mercury becomes a proper solvent for pieces of lead lodged in the human body.

On triturating or digesting amalgams for a length of time, a blackish or dusky-coloured powder arises to the surface, and may be readily washed off by water. Some of the chemists have imagined, that the amalgamated metal was here reduced to its constituent parts; but pure mercury is by itself reducible to a powder of the same kind; and the metallic particles in this process, united with the mercury, are found to be no other than the metal in its entire substance. Some metals separate more difficultly than others; gold and silver the most so. Boerhaave relates, that if the powder which separates from an amalgam of lead be committed to distillation with vinegar in a tall vessel, the mercury will rise before the vinegar boils; that, by a like artifice, quicksilver may be made to distil in a less degree of heat than that of the human body: but Dr Lewis, though he made many trials, was never able to succeed.

By a amalgamation with gold, mercury may become exceedingly fixed; so as not to be dissipable by the greatest heat. Concerning this, Dr Brandt relates the following curious experiment: "Having amalgamated fine gold with a large proportion of quicksilver, and strained off the superfluous mercury, he digested the amalgam in a close stopped vessel for two months with such a degree of heat, that a part of the quicksilver sublimed into the neck of the glass. The matter being then ground with twice its weight of sulphur, and urged with a gradual fire in a crucible, a spongy calx remained; which being melted with borax, and afterwards kept in fusion by itself for half an hour, in a very violent fire, still retained so much of the quicksilver as to become brittle under the hammer, and appear internally of a leaden colour. The metal being again amalgamated with fresh mercury, the amalgam again ground with sulphur, and exposed to an intense fire, a spongy calx remained as before. This calx being digested in two or three fresh parcels of aqua regia, a small portion of whitish matter remain- ed at last undissolved. The paper which covered the cylindrical glass wherein the digestion was performed, contracted, from the vapours, a deep-green circular spot in the middle, with a smaller one at the side; whereas the aqua regia digested in the same manner by itself, or with gold, or with mercury, gave no stain. The first solution, on the addition of oil of tartar per deliquium, grew red as blood; on standing, it depo- sited, first, a little yellow calx, like aurum fulminans; afterwards, a bright matter like fine gold; and at last, a paler precipitate, inclining to green; its own deep red colour and transparency remaining unchanged. Being now committed to distillation, a colourless liquor arose; and the residuum, perfectly exsiccated, yielded, on edulcoration, a yellow calx of gold; which the alkaline lixivium had been unable to precipitate. The second solution turned green on the admixture of the alkaline liquor, and let fall a white precipitate, which turned black and brown. The several precipitates were calcined with twice their weight of sulphur, and then melted with four times their quantity of flint, and twelve of pot-ash, in a fire vehemently excited by bellows. The scoria appeared of a golden colour, which, on pulverization and edulcoration, vanished. At the bottom was a regulus, which looked bright like the purest gold; but was not perfectly malleable. Broken, it appeared internally white; and the white part amounted to at least one-third its bulk. Besides this lump of metal, there were several others, white like silver, and soft as lead."

In Wilton's chemistry, we have a process for converting quicksilver into water, by dropping it by little and little into a tall iron vessel, heated almost to a white heat in the bottom. Over the mouth of this vessel were luted seven aludels; and on the top, a glass alembic head, with a beak, to which was fitted a receiver. The mercury was put in so slowly, that it required 16 hours for one pound. Every time that a little quantity of mercury was put in, it made a great noise, filling the aldel's head and receiver with white fumes. When the vessels were cooled, a little water was found in each of the receivers, and in the first and second some grains of crude mercury. The whole quantity amounted to 13 ounces and 6 drachms; which was expected to prove a powerful solvent of gold and silver; but, on trial, was found to be in no respect different from common water. On this experiment Dr Lewis has the following note.

"The possibility of converting mercury into water, or at least of obtaining a great quantity of water from mercury, has not only been believed by several great men in the chemical art, but some have even ventured to assert that they have actually made this change. Yet, nevertheless, they have delivered the history of this affair with such marks, as seem to make the reality of the change extremely doubtful. Mr Boyle (in his tract of the producibleness of Chemical Principles, annexed to Scept. Chemift, p. 235.) says, 'that he once obtained water from mercury without additament, without being able to make the like experiment succeed afterwards.' M. Le Febure, who is generally looked upon as an honest practitioner, directs a process similar to that above (Wilton's), for obtaining of this mercurial water. But it is to be suspected, as Mr Hales very well observes (in his Stetical Experiments, p. 200.), that Mr Boyle and others Mercury were deceived by some unheeded circumstance, when or Quick- silver, they thought they obtained a water from mercury, which should seem rather to have arisen from the lute and earthen vessels made use of in the distillation: for Mr Hales could not find the least sign of any moisture upon distilling mercury in a retort made of an iron gun-barrel, with an intense degree of heat; although he frequently cohabited the mercury which came over into the recipient. 'In a course of chemical experiments, I repeated Mr Hales's process, and urged the mercury, which was let fall by little and little, through an aperture made in the gun-barrel, with a most intense degree of heat, without obtaining any water; but it being suspected by a bystander, that the mercury in this experiment came over before it had been sufficiently acted upon by the fire, by reason of the looseness of the neck of the distilling instrument, the experiment was varied in the following manner. Sixteen ounces of mercury were heated in a crucible, in order to evaporate any moisture that might have been accidentally mixed with it; and an iron gun-barrel of four feet in length, being placed perpendicularly in a good furnace, and a glass-head and recipient fitted to its upper part, the mercury was let fall by little and little into the barrel, and the fire urged with bellows. After each injection, the mercury made a considerable noise and ebullition, and arose into the head; where it soon condensed and trickled down, in the common form of running mercury, into the recipient, without the least perceptible appearance of any aqueous humidity.'"

Mercury is difficultly amalgamated with regulus of antimony and copper; for which some particular manipulations are required. Two of Dr Lewis's receipts for reuniting quicksilver with copper, we have already given (n° 1153.): with regulus of antimony, mercury, he says, may be perfectly united, by pouring a small stream of melted regulus into a considerable portion of mercury, made almost boiling hot. Another method directed by Heuckel, is to put mercury into an iron mortar along with some water, and set the whole over the fire. When the water boils, a third or fourth part of melted regulus is to be poured in, and the mass ground with a pestle, till the amalgam is completed. The use of the water, as Dr Lewis observes, is to hinder the mercury from flying off by the heat of the regulus: but as the two are by this means not put together in so hot a state, the union is more difficult, and less perfect. The loss of the mercury, in the first process, may be prevented by using a large vessel, and covering it with a perforated iron-plate, through the hole in which the regulus is to be poured. This method is likewise applicable to the amalgamation of copper.

With sulphur, mercury unites very readily, forming by trituration, or simple fusion, a black powder or mass, called Ethiops mineral; which, by careful sublimation, becomes the beautiful red pigment called vermilion. (See Sulphur, sect. iv.)

The extensive use of mercurius dulcis in medicine has rendered it an object to chemists to find out some method of preparing it with less expense and trouble, dulcis in and with more certainty of its effects, than it can be by the most methods hitherto mentioned. This is now accomplished. plished through the industry of Mr Scheele, to whom chemistry in general has been so much obliged. His method is as follows:

"Take half a pound of quicksilver, and as much pure common aquafortis. Pour it into a small cucur- bit with a pretty long neck, stop the mouth with a little paper, and put it into warm sand. Some hours afterwards, when the acid appears no longer to act upon the quicksilver, the fire is to be augmented so as to make the solution nearly boil. This heat is to be continued for three or four hours, and the vessel now and then to be shaken. Towards the end, regulate the heat in such a manner that the solution shall gently boil for a quarter of an hour. In the mean time, dis- solve 4 ounces of pure common salt in six or eight pounds of water; pour this solution, still boiling, in- to a glass vessel, and immediately afterwards mix with it the above-mentioned solution of quicksilver, which also must be boiling, in small quantities at a time, with constant agitation. When the precipitate has settled, decant off the clear liquor, and pour hot water again on the precipitate, with which it is to be edulcorated, till the water standing upon it shall be entirely talte- less. Put the whole obtained by these means toge- ther, filter and dry it in a mild heat."

On this process it is remarked, that when the quick- silver no longer effervesces with the acid, one would imagine that a saturation had taken place. But this is far from being the case. By increasing the heat the quicksilver solution is still able to dissolve a great quantity; with this difference, however, that, whereas the quicksilver in the beginning is calcined, a great deal of it after- wards, in a metallic form, is dissolved, as appears from this, that not only no more elastic vapours a- scend; but also, that with fixed and volatile caustic al- kalies a black precipitate is obtained; otherwise, when the solution contains only calcined quicksilver, the precipitate is yellow. If the black precipitate be gently distilled, quicksilver arises, and there remains a yellow powder, which is that part of the metal that was calcined by the nitrous acid. The fire must at any rate be augmented, in order to keep the mercurial calx dissolved, the compound of this metal and nitrous acid being extremely apt to crystallize even in the heat. There commonly remains some undissolved quicksilver; but it is always better to take too much than too little; for the more metal the mercurial solu- tion contains, the more mercurius dulcis is obtained at last. The quantity here mentioned usually produces 8 ounces of mercurius dulcis. The mercurial solu- tion must be cautiously poured into that of sea-salt, that no mercury may follow. Two ounces of salt would be sufficient for the precipitation of all the quicksilver; but when so small a quantity is used, it may easily happen, that some superabundant corrosive sublimate may adhere to the precipitate, which water alone is incapable of entirely separating. Among other advantages this method of making mercurius dulcis polesifies, it is none of the least, that the powder is much finer than any to which it can be reduced in the common way by trituration, however long continued.

§ 8. Zinc.

This is a semimetal of a bluish white colour. It is the least brittle of any of the semimetals; and when amply supplied with phlogiston, which may be done by treating it in cloze vessels with inflammable mat- ters, it polesifies a semifusibility, by which it may be flat- tened into thin plates. When broken, it appears formed of many flat shining plates or facets, which are larger when slowly than when hastily cooled. When heated, it is very brittle; and crackles like tin, only louder, when bent. Exposed to the air, it contracts in length of time a yellowish rust. Its specific gravity, according to Dr Lewis, is to that of water as 7½ to 1. It begins to melt as soon as red-hot; but does not flow thin till the fire is raised to a white heat. Then the zinc immediately begins to burn with an exceed- ingly bright and beautiful flame. Kept just in fusion, it calcines slowly; not only on the upper surface, but likewise round the sides, and at the bottom of the crucible. If several pieces are just melted to- gether, the mass, when grown cold, may be broken into the same number; their union being prevented by a yellowish calx, with which each piece is covered over. M. Malouin relates, in the French Memoirs for 1742, that a quantity of zinc being melted five times, and the fusion continued fifteen hours each time, it proved, on every repetition, harder, more brittle, less fusible, and less calcinable: that after the two first fusions, its colour was grey; after the third, brown; and after the fourth, black: that the fifth rendered it of a slate-blue; and the sixth of a clear violet.

So violent is the deflagration of zinc, that the whole flowers of zinc, or wool; which, however, are easily reduced to a fine powder. These are used in medicine, and reck- oned an excellent remedy in epileptic cases. When once sublimed, they are by no means capable of be- ing elevated again by the most violent heat. In a heat far greater than that in which they first arose, they suffer no alteration; in a very vehement one, they melt, according to Henckel, into a semiopaque green glas. Vitrified with borax, they give a grey, or brownish, glas. From the brightness of the flame of burning zinc, and the garlic smell which it is said to emit, some have concluded that zinc contained the phosphoric acid; which, from some other circum- stances, is not altogether improbable.

The flowers of zinc have been thought very diffi- cultly, or not at all, reducible to their metallic form by an addition of phlogiston. But Dr Lewis observes, that this difficulty proceeds not from their unfitness to be reflored into the form of zinc, but from the volatility of the semimetal, which occasions its being dissipated in fumes, if the common methods are made use of. All calces, those of iron excepted, require a greater heat for their fusion than that in which the metal itself melts; and as a full melting heat is the greatest that zinc can sustain, it burns and calcines the infant of its revival, if the air is admitted; and in cloze vessels escapes, in part at least, through their pores. On mixing flowers of zinc with powdered charcoal, and urging them with a strong fire in a crucible, a defla- gration and fresh sublimation ensue: sufficient marks that the zinc has been reduced to its metallic form; for as long as it remains in the state of calx, neither of these effects can happen. If the vessel is so con- trived! trived as to exclude the air, and at the same time to allow the reviving semimetal to run off from the vehemence of the heat, into a receiver kept cool, the zinc will there concrete, and be preserved in its metallic state. It is still more effectually detained by certain metallic bodies, as copper, or iron; with which the zinc, when thus applied, unites more readily and perfectly than it can be made to do by any other means.

Homberg pretended to obtain an oil from the flowers of zinc, by dissolving them in distilled vinegar, and then distilling the solution in a glass retort. At first a quantity of phlegm arose; then the superfluous acid; and at last an empyreumatic oil. This last, which Homberg imagined to proceed from the flowers of zinc, Newmann very justly attributes to the distilled vinegar.

An oil of another kind was obtained by Mr Hellot from the above solution, by digesting the ash-colored residuum, which remained after the distillation, with the acidulous phlegm which came over, for eight or ten days; distilling the tincture to dryness; and repeating the extraction with the distilled liquor, till the quantity of dry extract thus obtained was very considerable. This resin-like matter, distilled in a retort with a stronger fire, yielded a yellowish liquor, and a white sublimate. The liquor discovered no mark of oil; but, upon being passed upon the sublimate, immediately dissolved it, and then exhibited on the surface several drops of a reddish oil. Some of this oil was taken up on the point of a pencil, and applied to gold and silver-leaf. In twenty-four hours, the parts touched appeared, in both, equally dissolved.

Zinc does not unite in fusion with bismuth, or the semimetal called nickel. It unites difficulty with iron; less so with copper; easier with the other metals. It renders iron or copper more easily fusible; and, like itself, brittle whilst hot, though considerably malleable when cold. It brightens the colour of iron almost into a silver hue, and changes that of copper into a yellow or gold colour. It greatly debases the colour of gold; and renders near an hundredth part of that most ductile metal brittle and untractable. A mixture of equal parts of each is very hard, white, and bears a fine polish; hence it is proposed by Mr Hellot for making specula. It is not subject to rust or tarnish in the air, like those metals whose basis is copper. It improves the colour and lustre of lead and tin, renders them firmer, and consequently fitter for several mechanic uses. Tin, with a small proportion of zinc, forms a kind of pewter. Lead will bear an equal weight, without losing too much of its malleability. Macuin observes, that arsenic, which whitens all other metals, renders zinc black and friable; that when the mixture is performed in close vessels, an agreeable aromatic odour is perceived on opening them; that zinc amalgamated with mercury, and afterwards recovered, proves whiter, harder, and more brittle than before, and no longer crackles on being bent.

Mixtures of zinc with other metals, exposed to a strong fire, boil and deflagrate more violently than with other zinc by itself. Some globules of the mixture are usually thrown off during the ebullition, and some part of the metal calcined and volatilized by the burning zinc; hence this substance has been called metallic nitre. Bismuth, Gold itself does not entirely resist its action. It very difficultly volatilizes copper; and hence the sublimes obtained in the furnaces where brass is made, or mixtures of copper and zinc melted, are rarely found to participate of that metal. On melting copper and zinc separately, and then pouring them together, a violent detonation immediately ensues, and above united with half the mixture is thrown about in globules.

Zinc does not unite in the least with sulphur, or with crude antimony, which scorch all other substances except gold and platinum; nor with compositions of sulphur and fixed alkaline salts, which dissolve gold itself. With nitre it deflagrates violently. Its flowers do not sensibly deflagrate; yet alkali double their weight of the salt more readily than the zinc itself. The alkaline mats appears externally greenish, nitre alkaline internally of a purple colour. It communicates a fine lilyed by purple to water, and a red to vinegar. The acetous flowers of tincture inspissated, leaves a tenacious substance which soon runs in the air into a dark red caustic liquor, the alkalinity of some of the pretended adepts.

§ 9. BISMUTH.

This semimetal, called also tin-glass, and by some naturalists marcasita officinarum, is somewhat similar to the regulus of antimony. It appears to be composed of cubes formed by the application of plates upon each other. Its colour is less white than that of regulus of antimony; and has a reddish tinge, particularly when it is exposed to the air. In specific gravity it approaches to silver; being nearly ten times heavier than water. It has no degree of malleability; breaking under the hammer, and being reducible by trituration to fine powder. It melts a little later than tin, and seems to flow the thinnest of all metallic substances. Bismuth is semifluid, like all other semimetals. When exposed to the fire, flowers rise from it; it is calcined; and converted into a litharge-like and glassy nearly as lead is: (See Glass). It may litharge even be employed, like that metal, in the purification and glazing of gold and silver by cupellation. (See Refining). When in fusion, it occupies less volume than in its solid state: a property peculiar to iron among the metals, and bismuth among the semimetals. It emits fumes in the fire as long as it preserves its metallic form; when calcined or vitrified, it proves perfectly fixed.

Bismuth mingles in fusion with all the metallic substances, except regulus of cobalt and zinc. The addition of nickel, or regulus of antimony, renders it of all the miscible with the former, though not with the latter. It greatly promotes the tenacity as well as facility of the fusion of all those metals with which it unites. It whitens copper and gold, and improves the colour of some of the white metals: mixed in considerable quantity, it renders them all brittle, and of a flaky structure like its own. If mixed with gold or silver, a heat that is but just sufficient to melt the mixture, will presently vitrify a part of the bismuth; which, having then no action on those perfect metals, separates, and glazes the crucible all round.

§ 10. § 10. REGULUS OF ANTIMONY.

This semimetal, when pure, and well fused, is of a white shining colour, and consists of lamines applied to each other. When it has been well melted, and not too hastily cooled, and its surface is not touched by any hard body during the cooling, it exhibits the perfect figure of a star, consisting of many radii issuing from a centre. This proceeds from the disposition that the parts of this semimetal have to arrange themselves in a regular manner, and is similar to the crystallization of salts.

Regulus of antimony is moderately hard; but, like other semimetals, it has no ductility, and breaks in small pieces under a hammer. It loses \( \frac{1}{4} \) of its weight in water. The action of air and water destroys its lustre, but does not rust it so effectually as iron or copper. It is fusible with a heat sufficient to make it red hot; but when heated to a certain degree, it fumes continuously, and is dissipated in vapours. These fumes form what are called the argentine flowers of regulus of antimony, and are nothing but the earth of this semimetal deprived of part of its inflammable principle, and capable of being reduced to its reguline state by an union with this principle.

There are different methods of preparing the regulus of antimony; but all of them consist merely in separating the sulphur which this mineral contains, and which is united with the regulus. It is plain, therefore, that regulus of antimony may be made by an addition of any substance to crude antimony in fusion, which has a greater attraction for sulphur than the regulus itself has. For this purpose, alkaline salts have been employed, either previously prepared, or contemporaneously produced in the process, by a deflagration of tartar and nitre. By this means, the sulphur was indeed absorbed; but the hepar sulphuris, formed by the union of the sulphur and alkali, immediately dissolved the regulus, so that very little, sometimes none at all, was to be obtained distinct from the scoria. Metals are found to answer better than alkaline salts, but the regulus is seldom or never free from a mixture of the metal employed. The way of obtaining a very pure regulus, and in great quantity, is to calcine the antimony, in order to dissolve its sulphur; then to mix the calx with inflammable matters, such as oil, soft soap, &c. which are capable of restoring the principle of inflammability to it. This method was invented by Kunckel. Another, but more expensive way of procuring a large yield of very pure regulus, is, by digesting antimony in aqua regis, which dissolves the reguline part, leaving the sulphur untouched, precipitating the solution, and afterwards reviving the precipitate by melting it with inflammable matters.

There are considerable differences observed in the regulus of antimony, according to the different substances made use of to absorb the sulphur. When prepared by the common methods, it is found to be very difficultly amalgamated with mercury; but Mr Pott has discovered, that a regulus prepared with two or five parts of iron, four of antimony, and one of chalk, readily unites with mercury into a hard amalgam, by bare trituration with water. Marble and quicklime succeed equally well with chalk; but clay, gypsum, or other earths, have no effect.

One earthy substance, found in lead-mines, and commonly called cawk, has a very remarkable effect upon antimony. This is found in whitish, moderately compact, and ponderous masses; it is commonly supposed galls with a spar; but differs from bodies of this kind, in not being acted upon by acids (see no. 1068). If a lump of cawk, of an ounce or two, be thrown red hot into 16 ounces of melted antimony, the fusion continued about two minutes, and the fluid matter poured off, "you will have 15 ounces like polished steel, and as the most refined quicksilver." Phil. Trans. no. 110. Dr Lewis mentions his having repeated this experiment several times with success; but having once varied it by mixing the cawk and antimony together at the first, a part of the antimony was converted into a very dark black vitreous matter, and part seemed to have suffered little change; on the surface of the mass some yellow flowers appeared.

Regulus of antimony enters into the compositions for metallic speculums for telescopes, and for printing-types. It is also the basis of number of medicinal preparations; but many of these, which were formerly much esteemed, are found to be either inert, uncertain, or dangerous in their operation. When taken in substance, it is emetic and purgative, but uncertain in its operation; because it only acts in proportion to the quantity of solvent matter it meets with in the stomach; and if it meets with nothing capable of acting upon it there, the regulus will be quite inactive. For these reasons, the only two preparations of antimony now retained, at least by skilful practitioners, are the infusion of glaigs of antimony in wine and emetic tartar. For making the glaigs of antimony we have the following process. "Take a pound of antimony; reduce it to fine powder, and set it over a gentle fire; timony. calcine it in an unglazed earthen pan, till it comes to be of an ash colour, and cease to fume: you must keep it continually stirring; and if it should run into lumps, you must powder them again, and then proceed to finish the calcination. When that is done, put the calcined antimony into a crucible; set it upon a tile in a wind-furnace; put a thin tile on the top; and cover it all over with coals. When it is brought into fusion, keep it so in a strong fire for an hour: then put into it an iron rod; and when the melted antimony, which adheres to it, is transparent, pour it upon a smooth, hot, marble; and when it is cold, put it up for use. This is vitrum antimonii, or fibium."

This preparation is more violent in its effects than the pure regulus itself; because it contains less phlogiston, consequently is similar to a regulus partially calcined, and so more soluble. Hence it is the most proper for infusion in wine, or for making the tartar emetic. It is obviously, however, liable to great uncertainties in point of strength; for as the antimony is more or less strongly calcined, the glaigs will turn out stronger or weaker in its operation, and consequently all the preparations of it must be liable to much uncertainty. This uncertainty is very apparent in the strength of different parcels of emetic tartar; accordingly Mr Geoffroy found by examination of different emetic tartars, that an ounce of the weakest contain- Regulus of ed from 30 to 90 grains of regulus; an ounce of moderate strength contained about 108 grains; and an ounce of the strongest kind contained 154 grains. For these reasons, the author of the Chemical Dictionary recommends the pulvis algarothi as the most proper material for making emetic tartar; being perfectly soluble, and always of an equal degree of strength. Emetic tartar, as he justly observes, ought to be a metallic salt composed of cream of tartar saturated with the regulus of antimony; and M. Beaumé has shown such a saturation to be possible, and that the neutral salt crystallizes in the form of pyramids. They are transparent while moist; but by exposure to a dry air, they lose the water of their crystallization, and become opaque. The preparation of this salt, according to M. Baumé, consists in mixing together equal parts of cream of tartar, and levigated glaas of antimony; these are to be thrown gradually into boiling water; and the boiling continued till there is no longer any effervescence, and the acid is entirely saturated. The liquor is to be filtered; and upon the filter is observed a certain quantity of sulphureous matter, along with some undissolved parts of the glaas of antimony. When the filtered liquor is cooled, fine crystals will be formed in it, which are a soluble tartar perfectly saturated with glaas of antimony. He observes, that the dissolution is soon over if the glaas is well levigated, but requires a long time if it is only grossly pounded.

The trouble of levigating glaas of antimony, as well as the uncertainty of dissolving it, would render pulvis algaroth much preferable, were it not on account of its price; which would be a temptation to those in use to prepare medicines, to substitute a cheaper antimonial preparation in its place. This objection, however, is now in a great measure removed by Mr Scheele; who demonstrated that the pulvis algarothi is no other than regulus of antimony half calcined by the deplogisticated marine acid in the corrosive sublimate made use of for preparing the antimonial caustic. If therefore we can fall upon any other method of deplogisticating the regulus, we shall then be able to combine the marine acid with it; and by separating them afterwards, may have the powder of algaroth as good as from the butter of antimony itself. One of the methods of deplogisticating the regulus is by nitre. Our author therefore gives the following receipt for the powder in question.

"Take of powdered crude antimony one pound; powdered nitre, one pound and an half; which, after being well dried and mixed, are to be detonated in an iron mortar. The hepar obtained in this manner is to be powdered, and a pound of it to be put into a glaas vessel, on which first a mixture of three pounds of water and 15 ounces of vitriolic acid is to be poured, and afterwards 15 ounces of powdered common salt are to be added; the glaas vessel is then to be put in a sand bath, and kept in digestion for 12 hours, during which period the mass is to be constantly stirred. The solution, when cool, is to be strained through linen. On the residuum one third of the above menstruum is to be poured, and the mixture digested and strained. From this solution, when it is diluted with boiling water, the pulvis algarothi precipitates, which is to be well edulcorated and dried."

As regulus of antimony, like other metallic substances, is soluble in liver of sulphur, it happens, that, on boiling antimony in an alkaline ley, the salt, uniting with the sulphur contained in that mineral, forms an hepatic sulphur, which dissolves some of the regulus part. If the liquor is filtered, and saturated with an acid, antimony and the regulus and sulphur will fall together in form of a yellowish or reddish powder, called golden sulphur of antimony. If the ley is suffered to cool, a like precipitation of a red powder happens. This last is called kermes mineral.

Nitre deflagrates violently with antimony, consuming not only its sulphureous part, but also the phlogiston of the regulus; and thus reduces the whole to an inert calx, called antimonium diaphoreticum. If equal parts of nitre and antimony are deflagrated together, the sulphureous part is consumed, as well as part of the inflammable principle of the regulus. The metallic part melts, and forms a semivitreous mass, of a reddish colour, called crocus metallorum, or liver of antimony. It is a violent emetic, and was formerly used tallow for making infusions in wine similar to those of glaas of antimony; but is now disused on account of its uncertainty in strength. It is still used by the farriers; but the substance sold for it is prepared with a far less proportion of nitre; and sometimes even without any alkaline salt being added to absorb part of the antimonial sulphur. This crocus is of a dull red colour; and, when powdered, assumes a dark purple.

§ II. ARSENIC.

This substance, in its natural state, has no appearance of a metal, but much more resembles a salt, which, as has been already observed, it really is when deprived of its phlogiston. When united to a certain quantity Arsenic of phlogiston, it assumes a metallic appearance; and found naturally in this state it is found, as Mr Bergman informs us, a metallic parts; particularly at Altatia in the mines called St Marieux. The masses in which it is found are frequently shapeless, friable, and powdery; but sometimes compact, and divided into thick convex lamellae, with a needle-formed or micaceous surface; it takes a polish, but soon loses it again in the air. When fresh broken, it appears composed of small needle-like grains of a leaden colour, soon becoming yellow, and by degrees blackish; exceeding copper in hardness, though as brittle as antimony.

Regulus of arsenic, whether found naturally or prepared by art, very readily parts with as much of its arsenic calx phlogiston as is sufficient to make it fly off in a white smoke; but this still retains a very considerable quantity of phlogistic matter, as is evident from its producing white kind. nitrous air by the affusion of nitrous acid, and from the experiments already related of the preparation of the acid of arsenic. This calx indeed is the form in which arsenic is most commonly met with. It is less volatile than the regulus; and by sublimation in a glaas vessel assumes an opaque crystalline appearance from becoming white on the surface; but that which crystalizes in the bowels of the earth does not appear to be subject to any such change.

White arsenic, though a true metallic calx, may be mixed in fusion with the same metals which will unite feric may with the regulus. This seems contrary to the general rule of other calces, which cannot be united with any metal. metal in its metalline state; but it must be remembered, that by this operation the arsenical calx is reduced to a regulus by the phlogiston of the metal: whence, in all fusions of this kind, some scoria rise to the top, consisting of the calcined metal and part of the white arsenic.

Eight parts of distilled water dissolve, by means of moderate heat, one part of calcined arsenic, and by boiling may be made to take up 15. The solution changes syrup of violet green, but the tincture of turnsole red. It is not changed by neutral salts, but slowly precipitates the solutions of metals, the arsenic united to the metalline calx falling to the bottom.

"It may be asked (says Mr Bergman), whether the whole of the arsenic, or only the arsenical acid, unites with the metallic calx, yielding the phlogiston to the menstruum of the other metal?" Certainly such a mutual commutation of principles does not appear improbable, if we consider only those cases in which the menstruum is vitriolic or nitrous acid; but as iron, for example, united with marine acid (which does not attract the phlogiston of white arsenic), as well as when it is joined to the nitrous acid, is precipitated, it would appear that the whole of the arsenic is united, at least in certain cases, to the metallic calces.

One part of arsenic is dissolved by 70 or 80 of boiling spirit of wine.

Arsenic dissolves partially in concentrated vitriolic acid, but concretes in the form of crystalline grains on cooling. These dissolve in water with much greater difficulty than the arsenic itself. On the blow-pipe they emit a white smoke, but form into a globule by fusion, which at first bubbles, but soon grows quiet, and is but slowly consumed even in a white heat. This fixity is occasioned by the acid carrying off the phlogiston of the arsenic, and thus leaving a greater proportion of its peculiar acid than what it naturally contains; and therefore the more frequently the operation is repeated, the more fixed the arsenic becomes, though it is scarce possible to dissipate the arsenical phlogiston as perfectly with this acid as with the nitrous; the effects of which have been already particularly mentioned.

The marine acid, which naturally contains phlogiston, dissolves about one-third of its weight of arsenic, a great part of which separates spontaneously on cooling in a state of saturation with the acid. This salt, which may be had in a crystalline form, is much more volatile than the former, readily subliming in a close vessel with a moderate heat; but is soluble with difficulty in boiling water. It is of a fine yellow colour, and scarcely differs from butter of arsenic, except in its degree of concentration. The nature of marine acid prevents it from disengaging the arsenical acid from the phlogiston of the semimetal, as will easily appear from what has been said concerning that acid. The arsenical acid, however, is easily made to appear by the addition of that of nitre, as will be understood from the directions given by Mr Scheele for the preparation of the acid of arsenic.

Arsenic is not precipitated from its solution in vitriolic and nitrous acids by the phlogisticated alkali, which yet very readily precipitates all other metals except from marine acid. From the marine acid, however, it is precipitated by its means of a white colour; but unless the solution be very acid, the addition of mere water will throw down a precipitate of the same colour.

Dephlogisticated marine acid deprives arsenic of its inflammable principle; so that in the distilling vessel we find water, acid of arsenic, and marine acid, regenerated.

Arsenic is dissolved by its own acid, and forms crystalline grains with it as well as with that of fluor and borax. Saccharine acid dissolves it likewise, and with other forms prismatic crystals; and a similar salt is also acids formed by the acid of tartar. Vinegar, and the acids of vinegar and phosphorus, form with it crystalline grains, which are scarcely soluble in water.

Solutions of fixed alkali dissolve arsenic; and, Liver of when loaded with it, form a brown tenacious mass, arsenic, called liver of arsenic. The arsenic is partly precipitated by mineral acids, though part of it gradually loses its phlogiston, and adheres more tenaciously. Solution made with volatile alkali seems to effect this decomposition more readily, as no precipitation is made by acids. Limpid solution of saline hepcur, dropped into a solution of white arsenic, floats upon the surface in form of a grey stratum, which at length disturbs the whole liquor.

By the affluence of heat solutions of arsenic attack some of the metals, particularly copper, iron, and zinc; metals, the solutions of the two last yielding crystals by evaporation. No alteration is made on these compounds by alkaline salts or by acids: volatile alkali does not discover the copper by changing the colour of the solution blue; nor does the phlogisticated alkali throw down any blue precipitate from the solution of iron. The reason of this is the superabundance of phlogiston in the solutions; for the arsenical acid takes up all metals: when united with copper, it shows a blue colour with volatile alkali; and when united with iron, it lets fall a Prussian blue in the usual way; but the quantity of phlogiston which converts the acid into white arsenic, prevents the appearance of these phenomena when the latter is made use of.

Arsenic, either in its calcined or reguline state, may unite easily with sulphur; in which case it appears, by fulminating of a red or yellow colour, according to the quantity of sulphur with which it is united. These compounds are spontaneously produced by nature; both of them sometimes pellucid and crystalline; with this difference, however, that the yellow seems to affect a lamellated, and the red a crystalline, form. These are called red and yellow orpiment, or realgar and orpiment; the specific gravity of realgar being about 3.225; of orpiment, 5.315. Both of these sublime totally with a moderate heat, unless when they happen to be mixed with other substances. They readily unite with those metals which form an union with the arsenic and sulphur of which they are composed. Silver mineralized by fusion with orpiment, forms a substance similar to what is called the red ore of that metal. Iron, in conjunction with orpiment, assumes a white, polished, and metallic appearance, similar to that of the white or arsenical pyrites; and by various combinations of these substances with metals of different kinds, many of the natural metalline ores may be produced.

Nitre, when treated with mineralized arsenic, decomposes trrous acid. tonates partly with the sulphur, and partly with the phlogiston of the arsenic; the alkaline basis of the salt either forming sal polychrest with the acid of the sulphur, or uniting with the alkali, and forming the neutral arsenical salt. By the addition of fixed alkali in proper quantity, either to orpiment or realgar, and then exposing the mixture to a subliming heat, nitre retains the sulphur, but lets go the greatest part of the arsenic; the hepatic mals, however, retains a small quantity of the latter; and if there is much alkali, scarce any of the arsenic arises.

On distilling orpiment with twice or thrice its quantity of corrosive sublimate, two liquids arise which refuse to unite; and at length, on augmenting the heat, a cinnabar arises. A butter of arsenic is found at the bottom of the receiver, of a ferruginous brown colour, but pellucid; in the open air it first sends forth a copious fume of a white colour, and then gradually attracts the moisture of the atmosphere, by which it is precipitated. It is remarkable that it unites so slowly with marine acid, that they seem to repel one another; nor can they be made to unite beyond a certain degree. By the diffusion of distilled water, a white powder will be precipitated, which, though ever so well washed, retains some acidity; for a portion of butter of antimony is produced by distillation, as is likewise true of the pulvis algaroth. The smoke has a peculiar penetrating smell, somewhat similar to that of phlogisticated vitriolic acid, and lets fall white flowers. The liquor which swims above, and which, by chemical authors, has been compared to oil, is yellowish and pellucid, separating a white arsenical powder by the addition of water and spirit of wine. It is not affected by the stronger acids; but effervesces, and lets fall a precipitate, with alkalies. On keeping it with a cucurbit with a long neck untopped, white flowers gradually concrete round the orifice, which are lax, and sometimes approaching to a crystalline form. And lastly, by spontaneous evaporation, pellucid crystals appear at the bottom of the liquor, which are soluble in water with great difficulty; but when dissolved, precipitate silver from nitrous acid, and let fall some arsenic on the addition of an alkali. When put into lime water, a cloud slowly surrounds them; on being exposed to the fire, they totally sublime without any arsenical smell, without decrepitation, or losing their transparency; but if ignited phlogistic matter comes in contact with them, the arsenical smell instantly appears. No traces of mercury are to be found in this liquor by treating it either with alkali or copper; not the slightest precipitation is made by it on being dropped into a solution of terra pendecra in the marine acid: from all which it appears, that this liquor is only a very dilute butter of arsenic, containing less of the mercury on account of the quantity of water it has. The butter contains the acid in its most concentrated state, and is therefore loaded with a larger quantity of arsenic: the former liquor will therefore be obtained in much larger quantity, by setting the mixture of corrosive sublimate and arsenic to stand a night in a cellar, or moistened with water, before it be subjected to distillation. As the common marine acid can dissolve only a determined quantity of the butter, it naturally follows, that what remains after complete saturation should totally refuse to mix. The acid, however, when too much diluted, precipitates the butter; but in proportion to its strength it dissolves a greater quantity.

Arsenic mineralized by sulphur is not dissolved by water, but is affected by the different acids, according to the particular circumstances of each. Nitrous acid and aqua-regia act most powerfully; the former soon destroys the red colour of the realgar, and converts it into yellow orpiment; its primary action being to calcine the arsenic, without affecting the yellowness of the sulphur. It makes no change on the colour of orpiment. Aqua-regia, by long digestion, takes up the arsenic, and leaves the sulphur at the bottom; and hence we may find out the proportions of the two ingredients. Some dexterity, however, is necessary in performing this operation with accuracy; for if, on the one hand, the menstruum be too weak, part of the arsenic will remain undissolved; and if, on the other, it be too strong, part of the sulphur will be decomposed; for strong nitrous acid is capable of decomposing sulphur by long digestion, having a greater attraction for phlogiston than the vitriolic acid itself. The colour of the residuum ought to be grey; for as long as any yellow particles remain, it is a sign that some of the arsenic also remains. If any iron be present in the compound, it is all dissolved, by reason of the superior attraction of the acid for it, before any of the arsenic is taken up, unless it shall have been calcined either by the access of air and heat employed in the operation, or by the too great power of the menstruum.

The pure regulus of arsenic may be obtained artificially from white arsenic, either by sublimation with oil, black flux, or other phlogistic materials; or by melting it with double its weight of soap and potashes; or lastly, by precipitation by means of some other metal, from orpiment or sandarack melted with sulphur and fixed alkali. By the first of these methods it is obtained in a crystalline form, octahedral, pyramidal, or even prismatic. Mr Bergman mentions a natural regulus of arsenic, named mspickel, which along with some sulphur contains a large quantity of iron united with the regulus into a metallic compound; but tho' regulus of the iron sometimes amounts to $\frac{1}{4}$ or even $\frac{2}{3}$ of the arsenic whole, it nevertheless remains untouched by the magnet. When ignited, it sends forth an arsenical smell, and soon becomes obedient to the magnet, even though the operation be performed on a tile without any additional phlogiston; it melts easily in an open fire, and in close vessels the greater part of the regulus sublimes, leaving the iron at the bottom.

The pure regulus of arsenic is vastly more volatile than any other metal, and therefore cannot be melted. It begins to send forth a visible smoke in $180^\circ$ of the Swedish thermometer, and is capable of inflammation; but in order to inflame it, it must be thrown into a vessel previously heated to a sufficient degree, otherwise it will be sublimed. The flame is of an obscure whitish blue, diffusing a white smoke and garlic smell. In close vessels it retains its metallic form, and may be sublimed of any figure we please.

Regulus of arsenic unites with many of the metals, but destroys the malleability of those with which it enters into fusion. It renders those more easy of fusion which are melted with difficulty by themselves; but tin, the most easily fusible of all the metals, becomes... Arsenic comes more refractory by being united with arsenic. This metal acquires a permanent and shining whiteness by its union with regulus of arsenic, and is able to retain half its own weight of the arsenical metal. The other white metals, become grey by fusion with this semifinal, platina only excepted. Gold fused in a close vessel with regulus of arsenic, scarcely takes up $\frac{1}{35}$ of its weight; silver $\frac{1}{4}$; lead $\frac{1}{6}$; copper $\frac{1}{8}$; and iron more than its own weight. The magnetic property of this last metal is destroyed by a large quantity of regulus, though the exact proportion which destroys it can scarcely be determined, as some of the iron is always taken up by the scoria; but according to Mr Bergman, less than an equal quantity is certainly sufficient. Bismuth retains $\frac{1}{75}$ of its weight; zinc $\frac{1}{7}$; regulus of antimony $\frac{1}{2}$; and manganese an equal quantity. Nickel and regulus of cobalt take up a large quantity; but how much cannot be determined, as it is next to impossible to procure any of those metals in a state of perfect purity. In a sufficient degree of heat, and by a trituration of several hours, regulus of arsenic takes up about $\frac{1}{5}$ of its own weight of mercury, forming an amalgam of a grey colour.

Regulus of arsenic, by reason of its volatility, may be expelled from all the metals with which it is united; but, in flying off, it generally carries along with it some of the metal with which it is united, gold and silver not excepted, if the degree of heat be great and very suddenly applied. Platina, however, perfectly resists the volatilization; and, by reason of its refractory nature, even retains a portion of the arsenic.

This semifinal cannot be united by fusion with alkaline salts until the phlogiston is considerably diminished, and the regulus approaches to the nature of pure arsenical acid. By adding regulus thereto or nitre in fusion, a detonation ensues, the phlogiston of the former is totally destroyed, and the acid uniting with the alkali of the nitre forms a neutral arsenical salt, similar to that made with white arsenic and nitre. By distillation with dry acid of arsenic, the regulus sublimes before it can be acted upon by the acid; but when thrown into the acid in fusion, soon takes fire, and sends forth a white smoke; for the acid, being in this instance deprived of its phlogiston, separates that principle from the regulus, and unites with it in such quantity as to regenerate white arsenic; while, on the other hand, the regulus, by this operation, is so far deprived of its phlogiston as to appear in the form of a calx. By distillation with corrosive sublimate, a smoking bitter, and finally quantity of mercurius dulcis and running mercury, are procured; which happens in consequence of a double elective attraction; the regulus of arsenic yielding its phlogiston to the base of the corrosive sublimate, which being thus readily calcined, reduces the former to perfect mercury, while the marine acid takes up the calx of arsenic. The regulus of arsenic readily unites with sulphur, and forms the same red and yellow compounds that have already been mentioned when speaking of white arsenic; it is soluble in hepar sulphuris, but may be precipitated by every other metal which can unite with the hepar.

Regulus of arsenic is not affected by the vitriolic acid, unless when concentrated and assisted by heat. The inflammable part of the regulus which phlogisticates the acid flies off, so that the remainder assumes the nature of white arsenic, and exhibits the same properties with menstrua as any other metallic calx: the same holds good with nitrous acid, except that it attracts the phlogiston more vehemently. Marine acid has little or no effect except when boiling.

Regulus of arsenic precipitates certain metals dissolved in acids, such as gold and platina diffused in aqua-regia, as well as silver and mercury in vitriolic and nitrous acids. Silver generally appears in beautiful polished spiculae, like the arbor Diane; but if the arsenic be suffered to stand long in the nitrous solution but little diluted, the silver spicule are again dissolved, the arsenic in the mean time being dephlogisticated. Solutions of bismuth and antimony are scarcely rendered turbid. Iron may be separated from regulus of arsenic by digestion with marine acid, or with aqua regia; neither of which will touch the arsenic, as long as any iron remains; but in order to succeed in this operation, subtile pulverisation is necessary as well as a just quantity and strength of the menstruum. Heat must also be carefully avoided. The regulus is also dissolved by hepar sulphuris and by fat oils, the latter forming with it a black mass like plaster.

§ 12. Cobalt.

Regulus of cobalt, or more properly pure cobalt itself (what we have under the name of cobalt being only a calx of the regulus), is a semifinal of a reddish white colour, clove-grained, so as to be easily reducible to powder, about 7.7 of specific gravity, and forming itself into masses of needle-like texture, placed upon one another. It is seldom or never found native, but almost always calcined and united with arsenic, the arsenical acid, sulphur, iron, &c. The zaffre used in commerce is an impure and grey calx of cobalt. When calx of cobalt mixed with three times its weight of pulverized flints, balt, and exposed to a strong fire, it melts into glas of a dark blue colour, called fumal, used in tinging other glasses, and in painting. With three times its weight of black flux, a small quantity of tallow and marine produced, it affords the semifinal known by the improper name of regulus of cobalt; but the reduction is very difficult. For this purpose a large quantity of flux must be made use of, and the crucible kept a considerable distance in a white-red heat, that the matter may become very fluid, and that the scoria may be completely fused into a blue glass; at which period the cobalt sinks in the form of a button to the bottom.

Cobalt melts in a strong red heat, is very fixed in the fire, and it is uncertain whether it can be volatilized in clove vessels. When suffered to cool slowly, when exposed to the other, and united in bundles, having a considerable resemblance to masses of basaltes separated from each other; in order to succeed in this crystallization, however, the cobalt must be melted in a crucible till it begins to boil, and, when the surface of the metal becomes fixed on being withdrawn from the fire, the vessel is then to be inclined; that which still remains fluid runs out, and the portion adhering to the lumps formed by the cooling of the surface is found covered with crystals.

This semifinal, exposed to the atmosphere, becomes covered with a dull pellicle, and undergoes a spontaneous calcination; but it may easily be calcined in the air. in any quantity by exposing it in powder in a shallow vessel, under the muffle of a cupelling furnace, and stirring it now and then to expose fresh surfaces to the air. After being kept red hot for some time, this powder loses its splendor, increases in weight, and becomes black; the calx being convertible, by a most violent heat, into a blue glass. By fusion it combines with vitrifiable earths, forming with them a beautiful blue glass extremely fixed in the fire; whence it is of the greatest use in enamel-painting, porcelain-painting, &c. The action of terra ponderosa, magnesia, and lime, on cobalt, is not known. Alkalies manifestly alter it; but what respect is not known.

Cobalt dissolves in concentrated vitriolic acid, when assisted by a boiling heat; the acid evaporating almost entirely in the form of sulphurous gas. The residue is then to be washed; a portion of it dissolves in the water, and communicates a greenish colour to it when warm, which changes to a rose colour when cold. M. Beaumé affirms, that by sufficiently evaporating the vitriolic solution of cobalt, two sorts of crystals are obtained; one white, small, and cubical; the other, greenish, quadrangular, six lines in length, and four in breadth. These last he only considers as the true vitriol of cobalt; the former being produced by certain foreign matters united to it. The crystals most commonly obtained have the form of small needles, and may be decomposed by fire, leaving a calx of cobalt not reducible by itself. They may likewise be decomposed by all the alkalies, by terra ponderosa, magnesia, and lime. According to Fourcroy, 100 grains of cobalt, dissolved in the vitriolic acid, afford, by precipitation with pure mineral alkali, 140 grains of precipitate; by the same alkali aerated, 150 grains. Diluted vitriolic acid acts on zaffre, and dissolves a part, with which it forms the salt already described.

Nitrous acid acts upon the semifemal with that violence which is its general characteristic; and the solution, when nearly saturated, appears either of a rosy brown or bright green colour. By strong evaporation it yields a salt in small needles joined together; which is very deliquescent, boils upon hot coals without detonation, and leaves a calx of a deep red colour. It is decomposed by the same substances as the former, and by excess of alkali the precipitate disappears.

Muriatic acid, assisted by heat, dissolves cobalt in part, but has no effect upon it in the cold. It acts more strongly on zaffre, forming a solution of a reddish brown, which becomes green by being heated. By evaporation it yields a very deliquescent salt in small needles, which becomes green when heated, and is soon after decomposed. Aqua-regia dissolves the metal rather more easily than the marine acid, but less so than the nitrous. The solution has been long known as a sympathetic ink.

Cobalt is not dissolved directly by the acid of borax; but when a solution of this salt is mixed with a solution of cobalt in any of the mineral acids, a double decomposition takes place; the alkaline basis of the borax uniting with the acid which held the cobalt in solution; and the calx, combining with the sedative salt, falls to the bottom in form of an insoluble precipitate.

This semifemal is calcined by being heated to ignition with nitre. One part of cobalt, and two or three of dry nitre, well powdered and mixed, when thrown into a red-hot crucible, produce small scintillations; a portion of the cobalt being converted into a calx of a red colour, more or less deep, and sometimes of a green. Sal ammoniac is not decomposed, by reason of the little attraction there is between the metal and ammoniac muriatic acid. M. Bucquet, who made the experiment with great care, could not obtain a particle of With volatile alkali. Sulphur does not unite with it but very difficultly, and the combination is promoted by liver of sulphur. Thus a kind of artificial ore may be produced, the grain of which will be finer or closer, and its colour whiter or yellower, in proportion to the quantity of sulphur in the mixture. M. Beaumé observes, that this compound cannot be decomposed by acids, and that fire cannot destroy all the sulphur.

§ 13. Nickel.

This was first discovered to be a semifemal of a peculiar kind by Cronstedt, in the years 1751 and 1754, by Mr who procured it in the form of regulus from its ore, but Cronstedt without being able to reduce it to a sufficient degree of purity; which indeed has not yet been done by any chemist. M. Bergman has laboured most in this way, though even he has not reduced it to the purity of other metallic substances. His experiments were made with some regulus made by M. Cronstedt, and whose specific gravity was to that of water exactly as 7.421 to 1. His attempts to purify it were made,

I. By Calcination and Scorification.

Nine ounces of powdered nickel were exposed for six hours, in several portions, to a most violent heat, calcination under the dome of an assay furnace. Thus the arsenic was first dissipated with a fetid smell, after which the odour of sulphur became perceptible; after this a white smoke arose without any smell of garlic, and which, according to our author, arose probably from the more dephtilicated part of the arsenic which now began to sublimate. The heaps (we suppose) after the matter had been poured out of the dishes, and yet retaining a great deal of heat), when hot, began to swell, and green vegetations arose from all the surface, resembling some kinds of moss, or the filiform lichen; a ferruginous ash-coloured powder remained at bottom; and 0.13 of the whole were dissipated during the operation. Half an ounce of this calx, fused in a forge for four minutes, along with three times its weight of black flux, yielded a regulus reticulated on the surface; the area of a hexangular figure, with very slender striæ, diverging from a centre, full of little tubercles; it weighed 0.73 of half an ounce; was obedient to the magnet; and, when scorified with borax, left a blackish glass.

By a second roasting the regulus again emitted a garlic smell; afterwards a visible fume without any smell, with vegetations as before. The roasted powder, reduced with black flux as before, still emitted a smell of arsenic; but, on repeating the fusion with the calx and borax, nothing but some obscure signs of cobalt appeared. A third calcination seemed to have much dissipated the arsenic, as it now emitted but little of that kind of smell; the vegetations were also gone; and the matter had rather a ferruginous than a green Nickel. green colour. Nearly the same phenomenon appeared after reduction in a fourth operation.

On performing the reduction with lime and borax, the regulus, when first melted, lost much of its ferruginous matter, which adhered to the black scoria; it soon acquired an hyacinthine colour, without any remarkable mixture of cobalt, was little obedient to the magnet, and its specific gravity was somewhat diminished, being now only 7.0823.

By a fifth calcination, gradually adding a quantity of powdered charcoal while the matter continued red hot, a prodigious quantity of arsenic, imperceptible before, flew off in the form of vapour; the arsenical acid being thus furnished with as much phlogiston as was necessary to make it rise in fume. The regulus was treated in this manner until no more arsenical smoke could be perceived; it was now of a lamellated and tenacious texture when reduced, but still diffused the arsenical odour on being removed from the fire. The roasting was therefore repeated a sixth time, and continued for ten hours; the addition of powdered charcoal continued to dilute the arsenic in invisible vapours, which yet were perceptible by the smell; the colour of the metallic calx was obscurely ferruginous, with a mixture of green scarcely visible. On reducing the regulus with equal parts of white flux, lime, and borax, a semiductile regulus was obtained, highly magnetic, and soluble in nitrous acid, to which it communicated a deep green colour; a blackish mass remained, which afterwards became white, and when laid on a burning coal, flies off without any remarkable arsenical smell. The regulus being then five times fused with lime and borax, the scoria resembled the hyacinth in colour, and the metallic part was surrounded with a green calx. The regulus, as before, was magnetic and semi-malleable. Lastly, it was exposed for 14 hours to a very strong heat; when the powdered charcoal was added by degrees without any dissipation of arsenic or loss of weight; the colour of the roasted powder was ferruginous, with a very slight tinge of green. On reduction, a very small globule, still magnetic, was found among the scoriae.

II. By Sulphur.

Eight hundred parts of Cronstedt's regulus of nickel, fused with sulphur and a small quantity of borax, yielded a mineralized mass of a reddish yellow, whose weight amounted to 1700. On exposing one half of this to the fire, it began to grow black; on which the heat was augmented until vegetations appeared; the remaining calx weighed 652. Melting this part with borax, and the other which had not been exposed to the fire, a sulphurated regulus of a whitish yellow colour was obtained, weighing 1102. The same regulus, calcined for four hours, was first covered with vegetations, and then, on the addition of powdered charcoal, diffused an arsenical odour; the metallic calx was green, and weighed 1038. A whitish yellow regulus was obtained, semiductile, highly magnetic, and extremely refractory, weighing 594. By fusion with sulphur a second time, it weighed 816; one half of which roasted to greenness, united by means of fire to the other half still sulphurated, weighed 509, and was almost deprived of its magnetic quality. A calcination of four hours, during which phlogiston was added, diffused a considerable quantity of arsenic; the powder put on an ash-colour, somewhat greenish, was in weight 569; and by reduction yielded a regulus whose surface was red, and which, on breaking, appeared of a white ash-colour, very friable, and weighing 432; the specific gravity 7.173.

On mineralizing the regulus a third time with sulphur, adding charcoal as long as any vestige of arsenic remained, which required a violent calcination of 12 hours, the remaining powder was of an ash-green colour, and weighed 364; but the regulus obtained by means of a reduction effected by the most violent heat in a forge for three quarters of an hour, was so refractory, that it only adhered imperfectly to the scoria, which were of a distinct hyacinthine colour; nor could it be reduced to a globule by means of borax, though urged by the same vehemence of fire. The absolute gravity of this regulus was 180; its specific gravity 8.666. Its magnetic virtue was very remarkable; for it not only adhered strongly to the magnet, but to any other piece of iron; and the small pieces of it attracted one another. It had a considerable ductility, was of a whitish colour, mixed with a kind of glittering red; dissolved in volatile alkali, yielding a blue solution, and a green one in nitrous acid.

An hundred parts of the same regulus, beaten out into thin plates, were covered, by a calcination of four hours, with a crust apparently martial, having under it a green powder, and within it a nucleus consisting of reguline particles still unchanged; the weight being increased by 5. The friable matter, reduced to powder, put on a brownish-green colour; and after a calcination of four hours more, concreted at the bottom in form of a friable black crust, strongly magnetic, and weighing 100: No vestiges of arsenic were discovered by a succeeding operation, in which charcoal was added; nor was the magnetic power destroyed, but the weight was increased to 105, and the colour somewhat changed. By fusion for an hour with lime and borax, this powder yielded a regulus of an angular structure, red, semiductile, and altogether magnetic; the specific gravity being 8.875. The same globule, dissolved in aqua-regia, was precipitated by green vitriol, as if it had been loaded with gold; but the precipitate was readily soluble in nitrous acid. Most of the reguli showed no signs of precipitation with green vitriol.

III. With Hepar Sulphuris.

Fifty-eight parts of regulus of nickel, which had been sulphurated before, being fused with 1800 parts of saline hepar sulphuris, then dissolved in warm water, filtered through paper, and precipitated by an acid, yielded a powder, which, by calcination till the sulphur was driven off, appeared of an ash-colour, and weighed 35. The insoluble residuum, deprived of its sulphur by means of fire, was likewise of an ash-colour, and weighed 334. On reducing this regulus by means of the black flux, a friable regulus was obtained, which had a very weak magnetic property; but, on fusion with borax, this quality was augmented. On mixing and melting together equal parts of calx of nickel, gypsum, colophony, and white flux, a powdery, squamous, and reguline mass was produced; which, by fusion with borax, afforded a regulus possessing the properties... Nickel.

Properties of nickel, but not entirely destitute of cobalt, which obeyed the magnet, and did not part with its iron even after two solutions in the nitrous acid, and various reductions by fusion with borax; the sulphur was also retained with great obstinacy.

On dissolving regulus of nickel by fusion, in hepar sulphuris made with fixed alkali, adding a quantity of nitre sufficient only to destroy a small part of the hepar, the regulus which had been suspended by it was separated, and fell to the bottom. On examining this regulus, it appeared more pure, and generally deprived of cobalt, but still containing iron. In like manner nickel is always very distinctly precipitated by regulus of cobalt, as this latter is attracted more powerfully by the hepar sulphuris. When dissolved by fusion with hepar sulphuris, this semimetal may be precipitated by adding iron, copper, tin, or lead, and even by cobalt; the regulus obtained is indeed scarcely ever attracted by the magnet; but we are not from thence to conclude that it does not contain any iron; for when the heterogenous matters, which impede its action, are properly removed, it then acknowledges the power of the magnet very plainly.

IV. By Nitre.

One part of Cronstedt's regulus was added to twelve of nitre ignited in a crucible, and kept red-hot for about an hour. Some weak flashes appeared first; then a large quantity of arsenic was emitted; and, lastly, the sides were covered with a blue crust occasioned by the cobalt, a green matter remaining at bottom. This, fused again for an hour, with twelve parts of nitre, tinged the internal sides of the vessel of a green colour; and, lastly, a brownish green mass, much less in quantity than in the former operation, was left at the bottom. This green matter, treated in the same way for two hours a third time, left a grey scoria at the bottom, which yielded no regulus with black flux.

Another portion of the same regulus, treated in the same way with nitre, was dissolved, and became green; yet on being freed by ablation from the alkaline salt, it yielded no regulus with black flux, but only scoria of a hyacinthine colour mixed with blue, tinged nitrous acid of a green colour, concreting into a jelly, and on evaporation leaving a greenish calx behind.

Another portion of Cronstedt's regulus was kept some hours in the crucible with 16 parts of nitre; by which means all the arsenic was first separated; then the phlogisticated nitrous acid; and, lastly, the sides of the vessel were penetrated by a kind of green efflorescences. The mass, after being washed with water, was of a dilute green colour, and tinged borax of a greenish brown. A green powder was still yielded, after treating this in the same manner with 12 parts of nitre; and on reducing it with one-half black flux, one-eighth borax, and as much lime, a yellowish white regulus, both magnetic and malleable, was obtained, possessing all the properties of nickel. Its specific gravity was 9,000; the phlogistic ingredient was used in small quantity, that the iron might, if possible, enter the scoria.

It having appeared from this and some other experiments, that nitre was capable of discovering the smallest quantity of cobalt contained in nickel, the products of the former operations were now subjected to its action. The regulus produced by repeated scorification thus became a little blue; that dissolved in volatile alkali (to be afterwards particularly mentioned) discovered a considerable quantity of cobalt; nor was there any one which did not thus discover more or less of that ingredient by this trial.

V. By Sal Ammoniac.

A calx of nickel, so much freed from cobalt that it did not tinge borax in the leaf, mixed with twice its weight of sal ammoniac, yielded, by sublimation, with a strong red heat, two kinds of flowers; one, which rose higher than the other, was of an ash colour; the other white. The bottom of the glas was stained of a deep hyacinthine colour; the residuum was divided into two strata; the upper one yellow, scaly, and shining like mosaic gold. With borax it afforded an hyacinthine glas, but not regulus; and in a few days liquefied in the air, acquiring a green colour and the consistence of butter. The residuum showed the same properties with calx of nickel; and the green solution showed no vestiges of iron with galls, but became blue with volatile alkali; which was also the case with the flowers. The lower stratum contained a calx, blackish on the upper part, but of a ferruginous brown in the under, with a friable and scarcely magnetic regulus, of a reddish white. The blackish calx yielded an hyacinthine glas with borax. Part of this stratum sublimed with twice its quantity of sal ammoniac; and with the same degree of heat as before, yielded flowers of a very fine white, with a residuum of ferruginous brown, greenish on the upper part towards the sides of the vessel, the bottom being stained of an hyacinthine colour as before. Twenty parts of sal ammoniac being added to a part of the inferior stratum reduced, the whole was sublimed in a retort; a blackish powder remained, which became green by calcination, and of an hyacinthine colour by scorification, as did also the bottom of the containing vessel. The sublimation being twice repeated, using a double quantity of sal ammoniac each time, the calx became at length very green, dissolving with the same colour in the nitrous acid, and yielding by reduction a white, brittle, and very little magnetic regulus. In all these sublimations, it was observed, that the volatile alkali rose first; then sal ammoniac; and, lastly, a part of the marine acid was forced over by the violence of the heat.

VI. With Nitrous Acid.

Having obtained a salt by crystallization from nickel, dissolved in nitrous acid, part of this was calcined with antimony, charcoal dust in a proper vessel, and during the operation a large quantity of arsenic was dissipated; a grey, semifluidicile, and magnetic regulus being obtained after reduction. A brittle regulus was obtained after a second solution, precipitation, and reduction; but by a third operation it became again semifluidicile and magnetic. By repeating this process a fourth and fifth time, the quantity became so much diminished that it could no longer be tried. In all these solutions, a blackish residuum appeared; which, when suffered to remain in the acid, grew white by degrees; but when edulcorated and laid on a burning coal, exhaled a fulphurous smoke, and left a black powder soluble in the nitrous acid.

VII. By VII. By Volatile Alkali.

Four hundred and eighty-seven parts of a calx of nickel, produced by dissolving Cronstedt's regulus in nitrous acid, and precipitating the solution by a fixed alkali, being immersed for 24 hours in a quantity of volatile alkali, yielded a residuum of fifty, having a blackish green colour. The solution, which was blue, by filtration and infiltration yielded a powder of a light blue colour, weighing 282; which, reduced with black flux, produced a white, semiductile, and highly magnetic regulus, weighing 35, whose specific gravity was 7,000. The scoriae were of a light red; but when mixed with borax, put on a hyacinthine colour, and yielded a regulus weighing 30. The two reguli united together proved very refractory; so that the mass could not be melted by the blow-pipe, even with the addition of borax. It sent forth neither an arsenical nor sulphureous smell on the addition of charcoal-dust; but, on a succeeding reduction, yielded hyacinthine scoriae; and the remaining flocculi, dissolved in nitrous acid, affording a very green solution, which, on the addition of volatile alkali, yielded a powder of the same colour.

From 50 parts of the blackish green residuum, 13 of a clear white, brittle, squamous, and little magnetic regulus, were obtained, the specific gravity of which was 9,333. At the bottom of the vessel was found a scoria of an obscurely blue colour, with the upper part hyacinthine. It was easily fused; and tinged borax, first blue, then of a hyacinth colour, upon which it became more strongly magnetic. By the assistance of heat it dissolved in nitrous acid, forming a solution of a beautiful blue colour. A black powder at first floated in the liquor, but became white, and fell to the bottom. After calcination it was for the most part dissipated, with a sulphurous smell, on being exposed to the fire; a little brown-coloured mass, fusible in volatile alkali, remaining at bottom. This solution was precipitated by phlogisticated alkali, and a powder thrown down of the colour of calx of nickel, which soon grew blue with volatile alkali.

From all these experiments it appears, that nickel cannot be obtained in a state of purity by any means hitherto known. From every other substance, indeed, it may be separated, except iron; but this resists all the operations hitherto described, and cannot be diminished beyond certain limits. The magnet not only readily discovers its presence, but some portions of the regulus itself becomes magnetic; but the tenacity and difficulty of fusion, which increase the more in proportion to the number of operations, plainly show that there is no hope of separating the whole quantity, unless we suppose the regulus of nickel itself to be attracted by the magnet; and there is certainly a possibility that one other substance besides iron may be attracted by the magnet. The great difficulty, or rather impossibility, of obtaining it in a state of purity, naturally raises a suspicion of its not being a distinct semi-metal, but a mixture of others blended together; and on this subject our author agrees in opinion with those who suppose it to be a compound of other metals. Indeed, Mr Bergman is of opinion, that "nickel, cobalt, and manganese, are perhaps no other than modifications of iron." And in order to ascertain this, he made the following experiments.

1. Equal parts of copper, of the gravity of 9,3243, and iron of 8,3678, united by fusion with black flux, yielded a red mass, whose specific gravity was 8,5441; composed and which tinged nitrous acid first blue, then green, nickel afterwards yellow, and at last of an opaque brown, ficially.

2. Two parts of copper and one of iron had a specific gravity of 8,4634; the mixture yielding first a blue, and then a green solution.

3. Equal parts of copper and iron, of the specific gravities already mentioned, with another part of cobalt whose gravity was 8,1500, yielded a metal of the gravity of 8,0300, imparting a brown colour to the solution.

4. Two parts of arsenic of 4,000, added to one of copper and another of iron, gave a brittle metal of 8,0468, which formed a blue solution.

5. One part of copper, one of iron, two of cobalt, and two of white arsenic, gave a brittle regulus of 8,4186; the solution of which was brownish, and separated in part spontaneously.

6. One part of copper, one of iron, four of cobalt, and two of white arsenic, formed a mass of 8,5714. The solution was somewhat more red than the former; and a similar effect took place on repeating the experiment, only that the specific gravity of the metal was now 8,2941.

7. One part of iron and four of white arsenic formed a metal which dissolved with a yellow colour; and, on the addition of Prussian alkali, immediately let fall a blue sediment.

8. One part of copper, eight of iron, fifteen of white arsenic, and four of sulphur, united by fire, on the addition of black flux, yielded a mass which, though frequently calcined and reduced, produced nothing but brown or ferruginous calces. It acquired a greenness with nitrous acid, but on the addition of phlogisticated alkali deposited a Prussian blue.

9. One part of iron was dissolved in five of the nitrous acid, and likewise separated by one part of copper and one of the calcined ore of cobalt, in the same quantity of the same acid. The whole of the solution of iron was then mixed with five parts of the solution of copper, whence a green and saturated nickel colour was produced; which, however, on the addition of three parts of the solution of cobalt, became evidently obscured. The alkaline lixivium dropped into this threw down at first a ferruginous brown sediment, the solution still remaining green; afterwards all the blue was precipitated; by which at first all colour was destroyed, but afterwards a red appeared, occasioned by the cobalt dissolved in the alkaline salt. The sediment, when reduced, yielded a regulus similar to copper, and at the same time ductile, which tinged both glaas and nitrous acid of a blue colour. If a saturated solution of nickel be mixed with half its quantity of solution of cobalt, the green colour is much obscured; but four parts of the former, on the addition of three of the latter, put off all appearances of nickel. See the article Nickel.

§ 14. Of Platina.

The properties of this metal have not as yet been thoroughly investigated by chemists, and there is therefore very little of all fore some disagreement concerning them. Formerly metals, it was supposed to be inferior in specific gravity to gold; gold; but now is generally allowed to be superior in that respect by little less than a fourth part; being to water in the proportion of 23 to 1 when perfectly freed from all heterogeneous matters. Mr Bergman says that its colour is that of the purest silver. The very small globules of it are extremely malleable; but when many of these are collected together, they can scarcely be so perfectly fused as to preserve the same degree of malleability. They are not affected by the magnet in the least, nor can they be dissolved in any simple menstruum excepting dephlogisticated marine acid. As it is commonly met with, however, platina has the form of small grains, its plates of a bluish black, whose colour is intermediate betwixt those of silver and iron. These grains are mixed with many foreign substances, as particles of gold, mercury, and blackish ferruginous, sandy grains, which by the magnifier appear scorified. The grains themselves, when examined by a magnifying glass, appear sometimes regular, sometimes round and flat, like a kind of button. When beat on the anvil, most of them are flattened and appear ductile; some break in pieces, and on being narrowly examined appear to be hollow, and particles of iron and a white powder have been found within them: and to these we must attribute the attraction of platina by the magnet; since, as we have already observed, pure platina is not attracted by it.

Mr Bergman, who carefully examined this metal, dissolved it first in aqua-regia composed of the nitrous experiments on marine acid. The solution at first exhibits a yellow colour, but on approaching to saturation became red, and the redness increases as the liquor becomes more loaded with metal. Crystals are produced by evaporation of a deep red colour, generally in small angular and irregular grains, whose true shape cannot be discovered. Their appearance is sometimes opaque and sometimes pellucid. After these are once formed, they are extremely difficult of solution, requiring much more water than even gypsum itself for this purpose.—The solution is not precipitated by vegetable fixed alkali, nor does the latter affect the crystals, except very faintly by digestion with them in a caustic state. Aerated mineral alkali takes them up and grows yellow, but without depositing anything, though it decomposes them at last by evaporating to dryness.

On the addition of a small quantity of vegetable fixed alkali, either mild or caustic, small red crystals soluble in water, and sometimes of an octohedral figure, are deposited. They are decomposed with difficulty by the mineral alkali, but not at all by the vegetable. If a larger quantity of salt is added at first, an insoluble spongy matter of a yellow colour is precipitated. Crystaline particles of the same kind are thrown down by an alkali saturated either with the vitriolic, nitrous, marine, or acetic acids, though all the platina cannot thus be separated from the menstruum.

Aqua-regia, composed of nitrous acid and common salt, dissolved the metal with equal facility as the former; only the solution was more dilute, and a yellow powder floated on the surface, a larger quantity being found at the bottom. On adding vegetable fixed alkali to the clear solution, a copious yellow powder, soluble in a large quantity of water, was deposited. A powder of a similar kind, was precipitated, tho' more slowly, and more of a crystalline nature; but mineral alkali, though used in much larger quantity, did not make any alteration. The collected powder was yellow, and agreed in property with that separated spontaneously in a former experiment.

On repeating the experiment with nitre and depurated spirit of salt, instead of nitrous acid and sea-salt, the platina was dissolved into gold-coloured liquor, a fine and greenish coloured granulated matter falling to the bottom, and the finer part of the same rising to the top. After saturating the superfluous acid, a metallic calx, insoluble in water, was thrown down by the vegetable alkali. The green powder is soluble in water, and is of the same nature with the precipitate thrown down by the vegetable alkali.

Platina precipitated from aqua-regia by a sufficient quantity of mineral alkali, the precipitate washed and dissolved in marine acid, on the addition of vegetable alkali immediately lets fall a crystalline powder, as it does also with nitre and other salts, having the vegetable alkali for their basis. The case is the same with calx of the platina dissolved in vitriolic acid. Nitrous acid also cools in marine acid; distinct saline precipitate without the affluence of marine acid.—The above phenomena are likewise produced by the precipitate thrown down by the vegetable solution in alkali after the saline powder has been deposited.

From these experiments our author concludes, 1. That the precipitate which is first thrown down, on the addition of vegetable alkali to solutions of platina, is a saline substance, and different from the calx of the metal. 2. That this saline precipitate is composed of calcined platina, marine acid, and vegetable alkali. 3. By means of vitriolic acid, a precipitate analogous to this may be obtained, composed of calcined platina, vegetable alkali, and vitriolic acid. 4. The whole solution of platina cannot be precipitated by vegetable alkali in form of a triple salt; but after passing a certain limit, a metallic calx in the usual way is produced.

As it has been denied by Margraaf and Lewis that mineral alkali is capable of separating platina from its acid, our author was induced to attend particularly to this circumstance. Having therefore tried the composition with mineral alkali, he found that each drop excited a violent effervescence, and at last that a yellow spongy matter, affording a genuine calx of platina, was precipitated: this was more speedily effected by using the dry mineral alkali, which had fallen to powder of itself. To determine, however, the difference between the two alkalies in a more accurate manner, he divided a very acid solution of platina into two equal parts. To one of these he added small portions of the vegetable, and to the other an equal weight of pieces of mineral alkali, waiting five minutes after every addition, till the effervescence should fully cease. After the first addition, small crystals appeared; in the former partly on the surface, and partly in the bottom; but in the latter no precipitate could be observed until 56 times the quantity of vegetable much mineral alkali had been added. The difference, however, was even greater than what appears from this experiment; precipitate for the vegetable alkali was crystallized, and therefore platina as charged with the water necessary to its crystalline vegetable form. Platina form; whereas the mineral alkali was spontaneously calcined; and though, in equal quantities of these two alkalies, the purely alkaline parts are as 3 to 2, yet three parts of vegetable alkali saturated only 1.71 of this aqua-regia, while two of the mineral alkali took up about 2.6.

The volatile alkali first throws down this metal in a saline form; the grains sometimes distinctly octahedral. Their colour is red when that of the solution is fo, but yellow when the solution is more dilute. After saturating the superabundant acid, the same alkali precipitates the platina truly calcined. This precipitate is dissolved in water, though with difficulty, and may be reduced to more regular crystals by evaporation. These are dissolved by the mineral alkali; but hardly any signs of decomposition are to be observed, unless the yellow solution, evaporated to dryness, be again dissolved in water; for then the metallic calx rests at the bottom, and the solution is deprived of its yellow colour. The vegetable alkali has scarce any effect in this way; for, after repeated evaporation, the solution remains clear and yellow; but here probably the fixed alkali takes the place of the volatile; for in larger quantities, and especially when the caustic vegetable alkali is made use of, the mixture smells of volatile alkali.

The volatile alkali, saturated with any acid, precipitates the platina in the same manner as the vegetable alkali in combination with acids; but these neutral salts precipitate only a determined quantity of platina; for after their effect has ceased, the liquor lets fall a pure calx of platina on the addition of vegetable or volatile alkali.

The calx of platina precipitated by mineral alkali, and then dissolved in any simple acid, shows nearly the same phenomena with volatile alkali as with the vegetable alkali. "Whereas (says Mr Bergman) we may conclude, that platina dissolved in acids forms at first, both with the volatile and fixed vegetable alkali, a triple salt, difficult of solution, and which therefore almost always falls to the bottom unless the quantity of water be very large." Calcareous earth, whether aerated or caustic, produces the same phenomena as the mineral alkali, without any crystalline appearance.

Platina has been remarkable ever since its first discovery for being the most infusible substance in the world. Messrs Macquer and Beaumé kept it in the most violent heat of a glaiss-house furnace for several days without perceiving any other alteration than that its grains adhered slightly to each other; but the adhesion was so slight that they separated even by touching. In these experiments the colour of the platina became brilliant by a white heat, but acquired a dull grey colour after it had been heated for a long time. They observed also, that its weight was constantly increased; which undoubtedly arose from the calcination of the iron it contained. Dr Lewis, after various attempts to fuse platina, found himself unable to succeed even in a fire which vitrified bits of glaiss-house pots and Hessian crucibles. Messrs Macquer and Beaumé first melted this refractory metal with a large burning-glaiss, 22 inches diameter and 28 inches focus. The power of this speculum was almost incredible, and far exceeded what is related of the lens of Tchirnhausen or the mirror of Villette. Its general effects are related under the article Burning-Glas.

And as platina resisted this intense heat more than five times as long as the most infusible substances formerly known, it appears to require a fire as many times stronger to melt it. It has been found, however, capable not only of fusion but of vitrification by the electric fire; and that it may also be melted by fire ex-electric fire, cited by dephlogisticated air; but M. de Lisle was the first who was able to melt it with the heat of a common forge when exposed to the blast of a double bellows in a double crucible. Thus its real specific gravity began first to be known. It must be observed, however, that this fusion was not performed on common platina, but on such as had been dissolved in aqua-regia and precipitated by means of sal ammoniac. M. Morveau repeated the experiment, and from 72 grains of platina obtained a regulus weighing 50½; which seemed to have undergone a very imperfect fusion; for it did not adhere to the crucible or take its form, but seemed to be merely platina revived. Its specific gravity was also found to be no more than 10.45; but it was nearly as malleable as silver; and when it had been sufficiently hammered, its specific gravity was augmented to no less than 20.170, which is more than that of gold itself. M. Morveau found that he could melt the precipitate with different fluxes, such as a mixture of white glaiss, borax, and charcoal, and platina, a mixture of white glaiss and neutral arsenical salt; and that the regulus thus obtained was more completely fused, but was not malleable, and obeyed the magnet; but the regulus obtained without addition did not show this mark of containing iron. He also found, that by means of the above mentioned flux of white glaiss, borax, and charcoal, he could melt crude platina. Since that time the fusion of platina has been accomplished by various chemists, and with different fluxes; and in proportion to the degree of purity to which the metal has been reduced, its specific gravity has also increased; so that it is now settled at 23, that of fine gold being 19.

Though Dr Lewis could not accomplish the fusion of platina by the methods he attempted, he was nevertheless able to alloy it with other metals. Equal with other parts of gold and platina may be melted together by metals, a violent fire, and the mixed metal formed into an ingot by pouring it into a mould. It is whitish, hard, and may be broken by a violent blow; but when carefully annealed, is capable of considerable extension under the hammer. Four parts of gold with one of platina form a compound much more fusible than the former, and likewise more malleable; so that it may be extended into very thin plates without being broken or even split at the edges. Dr Lewis remarks also, that though in this case it be alloyed with such a quantity of white metal, it nevertheless appears no paler than guineas usually are, which contain only one-twelfth of silver.

Equal parts of silver and platina melted together with a violent fire, form a much harder and darker-coloured mass than silver, which has also a large grain, though it preserves some ductility. Seven parts of silver with one of platina form a compound much more resembling silver than the other; but still coarser-grained and less white. From the experiments made on silver, however, it appears that no perfect union is formed. formed betwixt the two; for after the mixture has been kept in fusion for a considerable time, most of the platina separates and falls to the bottom. Lewis observed, that silver melted with platina was thrown up with an explosion against the sides of the crucible.

Silver did not appear to be in any degree meliorated by its union with this metal, excepting by the superior hardness communicated to it; but copper seemed to be considerably improved. A large proportion of platina, indeed, as two-thirds or equal parts, produced an hard, brittle, and coarse-grained compound; but when a smaller quantity of platina is added, as from $\frac{1}{6}$ to $\frac{1}{3}$, or even less, a golden-coloured copper is produced, very malleable, harder, susceptible of a finer polish, smoother-grained, and much less subject to calcination and rust than pure copper.

Of all metallic matters, however, zinc most readily unites with platina, and is most effectually dissolved by fusion. When the proportion of platina is considerable, the metal is of a bluish colour, the grain closer, without tarnishing or changing colour in the air, and they have not even the malleability of the semi-metal.

Platina unites readily with the compound metals, brafs formed of copper and zinc, and bronze made of copper and tin. In the latter it was remarkable, that the compound metal took up more platina than both its ingredients separately can do. This compound was hard and capable of receiving a fine polish, but is subject to tarnish.

Equal parts of brafs and platina formed a compound very hard, brittle, capable of receiving a fine polish, and not subject to tarnish. It is possible therefore that it might be used to advantage as a material for speculums; all materials for which, hitherto discovered, have the great inconvenience of tarnishing in the air, and that very quickly.

Platina amalgamates with mercury, but with much greater difficulty than gold, which will also separate the quicksilver after it has been united with the platina. The amalgamation of platina does not succeed but by very long trituration of the metals with water, as for instance a week; but if the trituration be performed with a mixed metal composed of gold and platina, the mercury seizes the gold, and leaves the platina untonched. Dr Lewis proposes this as a method of separating gold from platina; and it is that used in Peru, where gold and platina are sometimes naturally mixed in the ore; but we do not know whether this separation be quite complete.

Mr Morveau succeeded in uniting iron with platina, though Dr Lewis could not accomplish this. The latter succeeded, however, in uniting it with cast iron. The compound was much harder and less subject to rust than pure iron. It was also susceptible of a much finer polish.

Platina may be alloyed with tin, lead, or bismuth, but without any advantage. To lead and tin it gives the property of assuming blue, violet, or purple colours, by being exposed to the atmosphere.

Dr Lewis could not succeed in uniting platina with arsenic; but M. Scheffer affirms, that if only one-twentieth of arsenic be added to platina when red hot in a crucible, the two substances will be perfectly fused and united into a brittle grey mass. This experiment did not succeed with Mr Margraaf; for he, means of having exposed to a violent fire during an hour a mixture of an ounce of platina with a fusible glass, composed of eight ounces of minium, two ounces of flints, and one ounce of white arsenic, obtained a regulus of platina well united and fused, weighing an ounce and 32 grains; the surface of which was smooth, white, and shining, and the internal parts grey; but which nevertheless appeared sufficiently white when filed. The experiment succeeded imperfectly also in the hands of Dr Lewis; but M. Fourcroy informs us, that "it has since been repeated, and that platina is in fact very fusible with arsenic, but that it remains brittle. In proportion as the arsenic is driven off by the continuance of the heat, the metal becomes more ductile; and by this process it is that M. Achard and M. de Morveau succeeded in making crucibles of platina by melting it a second time in moulds." (a)

M. Fourcroy seems to deny that platina can be united with mercury, contrary to what is mentioned above.—" Platina (says he) does not unite with mercury, though triturated for several hours with that metallic fluid. It is likewise known, that platina resists the mercury used in America to separate the gold. Many intermediates, such as water, used by Lewis and Beaumé, and aqua-regia by Scheffer, have not been found to facilitate the union of these two metals. In this respect platina seems to resemble iron, to whose colour and hardness it likewise in some measure approaches." This last sentence, however, seems very little to agree with what he himself had before told us of M. Macquer's experiment of melting platina. "The melted portions (says he) were of a white brilliant colour, in the form of a button; they could be cut to pieces with a knife." This surely was a very small approach to the hardness of iron; and gives us an idea rather of the softness of tin or lead. "One of these masses was flattened on the anvil, and converted into a thin plate without cracking or breaking, but it became hard under the hammer." In another experiment indeed the button of platina was brittle, and sufficiently hard to make deep traces in gold, copper, and even iron; but this was obtained from precipitated platina urged for 35 minutes by a strong blast furnace. In an experiment of this kind M. Beaumé even succeeded in melting the precipitate, along with certain fluxes, into a vitriform substance by two different processes. The precipitate of platina, mixed with calcined borax, and a very fusible white glass, was exposed, for 36 hours, in the hottest part of a potter's furnace; and afforded a greenish glass, inclining to yellow, without globules of reduced metal. This glass, treated a second time with cream of tartar, gypsum, and vegetable alkali, was completely melted, and exhibited globules of platina dispersed through its substance. M. Beaumé separated them by washing, and found them ductile. The same chemist afterwards, together

(a) For a particular account of this process see before no 587. together with M. Macquer, exposed precipitate of platina to the same burning mirror with which they had fused the metal: the precipitate exhaled a very thick and luminous fume, with a strong smell of aqua-regia: it lost its red colour, resumed that of platina, and melted into a perfect brilliant button, which was found to be an opaque vitreous substance, of an hyacinthine colour at its surface, and blackish within; and may be considered as a true glass of platina. It may however be observed, that the saline matters with which it was impregnated contributed doubts to its vitrification.

"The orange-coloured precipitate obtained by pouring a solution of sal ammoniac into a solution of platina, appears to be a saline substance entirely soluble in water. This precipitate has a valuable property, discovered by M. de l'Isle, viz. that it is fusible without addition in a good furnace or common forge-heat. The platina melted by this process is a brilliant, dense, and close-grained button; but it is not mallable unless it has been exposed to a very strong heat. Macquer thinks that this fusion, like that of the grains of platina alone, exposed to the action of a violent fire, consists only in the agglomeration of the softened particles; which being exceedingly more divided and minute than the grains of platina, adhere to and touch each other in a greater number of points than the grains; and in that manner render the texture of the metal much more dense, though no true fusion may have taken place. It seems, however, that if platina in grains be capable of fusion by the burning-glass, and of becoming considerably ductile, the precipitate of this metal formed by sal ammoniac may likewise be fused on account of its extreme division; and that its not being as ductile as the button of platina fused by the solar heat, may perhaps depend on its retaining a part of the matter it carried down with it in precipitation, of which it may be possible to deprive it by fire."

It being so extremely difficult to bring platina itself into fusion, one of the first attempts to purify it was by cupellation with lead. Thus the softer metals would be scorched; and, running through the crucible along with the lead, leave the platina in as great purity as though it had been melted by itself. This operation, however, was found almost equally difficult with the fusion of the metal by itself. Lewis failed in the experiment, though he applied the most violent heat of the ordinary cupelling furnaces. The vitrification and absorption of the lead indeed took place as usual; but in a short time the platina became fixed, and could not by any means be rendered fluid. Messrs Macquer and Beaumé succeeded by exposing an ounce of platina with two ounces of lead in the hottest part of a porcelain furnace, where the fire is continued for 50 hours without intermission. At the end of the operation the platina was flattened in the cupel; its upper surface was dull and rough, and easily separated; but its under surface was brilliant, and it was found easily to extend under the hammer; and on every chemical trial was found to be perfectly pure, without any mixture of lead. M. de Morveau likewise succeeded in cupelling a mixture of one drachm of platina and two drachms of lead in M. Macquer's wind-furnace. The operation lasted eleven or twelve hours, and a button of platina was obtained which did not adhere to the cupel, was uniform, though rather rough, and of a colour resembling tin. It weighed exactly one drachm, and was not at all acted upon by the magnet. Thus it appears that platina may be obtained in plates or laminae, which may be forged, and consequently may be employed in making very valuable utensils; and this the more especially as Mr Beaumé has observed that different pieces of it may be welded and forged like iron. After having heated two pieces of pure cupelled platina to whiteness, he placed them one upon the other, and striking them briskly with a hammer, found that they united together as quickly and firmly as two pieces of iron would have done.

The great specific gravity of platina has rendered it a very desirable matter for such as wish to adulterate the precious metal, and can procure the platina easily. This, however, can only be done in South America, where platina is met with in plenty. In Europe the scarcity of platina renders it a more valuable object than even the gold itself. Fears of this fraud, however, have undoubtedly given occasion to the prohibition of exporting it. There are great differences among chemists concerning the quantity of platina that can be mixed with gold without destroying the colour of the latter. Dr Lewis, as has already been observed, informs us, that four parts of platina may be mixed with one of gold, and yet the mixture be no paler than that for guineas; while Fourcroy affirms, that "it greatly alters the colour of the metal, unless its quantity be very small: thus, for example, a 47th part of platina, and all the proportions below that, do not greatly affect the colour of the gold." But whether this be the case or not, chemistry has afforded various ways of separating even the smallest proportion of platina from gold; so that there is now no reason to prohibit the importation of it to Europe, more than that of any other metal with which gold can be alloyed. The following are the methods by which the platina may be most readily discovered:

1. By amalgamating the suspected metal with mercury, and grinding the mixture for a considerable time with water; by which the platina will be left, and the gold be practically remain united with the quicksilver.

2. By dissolving a little of it in aqua regia, and precipitating with alkaline salt; the remaining liquor, in case the metal has been adulterated with platina, will be so yellow, that it is supposed a mixture of one thousandth part would thus be found out.

3. By precipitation with sal ammoniac, which throws down the platina but not the gold. If mineral alkali be used, the gold will be precipitated, but not the platina, unless the precipitant is in very large quantity.

4. By precipitation with green vitriol, which throws down the gold, and leaves the platina united with the mementum.

All these methods, however, are not only attended with a considerable deal of trouble, but in some cases, most easily for instance in suspected coin, it might not be eligible to use them. The hydrostatic balance alone affords a certain method of discovering mixtures of metals with their gravity, without altering the texture of their parts. The great specific gravity of platina would very readily discover it if mixed with gold in any moderate quantity; and even in the smallest, the gravity of the mass could never be less than that of the purest gold; which circumstance... Manganese, circumstance alone, as gold is never worked without alloy, would be sufficient to create a just suspicion; after which some of the methods already mentioned might be tried. It is possible, however, that the hardness and ductility of platinum might render it more proper for alloying gold than even copper or silver, usually made use of for this purpose.

§ 15. Of Manganese.

This substance is now discovered to afford a semi-metal different from all others, and likewise to possess some other properties of a very singular kind. Mr Scheele has investigated its nature with the utmost care; and the result of his inquiries are as follows:

1. Two drachms of levigated manganese, digested for several days in a diluted vitriolic acid, did not appear to be dissolved or diminished in quantity; nevertheless a yellowish white precipitate was procured by saturating the acid with fixed alkali. The remaining manganese was not acted upon by more of the same acid, but the addition of another half ounce nearly destroyed the acidity of the menstruum when boiled upon it.

2. With concentrated vitriolic acid an ounce of manganese was reduced to a mass like honey, and then exposed to the fire in a retort till it became red-hot. Some vitriolic acid came over into the receiver; and after breaking the retort, a mass was found in it weighing 12½ drachms, hard and white in the inside, but red on the outside. A great part of it dissolved in distilled water, on the efflorescence of which at first it became very hot. The residuum after edulcoration weighed a drachm and an half, and was of a grey colour. Being calcined in a crucible with concentrated vitriolic acid till no more vapours arose, it was all dissolved by water excepting one drachm; which being again calcined with the same acid, an insoluble residuum of a white colour, and weighing only half a drachm, remained. This white residuum effloresced with borax, and melted into a transparent brown glass; it likewise effloresced with fixed alkali, changing into a brown mass, which yielded an hepatic smell with acids, and became at the same time gelatinous. The solution obtained by calcination was evaporated and set to crystallize. A few small crystals of selenite were first deposited, and afterwards some very fine large crystals of an oblique parallelopiped form, whose number increased as long as there was any liquid left. They tasted like Epsom salt, and Mr Westfeld supposes them to be alum; but according to Mr Scheele, they have no other resemblance to alum than that they contain the vitriolic acid.

3. By phlogisticated vitriolic acid the manganese was entirely dissolved. To procure this acid in purity, Mr Scheele dipped some rags in a solution of alkali of tartar, and after saturating them with the fumes of burning brimstone, put them into a retort, pouring on them some dissolved acid of tartar, luting on a receiver which contained levigated manganese and water. After a warm digestion of only one day, the liquid of the receiver had become as clear as water, and a little fine powder, consisting principally of siliceous earth, fell to the bottom.

4. Two drachms of levigated manganese, digested for several days with an ounce of pure colourless acid of nitre, did not appear to have deprived the menstruum of its acidity, or to have been affected by it in any degree. The liquor being distilled off, and the product of the distillation poured back on the residuum, a small quantity of it was dissolved. By a third distillation, and pouring back the liquor on the residuum, a complete solution was effected; and this quantity of acid appeared capable of dissolving nine drachms of the powder.

5. The solution of manganese thus saturated, was precipitated and divided into two equal portions. Into one and crystals of these some drops of vitriolic acid were poured, by obtaining which a fine white powder was thrown down, which, from the solution, however, did not settle to the bottom for some hours. It was soluble neither in boiling water nor in acids. The limpid solution, by evaporation, yielded some small crystals of selenite or gypsum.

6. From the other half of this solution, after evaporation by a gentle heat, about ten grains of small shining crystals of a bitter taste were obtained. On pouring some drops of vitriolic acid into the solution precipitated by a gentle heat, no precipitation, excepting of a little selenite, ensued; but as soon as it was precipitated to the consistence of honey, some fine acicular crystals, verging towards the same centre, began to form, but grew soft, and deliquesced in a few days after.

7. Phlogisticated nitrous acid dissolves manganese as readily as the phlogisticated vitriolic. A little le-dissolved by levigated manganese mixed with some water was put into phlogisticated to a large receiver, to which a tubulated retort was added. Some ounces of common nitrous acid were put into the retort, to which some iron-filings were added, taking care always to close the orifice with a glass stopple. The phlogisticated nitrous acid thus passed over into the receiver, and dissolved the manganese in a few hours; the solution was as limpid as water, excepting only a little fine siliceous earth. Another white precipitate, similar to that produced by adding vitriolic acid to the solution in pure nitrous acid, now began to fall; but in other respects this solution agreed with the former.

8. An ounce of purified muriatic acid was poured upon half an ounce of levigated manganese; which, it evaporated after standing about an hour, assumed a dark brown of salt colour. A portion of it was digested with heat in an open glass vessel, and smelled like warm aqua regia. In a quarter of an hour the smell was gone, and the solution became clear and colourless. The rest of the brown solution being digested, to see whether the muriatic acid would be saturated with manganese, an effervescence ensued, with a strong smell of aqua regia, which lasted till next day, when the solution was found to be saturated. Another ounce of acid was poured upon the residuum, which was followed by the same phenomenon, and the manganese was entirely dissolved, this acid, a small quantity of siliceous earth only remaining. The solution, which was yellow, being now divided into two portions, some drops of vitriolic acid were poured into the one, by which it instantly became white, and a fine powder, insoluble in water, was precipitated. Some small crystals of selenite were formed by evaporation, and the residuum exhibited the same phenomenon with those above mentioned with ni- Manganese acid. By evaporating the other half, some small shining angular crystals were obtained, similar to those procured by means of the nitrous acid.

9. Very little manganese was dissolved by fluor acid, even after several days digestion. A great quantity was required to form a saturated solution. It had very little taste, and gave a small quantity of precipitate with fixed alkali. But if a neutral salt, composed of fluor acid and sal ammoniac, be added, a double decomposition takes place, and the manganese is precipitated along with the fluor acid.

10. A drachm of phosphoric acid digested with as much powdered manganese, dissolved but little of it; phoric acid, and, though evaporated to dryness, the residue tasted very acid; but by adding more manganese the acid was at last saturated. On adding microcosmic salt to a solution of manganese, a decomposition takes place similar to that effected by the combination of fluor acid and volatile alkali.

11. Pure acid of tartar dissolved manganese partly in the cold, and more effectually by means of heat. The whole, however, could not be dissolved, though the acid was at last saturated by adding a great quantity of the mineral. On adding a solution of soluble tartar, a double decomposition took place.

12. Little was dissolved by distilled vinegar, though boiled on manganese; but after distilling spirit of verdigris several times upon it, the acid at last became saturated. The solution, evaporated to dryness, left a deliquescent mass. Little or none of the remaining manganese was dissolved by concentrated vinegar, though repeatedly distilled upon it.

13. With acid of lemons the whole was dissolved with effervescence, excepting only some white earth.

14. Water impregnated with fixed air likewise dissolved manganese, but parted with it on the addition of alkali, or spontaneously by exposure to the air.

From these experiments Mr Scheele concludes, that manganese has a strong elective attraction for all phlogistic substances; and that this attraction becomes stronger, if there be present an element which can unite with the phlogisticated manganese. Thus it attracts phlogiston more powerfully than even the nitrous acid itself in the moist way. By fumigation with phlogiston, manganese has the property of losing its black colour, and assuming a white one, which is unusual, the phlogiston generally communicating a black or dark colour to the substances with which it was united.

That manganese naturally contains some phlogiston, though but in small quantity, appears from evaporating a solution of it in vitriolic acid to dryness, and then distilling the mass in a glass retort in an open fire. When the retort begins to melt, the acid parts fly off from the manganese in a fuliginous state, leaving the former of its natural black colour. By distilling the mass remaining after evaporation of the nitrous solution, a green volatile nitrous acid remains, and the black calx of manganese remains as before. A solution of this mineral in vitriolic or nitrous acid, precipitated by fixed alkali, retains its colour; but when calcined in the open fire, again becomes black.

By losing its phlogiston, manganese becomes insoluble in pure acids; and therefore the residuum of the above mentioned distillations cannot be dissolved by adding more of the vitriolic or nitrous acids; but if that which has come over into the receiver be poured back into the retort, a solution will again take place by reason of the manganese refusing the phlogiston it had parted with to the acid.

On this principle our author explains the reason of the partial solutions of this mineral above mentioned. Part of it is dissolved, for instance in the vitriolic acid, manganese while the remainder is found insoluble. This happens explained (says he), "because the undissolved portion has parted with the little phlogiston it naturally possessed to that portion of manganese which is taken up by the vitriolic acid during the first digestion; for without that principle it is insoluble."

Manganese attracts phlogiston more strongly when combined with some acid than by itself, as appears from the following experiments.

1. Levigated manganese, digested or boiled with a solution of sugar, honey, gum Arabic, hawthorn, jelly, &c., remains unchanged; but on mixing the pounded mineral with diluted vitriolic, or pure nitrous acid, and boiling with then adding some of these substances, the whole is dissolved, the black colour vanishes by degrees, and the phlogiston solution becomes as limpid as water. So strong is the attraction of manganese for phlogiston in these circumstances, that metals, the noble ones not excepted, render it soluble in these acids in a limpid form. Consequently, the concentrated vitriolic acid, indeed, dissolves manganese entirely without any phlogiston. "It would be difficult (says Mr Scheele) to comprehend whence the phlogiston in this case should come, if we were not certain that several substances, which have a great attraction for phlogiston, can attract it in a red heat. Quicksilver and silver, when dissolved in the pure nitrous acid, really lose their phlogiston, which is a constituent part of these metals. This appears from the red vapours in which the acid arises; and the dissolved metallic earth cannot be again reduced to its metallic form, till it has acquired the lost phlogiston, which is effected either by precipitation with complete metals or by heat alone. Thus manganese can attract the quantity of phlogiston necessary for its solution by means of concentrated vitriolic acid from heat. It is not probable that the concentrated acid undergoes a decomposition in this degree of fire; for if you saturate half an ounce of this acid with alkali of tartar, and afterwards calcine in a retort, with a receiver applied, an ounce and a half of powdered manganese, with an equal quantity of the same vitriolic acid, then dissolve the calcined mass in distilled water, and likewise wash well the receiver, which contains some drops of vitriolic acid, which are also to be added to the solution, and lastly add the same quantity of alkali; there will be no mark of superabundant acid or alkali. Thence it may be concluded, that the phlogiston in the vitriolic acid, if there really exists any in it, contributes nothing to the solution. But the manganese precipitated by alkali contains a considerable quantity of it; in consequence of which it is afterwards entirely soluble in acids without any addition.

"The effects of volatile sulphurous acid on manganese, clearly prove what has been asserted. The manganese attracts the phlogiston contained in this acid, acidifies which is the cause of its great volatility, and which lives it renders..." Manganese renders the former soluble in the new pure vitriolic acid. If this solution be mixed with concentrated vitriolic acid and distilled, no volatile sulphureous acid is obtained; and if it be precipitated by means of fixed vegetable alkali, vitriolitic tartar is obtained; which proves that manganese has a stronger attraction than vitriolic acid for phlogiston in the moist way.

The effects of nitrous acid on this substance are similar to those of vitriolic acid. Could spirit of nitre sustain at great degree of heat as the concentrated vitriolic acid, it would also entirely dissolve the manganese by means of the phlogiston attracted by heat; but as this is not the case, it is necessary to add phlogiston in the manner above mentioned. The manganese decomposes phlogisticated nitrous acid, for the same reason that it does the volatile sulphureous acid; and that the phlogiston of this acid really combines with the manganese, is manifest from this, that the diffusion of vegetable acid produces no smell of aquafortis by displacing the phlogisticated acid of nitre. By distillation with pure vitriolic acid also, the nitrous acid is expelled, not in a smoking state, and of a yellow colour, but pure and colourless.

In the solution of manganese by means of gum arabic or sugar, a very considerable effervescence takes place, owing to the extrication, or probably rather the production, of fixed air from the mixture; but with phlogisticated acid of nitre no such phenomenon takes place, because the manganese is combined with pure phlogiston; and if this should be again separated, there is no cause for the production of fixed air. This mineral is also dissolved without effervescence, by uniting it with nitrous acid and metals, arsenic or oil of turpentine.

As muriatic acid dissolves manganese without addition, Mr Scheele is of opinion that this proves the existence of phlogiston in that acid, as has already been taken notice of. The manganese digested in the cold with spirit of salt assumes a dark brown colour; for it is a property of this substance that it cannot be dissolved into a colourless liquor without phlogiston, but has always a red or blue colour; but with spirit of salt the solution is more brown than red, on account of the fine particles of the manganese floating in the liquid. Here the mineral adheres but loosely to the acid, so that it may be precipitated by water.

The effects of acid of tartar and acid of lemons upon manganese are likewise explained on the principle already laid down, viz., the extreme attraction this substance has for phlogiston. Thus it attracts part of that naturally contained in these acids, decomposing one part of them, and being dissolved by the other. This destruction of the acid is similar to that of the sugar, gum arabic, &c., which render it soluble in nitrous acid; for if a proper quantity of these are added, the manganese will be dissolved, without a possibility of recovering the smallest particle of the vegetable substances employed; and if the solution be slowly evaporated and calcined, there will not remain the smallest mark of burned sugar or gum. During this decomposition, a pungent vapour arises, which, being collected, appears to be true vinegar. It is obtained in its purest state from diluted vitriolic acid, sugar, and manganese.

Fluor acid dissolves but very little manganese, owing to its precipitating a salt which envelopes the particles of manganese, and prevents the further action of the manganese.

In all precipitations of manganese, however, by means of mild fixed alkalies, the full quantity is not procured; because the fixed air, detached from the mineral, diffuses part of it.

Though manganese decomposes nitre, yet this effect does not happen till the mixture becomes red-hot. If manganese phlogisticated manganese be mixed with an equal quantity of nitre, and distilled in a glass retort, the mixture begins to grow black before the retort becomes red-hot, but no nitrous acid goes over. By lixiviation, no mark of uncombined alkali is met with; but phlogisticated nitrous acid is extracted by the application of tamarinds, or any vegetable acid. Three parts of phlogisticated manganese, mixed with one part of finely powdered nitre, yields no nitrous acid, though the nitre is alkalized as soon as the mixture becomes black in the retort.

Mr Scheele proceeds now to another set of experiments upon manganese united with phlogiston. In order to procure it in this state, the best method is to manganese dissolve in distilled water, and crystallize the salt obtained with solution of manganese in vitriolic acid, and then precipitate it with vegetable fixed alkali. In this state it is white like chalk; but by calcination in an open fire, the superfluous phlogiston flies off, and the calx regains its usual black colour. This change of colour likewise happens when the precipitation is made with caustic alkalies, whether fixed or volatile. The precipitate, indeed, in this case, is white when kept close from the air, but assumes a brown colour when exposed to it for any time: But when the precipitation is made by mild alkali, the white colour is preserved by the fixed air, which in this case it also contains. By diluting the solution with a considerable quantity of water, and precipitating with caustic alkali, the precipitate is brown from the very beginning, owing to the air in the liquid attracting the phlogiston from the manganese. The precipitate formed by lime-water is also brown; but on adding more of a strong solution of manganese, and afterwards precipitating with caustic alkali, the powder falls of a white colour; because the air, being already saturated with phlogiston, cannot take up any more. The results of Mr Scheele's experiments on this phlogisticated manganese are,

1. An ounce of this substance distilled by itself, in a glass retort, with a strong fire, yielded a great quantity of fixed air with some drops of water. The residuum poured warm out of the retort grew red-hot, and set the paper on fire.

2. On repeating the experiment with only a drachm of phlogisticated manganese, and tying a bladder to the neck of the retort, three ounce-measures of air came over: the residuum was of a light grey colour; dissolved in acids without addition of any more phlogiston; and took fire in that degree of heat in which sulphur smokes, but does not burn. From these experiments, says Mr Scheele, it is evident, that phlogiston does not separate from manganese if the access of air be prevented.

3. One part of finely powdered manganese boiled in four of oil-olive, effervesced violently, and dissolved into a kind of salve.

4. On distilling a mixture of finely powdered manganese and charcoal, with an empty bladder tied to the mouth of the retort, a quantity of fixed air was extracted. cated when the retort began to melt and dislocated the bladder. The residuum was mostly soluble in diluted vitriolic acid.

5. On distilling half an ounce of powdered manganese with two drachms of sulphur, the latter partly rose into the neck of the retort, and some volatile acid vapours penetrated through the lute. The distillation was continued till the retort began to melt; and, on cooling, the residuum was found to weigh ½ drachm. It was of a yellowish-grey colour; and dissolved in spirit of vitriol with effervescence, yielded an hepatic smell, some sulphur being also precipitated at the same time. By calcination in the open air, the sulphur was dissipated; but great part of the mass was rendered soluble on account of its having been penetrated by the acid vapour, and shot into crystals as though it had been formally dissolved in volatile sulphurous acid; and by repeating the calcination with more sulphur, the whole became at last entirely soluble, and was reduced to crystals.

Finely powdered manganese, triturated with nitre, and strongly calcined in a crucible, unites with the alkali of the nitre, while the acid is dissipated in the air. The mass formed by the union of the manganese and alkali is of a dark green colour, and soluble in water, communicating also a green colour to the liquid; but in a short time a fine yellow powder (an ochre of iron) falls to the bottom, leaving the liquor of a blue colour. By the addition of water, this solution first assumes a violet colour, grows afterwards red, and a precipitation of the manganese takes place, which resumes its natural colour as soon as it has fallen. The same precipitation takes place on the addition of a few drops of acid, or by exposure for some days to the open air. As for the dark red colour assumed by the solution when the precipitate is about to fall, Mr Scheele conjectures that the particles of manganese may naturally have a red colour, which becomes visible when the substance is dispersed through a menstruum without being perfectly dissolved.

7. By the addition of finely powdered white arsenic to the alkaline mass of nitre and manganese, the green colour disappears, and the whole becomes white; phlogisticated manganese being also precipitated on the addition of water. This arises from the more powerful attraction of manganese for the phlogiston of the arsenic than that of the arsenical acid itself; and for the same reason, if the mass be calcined with charcoal, or any other phlogistic substance, a colourless solution will be obtained.

8. Half an ounce of phlogisticated manganese, distilled in a retort with an equal quantity of powdered sal ammoniac, yielded first a concrete volatile salt, after which some sal ammoniac undecomposed arose in the neck of the retort. Half an ounce of pure dephlogisticated manganese, mixed with two drachms of powdered sal ammoniac, yielded alkali in its caustic state. Both residua were soluble in water; which shows that manganese attracts phlogiston from the volatile alkali.

9. On digesting finely powdered manganese for some weeks with pure nitrous acid and some volatile alkali, a great number of air-bubbles rise to the top, and the volatile alkali is entirely decomposed; for though the mixture be afterwards distilled in a retort with the addition of quicklime, not the least urinous smell can be perceived. This decomposition is effected by the manganese attracting the phlogiston of the volatile alkali; volatile for that the nitrous acid has no share in this, is proved by the following experiment.

10. An ounce of well triturated manganese was distilled with half an ounce of sal ammoniac; and a little phlogisticated alkali, such as that obtained from sal ammoniac gitter, and quicklime, was procured. On repeating this experiment, with the variation only of a bladder instead of a receiver, the same kind of air was obtained as that which rises to the top of the nitrous mixture. Though the emission of this air indicated a destruction of the volatile alkali, our author explains the reason of its being still obtained in a caustic state by the phlogiston taken from the alkali being more than sufficient to render the alkali soluble in muriatic acid; in consequence of which, the superfluous quantity combines with the manganese, and enables it to decompose the sal ammoniac in the ordinary way. It must be owned, however, that his reasoning on this subject is not entirely satisfactory, nor does the account he gives of his experiments seem entirely consistent with itself. See Scheele's Chem. Essays, Essay V. § xxxix.

11. Powdered manganese, distilled with an equal quantity of white arsenic, underwent no change, the arsenic flying off in its proper form; but with an equal quantity of yellow orpiment, some volatile sulphurous acid came over first, then a yellow sublimate, and at last a little red sublimate arose. On augmenting the fire by degrees, the orpiment remained obstinately attached to it. Similar effects ensued on treating manganese with an equal quantity of antimony; which likewise yielded a pungent sulphurous acid, but no sublimate. By calcination in the open air these compounds are decomposed; and the manganese, united with vitriolic acid, becomes soluble in water.

12. On distilling manganese with an equal quantity of finely pounded cinnabar, a volatile sulphurous acid nabar came over first; then a little cinnabar was sublimed into the neck of the retort; and at last the quicksilver, which had been the basis of the cinnabar, began to distil; the residuum, being a combination of manganese and sulphur, was similar to the compounds already described.

13. With an equal quantity of corrosive sublimate, with corrosive sublimate, and then mercurius dulcis, arose into the neck of the retort. The reason of this is, that the mercurius dulcis contains a portion of phlogiston; by being deprived of which it ceases to be mercurius dulcis, and becomes corrosive sublimate; but by reason of the strong attraction of manganese for phlogiston, the mercurius dulcis parts with that portion which is necessary to keep it in its mild state, and thus is converted into corrosive mercury.

Sect. IV. Inflammable Substances.

These may be divided into the following classes:

1. Sulphurs. 2. Ardent spirits. 3. Oils and fats. 4. Refins. 5. Bitumens; and, 6. Charcoal. § I. SULPHUR.

1. Common sulphur. For the extraction of this substance from its ores, see Sulphur. The artificial composition of it we have already related, n° 715; and have now only to take notice of a very few of its properties, which come more properly under this section.

Sulphur, as commonly used in commerce and the arts, is of a pale yellow colour, of a disagreeable and peculiar smell, which is rendered more sensible when it is heated or rubbed. By rubbing, it receives very curious electrical qualities: (See Electricity.) Its specific gravity is considerably greater than that of water, though less than earths or stones. In close vessels, sulphur is incapable of receiving any alteration. It melts with a very gentle heat; and then is sublimed, adhering to the capital in small, very fine, needle-like crystals, called flowers of sulphur. It may thus be sublimed many times without alteration. If sulphur is exposed to a heat barely sufficient to melt it, and very slowly cooled, it crystallizes in form of many needles crossing one another. Some of these pointed crystals may also be observed in the interior parts of the lumps of sulphur which have been melted, and cast into cylindrical moulds, as they are commonly sold; because the centre of these cylindrical rolls is more slowly cooled than the surface. Sulphur also gives this needle-like form to cinnabar, antimony, and many other minerals containing it. Sulphur may be decomposed in several ways. The most simple is by burning; which we have already taken notice of, n° 623. It may also be very effectually decomposed by mixing it with iron filings and water. In this case the phlogiston is dissipated, and the acid uniting with the iron forms a green vitriol.

It is very remarkable, that though sulphur is composed of vitriolic acid and phlogiston, yet the addition of more inflammable matter, so far from making the union stronger, weakens it to a great degree: and hence we have another method of decomposing this substance; namely, by combining it with a large quantity of oil, and distilling the compound.

Sulphur is capable of being easily dissolved in expressed oils, but very difficultly in essential ones. These compositions are called balsams of sulphur; and are sometimes employed in medicine, but are found to be of a very heating nature. They are much used by farriers. According to Mr Beaume, sulphur cannot be dissolved in oil, without a heat sufficient to melt it. A larger quantity is kept dissolved when the mixture is hot, than when cold; and consequently the sulphur, especially if it has been dissolved in a thin essential oil, crystallizes on cooling the mixture. The sulphur, thus separated from the oil, is found not to be altered in any respect from what it formerly was; but if the mixture is exposed to a degree of heat capable of entirely decomposing the oil, the sulphur is decomposed along with it, and the same products are obtained by distilling this mixture to dryness, as if a mixture of pure oil of vitriol and oil were distilled. These products are, first a portion of oil, when an essential oil was made use of in the composition of the balsam; then some volatile sulphureous acid, which is at first watery, and afterwards becomes stronger; along with this acid more oil arises, which becomes more and more thick towards the end of the distillation; and lastly, when the retort has been made red hot, nothing remains but a fixed coal.

In this process we find, that both the sulphur and oil are decomposed. The acid of the sulphur seems to attack the watery principle of the oil, while its phlogiston remains confounded with that of the oil, or is dissipated in vapours. Hence, though the vitriolic acid in sulphur is concentrated to the utmost degree, and perfectly free from water, what rises in this distillation is very aqueous, by reason of the water which it attracts from the oil.

Spirit of wine does not sensibly act upon sulphur in its liquid state; but if both the spirit of wine and spirit of sulphur meet in the state of vapour, they will then unite, and a perfect solution will take place. By methods of this kind, many combinations might be effected, which have been hitherto thought impossible.

Pure sulphur unites easily with all metals; gold, platinum, and zinc, excepted. The compounds, except with mercury, possess a metallic lustre without any ductility. The sulphur may be separated by exposing the mixture to a strong fire, (see Metallurgy,) or by dissolving the metallic part in acids. The sulphur, however, defends several of the metals from the action of acids; so that this dissolution succeeds but imperfectly. The reguline part of antimony is more easily separated from sulphur by means of acids than any other metallic substance. Alkaline salts will separate the sulphur from all metals in fusion, but they unite with it themselves, and form a compound equally capable of dissolving the metal.

Sulphur united with quicksilver forms the beautiful pigment called cinnabar, or vermilion; which is so much used in painting, that the making of it is become a distinct trade. Neuman relates, that in the making of cinnabar by the Dutch method, fix or eight parts of quicksilver are made use of to one of sulphur. The sulphur is first melted, and then the quicksilver is stirred into it; upon which they unite into a black mass. In this part of the process the mixture is very apt to take fire; of which it gives notice by swelling up to a great degree. The vessel must then be immediately covered. The mass being beaten to powder, is afterwards to be sublimed in large earthen jars almost of an equal wideness from end to end; these are hung in a furnace by a strong rim of iron. When the matter is put in, the mouth of the vessel is covered, the fire increased by degrees, and continued for several hours, till all the cinnabar has sublimed; care being taken to introduce at times an iron rod to keep the middle clear; otherwise the cinnabar concreting there, and stopping up the passage, would infallibly burst the vessels.

The quantity of sulphur directed in the common receipts for making cinnabar is greatly larger than the above; being no less than one-third of the quantity of quicksilver employed: accordingly it has been found, that the sublimate, with such a large quantity of sulphur, turned out of a blackish colour, and required to be several times sublimed before it became perfectly red; but we cannot help thinking, that by one gentle sublimation. Sublimation the superfluous sulphur might be separated, and the cinnabar become perfectly pure the second time. Hoffman gives a curious method of making cinnabar without sublimation; by shaking or digesting a little mercury with volatile tincture of sulphur, the mercury readily imbibes the sulphur from the volatile spirit, and forms with it a deep red powder, not inferior in colour to the cinnabar prepared in the common manner. Dr Lewis has found the common solutions of sulphur by alkalies, or quicklime, to have a similar effect. This cinnabar will likewise be of a darker or lighter colour, according as the solution contains more or less sulphur.

Sulphur is a principal ingredient in gun-powder, (see Gun-powder.) It also enters the composition of the pulvis fulminans. This consists of three parts of nitre, two of the dry alkali of tartar, and one part of sulphur, well ground together. If a little quantity of this powder is laid on an iron-spoon or shovel, and slowly heated, it will explode, when it arrives at a certain degree of heat, with astonishing violence and noise. The most probable opinion concerning this is, that the fixed air contained in the alkali is, by the acid vapours acting upon and endeavouring to expel it all at once, driven off with such force, that a loud explosion is produced.

2. Phosphorus of Urine. This is a very inflammable substance, composed of phlogiston united with a certain acid, the properties of which we have already taken notice of, n° 904 et seq. The preparation of it was long a secret, and only perfectly discovered by Mr Margraaff, who published it in the Berlin Memoirs in 1743. This process being by far the best and most practicable, we shall content ourselves with inferring it alone.

Two pounds of sal ammoniac are to be accurately mixed with four pounds of minium, and the mixture distilled in a glass retort; by which means a very penetrating, caustic alkaline spirit will be obtained. The residuum, after the distillation, is a kind of plumbum corneum; n° 812. This is to be mixed with nine or ten pounds of extract of urine, evaporated to the consistence of honey. (Seventy or eighty gallons of urine are required to produce this quantity of extract.) The mixture is to be made slowly in an iron pot set over the fire, and the matter frequently stirred. Half a pound of powdered charcoal is then to be added, and the evaporation continued till the whole is reduced to a black powder. This powder is to be put into a retort, and urged with a graduated heat, till it becomes red hot, in order to expel all the volatile alkali, fetid oil, and ammoniacal salt, that may be contained in the mixture. After the distillation, a black friable residuum remains, from which the phosphorus is to be extracted by a second distillation and a stronger heat. Before it is subjected to another distillation, it may be tried by throwing some of it upon hot coals. If the matter has been well prepared, a smell of garlic exhales from it, and a blue phosphorical flame is seen undulating along the surface of the coals.

The matter is to be put into a good earthen retort, capable of sustaining a violent fire. Three quarters of the retort are to be filled with the matter which is to yield the phosphorus, and it is to be placed in a furnace capable of giving a strong heat. Mr Margraaff divides the matter among six retorts, so that if any accident happens to one, the whole matter is not lost. The retorts ought to be well fitted to a receiver of moderate size, pierced with a small hole, and half full of water; and a small wall of bricks must be raised between the furnace and receiver, in order to guard this vessel against heat as much as possible. The retorts are to be heated by slow degrees for an hour and a half; then the heat is to be increased till the vessels are red hot, when the phosphorus ascends in luminous vapours. When the retort is heated till between a red and white, the phosphorus passes in drops, which fall and congeal in the water at the bottom of the receiver. This degree of heat is to be continued till no more comes over. When a retort contains eight pints or more, this operation continues about five hours.

In the first distillation, phosphorus never passes pure, but is always of a blackish colour, by reason of its containing along with it some part of the coal. From this, however, it may be purified by rectification in a small glass-retort, to which is fitted a receiver half full of water. A very gentle heat is sufficient; because phosphorus, once formed, is very volatile; and as the fuliginous matter was raised probably by the fixed air emitted by the charcoal in the instant of its union with the phosphoric acid, none of it can arise in a second distillation.

The phosphorus is then to be divided into small cylindrical rolls, which is done by putting it in glass-tubes immersed in warm water; for the phosphorus is almost as fusible as suet. It takes the form of the glass-tubes; from which it may be taken out, when it is cold and hardened. This must be done under water, lest the phosphorus should take fire.

This concrete continually appears luminous in a dark place; and by a very slight heat takes fire, and burns sometimes far more vehemently than any other known substance. Hence it is necessary to be very cautious in the distillation of it; for if the receiver should happen to break while the phosphorus is distilling, and a little flaming phosphorus fall upon the operator's legs or hands, it would burn its way to the bone in less than three minutes. In this case, according to Mr Hellot, nothing but urine will stop its progress.

Though phosphorus takes fire very readily by itself, it does not inflame at all by grinding it with other inflammable bodies, as camphor, gun-powder, or essential oils. In grinding it with nitre, some luminous flashes are observed; but the mixture never burns, unless the quantity of phosphorus be large in proportion to the nitre: rubbed pretty hard on a piece of paper or linen, it sets them on fire if they are rough, but not if they are smooth. It fires written paper more readily than such as is white, probably from the former having more aperitives. On grinding with iron-filings, it presently takes fire.

Oils ground with phosphorus appear, like itself, liquid luminous in a temperately warm place; and thus become a liquid phosphorus, which may be rubbed on the hands, &c. without danger. Liquid phosphorus is commonly prepared by grinding a little of the solid phosphorus with oil of cloves, or rubbing it first with camphor, and this mixture with the oil. A luminous amalgam, as it is called, may be obtained, by digesting a scruple of solid phosphorus with half an ounce of oil of lavender, and, when the phosphorus begins to dissolve and the liquor to boil, adding a drachm of pure quicksilver; then briskly shaking the glass for five or six minutes till they unite.

Rectified spirit of wine, digested on phosphorus, extracts a part of it, so as to emit luminous flashes on being dropped into water. It is computed that one part of phosphorus will communicate this property to 600,000 parts of spirit. The liquor is never observed to become luminous of itself, nor in any other circumstance except that above mentioned. By digestion for some months, the undissolved phosphorus is reduced to a transparent oil, which neither emits light nor concretes in the cold. By washing with water, it is in some measure revived; acquiring a thicker consistence, and becoming again luminous, though in a less degree than at first. During this digestion, the glass is very apt to burst.

Phosphorus is partially dissolved by expressed oils; and totally, or almost so, in essential oils and ether acids. When essential oils are saturated with it by heat, a part of the phosphorus separates, on standing in the cold, in a crystalline form. Concentrated spirit of salt has no action on it. In distillation, the spirit rises first, and the phosphorus after it unchanged. Spirit of nitre dissolves it, and the dissolution is attended with great heat and copious red fumes; so that great part of the spirit distils without the application of any external heat, and the phosphorus at last takes fire, explodes, and bursts the vessels. Oil of vitriol likewise dissolves phosphorus, but not without a heat sufficient to make the acid distil. The distilled liquor is white, thick, and turbid; the residuum is a whitish tenacious mass, which deliquesces, but not totally, in the air. Phosphorus itself is resolved into an acid liquor on being exposed two or three weeks to the air, its inflammable principle seeming by degrees to be dissipated.

Phosphorus has been reported to produce extraordinary effects in the resolution of metallic bodies; but from the experiments that have been made with this view, it does not appear to have any remarkable action on them; at least on the precious ones, gold and silver, for the resolution or sublimation of which it has been chiefly recommended. The following experiments were made by Mr Margraaff.

1. A scruple of filings of gold were digested with a drachm of phosphorus for a month, and then committed to distillation. Part of the phosphorus arose, and part remained above the gold, in appearance resembling glass: this grew moist on the admission of air, and dissolved in water, leaving the gold unaltered. Half a drachm of fine silver, precipitated by copper, being digested with a drachm of phosphorus for three hours, and the fire then increased to distillation, greatest part of the phosphorus arose pure, and the silver remained unchanged. Copper filings being treated in the same manner, and with the same quantity of phosphorus, the phosphorus sublimed as before; but the remaining copper was found to have lost its metallic brightness, and to take fire on the contact of flame. Iron filings suffered no change. Tin filings run into granules, which appeared to be perfect tin. Filings of lead did the same. The red calx of mercury, called precipitate per se, treated in the same manner, was totally converted into running quicksilver. 2. Regulus of antimony suffered no change itself, but occasioned a change in the consistence of the phosphorus; which, after being distilled from this semimental, refused to congeal, and continued, under water, fluid like oil-olive. With bismuth there was no alteration. A drachm of phosphorus being distilled and cohabited with an equal quantity of zinc, greatest part of the zinc sublimed in form of very light pointed flowers of a reddish-yellow colour: these flowers, injected into a red hot crucible, took fire, and run into a glass resembling that of borax. White arsenic, sublimed with phosphorus, arose along with it in form of a mixed red sublimate. Sulphur readily unites with phosphorus into a mass which smells like baper fulphuris. This does not easily take fire on being rubbed; but exposed to a moderate dry heat, it flames violently, and emits a strong sulphureous fume. If phosphorus is burnt in an open vessel, a quantity of acid remains behind; and if a glass bell is held over it, an acid likewise sublimes in the form of white flowers.

3. Mr Canton's phosphorus. This is a composition of quicklime and common sulphur. The receipt for making it is as follows. "Calcine some common oyster-shells, by keeping them in a good coal-fire for half an hour; let the purest part of the calx be pulverized and sifted. Mix with three parts of this powder one part of flowers of sulphur. Let this mixture be rammed into a crucible of about an inch and a half in depth till it be almost full; and let it be placed in the middle of the fire, where it must be kept red hot for an hour at least, and then set by to cool: when cold, turn it out of the crucible; and cutting or breaking it to pieces, scrape off, upon trial, the brightest parts; which, if good phosphorus, will be a white powder. This kind of phosphorus shines on being exposed to the light of the sun, or on receiving an electrical stroke.

4. Phosphorus of Homberg. This substance, which has the singular property of kindling spontaneously when exposed to the air, was accidentally discovered by Mr Homberg, as he was endeavouring to distil a rustic flavourless oil from human excrement. Having mixed the excrement with alum, and distilled over as much as he could with a red heat, he was much surprised at seeing the matters left in the retort take fire upon being exposed to the air, some days after the distillation was over. This induced him to repeat the operation, in which he met with the same success; and he then published a process, wherein he recommended alum and human excrement for the preparation of the phosphorus. Since his time, however, the process has been much improved; and it is discovered, that almost every vitriolic salt may be substituted for the alum, and most other inflammable substances for the excrement; but though alum is not absolutely necessary for the successe, it is one of the vitriolic salts that succeed best. The following process is recommended in the Chemical Dictionary.

Let three parts of alum and one of sugar be mixed together. This mixture must be dried in an iron shovel, over a moderate fire, till it be almost reduced to a blackish powder or coal; during which time it must be stirred with an iron spatula. Any large masses must be Sulphur be bruised into powder; and then it must be put into a glass matrafs, the mouth of which is rather strait than wide, and seven or eight inches long. This matrafs is to be placed in a crucible, or other earthen vessel, large enough to contain the belly of the matrafs, with about a space equal to that of a finger all round it. This space is to be filled with sand, so that the matrafs shall not touch the earthen vessel. The apparatus is then to be put into a furnace, and the whole to be made red hot. The fire must be applied gradually, that any oily or fuliginous matter may be expelled; after which, when the matrafs is made red hot, sulphureous vapours exhale: this degree of heat is to be continued till a truly sulphurous flame, which appears at the end of the operation, has been seen nearly a quarter of an hour: the fire is then to be extinguished, and the matrafs left to cool, without taking it out of the crucible; when it ceases to be red hot, it must be stopped with a cork. Before the matrafs is perfectly cold, it must be taken out of the crucible, and the powder it contains poured as quickly as possible into a very dry glass phial, with a glass stopper. If we would preserve this phosphorus a long time, the bottle containing it must be opened as seldom as possible. Sometimes it kindles while it is pouring into the glass phial; but it may be then extinguished by closing the phial expeditiously. A small quantity of this pyrophorus laid on paper, and exposed to the air, immediately takes fire, becomes red like burning coals, and emits a strong sulphureous vapour greatly resembling that which arises on decomposing liver of sulphur.

It has been generally alleged, that the common black phosphorus is impaired by being exposed to the light; but Mr Cavalli has discovered the fallacy of this supposition by the following experiment. Some portions of the same pyrophorus were inclosed in three glass tubes, and immediately sealed up hermetically. On the 20th of May 1779, two of them were suspended from a nail out of a window, and the third was wrapped up in paper and inclosed in a box, where not the least glimmering of light could enter. In this situation they were left for more than a year; after which one of those that had been kept out of the window was broke, along with that which had been kept in the dark, in the presence of Mr Kirwan; when the pyrophorus seemed to be equally good in each tube, taking fire in about half a minute after it was taken out of the tubes, and exposed to the air on a piece of paper.

There are many different kinds of pyrophorus; some of the most remarkable of which are described under the article Pyrophorus. Many theories have been invented to solve the phenomenon of their accension on the contact of air. This has been thought owing to the conversion of the earth of alum into lime, or to a remainder of the vitriolic acid attracting moisture from the atmosphere; but the formation of pyrophorus without either alum or vitriolic acid, shows that neither of these opinions can be just. It is most probable, therefore, that the heat is occasioned by the total distillation of that aqueous part which is essential to the constitution of terrestrial substances. In consequence of this, the water contained in the atmosphere is not only attracted with avidity, but decomposed by the matter reduced to such a state of extreme dryness. By these operations it gives out the latent heat contained in it, and this produces the accension in question.

§ 2. ARDENT SPIRITS.

See Fermentation and Distillation.

§ 3. OILS.

1. Essential Oils. Those oils are called essential which have evidently the smell of the vegetable from which they are drawn. For the method of procuring them, see Distillation. They are distinguished from all others by their superior volatility, which is so great as to cause them rise with the heat of boiling water. All these have a strong aromatic smell, and an acrid, caustic taste; in which respect also they differ from other oils. This taste is thought to proceed from a copious Supposed difengaged acid, with which they are all pene-cause of. The presence of this difengaged acid in essential oils, appears from the impression they make upon the corks of bottles in which they are kept. These corks are always stained of a yellow colour, and a little corroded, nearly as they are by nitrous acid. The vapour of these oils also reddens blue paper, and converts alkalies into neutral salts.

This acid is likewise supposed to be the cause of their solubility in spirit of wine. They are not all equally soluble in this menstruum, because they do not all contain an equal quantity of acid. As this acid is much more difengaged, they lose a great deal of it by repeated distillations, and therefore they become less and less soluble on being frequently distilled. By evaporation they lose their most volatile and thin part, in which the specific smell of the vegetable from which they are extracted resides; by which loss they become thick, and acquire the smell and consistence of turpentine, and even of resins. In this state they are no longer volatile with the heat of boiling water; and, if distilled with a stronger fire, they give over an oil which has neither smell nor taste of the vegetable whence they were extracted, but is entirely empyreumatic, and similar to those oils procured by distilling vegetable or animal substances with a strong fire. See Distillation.

To the class of essential oils, the volatile concrete called camphor seems most properly to belong. With Camphor, it agrees in its properties of inflammability, solubility in spirit of wine, and a strong aromatic flavour. The only differences between them are, that camphor is always in a solid state, and is incapable of decomposition by any number of sublimations.

It has, however, been found possible to decompose it by distillation with certain additions. By distilling fed by diluting it several times along with balsam, we obtain a fluid having the properties of an essential oil, soluble in water, with balsam, and separating again on the addition of spirit of wine. On distilling it eight times with dephlogisticated nitrous acid, we obtain a salt having the form of a parallelopiped, of an acid and bitter taste, and changing the juice of violets and turnsole red. This has the properties of a true acid; combines with fixed and volatile alkalies into neutral salts capable of being crystallized; dissolves copper, iron, bismuth, arsenic, and cobalt. cobalt. With manganese it forms regular crystals, in some measure resembling basaltes. It is distinguished from the acid of sugar by not precipitating lime from its solution in marine acid, and by forming with magnesia a white powder soluble in water.

According to Neumann, all the camphor made use of is the produce of two species of trees; the one growing in Sumatra and Borneo, the other in Japan. Of these, the Japan kind is the only one brought into Europe. The tree is about the size of a large lime, the flowers white, and the fruit a small red berry. All parts of the tree are impregnated with camphor; but the roots contain most, and therefore are chiefly made use of for the preparation of this commodity; though, in want of them, the wood and leaves are sometimes mixed.

The camphor is extracted by distillation with water in large iron pots filled with earthen heads stuffed with straw; greatest part of the camphor concretes among the straw, but part passes down into the receiver among the water. In this state it is found in small bits like gray salt-petre, or common bay-salt; and requires to be purified either by a second sublimation, or by diffusion in spirit of wine, filtration, and evaporation. If the first method is followed, there will be some difficulty in giving it the form of a perfect transparent cake. A difficulty of this kind indeed always occurs in sublimations; and the only way is to keep the upper part of the glass of such a degree of heat as may keep the sublimate in a half-melted state. Dr Lewis recommends the depuration of camphor by spirit of wine, and then melting it into a cake in the bottom of a glass.

Camphor possesses considerable antiseptic virtues; and is a good diaphoretic, without heating the constitution; with which intention it is often used in medicine. It is likewise employed in fire-works and several other arts, particularly in making varnishes. See Varnish.

This substance dissolves easily and plentifully in various spirits and in oils; four ounces of spirit of wine will dissolve three of camphor. On distilling the mixture, the spirit rises first, very little camphor coming over with it. This shows that camphor, however volatile it may seem by its smell, is very far from having the volatility of ether, and consequently is improperly classed with substances of that kind.

2. Empyreumatic Oils. Under this name are comprehended all those oils, from whatever substance obtained, which require a greater heat for their distillation than that of boiling water. These are partially soluble in spirit of wine, and become more and more so by repeated distillations. The empyreumatic oils obtained from animal substances are at first more fetid than those procured from vegetables; but by repeated distillations, they become exceedingly attenuated and volatile, becoming almost as white, thin, and volatile, as ether. They then acquire a property of acting upon the brain and nervous system, and of allaying its irregular movements, which is common to them with all other inflammable matters when highly attenuated and very volatile; but this kind of oil is particularly recommended in epileptic and convulsive affections. It is given from 4 to 10 or 12 drops; but, though prepared with the utmost care, it is very susceptible of losing its whiteness, and even its thinness, by a short exposure to air; which proceeds from the almost instantaneous evaporation of its more thin and volatile parts, and from the property which the less volatile remainder has of acquiring colour. To avoid this inconvenience, it must be put, as soon as it is made, into very clean glass bottles with glass stoppers, and exposed to the air as little as possible.

The most important observations concerning the method of making the pure animal oil are, first to feed, change the vessels at each distillation, or at least to make them perfectly clean; for a very small quantity of the thicker and less volatile part is sufficient to spoil a large quantity of that which is more rectified. In the second place, Mr Beaumé has observed, that this operation may be greatly abridged, by taking care to receive none but the most volatile part in each distillation, and to leave a large residuum, which is to be neglected, and only the more volatile part to be further rectified. By this method a considerable quantity of fine oil may be obtained at three or four distillations, which could not otherwise be obtained at fifty or sixty.

3. Animal Fats. Though these differ considerably from one another in their external appearance, and fats, probably in their medicinal qualities, they afford, on a chemical analysis, products similar in quality, and differing but considerably in quantity. They all yield a large proportion of oil, and no volatile salt; in which respect they differ from all other animal substances. Two ounces of hog's lard yielded, according to Neumann, two drachms of an empyreumatic liquor, and one ounce five drachms and 50 grains of a clear brown-coloured oil of a volatile smell, somewhat like horseradish. The caput mortuum was of a shining black colour, and weighed 10 grains.

Tallow being distilled in the same manner, two drachms of empyreumatic liquor were obtained from two ounces of it; of a clear brown oil, smelling like horseradish, one ounce six drachms and 12 grains. The remaining coal was of a shining black colour, and weighed 18 grains. A particular kind of acid is now found to be contained in it.

The marrow of bones differs a little from fats, Marrow, when chemically examined. Four ounces of fresh marrow, distilled in the usual manner, gave over three drachms and a scruple of a liquor which smelled like tallow; two scruples and an half of a liquor which had more of an empyreumatic and a fourth smell; two ounces and an half of a yellowish-brown, butteraceous oil, which smelled like horseradish; and six drachms and an half of a blackish-brown oil of the same smell. The caput mortuum weighed four scruples.

All animal fats, when perfectly pure, burn totally away without leaving any feces, and have no particular smell. In the slate in which we commonly find them, however, they are exceedingly apt to turn rancid, and emit a most disagreeable and noxious smell; and to this they are peculiarly liable, when long kept in a gentle degree of heat. In this state, too, an inflammable vapour arises from them, which when on fire is capable of producing explosions. Hence, in those works where large bellows are used, they have been often suddenly burst by the inflammable vapours arising from the rancid oil employed for softening the leather. The expressed unctuous oils of vegetables are subject to the same changes; but from this rancidity they may all be freed most effectually, by the simple process of agitating them well with water; which is to be drawn off, and fresh quantities added, till it comes off at last clear and infusible, without any ill smell. The proper instrument for performing this operation in large is a barrel-churn, having in it four rows of narrow split deals, from the centre to the circumference, each piece set at obtuse angles to the other, in order to give different directions to the oil and water as the churn turns round, thereby to mix them more intimately. The churn is to be swiftly turned round for a few minutes; and must then be left at rest, till the oil and water have fully separated; which will be in 15 or 20 minutes, more or less, according to the size of the churn. When this water is drawn off, fresh water is to be put in, and the churn again turned round, and this continued till the oil is perfectly sweet. If the oil and water are allowed to stand together for some days, a gelatinous substance is found between them, which is not very easily miscible either with oil or water. Chalk, quicklime, and alkaline salts, are found also capable of taking off the rancidity from oils and fats; but have the inconvenience of destroying a part of their substance.

§ 4. RESINS AND BALSAMS.

These are commonly reckoned to be composed of an essential oil thickened by an acid; as the essential oils themselves are found to be convertible into a similar substance, by the exhalation of their more volatile parts. True resins are generally transparent in a considerable degree, soluble in spirit of wine, and possessed of a considerable degree of flavour.

Resins are originally produced by inspissating the natural juices which flow from incisions made in the stems of growing vegetables, and are in that state called balsams. The balsams may be considered as essential oils thickened by losing some of their odoriferous principle, and of their finest and most volatile part. There are several kinds of balsams, which, however, differ from each other only in the smell and degree of consistence; and therefore all yield similar products on distillation. An analysis of turpentine therefore will be sufficient as an example of the analytical and natural properties of all the rest.

The true turpentine-tree is found in Spain and the southern parts of France, as well as in the island of Chio and in the Indies. It is a middling-sized evergreen tree, with leaves like those of the bay, bearing purplish imperfect flowers; and on separate pedicels hard unctuous berries like those of juniper. It is extremely resinous; and unless the resin is discharged, decays, produces fungous excrescences, fowls, bursts, and dies; the prevention of which consists wholly in plentiful bleeding, both in the trunk and branches. The juice is the Chio or Cyprus turpentine of the shops. This sort is quite of a thick consistence, of a greenish white colour, clear and transparent, and of scarcely any taste or smell.

The kind now called Venice turpentine, is no other than a mixture of eight parts of common yellow or black rosin with five parts of oil of turpentine. What was originally Venice turpentine is now unknown, Neumann relates, that the Venice turpentine sold in his country was no other than that prepared from the larix tree, which grows plentifully in some parts of France, as also in Austria, Tyrol, Italy, Spain, &c. Of this there are two kinds; the young trees yielding a thin limpid juice, resembling balsam of copaiba; the older, a yellower and thicker one.

The Straßburg turpentine is extracted from the silver-Strasbourg fir. Dr Lewis takes notice that some of the exotic firs afford balsams, or resins, superior to those obtained from the native European ones; as particularly that called balm of Gilead fir, which is now naturalized to our own climate. A large quantity of an elegant resinous juice may be collected from the cones of this tree: the leaves also, when rubbed, emit a fragrant smell; and yield, with rectified spirit, an agreeable resinous extract.

The common turpentine is prepared from different sorts of the pine; and is quite thick, white, and opaque. Even this is often counterfeited by mixtures of rosin and common expressed oils.

All the turpentines yield a considerable proportion of essential oil. From fifteen ounces of Venice turpentine, Neumann obtained, by distillation with water, four ounces and three drachms of oil. The same quantity distilled, without addition, in the heat of a water-bath, gave but two ounces and an half; and from the residuum treated with water, only an ounce could be obtained. The water remaining in the still is found to have imbibed nothing from the turpentine; on the contrary, the turpentine is found to imbibe part of the water; the residuum and the oil amounting to a full ounce on the pound more than the turpentine employed. When turpentine is distilled or boiled with water till it becomes solid, it appears yellowish; when the process is further continued, of a reddish brown colour: in the first state, it is called boiled turpentine; and in the latter, colophony, or rosin.

On distilling fifteen ounces of turpentine in a retort with an open fire, increased by degrees, we obtain first four ounces of a limpid colourless oil; then two ounces and two drachms of a yellowish one; four ounces and three drachms of a thicker yellow oil; and two ounces and one drachm of a dark brownish red empyreumatic oil, of the consistence of balsam, and commonly called balsam of turpentine.

The limpid essential oil called spirit of turpentine, is exceedingly difficult of solution in spirit of wine; tho' oil difficult, turpentine itself dissolves with great ease. One part of solution of the oil may indeed be dissolved in seven parts of rectified spirit; but on standing for some time, the greatest part of the oil subides to the bottom, a much greater proportion of spirit being requisite to keep it dissolved.

2. Benzoin. This is a very brittle brownish resin, of an exceedingly fragrant smell. The tree which produces benzoin is a native of the East Indies; particularly of Siam and the island of Sumatra. It is never permitted to exceed the fifth year; being, after this time, unfit for producing the benzoin. It is then cut down, and its place supplied by a young tree raised commonly from the fruit. One tree does not yield above three pounds of benzoin.

A tree supposed to be the same with that which affords Benzoin in the East Indies, is plentiful also in Virginia and Carolina; from whence it has been brought into England, where it grows with vigour in the open ground. The bark and the leaves have the smell of benzoin; and yield with rectified spirit a resin of the same smell; but no resin has been observed to issue from it naturally in this climate; nor has any benzoin been collected from it in America.

Benzoin dissolves totally in spirit of wine into a blood-red liquor, leaving only the impurities, which commonly amount to no more than a scruple on an ounce. To water, it gives out a portion of saline matter of a peculiar kind, volatile and sublimable in the fire. See 984 et seq.

The principal use of resins is in the making of lacquers, varnishes, &c. See VARNISH.

§ 5. BITUMENS.

These are inflammable mineral bodies, not sulphurous, or only casually impregnated with sulphur. They are of various degrees of consistence; and seem, in the mineral kingdom, to correspond with the oils and resins in the vegetable.

Concerning the origin of bitumens, chemists are not at all agreed. Some chemical writers, particularly Mr Macquer, imagine bitumens to be no other than vegetable resins altered in a particular manner by the admixture of some of the mineral acids in the earth; but Dr Lewis is of a contrary opinion, for the following reasons.

"Mineral bitumens are very different in their qualities from vegetable resins: and, in the mineral kingdom, we find a fluid oil very different from vegetable oils. The mineral oil is changed by mineral acids into a substance greatly resembling bitumens; and the vegetable oils are changed by the same acids into substances greatly resembling the natural resins.

"From bitumens we obtain, by distillation, the mineral oil, and from resins the vegetable oil, distinct in their qualities as at first. Vegetable oils and resins have been treated with all the known mineral acids; but have never yielded anything similar to the mineral bitumens. It seems, therefore, as if the oily products of the two kingdoms were essentially and specifically different. The laws of chemical inquiries at least demand, that we do not look upon them any otherwise, till we are able to produce from one a substance similar to the other. When this shall be done, and not before, the presumption that nature effects the same change in the bowels of the earth, will be of some weight."

There is a perfectly fluid, thin bitumen, or mineral oil, called naphtha, clear and colourless as crystal; of a strong smell; extremely volatile; so light as to swim on all known liquors, other perhaps excepted; spreading to a vast surface on water, and exhibiting rainbow colours; highly inflammable: formerly made use of in the composition of the supposed inextinguishable greek fire.

Next to this in consistence is the oleum petrae, or petroleum; which is groser and thicker than naphtha, of a yellowish, reddish, or brownish colour; but very light, so as to swim even on spirit of wine. By distillation, the petroleum becomes thinner and more subtile, a gross matter being left behind; it does not, however, easily arise, nor does it totally lose its colour by this process, without particular management or additions.

Both naphtha and petroleum are found plentifully in some parts of Persia, trickling through rocks or swimming on the surface of waters. Kempfer gives an account of two springs near Baku; one affording naphtha, which it receives in drops from subterraneous veins; the other, a blackish and more fetid petroleum, which comes from Mount Caucasus. The naphtha is collected for making varnishes; the petroleum is collected in pits, and sent to different places for lamps and torches.

Native petroleum are likewise found in many different places, but are not to be had in the shops; what is sold there for petroleum, being generally oil of turpentine coloured with alkanet root. The true naphtha is recommended against disorders of the nerves, pains, cramps, and contractions of the limbs, &c., but genuine naphtha is rarely or never brought to this country.

There are some bitumens, such as amber, ambergrise, pit-coal, and jet, perfectly solid; others, such as Barbadoes tar, of a middle consistence between fluid and solid. Turf and peat are likewise thought to belong to this class.

1. Amber. This substance melts, and burns in the fire, emitting a strong peculiar smell. Distilled in a strong heat, it yields a phlegm, an oil, and a particular species of acid salt. The distillation is performed in earthen or glass retorts, frequently with the addition of sand, sea-salt, coals, &c., which may break the tenacity of the melted mass, so as to keep it from swelling up, which it is apt to do by itself. These additions, however, make a perceptible difference in the produce of the distillation: with some the salt proves yellowish and dry; with others, brownish or blackish, and unctuous or soft like an extract: with some, the oil is throughout of a dark brown colour; with others, it proves externally green or greenish; with elixirated ashes, in particular, it is of a fine green. The quantity of oil and phlegm is greatest when coals are used, and that of salt when sea-salt is used.

The most advantageous method of distilling amber, however, is without any addition; and this is the method used in Prussia, where the greatest quantities of oil filled with salt and oil of amber are made. At first a phlegma, our additive liquor distills; then a fluid oil; afterwards one that is thicker and more ponderous; and last of all, an oil still more ponderous along with the salt. In order to collect the salt more perfectly, the receiver is frequently changed; and the phlegm, and light oil, which arise at first, are kept by themselves. The salt is purified, by being kept some time on bibulous paper, which absorbs a part of the oil; and changing the paper as long as it receives any oily stain. For the further depuration as well as the nature of this salt, see SUCCINUM.

2. Ambergrise. This concrete, which is only used as a perfume, yields, on distillation, products of a similar nature to that of amber, excepting that the volatile salt is in much less quantity. See AMBERGREASE.

3. Pit-coal. See the articles COAL and LITHAN. Pit-coal. Bitumens. This substance yields by distillation, according to the translator of the Chemical Dictionary, 1. phlegm, or water; 2. a very acid liquor; 3. a thin oil, like naphtha; 4. a thicker oil, resembling petroleum, which falls to the bottom of the former, and which rises with a violent fire; 5. an acid, concrete salt; 6. an inflammable earth (we suppose he means a piece of charred coal, or cinder) remains in the retort. The fluid oil obtained from coals is said to be exceedingly inflammable, so as to burn upon the surface of water like naphtha itself.

4. Peat. There are very considerable differences in this substance, proceeding probably from the admixture of different minerals; for the substance of peat is plainly of vegetable origin; whence it is found to answer for the smelting of ores, and the reduction of metallic calces, nearly in the same manner as coals of wood. Some forts yield, in burning, a very disagreeable smell, which extends to a great distance; whilst others are inoffensive. Some burn into grey or white, and others into red, ferruginous ashes. The ashes yield, on elixation, a small quantity of alkaline, and some neutral falt.

The smoke of peat does not preserve or harden flesh like that of wood; and the root into which it condenses is more apt to liquefy in moist weather. On distilling peat in close vessels, there arises a clear, insipid phlegm; an acid liquor, which is succeeded by an alkaline one; and a dark-coloured oil. The oil has a very pungent taste, and an empyreumatic smell; less fetid than that of animal substances, but more so than that of mineral bitumens. It congeals, in the cold, into a pitchy mass, which liquefies in a small heat: it readily catches fire from a candle; but burns less vehemently than other oils, and immediately goes out upon removing the external flame. It dissolves almost totally in rectified spirit of wine, into a dark, brownish-red, liquor.

§ 6. Charcoal.

This is the form to which all inflammable matters are reducible, by being subjected to the most vehement action of fire in close vessels; but though all the coals are nearly similar to one another in appearance, there is nevertheless a very considerable difference among them as to their qualities. Thus the charcoal of vegetables parts with its phlogiston very readily, and is easily reducible to white ashes; charred pit-coal, or, as it is commonly called, coal, much more difficultly; and the coals of burnt animal substances, far more difficultly than either of the two. Mr Macquer acquaints us, that the coal of bullock's blood parts with its phlogiston with the utmost difficulty. He kept it very red, in a shallow crucible, surrounded with charcoal, for six hours and more, stirring it constantly that it might be all exposed to the air, without being able to reduce it to white, or even grey ashes. It still remained very black, and full of phlogiston. The coals of pure oils, or concrete oily substances, and root, which is a kind of coal raised during the inflammation of oils, are as difficultly burnt as animal coals. These coals contain very little saline matter, and their ashes furnish no alkali. These coals, which are so difficultly burnt, are also less capable of inflaming with nitre than others more combustible; and some of them, in a great measure, resist even the action of nitre itself.

Charcoal is the most refractory substance in nature; no instance having been known of its ever being melted, or showing the least disposition to fusion, either by itself, or with additions: hence, charcoal is perfectly found to be the most proper support for such bodies as are to be exposed to the focus of a large burning glass. The only true solvent of charcoal is bapar sulphuris. By the violent heat of a burning-glass, however, it is found to be entirely diffusible into inflammable air, without having any residuum. See Aerology, no 129, and Charcoal.

The different substances mixed with different coals, render some kinds of charcoal much less fit to be used in reviving metals from their calces, or in melting them originally from their ores. The coals of vegetable substances are found to answer best for this purpose. See Metallurgy.

Sect. V. Vegetable and Animal Substances.

The only substances afforded by vegetables or animals, which we have not yet examined, are the mucilaginous, or gummy; and the colouring parts obtained by infusion, or boiling in water; and the calculous concretions found in the bodies of animals, chiefly in the human bladder. The colouring matter is treated of under the article Colour-Making, to which we refer; and in this section shall only consider the nature of the others.

§ 1. Mucilage or Gum.

The mucilage of vegetables is a clear transparent substance, which has little or no taste or smell, the consistence of which is thick, ropy, and tenacious, when united with a certain quantity of superabundant water. It is entirely and intimately soluble in water, and contains no disengaged acid or alkali.

When mucilage is dissolved in a large quantity of water, it does not sensibly alter the consistence of the liquor; but, by evaporation, the water grows more and more thick; and, at last, the matter acquires the consistence of gum-arabic, or glue; and this without losing its transparency, provided a heat not exceeding that of boiling water has been used.

Gums, and solid mucilages, when well dried and very hard, are not liquefied in the fire like resins, but swell, and emit many fumes; which are, at first, watery; then oily, fuliginous, and acrid. Distilled in close vessels, an aqueous acid liquor comes over, along with an empyreumatic oil, as from other vegetable substances; a considerable quantity of coal remains, which burns to ashes with difficulty.

Mucilages and gums are not soluble by oils, spirit of wine, alkalies, or acids, except in so far as they dissolve in these liquors by means of the water in which the alkali or acid are dissolved. They are, however, the most effectual means of uniting oil with water. Three parts of mucilage, poured upon one part of oil, will incorporate with it by titration or agitation; and the compound will be soluble in water. Vegetable gums are used in medicine, as well as the mechanic arts: but the particular uses to which each of them is applicable, will be mentioned under the name of each particular gum. The mucilage obtained from animal substances, when not too thick, is called jelly, or gelatinous matter; when further impregnated, the matter becomes quite solid in the cold, and is called glue. If the evaporation is still further continued, the matter acquires the consistence of horn.

This gelatinous substance seems to be the only true animal one; for all parts of the body, by long continued boiling, are reducible to a jelly, the hardest bones not excepted. Animal jelly, as well as vegetable mucilage, is almost insipid and inodorous; but, though it is difficult to describe the difference between them when apart, it is very easily perceived when they are both together. Acids and alkalies, particularly the latter, dissolve animal jellies with great ease; but the nature of these combinations is not yet understood. The other properties of this substance are common to it with the vegetable gums, except only that the animal mucilage forms a much stronger cement than any vegetable gum; and is therefore much employed for mechanical purposes, under the name of glue. See Glue, and Isinglass.

§ 2. Of the Human Calculus.

This substance has been repeatedly examined by the most eminent chemists. Mr Scheele, as has been related n°982, et seq., has been able to extract an acid from it. His account of it in other respects is to the following purpose:

1. All the calculi examined, whether flat and polished, or rough and angular, were of the same nature, and consisted of the same constituent parts.

2. The diluted vitriolic acid has no effect upon the calculus, but the concentrated acid dissolves it, and by abstraction from it is converted into the sulphurous kind, leaving a black coal behind.

3. Neither diluted nor concentrated spirit of salt had any effect upon it.

4. By means of nitrous acid, a new one was produced, and which is possessed of singular qualities, as already mentioned.

5. The solution of calculus in nitrous acid is not precipitated by ponderous earth, nor are metallic solutions sensibly altered by it.

6. It is not precipitated by alkalies, but grows somewhat yellower by a superabundance of the latter. In a strong digesting heat the liquor becomes red, and rings the skin of the same colour. It precipitates green vitriol of a black colour; vitriol of copper, green; silver, grey; corrosive sublimate, zinc, and lead, white.

7. The solution is decomposed by lime-water, and lets fall a white precipitate, soluble in the muriatic acid without any effervescence; but though there be an excess of precipitate, the liquor still remains acid; which happens also with animal earth, and that of fluor dissolved in the same acids. On evaporation to dryness, the matter will at last take fire; but when heated only to a dull red heat in a close crucible, it grows black, smells like burnt alum, and effervesces with acids; being convertible before the blow-pipe into quicklime.

8. Neither this solution, nor the alkaline mixture, is changed by the acid of sugar.

9. The calculus is not changed by acid of tartar, though it is dissolved even in the cold by alkali, when reduced to such a state of causticity as not to discover the least mark of aerial acid. The solution is yellow, and tastes sweetish; and is precipitated by all the acids, even by the aerial. It decomposes metallic solutions, but does not precipitate lime-water; and a smell of volatile alkali is produced by a little superabundance of alkali in the solution. Dry volatile alkali has no effect upon the calculus; but caustic volatile alkali dissolves it, though a pretty large quantity is required for this purpose.

10. Calculus is likewise dissolved by digesting in lime-water; and for this purpose four ounces of lime-water are required to twelve grains of the calculus; but the latter is partly precipitated by adding acids to the solution. By this union the lime-water loses its caustic taste.

11. Calculus is also dissolved entirely by pure water; but for this purpose a large quantity of fluid is required. Eight grains of calculus in fine powder will dissolve by boiling for a short time in five ounces of water. The solution reddens tincture of lacmus, but does not precipitate lime-water; and when it grows cold, the greatest part of the calculus separates in fine crystals.

12. On distilling a drachm of calculus in a glass retort, a volatile liquor was obtained resembling hartshorn, but without any oil; and in the neck of the vessel was a brown sublimate. On heating the retort thoroughly red hot, and then leaving it to cool, a black coal was left, weighing 12 grains, which retained its black colour on a red hot iron in the open air. The sublimate, which had some marks of fusion, weighed 28 grains, and became white by a new sublimation. Its taste was somewhat sourish, but it had no smell; it was soluble both in water and in spirit of wine; but a larger quantity of spirit than of water was requisite for this purpose. It did not precipitate lime-water, and seemed in some respects to agree with the sal succini.

From these experiments our author concludes, that the human calculus is neither calcareous nor gypseous congealed; but consists of an oily, dry, volatile acid, united with some gelatinous matter. The calculus is an composition oily salt, in which the acid prevails a little, since it is soluble in pure water; and this solution reddens the tincture of lacmus. That it contains phlogiston, appears from its solution in caustic alkalies and lime-water, but especially from the effects of the nitrous acid, by which it acquires quite different properties than from solution in alkalies; nor can it be precipitated from this solution. The animal gelatinous substance appears on distillation, by which a liquor is obtained resembling spirit of hartshorn, and a fine coal is left behind.

13. Calculus is found dissolved in all urine, even in that of children. On evaporating four kannes of fresh universally urine to two ounces, a fine powder is deposited as it in urine cools, and a part firmly adheres to the glass. The precipitated powder readily dissolves in a few drops of caustic fixed alkali; and has in other respects all the properties of calculus. Of the same nature is the tenacious sediment deposited by the urine of those who labour under an ague. Mr Scheele suspected at first, that there was in this urine some unknown menstruum which kept such a quantity of powder dissolved, and which might afterwards evaporate by exposure to the air; but altered his opinion on perceiving that the sediment was equally deposited in close vessels.

14. All urine contains some animal earth combined with phosphoric acid; by the superabundance of which acid, acid, the earth is kept dissolved; and by reason of this superabundant acid fresh urine communicates a red colour to laeum. By saturation with caustic volatile alkali a white powder is precipitated; of which three drachms and an half are obtained from four kannes of urine. It is soluble in nitrous acid; and on adding the vitriolic, some gypsum is precipitated. On evaporating the nitrous acid, another remained, which precipitated lime-water; and when mixed with lamp-black, afforded phosphorus by distillation; whence it is evident, that the white powder just mentioned contained lime and phosphoric acid.

15. From these experiments Mr Scheele concludes, that all urine contains, besides the substances already known (viz. sal ammoniac, common salt, digestive salt, Glauber's salt, microcosmic salt, sal perlatus, and an oily extractive matter), a concrete acid, or that of calculus, and animal earth. It is also remarkable, that the urine of the sick is more acid, and contains more animal earth than that of healthy persons. With regard to the sal perlatus, it was afterwards discovered by Mr Scheele not to be a peculiar acid, but only a phosphoric acid dignified by a small quantity of felsil alkali united with it. The analysis is confirmed by synthesis; for, by combining felsil alkali with phosphoric acid, our author obtained a true perlate acid.

In a supplement to Mr Scheele's dissertation on the calculus, Mr Bergman observes, that he could not succeed in dissolving it entirely either in pure water or in the nitrous acid, though the undissolved part was the least in proportion to the fineness of the powder to which the calculus was reduced. The undissolved part appears most conspicuous, when small pieces, or small calculi of a few grains weight only, are put into a superabundant quantity of menstruum, and kept in a degree of heat very near to that which makes water boil. Here it will be observed, that the greatest part of the piece is dissolved; but that at the same time some small white spongy particles remain, which are not affected either by water, spirit of wine, acids, or caustic volatile alkali. If the liquor be made fully to boil, these particles divide into white rare flocculi, and become almost imperceptible, but without any entire dissolution. Mr Bergman could not collect a sufficient quantity of them to determine their nature with accuracy; only he observed, that when exposed to a strong heat, they were reduced to a coal which burns slowly to ashes, and is not soluble in diluted nitrous acid.

"When calculus vesice (says he) is dissolved in nitrous acid, no precipitation ensues on adding the acid of sugar; whence one is readily induced to conclude, that there is no calcareous earth present, because this experiment is the surest way to discover it. But I have found, in a variety of experiments concerning elective attractions, that the addition of a third substance, instead of disuniting two already united, often unites both very closely. That the same thing happens here I had the more reason to believe, because the acid of sugar contains some phlogistic matter, though of such a subtle nature, that, on being burned, it does not produce any fusible coal; and the event of my experiment has shown, that I was not mistaken in my conjecture. In order to ascertain this point, I burned coals of the calculus to ashes, which were quite white, and showed in every respect the same phenomena as lime; caused some effervescence during their solution in acids, united with vitriolic acid into gypsum, were precipitated by the acid of sugar, and were partly soluble in pure water, &c. Notwithstanding this, there remains about one-hundredth part of the ashes insoluble in aquafortis; being the remainder of the substance above mentioned, which, together with the concrete acid, constitutes the calculus. If the calculus be dissolved in nitrous acid, the solution filtered and evaporated to dryness, and the dry mass calcined to whiteness, a calcareous powder is thus likewise obtained."

As pure vitriolic acid contains no phlogiston, our author supposed, that by dropping it, in its concentrated state, into a solution of calculus in nitrous acid, the calcareous earth, if any existed in it, would be discovered. In this he was not disappointed; for when the solution was saturated, some small crystals were thus immediately separated. These, on examination, were found to be gypsum; and, after being dissolved in distilled water, were precipitated by acid of sugar. When the solution of calculus was very much diluted, no change appeared at first on the addition of oil of vitriol; but after a little evaporation, the above mentioned crystals began to appear. Some calculi of the bladder or kidneys at least certainly contain lime, but seldom more than one half in an hundred parts, or one in two parts.

By the assistance of heat, concentrated vitriolic acid dissolves the calculus with effervescence, and the solution is of a dark brown colour. On adding a little water, a kind of coagulation takes place; but by adding more, the liquor again becomes clear, and assumes a yellowish colour. Mr Bergman agrees with Mr Scheele in supposing that the muriatic acid has no effect upon the calculus; but he is in doubt whether it may not extract some part of the calcareous earth.

The red colour assumed by the solution of calculus in aquafortis is remarkable. A saturated solution differs itself in a large open vessel, the liquor assumes at last a deep red colour, and scarcely contains any nitrous acid; for, on the one hand, paper tinged with lacmus scarce shows any reduces; and, on the other, the colour is destroyed irrecoverably by the addition of any acid. By quick evaporation the solution at last swells into innumerable bubbles; the foam grows redder and redder, and at last becomes dark red after it is quite dry. This dry mass communicates its colour to a much larger quantity of water than before, and dissolves very readily in all acids, even such as have no action on the calculus; but they entirely destroy the colour, and that the more quickly in proportion to their degree of strength; even alum has this effect on account of the small quantity of loose acid it contains. Caustic alkalies also dissolve the colouring matter, and destroy it, but more slowly.

Our author endeavours to account for this red colour produced by the nitrous acid, from the peculiar nature of that acid, and the effect it has upon phlogiston. In order to obtain it, a proportional quantity of acid must be made use of, and it ought to be diluted, that there may be no danger of going beyond the necessary limit. If too much be used, it will not produce the proper effect; but, by reason of its superabundance, more or less, or even the whole, will be destroyed in proportion to the quantity. By pouring it in an undiluted state on powdered calculus, it is converted in a few moments into mere foam. The acid of calculus is the more easily separated from the aquafortis by evaporation, as the latter is rendered more volatile by the inflammable particles of the former; alkali added to them both united does not produce any precipitation; a circumstance generally observed where two acids are united. In this case both the acids unite with the alkali, according to the different laws of their attraction. The red mass obtained after desiccation is, however, very different from the concentrated acid, such as is contained in the calculus; for it is of a darker colour, and very deliquescent: the least particle gives a rose colour to a very considerable quantity of water; but the muriatic and other strong acids always certainly destroy it; and, in a longer or shorter time, produce a colourless solution. This remarkable change depends, according to our author, more on the action of the nitrous acid upon the inflammable part, than upon any thing remaining behind.—Such red spots as are produced upon the skin by the solution, are likewise produced upon bones, glass, paper, and other substances; but more time is required for their becoming visible, though this too may be a little accelerated by means of heat.

The following is an abstract of Mr Higgins's experiments upon this subject.

1. Eight hundred and forty grains of dry and well powdered calculus were introduced into a glass retort. It was taken from a laminated stone with a small nucleus, which was likewise laminated. The outward crust appeared very porous, but increased in density towards the centre. By the application of heat, an elastic fluid was first slowly extricated; and which, on examination, appeared to be composed of equal parts of fixed and phlogisticated air. The last portions came over very fast, and were attended with an urinous smell; and, by continuing the distillation, it became evident that fixed and alkaline air came over together without forming any union, as they ought, on the common principles of chemistry, to have done; though our author is at a loss to know why they did not unite, unless they were prevented by the small quantity of inflammable air which came over along with them.

From the beginning of the 10th measure, a black, charry, and greasy matter began to line the conical tube and air-vessel adapted to the retort; and as the proceeds went on, the proportion of alkaline air decreased, while that of the inflammable air was augmented, until towards the end, when the last nine measures were all inflammable; after which no more would come over, though the retort was urged with a white heat. On breaking the distilling vessel, a black powder weighing 95 grains was found in it. On digesting this for an hour in ten ounces of distilled water, and then filtering and evaporating it to two ounces, a yellowish powder was precipitated, but no crystals were formed after standing a whole night. This powder was then separated by filtration, and the liquor evaporated to one ounce; during which time more powder was precipitated. It was then filtered a second time, and the liquor evaporated to half an ounce; when it began to deposit a white powder, and to emit a subacid astringent vapour, not unlike that of vitriolic acid. This white precipitate, when washed and dried, amounted only to one grain, had a shining appearance, and felt very soft, not unlike mica in powder. It was not changed, but rather looked whiter by exposing it to a fierce heat for ten minutes. It dissolved in distilled water without being precipitated by caustic volatile alkali. Mineral alkali, acid of sugar, and nitrated terra ponderosa, rendered the solution turbid; whence our author inferred, that the powder in question was felenite.

After the separation of this powder, the remaining solution was evaporated to dryness with a gentle heat. During the evaporation it continued to emit subacid vapours, leaving eleven grains of a powder of a dirty yellow colour, having an aluminous taste. To this powder he added as much distilled water as was nearly sufficient to dissolve it; after which it was set by for three weeks. At the expiration of this term several small, transparent, and cubical crystals appeared on the side of the vessel above the surface of the solution; and these likewise had an aluminous taste. The whole was then dissolved in distilled water, and the solution filtered. Acid of sugar produced no change in the liquor for at least five minutes, but an immediate cloudiness took place on a mixture with volatile alkali; and on filtering the liquor it was again rendered turbid by mineral alkali, though the caustic alkali already predominated. Nitrated terra ponderosa threw down a copious precipitate, and Prussian alkali discovered a final quantity of iron. This aluminous solution left a yellow substance on the filter; which, when collected and dried, weighed only half a grain; it dissolved without effervescence in nitrous acid; acid of sugar caused no precipitation, but caustic volatile alkali threw down a precipitate which dissolved in distilled water. This solution was rendered turbid by the acid of sugar and muriated terra ponderosa, but no effect was produced by caustic volatile alkali or lime-water.

The yellow powder first deposited by the solution weighed two grains and a half; and by exposure to a strong heat acquired a deep orange colour. On digestion with distilled water, the insoluble part was reduced to three-fourths of a grain, and appeared to be iron; while the soluble part was found to be nothing else but gypsum. Our author, however, is of opinion, that this iron is impregnated with a small portion of vitriolic acid, though not in such quantity as to render it soluble.

The charred matter remaining in the retort was reduced by lixiviation with water to 80 grains. These were calcined with a red heat in an open fire, but could not be reduced to a grey powder in less than three quarters of an hour. When thoroughly calcined and cold, it weighed only 21 grains, which communicated to hot distilled water a limy taste, and gave it the property of turning syrup of violets green. Diluted vitriolic acid had no effect upon it, but it was rendered turbid by aerated volatile alkali and acid of sugar. The remainder when well dried weighed 16 grains, which dissolved in nitrous acid at first with a little effervescence; and when this ceased, the solution went on very slowly, until the whole was taken up. Acid of sugar made no change in the liquid, but the whole was precipitated by caustic volatile alkali. Prussian alkali threw down a grain, or perhaps more, of blue; Calcium, blue; the precipitate digested with distilled vinegar lost a grain and an half, which was thrown down by caustic volatile alkali. The insoluble part being washed and digested in distilled water for half an hour, was partly dissolved; the solution was not affected by caustic volatile alkali, but acid of sugar and nitrated terra ponte rofa caused an immediate cloudiness. Seven grains and an half of the powder, which was insoluble both in acetic acid and distilled water, were readily taken up by diluted vitriolic acid, and precipitated by caustic volatile alkali: the 16 grains last treated, therefore, appeared to contain, of clay 7½ grains; of selenite, five grains; magnesia, one and a half; and of iron, one grain.

The proportions of the different ingredients in the whole calculus, therefore, according to Mr Higgins, are as follow:

| Iron | 2½ | |---------------|-----| | Selenite | 11 | | Clay | 7½ | | Alum | 8 | | Pure calcareous earth | 5 | | Aerated magnesia | 1½ | | Charry combustible substance | 59 |

In all 94½

In this experiment, a darkish yellow sublimate adhered to the neck of the retort; the inner part next the retort more compact, but the rest of a lamellar spongy texture. This sublimate, when carefully collected, was found to weigh 425 grains, and readily dissolved in eight ounces of hot distilled water. A coaly substance was separated from this solution by filtration, which, when washed and dried, weighed ten grains, and when exposed to a red heat burned with a greenish flame, emitting white fumes, which smelled like vitriolic sal ammoniac: the residuum after calcination weighed half a grain, and was of a whitish colour; appearing insoluble in distilled water, but dissolving with effervescence in nitrous acid. Acid of sugar caused a very small precipitation, which did not take place until the mixture had stood for some time; but caustic volatile alkali instantly threw down a precipitate, which was taken up, when washed, by the acetic acid. The quantity was too small to be examined with greater accuracy; but it seemed to possess the properties of magnesia. The saline solution had the colour of small beer; and, when evaporated to two ounces, did not deposit any sediment, or yield any crystals. The black matter with which the conical tube and air vessel were lined, weighed 28 grains, and adhered so fast to the glass, that it was impossible to collect the whole from the fragments of the glass. When dissolved in distilled water and filtered, four grains of coals, similar to that obtained from the former, were procured; but no signs of crystallization were observed after evaporation to one ounce, and suffering the liquor to stand all night.

By this treatment the solution acquired the consistence of treacle; so that it was plainly not crystallizable, and therefore its analysis was plainly to be attempted after a different method. It was now put into a tubulated glass retort, together with six ounces of distilled water to wash it down. By distillation in a sand-bath three ounces of water were procured—which differed in nothing from common distilled water, but in being coloured with a small quantity of the solution from the neck of the retort. On changing the receiver, about half an ounce of liquor of the same kind came over, after which the distillation began to be attended with an urinous smell. This continued barely perceptible for some time; but when about an ounce and an half had passed over, it became so very pungent, that our author could no longer doubt of its being in a caustic state. A small quantity of mild alkali, however, adhered to the lower part of the neck of the retort, some of which was washed down by the distillation; so that the proportions between the two could not be ascertained. The volatile alkaline solution in the retort had the colour of spirit of thornthorn, and like it became darker coloured by the contact of air; on account of the evaporation of part of the alkali, and the rest becoming less capable of suspending the coaly matter mixed with it.

After all the liquor had passed over, and nothing remained in the retort but a small quantity of black matter, the fire was raised; and, as the heat increased, this black substance acquired a white colour, with a kind of arrangement on the surface, which was occasioned by the heat applied to the bottom of the retort being only sufficient to raise the salt to the top of the matter in the retort; but as the sand became nearly red-hot, white fumes began to appear, which condensed on the upper part of the retort, and a little way down the neck. The process lasted until the matter was nearly red-hot, when the fumes ceased, and nothing more passed over. The sublimate, when collected, was found to weigh 72 grains, a black porous brittle substance remaining on the bottom of the retort, which weighed 12 grains. This residuum, when exposed to a strong heat, emitted white fumes, with a slight alkaline smell; by which process it was reduced, with very little appearance of combustion, to a grey powder weighing three grains, which was accidentally lost.

Five grains of this purified sublimate, mixed with as much quicklime, emitted no smell of volatile alkali; and, when thrown upon a red-hot iron, emitted white fumes. The same effect was produced by a mixture of equal quantities of vegetable alkali and sublimate. The remainder, consisting of 62 grains, was divided into two equal parts; the one of which was mixed with two ounces of distilled water, and on the other was poured 60 grains of vitriolic acid diluted with half an ounce of water. These two mixtures being suffered to remain for six weeks, seemed to be but little acted upon. That with vitriolic acid was then put into a small matras, and boiled on sand for half an hour with two ounces of distilled water, when the whole was taken up. The solution looked clear, and deposited nothing on standing. Mild mineral alkali had no effect upon it; but mild vegetable alkali threw down a copious sediment in white flocculi, which was redissolved by caustic alkali, lime-water, and partly by mild mineral alkali. Phlogisticated alkali, acid of sugar, and acid of tartar, had no effect upon it. The other portion of sublimate, which had been mixed with distilled water, was very little dissolved; but on pouring it into a matras some small round lumps were observable on the bottom of the glass. These were... Calculus, six or seven in number, some weighing a whole grain, others not more than one-half. They were very hard and compact, with a smooth surface, and in figure resembling the nucleus of the original calculus. The whole was then put into a matras with about three ounces of water. On boiling it on sand for three quarters of an hour, about one-half of it was taken up; the solution passed the filter very clear whilst hot; but on cooling became turbid, and at last deposited white flocculi, which were redissolved on the addition of caustic volatile alkali and lime-water. It turned syrup of violets green; which, however, our author thinks might have been occasioned by its retaining volatile alkali, though it had not the smallest appearance of any such impregnation. He has nevertheless frequently observed, that sometimes the purest vegetable alkali contains volatile alkali, notwithstanding the various operations and degrees of heat it undergoes before it can be brought to the degree of purity at which it is called salt of tartar.

On filtering the solution to separate what had been deposited by cooling, no change was produced in the filtered liquor by mineral alkali; but mild vegetable alkali produced a cloudiness, which was instantly taken up on adding mineral alkali and lime-water. Neither Prussian alkali, nor the acids of arsenic, tartar, sugar, or borax, nor any of the three mineral acids, had any effect upon it.

2. An hundred and twenty grains of the same calculus were put into a tubulated glass retort, and half an ounce of strong nitrous acid poured upon it. An effervescence immediately ensued; and some part of the extricated aerial fluid being preserved, appeared to be fixed air mixed with a small quantity of nitrous air. When the effervescence ceased, a quarter of an ounce more of nitrous acid was added. On digesting the mixture upon hot sand for an hour, it emitted nitrous vapour and nitrous air; but the latter in very small proportion. When the solution was completed, the whole was poured into a small matras, and gently boiled till the superabundant nitrous acid was nearly expelled. The solution was of a deep yellow colour and turbid; but on adding five ounces more of water, and digesting it for a quarter of an hour longer, it acquired the colour and consistency of dephlogisticated nitrous acid. On cooling it became somewhat turbid, and in a few days deposited a darkish yellow powder; which, when separated, washed, and dried, weighed little more than a quarter of a grain, and, on examination, was found to be a calx of iron.

Our author being desirous to know what effect the sun would have upon it, placed it in a window where the sun shone full upon it for four hours every day. Here a little moisture seemed daily to exhale from it, the weather being hot, and the matras, which had a short wide neck, being only covered with bibulous paper to keep out the dust. In this situation, in the course of a week, a few very small crystals appeared to float upon the surface. These in time fell to the bottom, where they adhered together so as to form a hard concretion, still retaining a crystalline appearance, but so small and confused, that it was impossible to distinguish their figure; and this deposition of crystals continued for a month, after which it seemed to cease. The solution was then filtered to separate the salt; after which one-half of the liquor was evaporated away, and the rest set in the usual place for a fortnight longer, but no more crystals appeared. The salt, which weighed three grains, was then digested in four ounces of distilled water; but no part seemed to be dissolved. Three ounces of the water were then decanted off, and six drops of vitriolic acid added to the remainder, which by the help of digestion seemed to dissolve the salt slowly; but on adding half an ounce more distilled water, the whole was readily taken up. Acid of sugar had no effect on this solution; but lime-water rendered it turbid. The whole was then precipitated with caustic volatile alkali, and the solution filtered, which likewise threw down the lime from lime-water. The precipitate was then washed, and distilled vinegar poured upon it, which did not take it up; but it was dissolved by marine acid. Phlogisticated alkali had no effect upon it; and the acid of sugar occasioned very little cloudiness after standing three or four hours; from which our author supposed that the matter was phosphorated clay.

The solution, being now free from iron and phosphorated clay, had a putrid taste, and looked clearer, though still retaining a yellow cast. Acid of sugar had no effect upon it; but nitrated terra ponderosa threw down a precipitate, as did likewise the caustic volatile alkali. Mild vegetable alkali caused no precipitation; which our author attributed to the solution of the manganese and clay by the fixed air extracted from the alkali. Two-thirds of the solution were then put into a small glass retort, and two ounces distilled off, which had no taste, but smelled very agreeably, and not unlike rose-water. After all the liquor had passed over, white fumes appeared in the retort, and these were soon followed by an aerial fluid. On collecting some of this, a candle was found to burn in it with an enlarged flame. Nitrous air did not diminish it in the least; and it seemed to be that species of air into which nitrous ammonia is convertible. No more than 13 or 14 inches of this kind of air could be obtained; and as soon as it ceased to come over, crystals were observed in the lower part of the neck of the retort. On augmenting the heat, a white salt began to sublime and adhere to the upper part of the retort; the operation was continued until the retort was red-hot; but, on breaking it, the quantity of sublimate was so small, that very little of it could be collected; though, from the small quantity obtained, our author was convinced of its being the same in quality with what was obtained in the former analysis. The salt which crystallized in the neck of the retort was nitrous ammonia, as appeared from its detonation per se, &c. A grey powder was left in the bottom of the retort, which hot distilled water partly dissolved: muriated terra ponderosa, acid of sugar, and vegetable alkali, rendered this solution turbid; but caustic volatile alkali had no effect upon it. The remaining part of the powder which was left by the distilled water, readily dissolved with effervescence in the marine acid, and was precipitated by caustic volatile alkali; the part soluble in distilled water appearing to be gypsum, and that soluble in marine acid to be magnesia.

From all these experiments, Mr Higgins concludes the composition of the human calculus to be vastly different. ferent from what either Mr Scheele or Mr Bergman have supposed it to be. "It appears (says he), that the calculus was composed of the following different compounds blended together; viz. selenite, alum, microcosmic salt, mild volatile alkali, lime, and caustic volatile alkali, combined with oil, so as to form a faponaceous mass; calc of iron, magnesia combined with aerial acid, clay enveloped by a faponaceous and oily matter, and the sublimate already described." Considering this to be the true state of the calculus in the bladder, the small proportions of clay, selenite, magnesia, and iron, which are the most insoluble of the ingredients; the great solubility of microcosmic salt and alum, and the miscibility of lime, volatile alkali, and oil, in water; tend to show, that the sublimate is the cementing ingredient. Indeed, its insolubility in water, and property of forming nuclei out of the body, as above observed, leave no room to doubt it. The proportion of the other ingredients, and very likely their presence, depend upon chance, volatile alkali and oil excepted; therefore this sublimate should be the object of our investigation.

Mr Higgins concludes his dissertation with some practical remarks concerning the remedies proper for dissolving the stone, for counteracting that disposition in the body which tends to produce it, and concerning the regimen proper for those who are to undergo the operation of cutting for it. "The effect of mild mineral alkali (says he) on the sublimate, is well worth the attention of those who may have an opportunity of trying its efficacy. Mild mineral alkali may be taken in large doses, and continued for a length of time with impunity to the most delicate constitutions, only observing a few circumstances; but this alkali, in a caustic state, must very often be attended with mischievous consequences. Besides, if we consider that it must enter the mass of blood before any part can reach the bladder, and the small portion of the dose taken fermented with the urine, and, lastly, the action of caustic alkali upon animal substances; we shall be at a loss to know on what principle caustic alkalis have been recommended in preference to mild. Soap itself might as well be recommended at once; for soon after caustic alkali is taken, it must be in a faponaceous state. Fixed vegetable alkali should be avoided, and the preference given to the other two alkalis. As it is evident that alkalis have no real action on the stone in the bladder, though their efficacy has been experienced in alleviating the disease when timely administered, their mode of action is only explicable in the following manner: They either prevent the generation of the sublimate in the system, or else keep it in solution in the mass of fluids; and being in the utmost degree of divisibility, its ultimate particles are capable of passing through the most minute emunctories; by which means it is carried off by other secretions as well as the urinary. Thus the urine, not being saturated with this matter, acts as a solvent on the stone; and as the most soluble parts are first washed away, it falls through time into fragments of irregular surfaces, which by their friction irritate and inflame the bladder, as has been observed by several practitioners.

"Allowing that the sublimate is the cementing substance in the calculus, and judging, from the effects of alkalis upon it, their modus operandi in the constitution, it remains now to inquire into the origin of the calculus. Mr Scheele has found this sublimate in the urine of different persons; and hence inferred, that it was a common secretion; but it still remains to be ascertained, whether there be a greater quantity of it procured from the urine of patients who labour under this disorder than in those who do not? If this should not be the case, may not a deficiency of volatile alkali in the constitution be the cause of concretions in the kidneys, bladder, &c.; or, which must have the same effect, too great a proportion of acid, which, uniting with the alkali, may take up that portion which would have kept the sublimate in solution until conveyed out of the system by the urinary and other secretions; and may not this be the phosphoric acid? If this latter should be the case, an increase of microcosmic salt must be found in the urine; but if the former, a decrease of the volatile alkali, and no increase of the neutral salt. The small quantity of phosphoric acid found in the calculus proceeds from the solubility of microcosmic salt. Do not volatile alkali and phosphoric acid constitute a great part of the human frame? and is there not a process continually carried on to generate these in the system? and is not this process liable to be retarded or checked by intemperance, &c., which may vary their quantities and proportions? and may not a due proportion of these be necessary to a vigorous and sound constitution? If so, no wonder that an increase or deficiency in either or both of these should be productive of several disorders."

On this subject, however, our author has not had sufficient leisure to make the experiments necessary for its elucidation. Indeed, it seems not easy to do so; as, in his opinion, at least 500 would be required for the purpose. "That the urinary sublimate is present in tubercles found in the lungs of persons who die of pulmonary consumptions, and likewise in what are called calculi vulgarly called chalk stones, is what I have experienced; found in but in what proportion, or whether in quantities sufficient to cause the concretion, is what I cannot say; but for I have had but a few grains of each to examine, please. I have every reason to suspect, that consumptions and scorbutic complaints very frequently arise from a superabundance of this sublimate in the system; and that it is chiefly the cause of the gout and rheumatism, and solely the cause of the stone in the bladder. I make no doubt but these disorders generally proceed from obstructions; and it is probable, that either a precipitation of this sublimate in the system, or else a deficiency of some other secretion, which would hold it in solution until conveyed out of the body, may be the chief cause of these obstructions; and likewise, that different degrees of precipitation may produce different symptoms and disorders.

"That mineral or volatile alkali and bark have been useful in the above disorders, has been affirmed by experienced physicians; and I know an instance myself of mineral alkali and nitrous ammonia being serviceable in a pulmonary complaint of some standing.

"With respect to the stone, when it acquires a certain magnitude, it is absurd to attempt to dissolve it in the bladder, it wastes too very slowly; and during this time the patient must suffer vast pain, particularly when..." when the stone acquires a rugged surface; therefore cutting for it at once is much preferable.

"Mineral alkali taken in the beginning of the complaint, and before the stone accumulates, will no doubt check its progress, and may in time change that dis-

**APPENDIX**

Containing such Discoveries as have appeared since the Compilation of the Article, and which could not be inserted in their proper Places.

I. **VITRIOLIC ETHER.**

M. Pelletier formerly proposed a method of rectifying this fluid by putting manganese into the vessels; but as the vitriolated manganese might perhaps communicate some injurious quality, another method is proposed by M. Tingry. After first drawing off the ether, he adds a diluted solution of volatile alkali, and avoids as much as possible the dissipation of the vapours: the ether is then redistilled. It may afterwards in this way be washed more safely, and with less loss. The little proportion of the ether which is separated in the water, may be again recovered, or the water may be again employed for the same purpose. M. Lunel proposes calcined magnesia for this purpose, as its salt is not soluble; though perhaps pure terra ponderosa might be better.

II. **NITROUS ACID.**

On this subject Mr Higgins has several curious and interesting observations. "It is not an easy matter (says he), to ascertain exactly the greatest quantity of dephlogisticated air, which a given quantity of nitrous acid may contain. I always found nitre to vary, not only in its product of phlogisticated and dephlogisticated air, but likewise in their proportion to one another. The purest nitre will yield, about the middle of the process, dephlogisticated air so pure as to contain only about \( \frac{1}{7} \) of phlogisticated air. In the beginning, and nearly about the latter end of the process, air will be produced about twice better than common air. On mixing the different products of a quantity of pure nitre, it was found that, by exposure to liver of sulphur, \( \frac{1}{2} \) part was left unabsorbed; and this was the utmost purity in which I obtained dephlogisticated air from nitre.

According to M. Lavoisier, 100 grains of nitrous acid contain 79\( \frac{1}{2} \) of dephlogisticated air, and 20\( \frac{1}{2} \) of phlogisticated air, which is not quite four to one. But his experiments contradict this; for whatever mode he adopted to decompose nitrous acid, it appeared that the proportion of dephlogisticated air was nearly as five to one of phlogisticated air.

Mr Cavendish has proved, that nitrous acid may be formed by taking the electric spark in a mixture of three parts of phlogisticated air, and seven of dephlogisticated air, which is but \( \frac{1}{4} \) more of dephlogisticated air than nitrous air contains; which may apparently contradict M. Lavoisier's, as well as my own, estimation of the proportion of the constituent principles of ni-

trous acid, when in its perfect state. The red nitrous vapour contains three parts of nitrous air and one of dephlogisticated air, or one of phlogisticated and three of dephlogisticated air; but nitrous vapour may be formed with a less proportion of dephlogisticated air; and which, though it may not be so condensible as a more perfect nitrous vapour, yet will, when in contact with pure alkali, unite with it, and form nitre, as was the case in the experiment of Mr Cavendish. The common straw-coloured nitrous acid contains more dephlogisticated air than the red nitrous acid or vapour; the proportion appears to be about four to one; but the colourless contains about five of dephlogisticated to one of phlogisticated air.

Having once a charge of nitrous and vitriolic acid Method of in a green glass retort, I put it in a sand pot to obtaining fill; but the pot being small, the edge came too near the retort, about a quarter of an inch or more above the charge; which, before the process commenced, and when it acquired more than the heat of boiling water, cracked it all round in that direction. Being thus situated, I was obliged to withdraw the fire, and before the charge got cold, to ladle it into an earthen pan. On introducing it into a fresh retort, I obtained from it nitrous acid nearly as colourless as water. The vitriolic acid used in this process not being very perfect, the goodness of the nitrous acid was attributed to the purity of the nitre from whence it was distilled; but in another process, though the same nitre was used with much purer vitriolic acid, the produce was of an high straw colour. On recollecting the above-mentioned circumstance, the vitriolic acid and nitre were next mingled in due proportion, and exposed in an earthen pan set in sand, to nearly the heat of boiling water, for half an hour or more, continually exposing fresh surfaces to the air. When the charge was quite cold, I introduced it into a retort, and distilled as colourless nitrous acid as the former. As no nitrous air was emitted during digestion, it must have imbibed dephlogisticated air from the atmosphere."

Mr Prout found, that strong nitrous acid will set fire to charcoal if it be rendered very dry. He likewise remarked, that charcoal exposed to the air a few hours after calcination, was unfit for the experiment. Charcoal, he observes, attracts moisture very forcibly. The first effect of the charcoal on the nitrous acid, he observes, is to withdraw a portion of its water from it; by which it is rendered highly concentrated, at the same time that the condensation of the water heats the charcoal in a small degree, but sufficiently to volatilize a nitrous vapour; which, as soon as it reaches that portion of dry charcoal next the humid part, is condensed. Nitric acid, when heated, generates heat enough to promote the decomposition of nitrous acid. Hence we see why the experiment will not succeed if the acid be poured on the surface of the charcoal.

The effect of nitrous acid on blood, according to Mr Higgins, is very singular. Two parts of blood procured fresh at the butchers, one of strong nitrous acid, and about one fifth of the whole of water, were digested in the heat nearly of boiling water (fresh portions of water being occasionally added until the whole of the acid was expelled), when it acquired almost the colour, and exactly the taste, of bile. When mixed with a large quantity of water, it acquired a fine yellow colour; and, on standing, deposited a substance of a brighter yellow, though the supernatant liquor still retained a yellow colour and bitter taste, but not so intensely as when the precipitate was suspended in it. The different stages of this process were well worthy of observation. No nitrous air was produced, and the acid was expelled in the state of a white vapour. The liquor was found to increase in bitterness as the acidity vanished. About the middle of the process, the solution first tasted acid, but was quickly succeeded by a bitter sensation. It appears that the nitrous acid took deploglificated air from the blood; for though red nitrous acid was used, it was expelled in a perfect state.

III. NITRE.

Though the artificial generation of the nitrous acid, from a mixture of deploglificated and phloglificated air, is now sufficiently understood, yet we do not well know in what manner nature performs the operation. Some chemists, particularly M. Thouvenel, have found, that putrefaction favours the production of nitrous acid. All animal substances, during their decay, give out a vast quantity of phloglificated air; therefore, if deploglificated air be present, it will unite to the phloglificated air in its nascent state, and form nitrous acid: but Mr Higgins has observed, that nitrous acid may be generated in plenty where there is no putrid process going on. "The chemical laboratory at Oxford (says he) is near six feet lower than the surface of the earth. The walls are constructed with common limestone, and arched over with the same; the floor is also paved with stone. It is a large room, and very lofty. There are separate rooms for the chemical preparations, so that nothing is kept in the laboratory but the necessary implements for conducting experiments. There is an area adjoining it on a level with the floor, which, though not very large, is sufficient to admit a free circulation of air. The ashes and sweepings of the laboratory are deposited in it. There is a good fink in the centre of this area, so that no stagnated water can lodge there. Notwithstanding all this, the walls of the room afford fresh crops of nitre every three or four months. Dr Wall, who paid particular attention to this circumstance, and who told me it contained fixed vegetable alkali, requested I would analyse it, and let him know what it contained. I found that two ounces of it contained six drachms of nitrated fixed vegetable alkali, and three of calcareous nitre. The nitre first appears in small whitish filaments as fine as cob-web, which, when they get a little larger, drop off; so that they never acquire sufficient growth to distinguish their figure to a naked eye. On finding that they contained fixed vegetable alkali, I concluded that it proceeded from minute vegetation; but in this I was mistaken; for I found that they were soluble in water, and that they detonated with charcoal at every stage of their growth. Having swept this saline efflorescence from the wall, I dug deep into it, but could not obtain nitre from it. When a part had been white-washed, it yielded nitre, but not so abundantly as a neighbouring spot which had not been treated in the same manner. Hence it is evident, that nitrous acid may be formed without the affluence of putrefactive processes in a still damp air, where there is a sublimate to attract it when half formed, whereby it is in time brought to perfection. The above facts moreover prove, that fixed vegetable alkali is a compound."

IV. MARINE ACID.

Mr Higgins informs us, that he has, with a view to decompose sea-salt, mixed it with manganese in various proportions, and exposed them in a reverberating furnace in a well closed crucible for three hours, to a heat nearly sufficient to melt cast iron. In the same manner he treated manganese, salt, and charcoal, as well as clay, salt, and charcoal, and salt and clay alone, with very little success. He treated calcined bones, salt, and charcoal, and calcined bones and salt, as well as lime and salt, in the same manner, without effecting any apparent change in the salt. He was informed, however, by Mr Robertson, apothecary in Bishopsgate-street, that he had partially alkalized it, by exposing it with clay to a fierce heat; but that soon after it got into contact with air, it became neutral again. "If common salt and litharge be fused (says Mr Higgins), it is in part decomposed; the acid suffers no decomposition, but unites with the lead; whereby it acquires, when the saline matter is washed away, a yellow colour. It is evident (adds he) from these facts, that the basis of marine acid is a combustible body, and quite different from light inflammable air, charcoal, or any known inflammable substance; and that it attracts deploglificated air with greater force than any substance hitherto discovered. Though charcoal will decompose all other acids, except a few, when united to bodies which will fix them until they acquire a sufficient degree of heat, yet it has no effect on marine acid."

According to Fourcroy, if alkaline air be confined by mercury, and deploglificated marine acid air be added to it (which must be done quickly, as the acid air would dissolve the mercury), each bubble produces a flight detonation, and furnishes a very amusing spectacle.

Though in this country the distillation of spirit of salt with clay has long been entirely laid aside for the distilling proceeds with oil of vitriol, yet it is still practised in other countries, and may be effected in the following manner: Having previously decrepitated the salt, and dried the clay, they are then to be ground, mixed, and sifted together. The mixture is next to be worked with a spatula, and then with the hands, until it is brought into a moderately stiff and uniform mass. This is to be divided into balls about the size of a pigeon's egg, so that they can pass through the neck of the retort; but before they are put into the distilling vessel, it is proper to dry them thoroughly. The retorts must be of stone ware, and carefully coated, in order to prevent them from breaking with the intense heat to which they are exposed. They are to be filled two-thirds full of materials, and the distillation must be performed in a reverberatory furnace. The receiver at first is not luted on, because that which rises in the beginning of the distillation, being very aqueous, is to be put by itself. When this has come over, another receiver is then to be applied, and cemented with fat lute, and covered with a cloth daubed with a mixture of lime and the whites of eggs. The heat is to be raised until the retort is red-hot, and continued in this degree until the distillation ceases.

Various proportions of clay and salt have been recommended for this process; but it seems probable that not less than ten parts of clay to one of salt, as Pott has directed, will be found necessary. Instead of the clay, some direct the use of bone; but this is inconvenient, on account of the iron it contains. Powdered talc has also been recommended, but this is not always free from iron; and where a very pure spirit is wanted, there is a necessity for having recourse to oil of vitriol, and glass or stone-ware vessels. As the marine acid cannot be separated from the earthy mixtures above mentioned, but by means of moisture, M. Beaumé advises to moisten the residuum, and repeat the distillation, by which more acid will be obtained.

As marine acid has very little action upon phlogistic matters, it cannot therefore affect oils, either expressed or essential, in a manner similar to the vitriolic or nitrous. M. Marges, however, has observed yellow crystals resembling amber formed in bottles, containing a mixture of oils and marine acid of moderate strength, which had stood for several months. The little effect which the marine acid has upon these substances was first supposed to be owing to its want of phlogiston in itself; but when it was afterwards found, that, by the application of certain substances which have a great attraction for phlogiston, the marine acid was rendered capable of uniting very readily with inflammable matters, the former theory was abandoned. It was now asserted, that the acid, instead of containing no phlogiston, was naturally endowed with a very considerable quantity; and that, in its new state, it was deplogisticated by the substances applied. On the other hand, the antiphlogisticians asserted, that no change was thus made upon it, farther than adding a quantity of pure air, which they suppose to be the basis of all acids. On this subject, however, M. Cornette maintains, that the marine acid seems to have so little action upon inflammable substances, merely because it is weaker than the rest; and likewise that it is often previously combined with some inflammable matter, by which its attraction is prevented. He maintains, that if the marine acid be concentrated in such a manner as to render its specific gravity to that of water as 19 to 16, it will then act upon oils with heat and effervescence, reducing them to a black and thick substance, and even burning them to a kind of coal. Some experiments have been made by Mr. Hafle, with a view to investigate the action of the marine and vitriolic acids upon balsams and oils; for which purpose he mixed two drachms of smoking spirit of salt with one of each of the oily substances to be tried. The results were, that Canada balsam gained one scruple in weight; balsam of capivi 19 grains; florax, and Venice turpentine, each one scruple; asphaltum 18 grains; but the essential oils of aniseed, benzoin, bergamot, coriander, and many others, were not altered in any degree. The action of this acid upon inflammable matters, however, is augmented by its being reduced into the form of air.

Gmelin relates, that, by distilling a mixture of five parts of salt, twelve of spirit of wine, and four of vitriolic acid, to which he had previously added one or two parts of water, he obtained a completely dulcified spirit of salt, and an imperfectly dulcified spirit of vitriol, upon rectifying the liquor.

Homberg found, that glass was corroded by the glass corrosive acid; and his observation has been confirmed by Dr. Priestley; who finds that its corrosive power is augmented by confining the acid in tubes hermetically sealed. Its power is exerted not only on flint-glass, but even on common green glass; though more powerfully on the former, where it chiefly attacks the lead used in its composition. By inclosing marine acid gas for some weeks in a glass tube exposed to heat, an incrustation was formed on the inside, while the air was diminished to $\frac{1}{3}$ of its original bulk, one half of which was absorbed by water; the other was phlogisticated air.

The marine acid is generally met with of a yellow or reddish colour, which by Macquer is given as one of its characteristic marks. In general, however, this colour is thought to proceed from iron; but Dr. Priestley acid has found that it may be produced by many different substances; and his observations have been confirmed by Scheele and other chemists. The Doctor is of opinion that it is occasioned for the most part, if not always, by a mixture of earth; and he was able to communicate it by means of calcined oyster-shells, calcined magnesia, pipe-clay, or pounded glass; but not by wood-ashes, from whence the air had been expelled by heat. It was effectually discharged by flowers of zinc, a coal of cream of tartar, and by liver of sulphur; but he found, that the colour which had been discharged by liver of sulphur, would return by mere exposure of the acid to the atmosphere, but not that which had been discharged by flowers of zinc.

Dephlogisticated Spirit of Salt.

When the action of this vapour upon anything is to be examined, the substance must be put into a bottle method of bleaching in such a manner as to remain in contact with it; or it may be put into a glass tube, which is suspended and fixed to the stopper, and thus introduced into the bottle. From its property of destroying all vegetable colours, it promises to be of very considerable use in the arts, provided it could be had in sufficient quantity, and cheap. It bleaches yellow wax, and when properly applied to linen, will whiten it sufficiently, and without injury, in a few hours. This may be effected by steeping the linen for that space of time in water impregnated with the deplogisticated marine gas. It unites with this fluid rather more easily than fixed air. Berthollet, in order to impregnate water with it without exposing the operator to the fume, which is extremely disagreeable, put the mixture of marine acid and manganese into a retort. To this he applied first an empty bottle, and then several others filled with water, and communicating with each other by means of bent tubes; surrounding the whole with ice. When the water in the bottles was saturated, the gas became concrete, and fell to the bottom; but with the smallest heat it arose to the top in bubbles. The specific gravity of the saturated water was to that of distilled water, when the thermometer was only five degrees above the freezing point, as 1003 to 1000. This impregnated water is not acid, but has an auster taste, and has the same action as the gas, though in a weaker degree. Mr Berthollet has observed, that the addition of alkalis does not prevent, but rather promotes, the discharge of colours; for which reason he directs to add a fixed alkali to the impregnated water in which linen is to be steeped for bleaching. This is the expeditious method hinted at under the article Bleaching; but which has not hitherto come into use, principally through the high price of the dephlogisticated gas.

The dephlogisticated marine acid does not discharge all colours with equal ease. Those of litmus and syrup of violets are entirely destroyed, and turned white. The colouring matter of Brazil-wood, and some green parts of plants, retain a yellow tint. The leaves of evergreen plants resist its action for a long time, and at last only acquire the yellow colour which they assume by long exposure to the air; and in general the changes of colour which vegetable matters suffer from this gas, are similar to those which take place on long exposure to the air; and by this operation the gas is converted into common marine acid.

Oils and animal fats are thickened by this gas; and by these and other inflammable substances it is reduced to the state of common marine acid. Light is said to produce the same effect. It unites with fixed alkalies and calcareous earths, but without any sensible effervescence; and thus they lose their peculiar taste and colour. M. Berthollet having boiled in a retort, to which a pneumatic apparatus was affixed, some of the dephlogisticated marine acid liquor with mineral alkalies, thus obtained a considerable quantity of elastic fluid, composed partly of fixed air, partly of the air contained in the vessels, and partly of air considerably purer than that of the atmosphere. The result of the combination was common salt. On repeating the experiment with lime, no fixed air was obtained; but that which came over became gradually more and more dephlogisticated. Volatile alkali, even when caustic, occasioned an effervescence, and emitted a peculiar kind of air, which was neither fixed nor dephlogisticated, but of a peculiar kind.

Green vitriol is changed to a red by the dephlogisticated gas, but the colour of blue and white vitriols is not affected. By the influence of light, it acts upon phosphorus, and the result is phosphoric and common marine acids. It does not dissolve ice nor camphor; in which respects it differs from the common marine acid gas.

On mixing marine acid, manganese, and spirit of wine, and distilling them with a very gentle heat, little air of any kind is produced, but a quantity of ethereal liquor very slightly acid. The proportions used by Pelletier were an ounce and a half of manganese, five ounces of concentrated marine acid, and three ounces of spirit of wine. "In this process (says Mr Keir), the whole of the dephlogisticated acid seems to have united with the spirit of wine, and to have formed ether. The difficulty of combining marine acid with spirit of wine, so as to form an ether, is well known; and though there have been some approximations to it, yet the only instances in which it has been completely effected, have succeeded in consequence of the marine acid being dephlogisticated; by which its action on spirit of wine, as well as on all inflammable matters, is greatly increased."

M. Pelletier has observed, that when we put a bit of phosphorus into dephlogisticated marine gas, the former is immediately dissolved, and a light is perceived, the vessel being filled at the same time with white vapours. He has likewise observed, that sea-salt, with an excess of pure air, thrown into heated vitriolic acid, produces a small detonation. To make this fall from in quantity, take, for instance, ten pounds of sea-salt, the acid in mixing it with three to four pounds of manganese, quantity, pour on the mixture ten pounds of vitriolic acid, and distil with Woulfe's apparatus. Pass the disengaged acid through a solution of fixed vegetable alkali, either caustic or otherwise. A little more than ten ounces of the new marine salt with excess of pure air is obtained, and a quantity of salt of Sylvius, or digestive salt. The salt with excess of pure air crystallizes first, and by means of repeated crystallizations, is entirely disengaged from the other.

V. Aqua Regia.

This acid, which is named from its property of dissolving gold, is compounded of the nitrous and marine acids. Gold and platinum cannot be dissolved in any other menstruum, nor can regulus of antimony and tin be so easily dissolved by any other as aqua regia. It may be made in various ways. 1. By adding the two acids to each other directly. 2. By dissolving in the nitrous acid some salt containing marine acid, particularly sal ammoniac and common salt. 3. By distilling nitrous acid from either of these salts. And, 4. In Dr Priestley's method of impregnating marine acid with nitrous acid vapour.

The only difference between those liquors prepared by the methods above mentioned is, that when sal ammoniac or sea-salt are dissolved in the nitrous acid, the aqua-regia contains a quantity of cubic nitre, or nitrous ammoniac, which, tho' it cannot much affect the acid as a solvent, may make a considerable difference in the nature of the precipitate. Thus, gold precipitated from an aqua-regia formed by the pure nitrous and marine acids, does not sublime, though it does so when precipitated from one made with sal ammoniac. There are no established rules with regard to the proportions of nitrous and marine acids, or of nitrous acid and sal ammoniac, which ought to be employed for the preparation of aqua-regia. The common aqua-regia is made by dissolving four ounces of sal ammoniac in 16 ounces of nitrous acid; but these proportions must be varied, according to the nature of the intended solution. Platina, for instance, is dissolved in the greatest quantity by equal parts of the two acids; regulus of antimony by four parts of nitrous acid to one of marine; and, in general, the greater the quantity of marine acid employed in the mixture, the less are the imperfect metals, particularly tin, calcined or precipitated by it. A mixture of two parts of spirit of nitre, and one of spirit of salt, dissolves nearly an equal weight of tin into a clear liquor, without forming any precipitate; but, for this purpose, the operation must be conducted slowly, and heat avoided as much as possible.

VI. Borax.

In a memoir in Crell's Chemical Annals, by M. Tychon, the author shows, by different experiments, that it may sometimes be purified by solution, filtration, and evaporation only; but that sometimes the operation is more easy and effectual by previous calcination; but then the product is a little lefened, especially if the calcined mass be not well powdered, and then boiled sufficiently in water. Powder of charcoal, he says, may be sometimes advantageously employed in the purification; but in general there is no difference between the crude and purified borax, except in the addition of extraneous matters; at least, as the quantity of acid is the same, the addition of mineral alkali is useless: these extraneous matters are an animal fat, and a sand composed of clay, lime, and a martial earth. If the oily matter of tartar be separated by passing the lixivium through a stratum of clay, as is supposed in the preparation of the crystals at Montpellier, it would suggest a method of greatly abridging the process of the purification of borax.

VII. Acid of Borax, or Sedative Salt.

On the preparation of this salt Mr Beaumé observes, that a little more acid ought to be added to the borax than what is just sufficient to saturate its alkaline basis. Unless this be done, the sedative salt remains confounded with the other saline matters in the solution, and of consequence the crystallization must be disturbed. The salt, though formed in an acidulated liquor, is easily deprived of its superfluous acid by draining upon paper. It does not crystallize as soon as the stronger acid separates it from its basis, even tho' the solution of borax had been previously made as strong as possible; but this delay is occasioned by the heat of the liquor; for as soon as it cools, a considerable quantity of crystals is formed.

The acid of borax does not fall into powder when exposed to the air, but rather attracts a little moisture from it. Its taste is at first somewhat sourish, then cooling and bitterish; and lastly, it leaves an agreeable sweetness on the tongue. It makes a creaking sound, and feels a little rough between the teeth; and when vitriolic acid is poured upon it, exhales a transient odour of musk. It is soluble, according to some chemists, in the proportion of one to 20 in cold water, or of one to eight in boiling water. Wenzel informs us, that 960 grains of boiling water dissolve 434 of the salt; while, on the other hand, Morveau affirms, that he could dissolve no more than 183 grains in a pound of distilled water. Roufs informs us, that fixed air acid of barium prevents the solution of the salt in water; and Morveau, that its solubility is much augmented by cream of tartar. When previously made red hot, it dissolves in water with a smell of saffron, and a grey powder of an earthy appearance is precipitated, which is soluble in vitriolic and marine acids, and may be again precipitated in the form of sedative salt.

Phlogisticated alkali makes no change on sedative salt in solution; but paper dipped in a solution of it in vinegar, and afterwards dried, burns with a green flame. It is capable of vitrification, though mixed with fine powder of charcoal; and with foot unites into a black mass like bitumen; which, however, is easily soluble in water, and can scarcely be reduced to ashes, but partly fumes. By the influence of heat it dissolves in oils, especially those of the mineral kind; and with these it yields solid and fluid compounds, which give a green colour to spirit of wine. Rubbed with phosphorus it does not prevent its inflammation; but a yellow earthy matter is left behind. It seems also to give to white and red arsenic a great degree of fixity, so as even to become vitreous in the fire; and this property it communicates also to cinnabar. When mixed and heated with powder of charcoal, it forms no liver of sulphur.

Sedative Salt combined,

1. With volatile alkali. The produce of this is a peculiar ammoniacal salt, which does not evaporate when thrown on burning coals, or otherwise intensely heated, but melts into glaas of a greyish colour, but transparent, which cracks when exposed to the air; and, on dissolution in water, floats into small crystals, which appear to have lost none of their alkaline basis. It may be decomposed by the acetic as well as the mineral acids, and by fixed alkalies and lime.

2. With magnesia this acid shoots into irregular crystalline grains soluble in vinegar and acid of ants; in which liquids they crystallize like small needles joined together at right angles. They are decomposed by all other acids, and likewise by spirit of wine. In the fire, however, they melt easily without any decomposition; and in the dry way sedative salt decomposes all the earthy salts formed by magnesia and any of the volatile acids.

3. With pure earth of alum, sedative salt forms a salt very difficult of solution, when one part of earth is ground with four times its weight of sedative salt and water. The same kind of earth, mixed with half its weight of sedative salt, forms a hard grey mass, resembling pumice stone; part of which is soluble in water, and yields a mealy sediment, together with some sedative salt unchanged.

4. With fibrous earth the sedative salt does not unite in the moist way; but, on melting, one part of acid with two of this earth, we obtain a frothy, hard, greyish-white mass, from which, however, the acid may be again procured.

5. Gold is not acted upon in the wet way by acid of borax; nevertheless Roufs observed, that when sedative salt was melted with gold-leaf, it did not vitrify, but became frothy and hard, did not colour the flame of spirit of wine, and only a little of it was soluble in water in which sedative salt had been crystallized. A solution of borax in which sedative salt was dissolved, did not precipitate gold.

6. Platinum is not precipitated from aqua regia by sedative salt.

7. Silver is not affected by melting with an equal quantity of sedative salt; but the latter is vitrified in such a manner as to become insoluble in water.

8. Mercury is not dissolved either in the dry or wet way; but a solution of borax saturated with sedative salt precipitates it in a yellow powder from nitrous acid.

9. With copper. On this metal sedative salt acts but weakly, even when the solution is boiling hot; nevertheless, as much of the metal is dissolved, as gives a little white precipitate on the addition of fixed alkali; but volatile alkali does not throw down a blue precipitate, nor turn the solution of that colour. The solution of borax precipitates all solutions of copper in acids, and then the sedative salt unites with the copper in form of a light green jelly, which, after drying, is of very difficult solution in water. Bergman says, it is of an agreeable green colour, which it preserves after being dried; and that, when exposed to the fire, it melts into a dark-red vitreous substance. Wenzel affirms, that by long continued trituration of copper filings with sedative salt he obtained a solution of the metal, which yielded crystals on being evaporated. With twice its weight of copper in a covered crucible, an insoluble vitreous mass was obtained.

10. Tin is not apparently acted upon by boiling with sedative salt; nevertheless, the solution becomes turbid on the addition of an alkali. By melting the calx with half its weight of sedative salt, we obtain a black mass like the dark coloured tin ore. By rubbing for a long time filings of tin with sedative salt and water, and afterwards digesting the mixture with heat for one day, an hard, sandy, and irregularly shaped salt was obtained, which, by dissolution in water, yielded transparent, white, polygonous crystals; and a salt of the same kind was obtained from the flag produced by melting equal parts of sedative salt and tin filings.

11. Lead is not acted upon directly; but, on adding a solution of borax to solutions of the metal in vitriolic, nitrous, marine, or acetic acids, the sedative salt unites with the lead. One part of sedative salt with two of minium gives a fine, greenish-yellow, transparent, and insoluble glass.

12. With iron. The acid of borax dissolves this metal more easily than any other. The solution is amber-coloured, and yields an ochre sediment, with clusters of yellow crystals containing a little iron. The metal is precipitated by borax from its solutions in vitriolic, nitrous, marine, and acetic acids, and the precipitates are soluble in sedative salt. A solution of iron may also be obtained by melting this salt with iron filings, and lixiviating the mass.

13. Zinc communicates a milky colour by digestion with solution of sedative salt. By evaporation it affords a confused saline mass, and a white earthy powder by precipitation with alkali. Flowers of zinc, melted with sedative salt, form a light green insoluble flag.

14. Bismuth, in its metallic state, is not acted upon by sedative salt, but is precipitated by borax from a mixture of vitriolic and marine acids, in form of a very white powder, which keeps its colour when exposed to air, and melts in the fire to a white, transparent, and permanent glass.

15. Regulus of antimony is not acted upon directly, but its calx is dissolved when precipitated by borax from a solution in aqua regia.

16. White arsenic unites with sedative salt either in the dry or moist way, and forms a crystallizable compound, forming either pointed ramifications, or a white, greyish, and yellowish saline powder.

16. On regulus of cobalt the acid has no direct action; but borax precipitates it from its solution, and the calx melts with the salt into a flag of a bluish-grey colour; and this, by lixiviation and evaporation, affords a sedative salt impregnated with cobalt, of a reddish white colour, and of a ramified form.

18. Nickel is precipitated from its solution, and the sedative salt unites with it into a saline substance difficult of solution.

A variety of opinions have been formed concerning the nature of sedative salt. M. Beaumé and M. Cadet particularly have made a great number of experiments on the subject; but as none of these have led to any certain conclusion, we forbear to mention them at present. Those of Messrs. Exchaquet and Struve have indeed established some kind of relation between the acids of borax and phosphorus, and they have made several attempts to analyze the former, but with little success. The most remarkable of these experiments are the following. 1. They distilled, with a strong salt, heat, two parts of phosphoric acid evaporated to the confluence of honey, one of sedative salt, and two of water. Towards the end of the distillation a very acid liquor was obtained; and the residuum was a white earth, in quantity above three-fourths of the sedative salt employed, and which, on examination, was found to be the siliceous earth; the liquor which passed over into the receiver being found to be the volatile phosphoric acid. If, in this experiment, too much phosphoric acid be added, a greasy matter remains; and, if too little, a part of the sedative salt will remain undecomposed. In their attempts to compose borax, they combined phosphoric acid with mineral alkali, the result of which was a compound resembling borax in many respects. When exposed to the fire, it melts into a very fusible glass, which has a mild taste, and seems neutral, but, on exposure to the air, becomes moist and acid. On being saturated with alkali a second time and vitrified, it again deliquesces and becomes acid; and the more frequently this operation is repeated, the greater is the resemblance it bears to borax. In this experiment they supposed that the alkali was decomposed, and converted into an earth similar to that of sedative salt.

With earthy substances the results were very remarkable. With earth of alum a crystallizable salt was obtained, which made paper burn with a green flame. Fixed alkali added to a solution of this salt precipitates an earth, and the salt then formed by crystallization resembles borax in several properties.—In the dry way the earth of alum, with the phosphoric acid, melts into a glass of the same fusibility as that of borax, and like it is fixed in the fire. The solution of this glass did not crystallize. Common clay clay digested with phosphoric acid produces silky crystals resembling sedative salt. When dried with their mother-water, these give a clear glass, which, when united with mineral alkali, has the taste of borax, smells in the same manner, and has the same effect upon metals. With lime, magnesia, and terra ponderosa, this acid produces fusible glasses, insoluble in water, and which communicate a green colour to flame. Earth of bones and selenite mixed with the acid gave a white, hard, shining glass, like the best crystal, but as fusible as the glass of borax, and which continued flexible after it had ceased to be red-hot. Two parts of gypsum, with one of phosphoric acid, gave a milk-white glass fit for soldering metals and enamelling. In these experiments, however, it must be remembered, that unless the heat be raised very quickly, the phosphoric acid will be evaporated before any fusion takes place.

VIII. Acid of Amber.

It was known to Agricola, that a particular kind of salt could be obtained from amber by distillation; but neither he, nor any succeeding chemist for some time, ascertained its acid properties. On the contrary, some erred so far as to imagine that it was a volatile alkali; but, about the beginning of the present century, its acidity began to be generally acknowledged. This property indeed discovers itself by the taste, which is manifestly acid and empyreumatic, along with the peculiar flavour of amber. According to Scheele, also, the aqueous fluid which passes over in the distillation of amber, is an acid resembling vinegar both in taste and chemical properties; and which of consequence ought not to be confounded with the true acid of amber, which manifests qualities of a very different kind.

The properties of salt of amber can hardly be improved until it has been purified; for which, of consequence, various methods have been proposed. Pott recommends crystallization, after having filtered the solution through cotton-wool, in order to retain the oil. Cartheuer attempts the purification by dissolving the impure salt in spirit of wine, then diluting with five times its quantity of water, and crystallizing the salt. Others recommend sublimation with common salt or sand, and Bergman with pure clay.

The salt of amber dissolves, by the affluence of heat, in nitrous and marine acids, and in the vitriolic without heat. In none of these combinations, however, does it either alter the dissolving acids, or suffer any alteration itself, except that it becomes whiter; with nitre it detonates and flies off; and if the quantity of salt of amber has been greater than that of nitre, the latter is alkalized. Stockar informs us, that it expels the marine acid from sal ammoniac, and sublimes before that salt; with which it does not form any union. When sublimed from common salt, it does not alter the latter in any other respect than giving it a darker colour. It precipitates calcareous earth from its solution in vinegar; and it decomposes sugar of lead; but the precipitate differs from plumbum corneum. It does not prevent the solution of lead in the acids sea salt and nitre; nor does it produce any sulphurous smell by calcination with charcoal. Hence it appears that it is neither a vitriolic, nitrous, nor marine acid; and M. Boude-

lin must have been mistaken, when he affirms, that, Acid of after detonation of this salt with nitre, he obtained a Amber and residuum, which tasted like common salt, decrepitated in the fire, yielded crystals of a cubical form, precipitated silver and mercury from the nitrous acid; and thence concluded that it was the same with acid of sea-salt. It is very dear, as only about half an ounce can be obtained from a pound of amber.

Acid of Amber combined,

1. With fixed vegetable alkali. By saturating salt of amber with the fixed vegetable alkali, and then slowly evaporating the solution, we obtain, according to Wenzel, a light deliquescent saline mass; but, according to Stockar, whose experiments are confirmed by those of Mr Keir, the solution above mentioned affords shining white transparent crystals of a triangular prismatic figure, with the terminating points truncated. These crystals readily dissolve in water, deliquesce in the air, and have a peculiarly bitter saline taste. In the fire they decrepitate, melt, and remain neutral; though Wenzel has observed, that with intense heat they are decomposed and become alkaline. These crystals do not change aquafortis into aqua-regia; and though they precipitate both the solutions of lead and silver, the precipitates are neither plumbum corneum nor luna cornea.

2. With mineral alkali. This combination produces long three-sided columnar crystals, intermixed with some that are foliated. These crystals do not deliquesce in the air, and have a saline, bitter, and smoky taste. They are less soluble than common salt, and melt with more difficulty than nitre. They do not become alkaline on burning coals, and, in their other properties, resemble the former.

3. With volatile alkali. This salt shoots into acicular crystals, having a sharp, saline, bitter, and cooling taste; when heated in a silver spoon, they melt and evaporate entirely; in close vessels they sublime. They do not precipitate solution of silver, nor change spirit of nitre into aqua-regia. A powerful antispasmodic remedy is prepared from rectified spirit of hawthorn and salt of amber.

4. With lime. This shoots into oblong pointed crystals, which do not deliquesce in the air, and are soluble with difficulty even in boiling water; nor, according to Mr Stockar de Neuforn, can they be decomposed by distillation either with acetous or marine acids. They detonate by distillation with nitrous acid; and are decomposed, either in the moist or dry way, by the vitriolic. When mixed with common sal ammoniac in the dry way, they suffer a decomposition; the succinated ammoniacal salt flying off, and the combination of marine acid with lime remaining behind.

5. With magnesia. This yields a white, gummy, frothy, saline mass, which acquires a yellowish colour when dried by the fire; and, when cool, deliquesces in the air. It is decomposed by alkalies and lime, as well as by the vitriolic acid.

6. With clay. By uniting the acid of amber with an edulcorated precipitate of alum with vegetable alkali, Wenzel obtained prismatic crystals, which could not be decomposed by alkalies.

7. With silver. The acid of amber has no effect on silver. silver in its metallic state; but with its precipitate forms thin oblong crystals, radiated and accumulated upon one another, from which the silver may be separated by alkalies, by quicksilver, and by copper.

8. With copper. By a long digestion of copper with acid of amber a green solution is obtained, which by mixture with common salt is rendered turbid, by vitriolic acid white, and lets fall a green precipitate on the addition of fixed alkali. Wenzel, however, could not obtain this precipitation by alkalies. His solution yielded groups of green crystals, gave a crust of copper to zinc, and was precipitated by liver of sulphur.

9. With iron. Wenzel dissolved a precipitate of this metal in acid of amber, and from the solution obtained small, brown, transparent, and stellated crystals. Zinc precipitated the metal, but not alkalies. From a slightly coloured solution of metallic iron, Pott obtained, by means of alkali, a white precipitate, which soon became yellow, and at length green, by pouring water upon it.

10. With tin. Acid of amber dissolves tin when precipitated by a fixed alkali; and the solution yields thin, broad, and foliated transparent crystals. Alkalies throw down but little from this solution; liver of sulphur more; and lead, iron, or zinc, nothing.

11. With lead. Acid of amber whitens the surface of lead in its metallic state, but does not dissolve it; neither can lead be precipitated from its solutions in nitrous and marine acids by salt of amber, though this is denied by Pott. According to Stockar, however, it forms a white precipitate with sugar of lead. This metal precipitated by an alkali, and dissolved in acid of amber, forms long foliated crystals lying upon one another; from the solution of which the lead may be precipitated by alkalies in the form of a grey powder, and by zinc in its metallic state.

12. Zinc, in its metallic state, is readily dissolved by the acid of amber; and by a combination with the precipitate formed by fixed alkali, we obtain long, slender, foliated crystals, lying upon one another. The solution lets fall a white precipitate on the addition of fixed alkali; but this is denied by Stockar, who says that volatile alkali produces a red precipitate.

13. Bismuth. By means of heat, Stockar obtained a solution of this semimetal in acid of amber, which was decomposed by alkalies. Wenzel obtained, from a precipitate of bismuth prepared by means of fixed alkali, small, slender, foliated, and yellow crystals; which alkalies cannot decompose, though black precipitates are thrown down by lead and zinc.

14. Regulus of antimony. Little or none of this semimetal, in its reguline form, is dissolved in the acid of amber; but it attacks the precipitate made with fixed alkali. This solution is very copiously precipitated by liver of sulphur, but not by alkalies.

The combinations of this acid with gold, platinum, nickel, arsenic, and manganese, have either been found impracticable, or not yet attempted; all those above described are non-dissolvent, and part with their acid when exposed to fire. The elective attractions of this acid, according to Bergman, are singular, as it adheres more strongly, not only to terra ponderosa and lime, but to magnesia, than to fixed alkali.

On the origin of salt of amber, Mr Keir remarks, that "it deserves to be considered as a pure and distinct acid. No proofs have been adduced of its being a modification either of the marine or vegetable acids, Amber and as Mr Cornette and M. Hermbtadt have supposed, nations. The former, having distilled spirit of salt with oil of lavender, obtained an acid which smelled like salt of amber, but on examination was found to retain the properties of the muriatic acid. He also relates, that when purifying a considerable quantity of the salt of amber which he had prepared himself, some sea-salt was separated, which in the distillation had arisen along with it. But this observation cannot be justly applied to show any resemblance betwixt these two, any more than the smell in the former case could show an analogy betwixt it and oil of lavender. This mixture of sea-salt with acid of amber, however, may readily explain the mistake of M. Bourdelin already mentioned. M. Weltrumb and M. Hermbtadt have both laboured in vain to convert the acid of amber into acids of sugar and tartar by frequent distillations with spirit of nitre; and their want of success confirms the account already given, that the acids of nitre and amber have no action upon each other, farther than that the former is phlogisticated or changed into red fumes, and the latter becomes whiter. Nevertheless, if Mr Scheele's observation of the identity of the acid liquor, which comes over in the distillation of amber with acetic acid, holds good, we shall have the best reason yet given to ascribe the origin of this acid to the vegetable kingdom; and when we consider the very different properties that are affixed by the vegetable acids, which, however, are convertible into one another, no reason can be drawn from the diversity of its properties with those of other vegetable acids, against its having a common origin with them. Indeed the natural history of amber, its similarity to gums and resins, and its involved insects, afford other arguments in favour of the opinion.

IX. Acid of Arsenic.

M. Berthollet remarks upon Mr Scheele's pro-cess of preparing arsenical acid. He mixes common white arsenic with acid, nitrous ammonia, and distills the mixture. At first phlogisticated nitrous acid passes over, then the volatile alkali, and lastly the arsenical acid remains in the retort in form of a vitreous mass, which deliquesces into a very dense acid liquor, reddening syrup of violets, and effervescing with alkalies. M. Macquer had formerly described this process, and observed, that the nitrous acid passes over first, and then the volatile alkali; but was of opinion that the residuum was nothing but arsenic. He mentions a detonation which took place in his experiment; but nothing of this kind was observed by M. Pelletier: he only informs us, that the nitrous acid was driven over with great violence, while that of arsenic united with the volatile alkali. M. Berthollet, who has endeavoured to ascertain the weight gained by the conversion of sulphur, phosphorus, and arsenic, into acids, determines that of arsenic to be about one-ninth of the whole. At the same time he observes, that this additional weight does not discover the whole weight of the air contained in the the arsenic, as it had that necessary to convert it into calx before the operation of converting it into an acid was begun. On the other hand, M. Bergman affirms, that one-fifth of white arsenic is phlogiston, and that this calx is converted into acid merely by being deprived of its phlogiston. Thus the facts related by these two celebrated chemists differ enormously from one another; M. Berthollet affirming that the arsenic gains a ninth of its original weight in the process of acidification; and M. Bergman, that it loses a fifth part of the same. M. Berthollet endeavours to reconcile this, by supposing that Bergman had employed marine acid for the preparation of his arsenical acid, which is well known to carry off with it some part of most of those substances with which it is capable of combining; and to this he attributes the loss of weight in Bergman's process.

IX. Acid of Molybdæa.

The opinion of M. Bergman concerning the metallic nature of the acid of molybdæa has obtained some confirmation from the experiments of M. Pelletier. He was not able indeed to obtain any regulus; but by means of oil alone he procured, by two hours vehement heat, a substance slightly agglutinated with a metallic lustre, containing small round grains of a grey metallic colour, very visible by the help of a magnifier. These he supposes to have been a true regulus of molybdæa; which he found to possess the following properties. 1. It is calcinable by fire into white calx. 2. It detonates with nitre, and the residuum is a calx of molybdæa united with the alkali of the nitre. 3. It is converted into a white calx by means of nitrous acid. 4. It yields inflammable air when treated with alkalies in the dry way, and forms peculiar compounds with them. 5. It forms regenerated molybdæa with sulphur. 6. It unites, and forms peculiar substances with metals. By uniting it with silver, iron, and copper, we have friable reguline masses; and refractory powders with lead and tin.

Our author, in consequence of his experiments, considers molybdæa as a metallic substance mineralized by sulphur; and the earth called the acid of molybdæa as a calx much dephlogisticated, which has retained part of the air contained in the nitrous acid. He observes likewise an analogy between molybdæa and antimony in their chemical results. Both of them yield vitrifiable argentine flowers by similar operations, and both are changed into white earths by nitrous acid; but they differ in the two following respects. 1. The latter easily gives a fusible regulus; but the molybdæa seems to be the most refractory of all the semimetals. 2. The calx of regulus of antimony is soluble by alkalies in the moist way, but that of molybdæa is not.

X. Acid of Tungsten or Wolfram.

Mr Luyart, who has examined this mineral, gives the following account of it. 1. It is infusible by the blow-pipe, though the angles of the pieces into which it is broken are thereby rounded. 2. It effervesces with microcosmic salt, and melts before the blow-pipe into a reddish glass. 3. With borax it effervesces; and by the outward flame of the blow pipe is changed into a reddish glass; by the internal flame into a greenish one. 4. Heated itself in a crucible, it swelled, became spongy, semifluidified, and was attracted by the magnet. 5. With an equal part of nitre it detonated, or boiled up with a blue flame round the edges, and nitrous vapours arose. The mass was soluble in water, and let fall a white precipitate with acid. 6. It melted readily with fixed alkali, leaving a kind of black matter in the crucible, and a smaller quantity of lighter coloured substance on the filter. These residues showed a mixture of iron and manganese. 7. With nitrous acid the filtered solution let fall a white precipitate, at first sweet, but afterwards bitterish and sharp, and which caused a disagreeable sensation in the throat; and the acidity of the solution of it was manifest, by its turning the tincture of turpentine red.

Having examined the substance by means of liquids in Mr Scheele's way, they obtained the same yellow powder which L. had characterized as the acid of tungsten, along with a very small residuum, which appeared to contain a mixture of tin. Proceeding farther in the analysis, they found that wolfram is composed of manganese, calx of iron, the yellow matter called the acid of tungsten by Bergman and Scheele, with a very little mixture of quartz and tin, and which they considered as accidental.

They now proceeded to examine the yellow matter, Of the yellow powder by the two celebrated chemists just mentioned, it was found to be a simple acid salt, but which turned out very acid by Mr Scheele. In order to procure a Scheele quantity of it, they melted six ounces of wolfram with as much vegetable alkali, dissolved the mixture in distilled water, filtrated the liquor, and evaporated it to dryness. Thus they obtained a white salt; upon which, when dry, they poured nitrous acid, and set it to boil in a sand-bath; by which operation it became yellow. They then decanted the liquor, pouring fresh acid upon the residuum; and repeated the operation a third time in order to deprive it of all the alkali. The remaining powder was then calcined in a cupping furnace under a muffle, when it came out quite pure and yellow. The properties of it were then found to be as follow. 1. It is entirely infusible, and of the specific gravity of 6.12. 2. Before the blow-pipe, it continues yellow in the exterior flame even though put on charcoal; but grows black and swells, though it does not melt, in the internal flame. 3. In the internal flame it forms a blue transparent glass with microcosmic salt. The colour vanishes in the external flame, but appears again in the internal one; but by a continuance of this operation, it at last loses its colour so much that it cannot be recovered. 4. It effervesces, and forms a brownish yellow transparent glass with borax, which keeps its colour in both flames. 6. When triturated with water, it forms an emulsion which passes through filters without becoming clear, and continues a long time without any deposition. 7. It is insoluble in acids, but dissolves readily in the vegetable alkali both in the moist and dry way; though the produce has always an excess of alkali. 8. On adding nitrous acid in greater quantity than what is necessary to saturate this excess, a white powder falls, which is the same with the acid of tungsten discovered by Mr Scheele; but which Mr Luyarts will not not allow to be a simple acid, though they admit that it contains one; and affirm, that its properties are various according to the circumstances of its precipitation. The properties of it, as described by them, are the following. 1. It is fusible before the blow-pipe, exhibiting the same phenomena as the yellow matter. 2. By calcination in a little pot or telft, it emits the smell of nitrous acid, and turns yellow; but, on cooling, remains white, insipid, and insoluble; and this residuum melts by itself before the blow-pipe. 3. A yellow colour is produced either by vitriolic or marine acids; and the filtrated liquor affords a neutral salt with basis of fixed alkali, according to the nature of the acid employed. If the vitriolic acid is employed, and the operation performed in a retort, a quantity of nitrous acid passes over. 4. If, instead of pouring the acid on the salt, it be poured upon its solution, no precipitate will be formed, not even by making the liquor boil, if the quantity of acid is small; only the solution loses its sweet taste, and acquires more bitterness. On pouring on a large quantity of acid, and causing the liquor boil, a yellow precipitate is formed in every respect similar to the yellow matter so often mentioned. 5. This salt is completely dissolved by boiling with vinegar. On leaving the solution to cool, a white waxy matter adheres to the sides of the vessel; which being washed and kneaded with the fingers, forms an adhesive mass like bird-lime, having a fat and greasy taste. By exposure to the air, it acquires a dark grey colour, loses its adhesive property, and becomes bitter. It dissolves in water; and gives it first a sweet, then a bitter taste, making the tincture of turnsole red. 6. On evaporating the alkaline solution to dryness, pouring acetic acid upon the residuum, and then making it boil, the greater part of the residuum was dissolved, and on cooling afforded feathery crystals. These when edulcorated had a sweet taste, though less strong than that of the former salt, which afterwards became bitter. Their solution turned blue paper red; was precipitated, and became like an emulsion with spirit of wine; and the residuum, which did not dissolve, appeared to be of the same nature. The crystals dissolved in fresh acetic acid, and communicated a blue colour to the acid; but this gradually disappeared on cooling, and a glutinous matter was deposited on the sides of the vessel, which had the properties of the former substance of that sort. If, in place of letting the solution cool, it should be kept boiling, the blue colour disappears, and nothing is precipitated. By adding spirit of wine when the liquor is almost evaporated to dryness, a white powder is precipitated; which, after being edulcorated with fresh spirit of wine, tastes exceedingly bitter, and is very soluble in water. This solution, however, does not reddish blue paper, nor make a blue with vinegar. With vitriolic acid its solution is blue; with vitriol of copper it forms a white precipitate. All these salts, by calcination, first become blue, then yellow, and lastly white. 7. On pouring a quantity of lime-water upon the solution of the precipitate formed by the nitrous acid, as well as on those obtained by the acetic acid, white precipitates were formed, all of which were a true regenerated tungsten. Having afterwards impregnated the liquors with fixed air, and boiled them in order to precipitate the lime more completely, they found in the solutions, after they were filtrated and evaporated to dryness, neutral salts formed of the precipitating acids, joined with alkaline and calcareous bases. This proved, that both alkali and acid were concerned in the precipitation. 8. On pouring the vitriolic solutions of iron, copper, and zinc, as well as that of marine mercurial salt, alum, and Prussian alkali, upon the solution of the precipitate formed by the nitrous acid, no precipitation ensues, and the acetic salts of copper and lead give white precipitates; but the Prussian alkali forms no precipitate with the acetic salts. Hence it appears, that this salt is not a simple acid, but rather a salt composed of the yellow matter, fixed alkali, and the precipitating acid; and its composition appears more fully from the following experiments with the volatile alkali.

1. The yellow powder dissolves entirely in volatile alkali, but without any perfect saturation taking place; and the alkali always prevails. 2. The solution being set in a sand-bath, produced needle-like crystals, which had a sharp bitter taste, exciting a disagreeable sensation in the throat. Their solution turned the tincture of turnsole red, and the liquor from which they were crystallized had the same properties. 3. Having repeated this operation with different quantities of the same crystals, leaving some longer on the fire than others, solutions were obtained, whose acidity was in proportion to the time they had remained on the fire; but during the operation they all emitted the smell of volatile alkali. By calcination this alkali was entirely distillated, and the residuum was a yellow powder, perfectly similar to that with which the operation was begun. On making use of a retort for the operation, the remaining powder was blue. 4. This salt precipitates the vitriolic salts of iron, copper, zinc, and alum, calcareous nitre, marine mercurial salt, the acetic salts of lead and copper; and with lime-water regenerates tungsten. The vitriolic acid decomposes it, and forms a blue precipitate; the nitrous and marine acids produce a yellow; but no precipitate is occasioned by the Prussian alkali.

Having poured nitrous acid upon a portion of the solution with excess of alkali, a white powder was precipitated, which, after edulcoration, had a taste at first sweet, but afterwards sharp and bitter, and its solution turned the tincture of turnsole red. This, on examination, appeared to be a triple salt formed of the yellow powder, volatile alkali, and the precipitating acid.

The following experiments realize the conjecture of Bergman, that the acid of tungsten is the basis of a particular feminal acid.

1. "Having kept 100 grains of the yellow powder (says M. Luyart) in a Zamora crucible well covered, and set the whole in a strong fire for half an hour, it became a spongy mass of a bluish black colour, the surface of which was crystallized into fine points, like plumose antimony, and the inside compact, and of the same colour. It was too hard to be broken in pieces by the fingers; and, when ground, was reduced to a dark-blue colour.

2. "Having mixed 100 grains of the same powder with 100 of sulphur, and put the mixture in a Zamora crucible on a strong fire for a quarter of an hour, it came out a dark-blue mass, which was easily broke by..." the fingers; and the inside presented a crystallization like needles as the last, but transparent, and of the colour of a dark lapis lazuli. This mass weighed 42 grains, and when placed on burning coals yielded no smell of sulphur.

3. "Having put another 100 grains of this powder into a Zamora crucible, provided with charcoal, and well covered, and placed it in a strong fire, where it remained an hour and a half, we found, on breaking the crucible after it was cool (a), a button, which fell to powder between the fingers. Its colour was dark brown; and on examining it with a glass, there was seen a congeries of metallic globules, among which some were the bigness of a pin's head, and when broken had a metallic appearance at the fracture in colour like steel. It weighed 60 grains; of course there was a diminution of 40. Its specific gravity was 17.6. Having calcined part of it, it became yellow, with \( \frac{1}{4} \) increase of weight. Having put one portion of this substance powdered, in digestion with the vitriolic acid, and another with the marine acid, neither of them suffered more diminution than \( \frac{1}{4} \) of their weight; then decanting the liquor, and examining the powder with a glass, the grains were still perceived of a metallic aspect. Both the acid liquors gave a blue precipitate with the Prussian alkali, which let us know that the small diminution proceeded from a portion of iron which the button had undoubtedly got from the powder of the charcoal in which it had been set. The nitrous acid, and aqua-regia, extracted likewise from two other portions the ferruginous part; but besides, they converted them into yellow powder, perfectly similar to that which we used in this operation.

4. "Having put 100 grains of gold and fifty of the yellow powder in a Zamora crucible furnished with charcoal, and kept it in a strong fire for three quarters of an hour, there came out a yellow button, which crumbled in pieces between the fingers; the inside of which showed grains of gold, separated from others of a dark-brown colour. This demonstrated there had not been a perfect fusion, and likewise that this substance was more refractory with gold, since the heat which it endured was more than sufficient to have melted it. The button weighed 139 grains; of course there was a diminution of 11 grains. Having put this button with lead in the cupelling furnace, the gold remained pure in the cupel; but this operation was attended with considerable difficulty.

5. "Having made a mixture of platina and yellow powder in the preceding proportions, and exposed it to a strong fire, with the same circumstances, for an hour and a quarter, it produced a button which crumbled with ease between the fingers, and in which the grains of platina were observed to be more white than usual, and some of them changed feebly in their figure. This button weighed 140 grains, and of consequence there had been a loss of 10 grains. When calcined, it took a yellow colour, with very little increase of weight; and after washing it to separate the platina, there remained 118 grains of a black colour.

Having placed this portion again to calcine over a strong fire in a muffle, it suffered no sensible alteration in weight or colour; for it neither grew yellow, nor took the brown colour of the platina, but kept the same blackness as before it was calcined. It must be attended to, that in the washings there was not so much care taken to collect all the platina as to deprive it of the yellow colour, and for this reason the water carried off part of the fine black powder; and consequently the increase which the platina preferred, after being washed and calcined the second time, ought to be computed more than the 18 grains which it showed by its weight.

"Having mixed the yellow powder with other metals in the preceding proportions, and treated them in the same manner, the result was as follows:

6. "With silver it formed a button of a whitish-brown colour, something spongy, which with a few strokes of a hammer extended itself easily, but on continuing them split in pieces. This button weighed 142 grains, and is the most perfect mixture we have obtained, except that with iron.

7. "With copper it gave a button of a copperish red, which approached to a dark brown, was spongy, and pretty ductile, and weighed 133 grains.

8. "With crude or cast-iron, of a white quality, it gives a perfect button, the fracture of which was compact, and of a whitish brown colour; it was hard, harsh, and weighed 137 grains.

9. "With lead it formed a button of a dull dark-brown, with very little lustre; spongy, very ductile, and splitting into leaves when hammered; it weighed 127 grains.

10. "The button formed with tin was of a lighter brown than the last, very spongy, somewhat ductile, and weighed 138 grains.

11. "That with antimony was of a dark-brown colour, shining, something spongy, harsh, and broke in pieces easily; it weighed 168 grains.

12. "That of bismuth presented a fracture, which, when seen in one light, was of a dark-brown colour, with the lustre of a metal; and in another appeared like earth, without any lustre; but in both cases one could distinguish an infinity of little holes over the whole mass. This button was pretty hard, harsh, and weighed 68 grains.

13. "With manganese it gave a button of a dark bluish-brown colour and earthy aspect; and on examining the internal part of it with a lens, it resembled impure drops of iron; it weighed 107 grains."

XI. Acid of Ants.

Ettmuller is among the first authors who mentions the existence of this acid, and speaks of obtaining it by distillation. Nothing of its properties, however, was known, until Margraaf undertook to examine it; of whose experiments we have an account in the Memoirs of the Berlin Academy for 1749. Since his time a number of chemists have prosecuted the subject to

(a) "The first time we made this experiment, we broke the crucible without letting it cool entirely; and as soon as the matter was in contact with the air, it took fire, and its dark brown colour turned instantly yellow." to a considerably greater length; but Mr Keir prefers the researches of Arvidson, Bucholtz, and Hermbsadt, to the rett.

The acid in question is a natural juice which the insects discharge when irritated, and which is very pungent to the smell as well as taste. Thus it may instantly be perceived on turning up an ant-hill in spring or summer. The *formice rubrae* of Linnæus are those insects which have hitherto supplied this acid. Mr Arvidson advises to collect them in the months of June and July, by laying some smooth sticks upon an ant-hill; which being then disturbed, the ants will run upon the sticks in great numbers, and may then be swept off into a vessel containing water until it be full. Hermbsadt collects them in the same manner, but into a dry bottle, to avoid the evaporation of the superfluous liquid. Bucholtz having moistened the inside of a narrow necked glass bottle with honey and water, sunk it into a disturbed ant-hill until the mouth was level with the ground; on which the insects, allured by the smell of the honey, went into the bottle, and could not get out.

For obtaining the acid, Margraaf employed distillation, with the addition of fresh water. Thus he obtained, from 24 ounces of fresh ants, 11 ounces and two drachms of acid, some volatile alkali, empyreumatic oil, and a residuum containing earth and fixed salt. Arvidson made use of two methods: One consisted in distilling the ants when dry; from a pound of which, in this state, he obtained eight ounces of acid besides the empyreumatic oil. His other method was to inclose, in a piece of linen, the ants previously cleaned by washing in water, then to pour boiling water upon them, and to repeat the operation until it could extract no more acid; which is then obtained by squeezing the linen, mixing all the liquors, and filtering them. Thus from a pound of ants he obtained a quart of acid liquor, which tasted like vinegar, but was specifically heavier. By distillation Hermbsadt obtained from a pound of dry ants ten ounces and a half of yellow empyreumatic liquor, which did not taste more strongly acid than the spirit obtained by distilling wood, on which swam three drachms of a brown fetid oil, in all respects like that of hartshorn. In the retort was left a black residuum weighing one ounce six drachms, which exhibited signs of containing volatile alkali. By distilling a pound of ants with three of water, according to Mr Margraaf's method, he obtained an acid liquor and some oil in the receiver; and from the surface of that which remained undistilled, he collected a drachm and an half of fat oil.

The specific gravity of the acid liquor obtained by Mr Arvidson's maceration was 1.0011; that of the same liquor, when distilled, 1.0075; and of the acid concentrated by freezing, 1.0433. According to Bucholtz, the acid liquor thus obtained by maceration did not grow in the least mouldy in the space of four weeks; during which it was allowed to rest in order to free itself perfectly from the impurities it contained. Mr Hermbsadt, however, prefers Margraaf's method of distillation to that of Arvidson's macerations, not only as being a more perfect analysis, but as less laborious; though he finds fault also with Margraaf's method, as diluting the acid too much, and altering it so that it has not the smell of living ants. He totally disapproves of the method of distilling dried ants, as the acid is thus in a great measure decomposed, and the remainder united with much oil. To avoid all these inconveniences, he contrived another method, namely, to express the juice of the insects; by which means he obtained at once a concentrated liquor fit for distillation. In this way he obtained from two pounds of dried ants 21 ounces and two drachms of juice, which had a pungent and highly acid smell, resembling the vapours of fluor acid; in taste resembling concentrated vinegar and acid of tartar; to which last it might be compared for strength of acidity. By distilling eight ounces of this expressed liquor, he obtained five ounces and a half of clear acid, equal in strength to a very concentrated vinegar.

The acid, when thus procured in purity, has a pungent, not unpleasant smell, a sharp, caustic taste, and of the purest an agreeable acidity. It reddens blue paper, syrup of acid violets, and litmus; blackens the vitriolic acid, and converts part of it into a sulphurous vapour. It is also decomposed by distillation with nitrous acid. Spirit of salt likewise, when dephlogisticated, decomposes it, but not in its ordinary state. It does not form sulphur by an union with phlogiston, but produces inflammable vapours by dissolving iron or zinc. By the assistance of a gentle heat it dissolves foot, but oils with much more difficulty, and powder of charcoal not at all. It does not unite with vitriolic ether; but in distilling a mixture of this acid with spirit of wine, Mr Arvidson saw some traces of an ether, and M. Bucholtz perfectly succeeded in making an ether by means of it. It unites with fixed alkali, forming, according to M. Margraaf, a neutral salt, consisting of oblong deliquescent crystals, from which very little acid could be procured by distillation per se; but on adding concentrated oil of vitriol, a very strong and pure acid was obtained; from a mixture of which with spirit of wine, M. Bucholtz readily obtained a true ether. With mineral alkali it forms deliquescent foliated crystals of a saline bitter taste, and soluble in twice their weight of water. With volatile alkali it forms an ammoniacal liquor; which, according to Arvidson, cannot be brought into a dry state; but Mr Arvidson says he has obtained crystals from it, though very thin and deliquescent. Margraaf obtained dry crystals by uniting this acid with chalk or coral; and Arvidson observes that this salt is transparent, cubical, or rhomboidal, nondeliquescent, soluble in eight parts of water, of a bitter taste, and insoluble in spirit of wine. No acid can be obtained from it by distillation per se. From a solution of magnesia in this acid, Mr Arvidson obtained some saline particles by deposition, and afterwards an efflorescence of transparent salt rising round a saline mass. This salt had scarcely any taste, was soluble in 13 parts of water, and insoluble in spirit of wine. With ponderous earth the acid formed a cluster of bitter needle-like crystals, which did not deliquesce, were soluble in four times their quantity of water insoluble in spirit of wine, and when burnt gave out a smell like that of burnt sugar, leaving a coal which afterveced with acid. It unites with difficulty to the earth of alum, and can scarcely be saturated with it. It does not precipitate silver, lead, or mercury, from their solution in nitrous acid; whence it seems to have no affinity to the ma- rine acid: and as it does not precipitate lime from the marine acid, it seems to have as little with the vitriolic. From his experiments, however, Margraaf concluded, that the acid of ants, in many respects, though not in all, has a great affinity with the acetic acid. From this it is distinguished by forming different compounds, and likewise by having different affinities. It lodges the acetic acid also in all instances, and the arsenical acid from cobalt and nickel. It has a greater attraction for fixed alkalies than for lime.

As a solvent it acts but weakly upon copper; not at all, or very little, on silver, lead, tin, regulus of antimony, or bismuth, but strongly on iron or zinc. It dissolves, however, the calces of copper, silver, zinc, and lead, without affecting those of tin, regulus of antimony, or bismuth. The calx of quicksilver, according to Margraaf, is revived by it. According to Arvidson, it crystallizes with iron, zinc, or lead; does not act upon the regulus of antimony, of arsenic, cobalt, or nickel; though it dissolves, their calces as well as the precipitate of manganese. Gold, mercury, and the calx of platina, are not affected by it; but it crystallizes with those of copper, silver, lead, bismuth, and mercury.

In its strength of attraction, the acid of ants exceeds those of vinegar, borax, and the volatile sulphuric and nitrous acids. Insects armed with stings, as bees, wasps, and hornets, are likewise said to discharge a very acid juice when irritated; and Mr Bonnet has observed a very strong acid ejected by a caterpillar which he distinguishes by the name of grande cheville du faule a queue fourchue. None of these, however, have been as yet particularly examined.

XII. Acid of Apples.

That the juices of unripe fruits contain some kind of acid has been universally known, and attempts to investigate the nature of it have been made some time ago: but it is to Mr Scheele that we owe the discovery of the particular acid now treated of. He had observed that the juice of citrons contained a particular acid; which, by being united with lime, formed a salt very insoluble in water; and which therefore by means of lime could be readily separated from the mucilaginous part of the juice. By adding vitriolic acid to this compound of lime with the acid juice, almost in the same manner in which he used to procure the acid of tartar, the lime was again separated, and the pure acid of citrons obtained. Proceeding in the same manner with other fruit, he found that an acid, agreeing in every respect with that of citrons, could be procured from the juice of the ribes grossularia. Examining the juice which remained after the separation of the former acid from the citrons, he found that it still contained another acid; which being saturated with more calcareous earth, formed a salt easily soluble in water, and therefore remained suspended in the juice. To separate this new salt, he added some spirit of wine, by which the salt was precipitated; but finding that it still contained much gummy matter, he judged that it would be proper to attempt a separation of this gum before he precipitated the salt. For this purpose he evaporated some of the juice of the ribes grossularia to the consistence of honey, dissolving the mass afterwards in spirit of wine. Thus the acids, which are soluble in the spirit, were easily separated by filtration from the insoluble gum. He then evaporated the spirit, adding to the remainder twice its quantity of water, with as much chalk as was necessary for the saturation. The liquor was next boiled for two minutes; during which the insoluble salt was precipitated, and the liquor separated from it by filtration contained the solution of chalk in the new acid. To this solution he added spirit of wine, which again precipitated the salt, while some saponaceous and saccharine matters remained dissolved in the spirit.

Having thus at last obtained the salt in a state of purity, he proceeded to examine its nature; and found, that:

1. That some of it spread on his nail, soon dried, and assumed the appearance of varnish. 2. It was very soluble in water, and turned litmus red. 3. When the solution had stood some days exposed to air, it was found to have deposited a number of small crystals, which could only be dissolved by a quantity of boiling water; and this salt was also found to be completely neutralized, so that it yielded its calcareous earth to a fixed alkali. 4. The salt was decomposed by heating per se in a crucible, and left a mild calcareous earth. 5. The acid was separated from the earth by adding oil of vitriol diluted with water until gypsum was no longer precipitated, and the new acid was left disengaged, so that it could be separated by filtration. 6. By this operation, however, all the lime was not precipitated, so that the separation of the acid was not complete. 7. He observed that the acid had a greater attraction for lead than for lime; and therefore made use of the method he had formerly discovered for separating the acid of forrel. To the acid, he added a solution of sugar of lead; by which the acid was precipitated along with the lead, and the vinegar was left in the liquor. To this precipitate, cleaned from how produced the acetous acid by filtration, he added vitriolic acid, cured in which expelled the weaker vegetable one, and thus left it quite pure and free from any heterogeneous mixture.

The juice of apples, either ripe or unripe, was found to contain no acid of citrons, but a large quantity of the new acid; which, being thus alone, he could more easily procure by a single operation. The best method of procuring this he found to be by saturating the juice of the apples with a solution of fixed vegetable alkali, and pouring a solution of sugar of lead to that of the salt just mentioned. The effect of this was a double decomposition, and a precipitate of lead combined with the new acid. To the edulcorated precipitate he then added a dilute vitriolic acid till he could no longer perceive any sweet taste in the liquor; for the first portions of the vitriolic acid dissolve a part of the calx of lead, and impart a sweetish taste to the liquor, which is sensible notwithstanding its acidity; but when the quantity of vitriolic acid is sufficient to saturate the whole of the calx, all the metal falls to the bottom, and the sweetness ceases; so that the acid is at once obtained pure.

The acid of apples is possessed of the following properties:

1. It cannot be crystallized, but always remains in a liquid state; or, if much evaporated, attracts the moisture of the air. 2. With fixed alkalies, it is of apple. of all kinds it forms deliquescent falt. 3. With calcareous earth it forms small irregularly shaped crystals, which cannot be dissolved but in a large quantity of boiling water; but if the acid is superabundant, the salt readily dissolves in lime-water. 4. It is affected by ponderous earth in the same manner as by lime.

5. Earth of alum forms, with the acid of apples, a salt not very soluble in water. 6. With magnesia the acid forms a deliquescent falt. 7. Iron is dissolved into a brown liquor, which does not crystallize. 8. The solution of zinc affords fine crystals. 9. On other metals it has no remarkable effects. From the acid of citrons it differs. 1. The acid of citrons shoots into fine crystals. 2. The acid of apples can be easily converted into that of sugar, which Mr Scheele could not accomplish with that of citrons; though Mr Wecklumb has since done it. 3. The falt formed with the citron acid and lime is almost insoluble in water; but that with acid of apples and lime is easily soluble. 4. Acid of apples precipitates mercury, lead, and silver, from their solution in nitrous acid, and likewise the solution of gold, when diluted with water; but the acid of citrons does not alter any of these solutions. 5. The acid of citrons seems to have a greater attraction for lime than that of apples.

It is remarkable that this acid is the first produced in the process for making sugar. If a diluted acid of nitre be drawn off from a quantity of sugar until the mixture becomes a little brown, which is a sign that all the nitrous acid is evaporated, the syrup will be found to have acquired a sourish taste; and if, by means of lime, we next separate all the acid of sugar, another will still remain, which dissolves the calcareous earth. When this acid is saturated with chalk, and the solution filtered and mixed with spirit of wine, a coagulation takes place. On separating the curdled part by means of a sieve, dissolving it in water, and then adding some vinegar of lead, the calx of lead will be precipitated; and if the new acid is then separated from the metal by means of diluted oil of vitriol, it will be found to possess all the properties of the acid of apples, and is indeed the same. The spirit of wine, which has been employed to precipitate the calcareous salt, leaves on evaporation a residuum of a bitter taste, very deliquescent, and similar to the saponaceous extract of the citron.

The following are the results of Mr Scheele's experiments with the nitrous acid upon different substances. 1. From gum Arabic he obtained both the acids of apples and of sugar. 2. The same products nitrous acid were obtained from manna. 3. From sugar of milk he obtained not only its own peculiar acid, but those of apples and sugar. 4. Gum tragacanth, during its solution in nitrous acids, lets fall a white powder, which was found to be the acid of the sugar of milk. This gum contained also the acid of apples and of sugar, and a salt formed from lime and the acid of apples. 5. Starch left an undissolved matter; which being separated by filtration, and washed, resembled a thick oil like tallow, which, however, was found to be very soluble in spirit of wine. By distillation he obtained from this oily matter an acid similar to that of vinegar, and an oil which has the smell of tallow, and congeals by cold; and, besides these substances, he found that starch yielded the acids of apples and sugar. 6. From the root of satep he obtained the acid of apples, with a large quantity of calcareous saccharine falt. 7. Extract of aloes indicated the existence of the acids of sugar and apples, and lost the greatest part of its bitter taste. During the digestion a resinous matter was separated, which smelled like flowers of benzoin, and took fire on being heated in a retort. 8. Extract of colocynth was converted by nitrous acid into a resinous substance, and showed some signs of containing acid of sugar. 9. The extracts of Peruvian bark and of the other plants examined by Mr Scheele, gave both the acids of apples and sugar. 10. These two acids were likewise obtained from an infusion of roasted coffee, evaporated to the consistence of a syrup. 11. The same products were obtained from an extract of rhubarb, which yielded also a resinous matter. 12. Juice of poppies afforded the same results. 13. Extract of galls did the same. 14. The essential oils afforded little or none of the acids; but the oil of parsley seeds seemed to be entirely convertible into them. 15. With a very concentrated acid he was able also to decompose animal substances. From glue he thus obtained fine crystals of acid of sugar, and afterwards acid of apples. Isinglass, whites and yolks of eggs, afforded the same products. From all these substances, especially the last, a fat matter was separated; but it was remarkable that the gas, expelled during the process, was composed of a little fixed air, a great quantity of phlogisticated air, and very little nitrous air; whereas no phlogisticated air is obtained in the usual process for preparing acid of sugar. He observed also, that in the process for this acid, a small quantity of vinegar is found in the receiver. He could not obtain the acid of sugar from the saponaceous extract of urine; but got instead of it a salt, which, when completely purified, resembled exactly the flowers of benzoin. The same salt is precipitated in abundance by adding to the extract of urine a little vitriolic or marine acid; and Mr Scheele had already remarked that the same salt is obtained in the distillation of sugar of milk.

From the various experiments which have been made on this acid, it seems, according to Mr Keir, to be in nature of this intermediate state between tartar and acid acid of sugar. This, however, ought not to prevent it from being accounted a separate and distinct acid, otherwise we might confound all the vegetable acids with one another. It approaches more nearly to the nature of acid of milk than of any other. From this also, however, it is distinguished, because the salt formed by the union of acid of milk with lime is soluble in spirit of wine, but not that from lime and the acid of apples. According to Mr Hermstedt, if three parts of smoking nitrous acid be abstracted from one part of sugar, and if the brown acid mass which remains in the retort be diluted with six times its weight of distilled water, and saturated with chalk; two compounds will be formed; one consisting of the acids of tartar and lime, which will precipitate; and the other of lime and the acid of apples, which will remain suspended. If the calcareous earth be precipitated from this latter solution by adding acid of sugar, a pure acid of apples will be left in the liquor. Acetous Acid and he further informs us, that this acid of apples may be changed entirely into those of sugar and vinegar, by means of strong nitrous acid.

XIII. Acetous Acid.

It is generally believed, that the combination of this acid with volatile alkali is altogether incapable of crystallization; but Scheffer and Morveau informs us, that it may be reduced into small needle-shaped crystals, when the spiritus Mindereri is evaporated to the consistence of a syrup, and left exposed to the cold. The salt has a very sharp and burning taste, but a considerable quantity is lost during the evaporation. Westendorf, by adding his concentrated vinegar to volatile alkali, obtained a transparent liquor which did not crystallize. By distillation it went over entirely into the receiver, leaving a white spot on the retort. A saline transparent mass, however, appeared in the receiver under the clear fluid. On separating it from the liquid, and exposing it to a gentle heat, it melted, threw out white vapours, and in a few minutes shot into sharp crystals resembling nitre. These remained unchanged in the cold; but when melted with a gentle warmth, smoked and evaporated. Their taste was first sharp and then sweet.

The salt formed by uniting acetous acid with calcareous earth has a sharp bitter taste, and shoots into crystals somewhat resembling ears of corn. These do not deliquesce in the air, unless the acid has been superabundant. They are decomposed by distillation per se, the acid coming over in white inflammable vapours smelling like acetous ether, somewhat empyreumatic, and condensing into a reddish brown liquor. By rectification this liquor becomes very volatile and inflammable; on adding water, it acquires a milky appearance, and drops of oil seem to swim upon the surface; a reddish brown liquor, with a thick black oil, remain after rectification in the retort. On mixing this calcareous salt with that of Glauber, a double decomposition takes place; we have a gypsum and the mineral alkali combined with acetous acid. By calcination, the mineral alkali may be obtained from this salt in a state of purity. This acetous calcareous salt is not soluble in spirit of wine.

On saturating this acid with magnesia, and evaporating the liquor, we obtain a viscid saline mass like mucilage of gum arabic, which does not shoot into crystals, but deliquesces in the air. It has a sweetish taste at first, but is afterwards bitter. It is soluble in spirit of wine, and parts with its acid by distillation without addition.

Acetous acid dissolves zinc both in its metallic and calciform state, and even when mixed with other metals. By concentrated vinegar the zinc is dissolved with great heat, sulphurous smell, and exhalation of inflammable matter. By this union we obtain a congealed mass, which on dilution with water shoots into oblong sharp crystals at the first crystallization, and afterwards into crystals of a flattened form. From this liquor indeed crystals of various forms have been obtained by different chemists. Monnet obtained from it a pearl-coloured salt in friable talky crystals; which when thrown on the coals, fulminated a little at first, and gave a bluish flame, and then melted, letting its acid escape, while a yellow calx remained. Hellot informs us, that this salt by distillation per se into water, affords an inflammable liquor, and an oil at first yellow and then green, with white flowers burning with a blue flame. Westendorf obtained no oil in this distillation, but some acetous acid; a sweet-tasted empyreumatic liquor impregnated with zinc; sweet flowers, or sublimate, soluble in water, and burning with a green flame. On applying a stronger heat, the zinc was sublimed in its metallic form, leaving a spongy coal at the bottom of the retort. The solution gives a green colour to syrup of violets, lets fall a white precipitate on the addition of alkalies or an infusion of galls. It is not precipitated by common salt, vitriolated tartar, vitriolic or marine acids, blue vitriol, or corrosive sublimate; but forms a red precipitate when added to solution of gold; a white precipitate with solution of silver; a crystalline pearly precipitate with solution of mercury; and crystalline precipitates with solutions of bismuth and tin. According to Bergman, it is decomposed by acid of arsenic.

Though regulus of arsenic is not soluble in this Its phenomacid, its calx may be dissolved either in common or mera with distilled vinegar. M. Cadet obtained a smoking liquor arsenic, by distillation from a mixture of white arsenic and terra foliata tartari. This experiment has been repeated by the chemists of Dijon, and attended with the following curious circumstances. "We digested (say they), in a sand-bath, five ounces of distilled vinegar on white pulverized arsenic; the filtrated liquor was covered, during evaporation, with a white saline crust. Of this substance were formed 150 grains; on which fixed alkali appeared to have no effect, and which was at first considered as pure arsenic. However, a cat, which had swallowed 72 grains of it, was only affected with vomitings that day and the next, and afterwards perfectly recovered. A similar dose vinegar was given to a little dog; but as he ran away, supposed to effect it had upon him could not be discovered; but by the returned afterwards in good health, and never showed any uneasiness: whence it may be concluded, that vinegar is in some measure an antidote against the pernicious qualities of arsenic.

"On redissolving this saline crust in pure water, filtering and mixing it with liquid alkali, an irregularly crystallized salt was formed in it after a few days standing. By this salt a yellow precipitate was thrown down from the nitrous solution of silver; whereas the solution of arsenic and terra foliata tartari threw down a white one.

"Equal parts of terra foliata tartari and arsenic, distilled in a retort, gave first a small quantity of limpid liquor with a penetrating smell of garlic, and which had the property of reddening syrup of violets; while solution of arsenic in water turns that syrup green. The vinegar which now arose was not saturated with arsenic, but effervesced strongly with fixed alkali, with which it became turbid, but did not let fall any precipitate. On changing the receiver, there came over a reddish brown liquor, accompanied with thick vapours, diffusing an intolerable smell, in which that of arsenic could scarcely be distinguished. On continuing the operation, a black powder sublimed into the neck of the Acetous acid, together with a little arsenic in its metallic form, and a matter which took fire by a lighted candle like sulphur.

"The red liquor still preserved its property of smoking though cold; diffusing at the same time its peculiar and abominable fetor, from which the apartment could scarcely be freed in several days. This liquor does not alter the colour of syrup of violets, but effervesces slightly with fixed alkali, letting fall at the same time a yellow precipitate, which, however, disappeared on an attempt to separate it by filtration.

"M. Cadet had observed, that the smoking liquor of arsenic did not kindle at the approach of a lighted candle; but that, on pouring it from the receiver into another vessel, it had kindled the fat lute with which the junctures had been closed, and which had been dried during the operation: but we, being desirous of examining more fully the nature of the red liquor which collects at the bottom, and has the appearance of oil, having decanted that which swams on the top, and poured the remainder on a filter of paper, before many drops had passed, there arose a thick smoke forming a column from the vessel to the ceiling; a flight ebullition was perceived at the sides of the vessel, and a beautiful rose-coloured flame appeared for a few moments. The paper filter was burnt at one side, but most of it was only blackened. After the flame was extinguished, a fat reddish matter remained; which, being melted on burning coals, swelled considerably, emitting a white flame. It then sunk, and left on the coal a black spot, which could not be effaced but by the most vehement fire.

"At the time these observations were made, the liquor had been distilled for three weeks, and the bottle frequently opened. The inflammability could not proceed from the concentration of the vinegar; for the rose-colour of the flame, the precipitation of the sublimate, and the fixity of the spot remaining on the coal, evidently showed that the two substances were in a state of combination; which is also further evinced by the loss of the inflammable property when the liquor was decomposed by fixed alkali.—The smell of the liquor, however, though so intolerably fetid, was attended with no other inconvenience than a disagreeable sensation in the throat, which further strengthens the suspicion that vinegar is an antidote against arsenic.

"The saline brown mass remaining in the retort was partly dissolved by hot water; and the filtrated lixivium was very limpid, but emitted the peculiar smell of the phosphoric liquor. By evaporation it yielded a salt which did not deliquesce in the air, of an irregular shape; and which being put on burning coals, did not smell sensibly of arsenic; lost its water of crystallization; and became mealy and white without being dissipated by heat. On exposing the residuum to the air, it was found next day resolved into a liquor; whence it is probable that most of it was composed of crystallized alkali, having received from the decomposition of the vinegar as much fixed air as was necessary for its crystallization."

This acid does not act upon mercury in its metallic state, but dissolves the mercurial calces, as red precipitate, turbith mineral, and the precipitate formed by adding fixed alkali to a solution of mercury in nitrous acid; with all which it forms white, shining, fealy crystals, like those of sedative salt.

Vinegar does not act upon silver in its metallic state, but readily dissolves the yellow calces precipitated from its solution in nitrous acid by microcosmic salt and volatile alkali. By the help of a boiling heat also it very copiously dissolves the precipitate obtained by means of a fixed alkali. The last mentioned solution yields shining, oblong, needle-shaped crystals, which are changed to a calx by means of several acids, especially the muriatic. The silver is thrown down in its metallic form by zinc, iron, tin, copper, and quicksilver.

Though the acetous acid has no effect upon gold in its metallic state, yet a solution of this metal is decomposed by crude vinegar, which produces both a metallic precipitate and dark violet-coloured powder. Distilled vinegar throws down the gold in its metallic form. The precipitate by fixed alkali digested with acetous acid is of a purple colour. This, as well as fulminating gold, is dissolved by Weftendorf's concentrated vinegar; the fulminating gold very easily. The solution is of a yellow colour; and with volatile alkali affords a yellow precipitate; with lixivium sanguinis, a blue one; both of which fulminate. The dry salt of gold dissolves in the acetous acid, and produces oblong yellow crystals.

This acid has no effect on fat oils, farther than that, when distilled together, some mixture takes place, as able the Abbé Rozier has observed. Neither does distilled vinegar act upon essential oils, though M. Weftendorf's distilled vinegar dissolved about a fifth part of oil of rosemary, and about half its weight of camphor. The latter solution was inflammable, and let fall the camphor on the addition of water. The acid dissolves all the true gums, and some of those called gum-resins, after being long digested with them. By long boiling, Boerhaave observes, that it dissolves the bones, cartilages, flesh, and ligaments of animals.

The concentration of this acid may be effected by combining it with alkalies, earths, and metals. By none of these combining it with copper, and then crystallizing and acetic acid, distilling the compound, we obtain the acid in the highest state of concentration in which it is usually met with. To produce this strong acid, we have only to distill verdigris, or rather its crystals in a retort. The operation must be begun by a very gentle fire, which brings over an aqueous liquor. This is to be set aside, in order to procure the more concentrated acid, which comes over with a stronger fire. On changing the receiver, and augmenting the heat, we obtain a very strong acid, which comes over partly in drops, and partly in white vapours. It is called radical vinegar, or sometimes spirit of Venus, and has a very pungent smell, almost as suffocating as that of volatile sulphurous acid. As the last portions of it adhere pretty strongly to the metal, we are obliged to raise the heat to such a degree as to make the retort quite red, in order perfectly to separate them. Hence some part of the metal is raised along with the acid, which, dissolving in the receiver, gives the liquor a greenish colour; but from this it may be easily freed by a second distillation, when it rises with a very gentle heat, and... and becomes extremely white. Crystals of verdigris afford about one half their weight of radical vinegar; but verdigris itself much less, and of a more oily quality.

If this acid be heated in a wide-mouthed pan, and fire applied to it, it will burn entirely away like spirit of wine. This observation we owe to the count de Lauragais, who has likewise observed, that it is capable of crystallization. This, however, takes place only with the last portions which come over, and the crystals appear in the form of plates or needles. The marquis de Courtrivon, who has repeated and confirmed the experiment of the count de Lauragais, supposes this phenomenon to be owing to a sulphur-like mixture of acetous acid and phlogiston. Leonhardi supposes an analogy between these crystals and the white salt of copper expelled at the end of the operation by the count de Laffone. This salt was at first very white, and fixed on the neck of the retort pretty thick; but unless quickly collected, was soon destroyed by the succeeding vapours. When exposed to the air, it attracts moisture, and runs into a greenish liquid. It is uncommonly light, and in such small quantity, that scarce five or six grains can be collected from a pound of verdigris. Its taste is acid, astringe, very unpleasant, and permanent. It readily and totally dissolves in water, and partially in spirit of wine, leaving a yellow powder totally soluble in volatile alkali, and which burns with a green flame. From this salt, volatile alkali acquires a blue colour, and litmus a red one; and thus it discovers itself to be composed of acetous acid and copper.

Experience has shown that radical vinegar differs considerably in its properties from the common acid. It has a greater attraction for alkalies, forms with them more perfect combinations, and is less volatile. M. Berthollet observes, that when vinegar concentrated by frost and radical vinegar, are reduced to equal densities, by adding water to the heavier of the two, they differ very much both in smell and taste. Laffone found, that radical vinegar formed a crystallizable compound with volatile alkali; and Berthollet has observed the same with regard to fixed vegetable alkali. The crystals of the latter with radical vinegar were flat, transparent, and flexible, slowly deliquescent in the air. On comparing the salts formed by the two acids, he found, that the acetous salt rendered the syrup of violets green; but its colour remained unaltered with that made with radical vinegar. The latter also required a stronger fire to expel part of its acid; it was also whiter, and had a less acid taste. On pouring radical vinegar on the acetous salt, the solution afforded, by evaporation and crystallization, a salt perfectly similar to that procured directly from radical vinegar and fixed alkali. On distilling the mixture, the radical vinegar appeared to have expelled the common acetous acid, as the liquor which came over effervesced with vegetable alkali, and formed with it a terra foliata tartari.

"It seems probable (says Mr Keir), that the radical vinegar contains a larger portion of the aerial principle than the common acetous acid; by which it undergoes a change similar to that of marine acid, when brought into that state in which it is said to be dephlogisticated. This air it may acquire from the metallic calx, which being deprived of its air is reduced to its metallic state. Those who believe in the phlogiston of metals, may say that the acid is dephlogisticated by imparting its phlogiston to the metal, which is thereby metallized. It appears, however, to be very distinct from common acetous acid, and deserves to have its properties and compounds farther investigated."

Concentrated acetous acid, of a great degree of strength, may also be obtained by distilling terra folia-tartari with vitriolic acid; but Leonhardi observes, pure from that the acid thus obtained is always more or less contaminated with the volatile acid of sulphur. He observes also, that the method proposed of separating the sulphurous acid by a second distillation from salt of tartar is not effectual, because the sulphurous acid has less attraction for alkalies than the acetous. Wettendorff recommends the neutral salt formed by acetous acid and mineral alkali, instead of the terra folia-tartari. Thus, in the first place, we readily obtain crystals free from the inflammable matter of the vinegar; and, in consequence of this, though we distil it afterwards with concentrated oil of vitriol, no sulphurous taint can be produced. Even supposing this to be the case (he says), it may be removed by a second distillation from some mineral alkali. Mr Keir, however, observes, that "probably all the acids distilled from acetous salts by means of the vitriolic, partake of the property of that procured by distilling crystals of verdigris; and none of them can compare with that from which Mr Lonitz obtained acetous ether without addition, as a pure concentrated and unaltered vinegar."

XIV. Acid of Benzoin.

The properties of this acid have been investigated by M. Lichtenstein, and are as follow. 1. Exposed to sunlight's heat of a candle in a silver spoon, it melts as clear account of as water, without burning, though it is destroyed by contact of flame. 2. When thrown upon coals, it evaporates, without residuum, in a thick white smoke. 3. It is not volatile without a considerable degree of heat. 4. By very slow cooling its aqueous solution yields large crystals, long, thin, and of a feathery shape. 5. It is soluble in the concentrated acids of nitre and vitriol, but separates from them, without decomposition, on the addition of water. 6. By the other acids it cannot be dissolved without heat, and separates from them also without any change, merely by cooling. 7. It is copiously dissolved by spirit of wine, and precipitated from it on the addition of water. 8. With alkalies it forms neutral salts, very soluble in water, and of a sharp saline taste. With vegetable alkali it forms crystals of a pointed feathery form; with mineral alkali it yields larger crystals, which fall into powder on being exposed to the air; and with volatile alkali it is difficultly crystallizable into small, feathery, and deliquescent crystals. It is separable from alkalies by the mineral acids. 9. With calcareous earth it forms white, shining, and pointed crystals, not easily soluble, and which have a sweetish taste without any pungency. 10. With magnesia it Acetous acid small feathery crystals are formed, of a sharp saline taste, and easily soluble in water. An astringent salt is formed with earth of alum.

All these earthy salts are easily decomposed by the mineral acids as well as by alkalis. The acid of benzoin itself reddens litmus, but has little effect upon syrup of violets.

Messrs. Hermbstadt and Lichtenstein have both tried the effects of nitrous acid upon that of benzoin. In this operation, however, a great obstacle arose from the volatility of the acid of benzoin, which prevented it from bearing any considerable heat without passing over into the receiver. By repeated distillations, however, the acid of benzoin, diminished in its volatility, assumed a darker colour, and acquired a bitterish taste. A coal was also left at the bottom; and, at the end of the third operation, when the nitrous acid had been all drawn off, Mr. Hermbstadt observed, that some brown drops came over which had the appearance of a dark-coloured transparent oil, soluble in distilled water, emitting acrid fumes, and having a very caustic taste. On distilling this acid liquor a second time, a yellow saline mass was obtained, which, when dissolved in distilled water, formed a fluid acid, which precipitated a solution of sugar of lead and lime-water. On examining the charred residuum left in the retort, he observed, that, after calcination, some of the earth had been vitrified, while another was of a soft consistence, and had acquired a caustic taste. From a mixture of the above-mentioned dark-brown acid and spirit of wine, he obtained an ether, which differed from the nitrous in being much less volatile, and smelling like bitter almonds.

From this residuum Mr. Lichtenstein obtained a resinous substance, to which he attributes the volatility of the acid of benzoin, as well as the smell of bitter almonds already mentioned.

Scheele failed in his attempt to obtain ether from flowers of benzoin and spirit of wine; but, by adding a little spirit of salt, he obtained a kind of ether which fell to the bottom. On dissolving this in alkalized spirit of wine, and drawing off the latter by distillation, he obtained from it a quantity of flowers of benzoin. From Peruvian balsam also Lehman obtained a quantity of the acid of benzoin. It may also be procured from urine, either by precipitation, from the saponaceous extract (A), or by repeatedly distilling from it spirit of nitre, as in the preparation of acid of sugar. In the urine it is found combined with volatile alkali, by which it becomes soluble in spirit of wine.

XV. SEBACEOUS ACID.

This is said to have been first discovered by Mr. Gruitznacker, who published an account of it in 1748. It was afterwards more accurately treated of by Mr. Rhades in 1753. Its properties were investigated by Messrs. Segner and Knappe in 1754; and afterwards more fully by Dr. Crell, of whose discoveries an account is given in the Philosophical Trans-

Vol. IV. Part II.

(A) By this is meant urine evaporated to a thick consistence, and deprived of most of its salts by solution in spirit of wine. still ing the astringent matter in question, when an acid liquor comes over, which has the property of blackening solution of vitriol. Scheele has observed, that when galls in substance are exposed to distillation, an acid liquor rises of an agreeable smell, without oil, and afterwards a kind of volatile salt, which is the true acid of the galls. Hence he infers, that this salt is contained ready formed in the galls themselves; but so much involved in some, gummy or other matter, that it cannot be easily obtained separately.

The acid of galls is capable of being separated by crystallization. In an infusion made with cold water, Scheele observed a sediment which appeared to have a crystalline form, and which was acid to the taste, and had the property of blackening solution of vitriol. By exposing the infusion for a long time to the air, and removing from time to time the mouldy skin which grew upon it, a large quantity of sediment was formed. On redissolving this in warm water, filtering and evaporating it very slowly, an acid salt was obtained in small crystals like sand, which had the following properties: 1. It tasted acid, effervesced with chalk, and reddened litmus. 2. Three parts of boiling water dissolved two of the salt; but 24 parts of cold water were required to dissolve one. 3. It is likewise soluble in spirit of wine; four parts of which are required to dissolve one of the salt when cold, but only an equal quantity when assisted by a boiling heat. 4. The salt is destructible by an open fire, melts and burns with a pleasant smell, leaving behind a hard insoluble coal, which does not easily burn to ashes. 5. By distillation an acid water is first obtained without any oil; then a sublimate, which remains fluid while the neck of the retort is hot, and then crystallizes. This sublimate has the taste and smell of flowers of benzoin; is soluble in water and in spirit of wine; reddens litmus; and precipitates metallic solutions of the following colours, viz. gold of a dark brown; silver of a grey colour; copper of a brown; iron of a black; lead of a white colour; mercury of an orange; bismuth, lemon-coloured. The acid of molybdena became yellow coloured, but no precipitate ensued. Solutions of various kinds of earths were not altered; but lime water afforded a copious grey-coloured precipitate. 6. By treating this acid with that of nitre, in the manner directed for producing acid of sugar, it was changed into the latter.

XVII. Identity of the Vegetable Acids.

On the proofs of the identity of the vegetable acids with one another, Mr Keir makes the following remarks: "The experiments and observations which have been made, prove evidently a strong analogy between the acetous acid, spirit of wine, tartar, and acid of sugar; and they seem to show the existence of a common principle or basis in all of them, modified either by the addition of another principle not common to all of them, or by different proportions of the same principle. None of the opinions on this subject, however, are quite satisfactory. The production of the acetous acid by treating spirit of wine with other acids, does not prove that the acetous acid was contained in the spirit of wine, but only in concurrence with them, that they contain some common principle. There is no fact adduced to support Morveau's identity of opinion, that fixed air is absorbed during the acetous fermentation; or that the presence of this fixed air is necessary. The decomposition of all vegetable acids by heat, and the production therefrom of fixed and inflammable gases, show that these acids contain some of the same principles as these elastic fluids, but do not prove that the gases existed in the fluids. We have good reason to believe that acetous acid does not contain any fixed air ready formed; for it yields none when vitriolic acid is added to it, or to foliated earth; nevertheless, my opinion that vegetable and animal acids are, by heat, in a great measure convertible into fixed air, seems to be sufficiently proved by experiments. Thus Hales has shown the great quantities of this gas which tartar yields on distillation. Berthollet quantities has obtained the fixed and inflammable gases from foliated earth; and Dr Higgins has verified this experiment, and deduced the quantities. From 7680 grains tained from of foliated earth, the Doctor obtained

| Caustic alkali | 3862.994 grains earth | | Fixed air | 1473.564 | | Inflammable air | 1047.6018 | | Oily matter retained in the residuum | 78 | | Oil | 182 | | Water condensed | 340 | | Deficiency attributed chiefly to water | 726.9402 |

As fixed and inflammable gases may be obtained from every vegetable substance by fire, nothing can be inferred from these experiments to explain particularly the nature of the acetous acid, excepting that it contains some of the inflammable matter common to the vegetable kingdom, and especially of the matter common to vegetable acids; all which also, when analysed, furnish large quantities of these two gases.

"Although we are far (adds our author) from the knowledge requisite to give a complete theory of the acetous fermentation, yet it may be useful to explain the ideas that appear most probable. In all the instances that we know of the formation of acids, whether effected by combustion, as the acids of sulphur and phosphorus, or by repeated abstractions of nitrous acid, as in the process for making acid of sugar, a very sensible quantity of pure air is absorbed. In the case of Air absorb-combustion we know, from the weight acquired, that in the formation there is a great absorption of air; and in the latter of all acids, of acids being produced by application of nitrous acid, as this acid confits of nitrous acid and pure air and as in these operations a quantity of the nitrous gas is expelled, there seems little doubt but that there also the pure air of the nitrous acid is united with the substance employed in the formation of the new acid. Hence, from all that we know, the absorption of air takes place in all acidifying processes. But it also actually takes place in the acetous fermentation, as has been observed, particularly by the Abbe Rozier; and it is generally known, that air is necessary to the formation of vinegar. The next question is, What is the basis? And from the experiments already related, of forming the acetous acid by means of spirit of wine, it seems probable, either that this spirit is the basis of the acetous acid, or that it contains this basis: and from the convertibility of the acids of tartar and of sugar..." Practice.

density of sugar into the acetous acid by the processes above described, it seems probable that these also contain the same common basis; which, being united with a determined quantity of pure air, forms acid of tartar; with a larger quantity, acid of sugar; and with a still larger, the acetous acid.

An inflammable spirit is said to appear at the end of the distillation of radical vinegar from verdigris. Now, if the ardent spirit were contained in the verdigris, as it is more volatile than the acid, it ought to come over first; but as it appears only towards the end of the distillation, it seems to be formed during the operation; and I imagine, that the metal, when almost deprived of its acid, attracts some of the air of the remaining acid; and the part or basis of the acid thus deprived of its air becomes then an inflammable spirit, and in some cases an oil appears. But as the quantity of acid thus decomposed is very small, and little air of consequence remains united with the metallic part of the verdigris, the copper appears rather in a metallic than calciform state after the operation. But zinc, during its solution in concentrated vinegar, decomposes the acid as it does the vitriolic and other strong acids, and accordingly inflammable vapors are produced; and what is remarkable, these vapors have a sulphurous smell. Iron always, during its solution in concentrated vinegar, produces an expulsion of inflammable vapors; which, however, do not explode like inflammable gas.

We must not imagine that we are yet able to explain completely what passes in the acetous fermentation, or that the acetous acid is a compound of mere spirit and pure air. Besides this combination of spirit and air, it is observed, that a precipitation always takes place before the fermentation is completed, of some mucilaginous matter, which deposits the vinegar to putrefy, and from which it therefore ought to be carefully separated. Stall affirms, that without a deposition of such sediment, vinegar cannot be made from sugar, wine, or other juice. Besides the matter that is deposited, probably as much remains in the liquor as can be dissolved therein; for, by distillation, much of a similar extractive matter is left in the retort. What the nature of this matter is, and how it is formed, has not yet been examined. Though distillation frees the acid from much of this extractive substance, yet we have no reason to believe that we have ever obtained it entirely free from inflammable matter; as it retains it even when combined with alkalies and with metals. When sugar of lead and other acetous salts are distilled with a strong heat, the substances remaining in the retort have been observed to possess the properties of a pyrophorus; and this will happen whatever pains have been taken to purify the vinegar employed. See the article PYROPHORUS. This fact shows the existence of an inflammable matter in this acid; and which may perhaps be essential in its composition, and necessary to its properties. Although fermentation is the usual mode of obtaining acetous acid, yet it appears from the instances observed by latter chemists, that it is not essential to its formation, but that it is also formed in various chemical processes; and the acids obtained by distillation from woods, wax, &c. are very analogous to vinegar. It appears also on treating the acid of sugar with nitrous acid, as has been observed both by Weftzumb and Scheele. The latter further acquaints us, that he obtained it in analyzing a tallow like oil, which remained undissolved upon digesting starch in nitrous acid. As acid of sugar also may be obtained from a variety of animal substances, and as this acid is convertible into the acetous, we have one reason more added to many others, to prove that the matters of vegetable and animal substances are not capable of any chemical distinction."

XVIII. ADDITION TO SECT. I. § 20. CONCERNING THE VOLATILITY OF A MIXTURE OF MARINE AND NITROUS ACIDS.

This is much less sensible when the acids are weak than when they are concentrated. On mixing the two when moderately smoking, and which had remained for a long time separate without occasioning any disturbance, a vastly smoking aqua-regia has been produced, which would either drive out the stopple, or burst the bottle in warm weather. On distilling a pretty strong nitrous acid from sal ammoniac, M. Beaumé observed, that the vapors which came over were so exceedingly elastic, that notwithstanding every precaution which could be taken in such a case, the distillation could not be continued. By letting this escape, however, Mr Cornette observed, that the distillation of these two substances may be carried on to the end without any inconvenience, and the aqua-regia will then be no longer troublesome.

XIX. TEST FOR ACIDS AND ALKALIES.

The general method recommended for discovering a small quantity of acid or alkali in any liquid, is by trying it with any vegetable blue, such as syrup of violets; when, if the acid prevails in the liquor, the syrup will acquire a red colour, more or less deep according to the quantity of acid; or if the alkali prevail, it will change the syrup green in like proportion. Since the late improvements in chemistry, however, the syrup has been found deficient in accuracy, and the infusion of turpentine, or of an artificial preparation called litmus, have been substituted instead of it. The infusion of litmus is blue, and, like syrup of violets, becomes red with acids. It is so sensible that it will discover one grain of oil of vitriol though mixed with 100,000 of water. Unfortunately, however, this infusion does not change its colour on mixture with alkalies; it is therefore necessary to mix it with just as much vinegar as will turn the infusion red, which will then be restored to its blue colour by being mixed with any alkaline liquor. The blue infusion of litmus is also a test of the presence of fixed air in water, with which it turns red, as it does with other acids.

The great sensibility of this test would leave very little reason to search for any other, were it always an exact test of the point of saturation of acids and alkalies; but, from the following fact, this appears to Mr Watt to be dubious. A mixture of phlogisticated nitrous acid with an alkali will appear to be acid by the test of litmus, when other tests, such as the infusion of the petals of the scarlet rose, of the blue iris, of violets, and of other flowers, will show the same liquor to be alkaline, by turning green so evidently as to leave no room to doubt.

When Mr Watt made this discovery, the scarlet ro- Test for A-ces, and several other flowers, whose petals change their cids and Al-colour by acids and alkalis, were in flower. Having stained paper with their juices, he found that it was not affected by the phlogisticated nitrous acid, excepting in so far as it acted the part of a neutralizing acid; but he found also, that paper stained in this manner was much less easily effected than litmus was; and that, in a short time, it lost much of the sensibility which it possessed at first; and having occasion in winter to repeat some experiments in which the phlogisticated nitrous acid was concerned, he found his stained paper almost useless. Searching, therefore, for some other vegetable which might serve for a test at all seasons of the year, he found the red cabbage to answer his purpose better than any other; having both more sensibility with regard to acids than litmus, being naturally blue, and turning green with alkalis, and red with acids; to all which is joined the advantage of its being no farther affected by the phlogisticated acid of nitre than as it acts as a real acid.

To prepare this test, Mr Watt recommends to take the fresh leaves of the cabbage; to cut out the large stems, and mince the thin parts of the leaves very small; then to digest them in water at about the heat of 120 degrees for a few hours, when they will yield a blue liquor; which, if used immediately as a test, will be found to possess great sensibility: but as in this state it is very apt to turn putrid, some of the following methods must be used for preserving it.

1. After having minced the leaves, spread them on paper, and dry them in a gentle heat; when perfectly dry, put them up in glass bottles well corked; and, when you want to use them, acidulate some water with vitriolic acid, and digest or infuse the dry leaves in it, until they give out their colour; then strain the liquor through a cloth, and add to it a quantity of fine whiting or chalk, stirring it frequently, until it becomes of a true blue colour, neither inclining to green nor purple; when you perceive that it has acquired this colour, filter it immediately; otherwise it will become greenish by standing longer on the whiting. This liquor will deposit a small quantity of gypsum, and, by the addition of a little spirit of wine, will keep good for some days; but will then become somewhat putrid and reddish. If too much spirit is added, it destroys the colour. If the liquor is wanted to keep longer, it may be neutralized by a fixed alkali instead of chalk.

2. As thus the liquor cannot be long preserved without requiring to be neutralized afresh just before it is used; and as the putrid fermentation which it undergoes, and perhaps the alkalis or spirit of wine mixed with it, seem to lessen its sensibility; in order to preserve its virtues while kept in a liquid state, some fresh leaves of the cabbage, minced as above directed, may be infused in a mixture of vitriolic acid and water, of about the degree of acidity of vinegar; and it may be neutralized, as it is wanted, either by means of chalk, or of the fixed or volatile alkali. It must be observed, however, that, if the liquor has an excess of alkali, it will soon lose its colour, and become yellow; from which state it cannot be restored; care should therefore be taken to bring it very exactly to a blue, and not to let it verge towards a green.

3. In this manner, Mr Watt prepared a red infusion of violets; which, on being neutralized, formed a very sensible test, though he did not know how long these properties would be preserved; but he is of opinion that the coloured infusions of other vegetables may be preserved in the same manner by the antiseptic power of the vitriolic acid, in such a manner as to lose little of their original sensibility. Paper fresh stained with these tests, in their neutral state, has sufficient sensibility for many experiments; but the alum and glue which enter into the preparation of writing paper, seem, in some degree, to fix the colour; and paper which is not sized becomes somewhat transparent when wetted; which renders small changes of colour imperceptible. Where accuracy is required, therefore, the test should be used in a liquid state.

4. Our author has found that the infusion of red cabbage, as well as of various flowers in water, and other tests, acidulated by means of vitriolic acid, are apt to turn mouldy in the summer season, and likewise that the moulding is prevented by an addition of spirit of wine. He has not been able to ascertain the quantity of spirit necessary for this purpose, but adds it by little and little at a time until the process of moulding is stopped.—Very sensible tests are afforded by the petals of the scarlet rose, and of the pink coloured lychus treated in the above-mentioned manner.

XX. Volatile Alkali.

Mr Higgins claims the first discovery of the constituent parts of volatile alkali, or at least of an experiment leading to it. "About the latter end of March 1785 (says he), I found that nitrous acid from poured on tin filings, and immediately mixed with nitrous acid, generated volatile alkali in considerable abundance: so singular a fact did not fail of deeply impressing my mind, though at the time I could not account for it. About a fortnight after, I mentioned the circumstance to Dr Brocklesby. He told me he was going to meet some philosophical gentlemen at Sir Joseph Banks's, and defined I would generate some alkali to exhibit before them: accordingly I did; and had the pleasure of accompanying him thither. The December following I mentioned the fact to Dr Caulet, and likewise the copious generation of volatile alkali from Prussian blue, vegetable alkali, and water; on which we agreed to make a set of experiments upon the subject. At present I shall only give an account of the following, which drew our particular attention. Into a glass cylinder, made for the purpose, we charged three parts of alkaline air, and to this added one part of dephlogisticated air; effects of we passed the electrical spark repeatedly in it, without apparently effecting the smallest change. When it had received about 100 strong shocks, a small quantity of moisture appeared on the sides of the glass, and the brass conductors seemed to be corroded: when we had passed 60 more shocks in it, the quantity of moisture seemed to increase, and acquire a greenish colour, though at this time the column of air suffered no diminution. On examining the air, it burned with a languid greenish flame, from which we inferred that the dephlogisticated air was totally condensed: it still retained an alkaline smell; and the alkaline part was not readily absorbed by water. "From Mr Cavendish's famous discovery of the constituent parts of water we could readily account for the loss of the dephlogisticated air in this experiment; but the quantity of water was more than we could expect from this: therefore water must have been precipitated from the decomposed alkali; for volatile alkali, from its great attraction to water, must keep some in solution, even in its aeriform state. From the above circumstances it might be expected, that a contraction of the column of air should take place; but it must be considered, that the union took place gradually in proportion as the alkali was decomposed; and that, in this case, the expansion must equal the condensation. During the spring of 1786, I had often an opportunity of mentioning different facts to Dr Austin relating to volatile alkali, who at that time was too much engaged to pay attention to the subject. In the end of August 1787, he gave me an account of a set of experiments which he had made, and which actually proved, that volatile alkali consists of light inflammable and phlogisticated airs; not knowing at that time what Messrs Hofman and Berthollet had done. Without depreciating the merit of these two gentlemen, Dr Austin has an equal claim to the discovery, laying aside priority; as his experiments are as decisive as theirs. Dr Priestley made the first step towards our knowledge of volatile alkali."

XXI. PRUSSIAN BLUE.

The acid of this substance, as far as it contains an acid, is supposed to be that of phosphorus. Mr Woulfe proposed a test of this kind for discovering iron in mineral waters, which, he observed, would not be affected by acids; but the lixivium described by him had the bad property of letting fall the Prussian blue it contains in a few weeks. The precipitate of copper, however, treated again with alkali, retained this property upwards of nine months. The volatile alkali, he observes, is dissolved by the Prussian acid; and the crystals deposited are rendered blue by the colouring matter, though the colour at first is lost by the union of the alkali with the substance already made. The metals were precipitated by this test of the following colours: Gold of a brownish yellow; the precipitate afterwards becoming of a full yellow; platinum of a deep blue, but when quite pure, of a yellow colour, turning slightly green. Silver in the nitrous acid was precipitated of a whitish colour; copper from all the different acids was precipitated of a deep brown colour, the liquid remaining greenish; green vitriol let fall a deep blue powder, leaving a colourless lixivium; sugar of lead and muriated tin gave a white powder; nitrated mercury a white or yellowish precipitate; the Illfeld manganese a brownish, but that from Devonshire a blue, which first became ash-coloured and then reddish. Nitrated bismuth afforded a white precipitate, and the lixivium was slightly green; muriated antimony yielded a white precipitate, with a yellowish lixivium; vitriolated zinc a whitish; cobalt in aqua-regia a reddish white powder; the precipitate of arsenic and the different earths was commonly white.

XXIII. NEW CHEMICAL NOMENCLATURES.

I. Of that proposed in 1787 by Messrs Morveau, Berthollet, Fourcroy, and Lavoisier.

When this nomenclature was first published, M. Lavoisier informs us, that some blame was thrown upon the authors for changing the language, which had received the sanction of their masters, and been adopted by them. In answer to this, however, he urges, that Messrs Bergman and Macquer had expressed a wish for some reformation in the chemical language. Mr Bergman had even written to M. Morveau on the subject in the following terms: "Show no favour to any improper denomination: Those who are already possessed of knowledge, cannot be deprived of it by new terms; those who have their knowledge to acquire, will be enabled by your improvement on the language of the science to acquire it sooner."

The following is M. Lavoisier's explanation of the principles on which his new language is composed.

"Acids consist of two substances, belonging to that order which comprehends such as appear to us to be simple substances. The one of these is the principle of acidity, and common to all acids; from it therefore should the name of the class and genus be borrowed. The other, which is peculiar to each acid, and distinguishes them from one another, should supply the specific name. But in most of the acids, the two constituent principles, the acidifying and the acidified, may exist in different proportions, forming different degrees of equilibrium or saturation; this is observed of the fulphoric and sulphureous acid. These two states of the same acid we have expressed by varying the termination of the specific name.

"Metallic substances, after being exposed to the compound action of air and fire, lose their metallic lustre, gain an increase of weight, and assume an earthy appearance. In this state they are, like acids, compound bodies, consisting of one principle common to them all, and another peculiar to each of them. We have therefore in like manner classified them under a generic name, derived from the principle which is common to them all. The name which we have adopted is Oxide: The peculiar names of the metals from which they are formed, serve to distinguish these compounds from one another.

"Combustible substances, which, in acids and metallic oxides, exist as specific and peculiar principles, are capable of becoming, in their turn, the common principle of a great number of substances. Combinations of sulphur were long the only compounds of this sort known; but of late the experiments of Messrs Vandermonde, Monge, and Berthollet, have shown that coal combines with iron and perhaps with various other metals; and that the results of its combination with iron are, according to the proportions, steel, plumbago, &c. It is also known from the experiments of M. Pelletier, that phosphorus combines with many metallic substances. We have therefore arranged these different combinations together under generic names, formed from the name of the common substance, with a termination indicating this analogy; and have distinguished them from each other by specific names derived from the names of the peculiar substances." "It was found somewhat more difficult to form a nomenclature for the compounds of those three simple substances; because they are so very numerous, and still more, because it is impossible to express the nature of their constituent principles, without using more compound names. In bodies belonging to this class, such as neutral salts for instance, we had to consider, 1. the acidifying principle common to them all; 2. the acidifiable principle which peculiarizes the acid; 3. the saline, earthy, or metallic base, which determines the particular species of the salt. We have derived the name of each class of salts from that of the acidifiable principle, common to all the individuals of the class; and have then distinguished each species by the name of the saline, earthly, or metallic base peculiar to it.

"As salt, consisting of any three principles, may, without losing any of these principles, pass through different states by the variation of their proportions; our nomenclature would have been defective without expressions for these different states. We have expressed them chiefly by a change of termination, making all names of salts in the same state to end with the same termination."

2. Nomenclature by M. Wiegleb.

In Wiegleb's General System of Chemistry translated by Hopson, we have another nomenclature formed on different principles. In this he gives to fixed vegetable alkali the name of Spodium, from the Greek word σπόδιον (spodion). The mineral alkali he calls natrum, the name by which it was anciently distinguished; and the volatile alkali ammonium, from sal ammoniac which contains it in great quantity. The compound salts may be distinguished into double, triple, and quadruple; though, in the scheme given in the work, the first division is omitted, as tending only to create confusion. The irregular salts, consisting of those which are triple and quadruple, are admitted. Such as are imperfect by reason of an excess of acid, he says, are best denominated by converting the adjective, expressive of the base, into a participle; a practice which, on many occasions, though countenanced by the authority of a late eminent writer, seems awkward and stiff. The excess of acid is denominated by the word hyperoxys, and a defect of it by hypoxys. Hence his denominations are formed in the following manner.

Salts with excess of acid. Cream of tartar, or tartaros fpodatus, or tartaroxys fpodicus. Acid vitriolated tartar, or vitriolum fpodatum, nitrioloxys fpodicus.

The salts which are imperfect from a defect of acid have their denominations by mentioning the base before the acid, and expressing the former substantively, the nomenclature adjectively. Thus,

Salt of tartar, aerated vegetable Oxyfpodium, aerocraticum. Alkali, fpodium aerocraticum. Aerated volatile alkali, ammoniacum aerocraticum, Chalk, or calx aerocratica, Borax, or natrum boracicum.

With respect to other terms, Mr Wiegleb expresses the acid with which any base is combined, by the termination eratia, from the Greek ἐρατία (robur), added to it; excepting only those with the nitrous and muriatic acids; and there (for what reason does not appear) he calls Aponitra and Epimuria. His genera of salts are as follow.

1. Vitriols (Sulphurocrates). 2. Nitres (Aponitra). 3. Murias (Epimuria). 4. Boraxes. 5. Fluoricrates. 6. Arsenicates. 7. Barylithocrates, (those with acid of tungsten). 8. Molybdanocrates. 9. Photocrates, (with acid of phosphorus). 10. Electrocrates. 11. Oxycrates, (with the acetous acid); or epoxycrates, (with the aerated acid). 12. Tartars; or, with the acid changed by fire, pyro-tartars. 13. Oxalidocrates. 14. Cecidocrates (with acid of galls). 15. Citriocrates. 16. Melicrates (with the acid of apples). 17. Benzicrates. 18. Xylocrates. 19. Gummicrates. 20. Camphorocrates. 21. Aerocrates. 22. Galactocrates. 23. Gala-melicates (with acid of sugar of milk). 24. Myrmecrates. 25. Cyanocrates (with the colouring matter of Prussian blue). 26. Steatocrates. 27. Bombycirates. 28. Zoolithocrates, (with acid of calculus).

On the subject of nomenclatures it is obvious to remark, that whatever may be the defects of the old one, we are ready to be involved in much greater difficulties by the introduction of a new one. Or supposing a new language to be adopted, where would be the security for its permanence? That which appears most specious at one period, may still be superseded by the refinements of another; and colourable pretensions would never be wanting to successive innovators. Hence a continual fluctuation, and an endless vocabulary. As the nomenclature first above mentioned, however, has attracted no small degree of attention, we shall here subjoin a scheme of it, as well for the satisfaction of our readers in general, as for the gratification of those in particular who may have imbibed the doctrines of its authors.

[Follows, the Whole-sheet Table.] ### A TABLE, EXHIBITING

Proposed by Messieurs De Morvea

#### I. SUBSTANCES THAT HAVE NOT BEEN YET DECOMPOSED.

| NAMES NEWLY INVENTED OR ADOPTED | ANCIENT NAMES | |----------------------------------|---------------| | Light. | Latent heat, or matter of heat. | | Caloric. | The base of vital air. | | Oxigene. | The base of inflammable gas. | | Hydrogene. | The base of phlogisticated air, or of atmospheric mephitic. | | Azote, or the radical principle of the nitric acid. | Pure coal. | | Carbone, or the radical principle of the carbonic acid. | | | Sulphur, or the radical principle of the sulphuric acid. | |

#### II. THE SAME SUBSTANCES REDUCED INTO THE STATE OF GAS BY THE ADDITION OF CALORIC.

| NAMES NEWLY INVENTED OR ADOPTED | ANCIENT NAMES | |----------------------------------|---------------| | Oxigenous gas. | Depthlogisticated or vital air. | | Hydrogenous gas. | Inflammable gas. | | Azotic gas. | Phlogisticated air, or atmospheric mephitic. | | Sulphuric vitreus. | Water. | | With less of sulphur. | Nitric acid. | | With an excess of nitrous acid. | Carbonic acid. | | Sulphuric vitreus. | Sulphur. | | With less of sulphur. | Sulphure of salt. | | With more of salt. | Phosphoric acid. | | With a mixture of phosphoric acid and muriatic acid. | | | With an excess of oxygen. | Boracic acid. | | Oxygenate acid. | Fluoric acid. | | Succinic acid. | |

#### DENOMINATIONS newly appropriated to several Substances.

| New Names | 1 | 2 | 3 | 4 | 5 | 6 | 7 | |-----------|---|---|---|---|---|---|---| | Mucous matter. | Glutinous matter, or gluten. | Sugar. | Starch. | Fixed oil. | Volatile oil. | The aroma, or aromatic principle. | | Mucilage. | Glutinous matter. | Saccharine matter. | Amylaceous matter. | Fat oil. | Essential oil. | Spiritus rectus. |

*As the substances in the lower part of this column cannot be reduced into a gaseous state, and not only the...* ## A Table Exhibiting the Chemical Nomenclature

Proposed by Messrs. De Morveau, Lavoisier, Berthollet, and De Fourcroy, in May 1787.

### New Names Newly Appropriated to several Substances, which are more compound in their Nature, yet enter into new Combinations without being decomposed.

| New Name | Mixtures matter, &c., glass. | Olieous matter, &c., glass. | Sugar. | Starch. | Fixed oil. | Volatile oil. | The essence, &c., distillation principle. | Refineries. | Calomel. | Refined matter, &c., applied. | Refined matter, &c., zinc. | Essence, &c. (in which are contained all the dominions) | Ethereal essence, &c., principle | Aerated water, &c., water principle | Alcohol or spirits of wine. | Alcohol or spirits of water. | |----------|-------------------------------|-----------------------------|--------|---------|-------|-----------|--------------------------------|------------|--------|-------------------------------|----------------|---------------------------------|----------------------------|--------------------------------|--------------------------------|--------------------------------| | Sulphur. | Dinitrous acid. | Espiritus vitæ. | Spiritus vitæ. | Spiritus Vitæ. | Aqua vitae. | Spiritus aquæ. | Anhydride of acids of spirits of wine. | Spiritus aquæ. | Spiritus aquæ. | Spiritus Vitæ. | Spiritus Vitæ. | Animal spirits of wine. | Spiritus aquæ. | Spiritus aquæ. | Spirits of wine, &c., spirit of wine. | Spirits of wine, &c., spirit of water. |

The substances are divided into various groups based on their chemical composition and properties:

- **Substances that have not been changed by decomposition** - **The same substances reduced into the state of air by the action of heat** - **The same substances combined with oxygen.** - **The same substances in an oxidized gaseous state.** - **These oxidated substances neutralized by the addition of base.** - **The same primary substances combined with other substances but not oxidized.**

Each group contains detailed entries for various compounds with descriptive names based on their properties and uses. TABLE, showing the Manner in which Natural Bodies, considered in a Chemical View, may be divided into Classes; with their several Subdivisions; their Properties defined; and the Manner in which they are obtained, pointed out.

NATURAL BODIES, considered as the Objects of Chemistry, may be divided into the following Classes, viz. 1. SALTS. 2. EARTHS. 3. METALS. 4. INFLAMMABLES. 5. WATERS. 6. AIRS.

I. SALTS.

These are soluble in water, sapid, and not inflammable. They are either ACIDS or ALKALIES.

1. Acids are distinguished by turning syrup of violets red, or forming with alkalies neutral salts; and are supposed to consist of dephlogisticated air condensed, as their acidifying principle. The different acids yet known are, 1. Vitriolic, fixed. The most ponderous of all fluids next to mercury, the most fixed in the fire, and the most powerful as a solvent of all the acids. Obtained chiefly from sulphur by inflammation. 2. Vitriolic, volatile. Obtained also from sulphur by inflammation; air being admitted during the process. It acts less powerfully as a solvent than when in its fixed state. 3. Nitreous, or Aquafortis: a volatile fluid, generally met with of a reddish colour, and emitting noxious fumes, when in its concentrated state; though this is found not to be essential to it, but owing to a mixture of phlogiston. In its pure state it is almost as colourless as water, and smokes very little. It is next in strength to the vitriolic acid, and obtained chiefly from nitre. It consists of dephlogisticated and phlogisticated air condensed, and may be obtained by taking the electric spark for a long time in a mixture of these. By uniting with some metals it appears to be converted into volatile alkali. 4. Muriatic, or spirit of sea-salt. A volatile fluid, generally of a fine yellow colour; though this also is owing to the admixture of foreign substances, generally of iron. Inferior in power to the former, and obtained from sea-salt. Naturally this acid seems to be in an aerial state, but easily contracts an union with water. On mixture with manganese, it is wholly converted into a yellow, and almost indescribable vapour, called dephlogisticated spirit of salt; but which, on mixture with inflammable air, recomposes the marine acid. 5. Fluor acid. Obtained from a species of spar: has little acid power, but is remarkable for its property of corroding glass. 6. Acid of borax, or sedative salt. Obtained from borax in the form of scaly crystals; found also naturally in some waters in Italy, and in certain minerals in other countries. 7. Acetous acid. Obtained by allowing any fermentable liquor to proceed in the fermentation till past the vinous state. It is much less corrosive, and less powerful as a solvent, than the vitriolic, nitrous, or marine acids. 8. Acid of tartar. Procured from the hard substance called tartar, deposited on the sides of wine vessels. 9. Acid of sugar. Found naturally in the juice of sorrel, and procured artificially by means of nitrous acid from sugar and a great variety of other substances. Assumes a dry form. 10. Acid of phosphorus. Obtained artificially from urine, and in large quantity from calcined bones; found naturally in some kinds of lead-ore; and in vast quantities in Spain united with calcareous earth. Assumes a solid form, and melts into glass. 11. Acid of urine. Procured from the animal from which it takes its name, by expression, or distillation, in a fluid form. 12. Acid of amber. Obtained in a solid form from amber. 13. Acid of arsenic. Obtained from that substance by means of nitrous acid. Is extremely fixed in the fire. 14. Acid of molybdena. Procured from that substance by means of nitrous acid. Resembles a fine white earth. 15. Acid of lapiss ponderosa, tungsten, or wolfram. Obtained as an acid, per se, from this substance by Mr Scheele; but its real acidity is denied by other chemists. Is in the form of a yellow powder. 16. Acid of milk. Obtained in a fluid form from that liquor. 17. Acid of sugar of milk. Obtained in form of a white powder, by means of nitrous acid, from sugar of milk. 18. Lithophoric acid. Obtained in a solid form from human calculus, by means of nitrous acid. 19. Acid of benzoin. Obtained in a solid form from that gum by sublimation or lixiviation with quicklime. 20. Acid of lemons. Obtained from the juice of that fruit by crystallization. 21. Sebaceous acid, or acid of fat. Obtained in a fluid state from fuel by distillation. 22. Acid of citrons. Obtained in a fluid from the juice of that and other fruits. 23. Acid of apples. Obtained in a fluid state from the juice of apples and other fruits. 24. Acid of sorrel. Obtained in a solid form from the juice of that plant; the same with acid of sugar.

II. ALKALIES. These turn syrup of violets green, and with acids form neutral salts. They are, 1. Fixed vegetable, or Potash. Always obtained from the ashes of burnt vegetables. A deliquescent salt. 2. Fixed fulgurite. A solid crystalline salt, sometimes found native, as the natrum of Egypt; and sometimes by burning seaweed as kelp. 3. Volatile. Obtained from sal ammoniac, from the foot of burning bodies, and from the putrefactive fermentation. It is naturally in the state of an invisible and elastic vapour, constituting a species of aerial fluid, and consists of phlogisticated and inflammable air.

ACIDS, by their union with other bodies, form

NEUTRAL SALTS. These are always composed of an acid and an alkali, and are of many different kinds, as may be seen in the following table.

EARTHY SALTS. Composed of an acid joined to an earthy basis, as alum and gypsum. See the following table.

METALLIC SALTS. Formed of an acid and metal. The principal of these are vitriols; the others may be seen in the following table.

ESSENTIAL SALTS. Obtained from vegetables, and contain an acid joined with the juices of the plant in a particular manner not to be imitated by art. To these belong sugar, manna, honey, and others of that sort.

II. EARTHS. II. EARTHS.

These are solid bodies, not soluble in water, nor inflammable; and if fused in the fire, never resume their earthy form again but take that of glass. They are divided into absorbent, crystalline, and argillaceous.

I. Absorbent Earths are capable of being united with acids, and are either calcareous, or not calcareous.

a. The calcareous absorbent earths are,

1. Limestone, or marble. This is of infinite variety as to colour and texture. Marble is the hardest and finest. Those kinds of limestone which feel unctuous to the touch, are generally impregnated with clay; those that feel gritty, or where the lime is hard and weighty, contain sand; this is the best for building; the other for manure.

2. Chalk. A white, friable, soft substance. This is much more free of heterogeneous matters than any limestone, and is easily calcined into quicklime. It is probably nothing else than lime-stone suddenly concreted without being crystallized.

3. Sea shells, are likewise a calcareous earth, and yield a very fine quicklime. These are used in medicine.

4. Terra ponderosa. A fine white earth sometimes found combined with fixed air, but more commonly with the vitriolic acid, and forming with it a very heavy compound named spathum ponderosum. It is found in mines and veins of rocks.

b. The absorbent earths which cannot be reduced into quicklime are,

1. Magnesia alba. A white earth, usually found combined with the vitriolic acid, and forming bitter purging salt. It is likewise obtained from the mother-lye of nitre, the ashes of burnt vegetables, &c.

2. Earth of alum. A particular kind of absorbent earth, found in many places mixed with sulphureous pyrites, as in Yorkshire &c. Clay of any kind may by a particular process be converted into this earth.

3. Earth of animals. This is obtained by the calcination of animal substances, and by precipitation in the process for making acid of milk. It can hardly be converted into glass; and is therefore used as a basis for white enamels, &c. It is said to consist of the phosphoric acid united to calcareous earth.

II. Crystalline or Vitreous Earths, are hard, and strike fire with steel; may be calcined in the fire; but are not soluble in acids.

Of this kind are,

1. Sand and Flint; found plentifully everywhere. With alkaline substances they are easily changed into glass; and hence termed vitreous.

2. Precious stones of all kinds are likewise referable to this class; but they are of a much greater degree of hardness and transparency than the others.

III. Argillaceous Earths are distinguished by acquiring a very hard consistence when formed into a paste with water, and exposed to a considerable degree of heat; not soluble in acids. They are,

1. Common clay. It is of many different colours; but chiefly red, yellow, or white. The purest is that which burns white in the fire.

2. Medical bones. These are of different sorts; but are only a purer kind of clay, sometimes mixed with a little iron or other matter.

3. Lapis nephriticus, or fleatite. These are indurated clays, found in various parts. They are at first soft, and readily cut; but turn extremely hard in the air. Many other varieties of these earths might be mentioned; but as they do not differ in their chemical properties so much as in their external appearance, and being all mixed with one another, they more properly belong to the natural historian than the chemist.

III. METALLIC SUBSTANCES.

These are bodies of a hard and solid texture; fusible in the fire, and resuming their proper form afterwards; not miscible with water, nor inflammable. They are divided into Metals and Semimetals.

I. Metals are malleable; and the species are,

1. Gold. The most ponderous and fixed in the fire of all bodies except platina, and the most ductile of any. It has a yellow colour, and is more commonly found in its metallic state than any other metal. It has no proper ore; but is found in the ores of silver, and almost all sands contain some of it.

2. Silver is next to gold in malleability and ductility; but less fixed in the fire than either it or platina. It is sometimes found in its native state; but most commonly in that of an ore with sulphur, sometimes with arsenic, and assuming different appearances.

3. Platina. A white metal of a greater specific gravity than gold, and altogether as fixed in the fire; the most difficult to be melted of all known substances; resisting the tests which have usually been applied for discovering the purity of gold, supposed from hence to be the snirius of the ancients. Found in South America.

4. Copper. Of a reddish colour; hard and honourable; admits of being extended greatly under the hammer, either hot or cold. Is difficult of fusion. It is generally found in the state of an ore with sulphur. There are a great variety of ores of it, extremely beautiful, blue, red, green, and yellow.

5. Iron. A grey-coloured metal, extremely ductile when hot; the lightest of them all except tin. It is the only metal certainly known to admit of being welded; though platina is likewise said to possess some share of this property. It is likewise the only one capable of being tempered by cooling. It is found almost everywhere; and its ores are infinitely various.

6. Tin. A white soft metal, the lightest of the whole, and very ductile. The ores of it are generally arsénical, and assume a crystalline appearance; their colour being most usually of a dark brown, and sometimes very beautiful. Table.

7. Lead. A metal of a dull bluish colour, exceedingly soft and malleable, and very weighty. Seldom found in its metallic state, but usually in an ore with sulphur or arsenic; but seldom with sulphur alone. The principal ores of it are the cubic, called galena, and the glaify, called spar.

8. Mercury or quicksilver; formerly accounted a semimetal, on account of its fluidity, but now reckoned among the most perfect metals. It is a white, opaque, metallic body; fluid, except in a very intense degree of cold; very heavy, and easily volatilized by heat. Sometimes found in its fluid form, but usually in a beautiful red ore with sulphur, called cinnabar.

II. SEMIMETALS are brittle, and do not stretch under the hammer. They are,

1. Zinc. A bluish white substance of a fibrous texture, considerably hard and sonorous, with a small degree of ductility; easily fused and volatilized. Its principal ore is lapis calaminaris.

2. Bismuth, or tin-glafs. A white, ponderous, hard, brittle, and sonorous body, of a plated texture; easily fused and vitrified. It is only reduced to an ore by arsenic. Its appearance much the same with regulus of antimony.

3. Antimony. A blackish substance, of a fibrous needle-like texture; hard, brittle, and of a considerable weight; not difficult of fusion, and easily convertible into glass. Its only ore is with sulphur, which is the crude antimony.

4. Arsenic. A bright, sparkling, whitish-coloured semimetal; of a plated texture; very brittle, and extremely volatile. It is generally found in the ores of other metals.

5. Cobalt. A brittle semimetal fusible in a moderate heat, and easily convertible into a beautiful blue glass called smalt. It is always obtained from an arsenical ore, likewise called cobalt.

6. Nickel. A reddish white substance, of a close texture, and very bright; easily melted, but very difficult to vitrify.

IV. INFLAMMABLE SUBSTANCES.

Are those which continue to burn of themselves when once set on fire. They are divided into oils, sulphur or brimstone, alcohol or ardent spirits, and charcoal.

I. Oils are thickish, viscous fluids, not miscible with water. Divided into animal, vegetable, and fossil.

a, b, The animal and vegetable oils are,

1. Expressed. These are of a mild and bland taste, inodorous, and not soluble in alcohol. They are obtained by expression, as oil of olives, rape-seed, almonds, &c. Animal fats are of the same nature, as is also wax.

2. Essential. These are always obtained by distillation, possess the taste and flavour of the subject from whence they are drawn, and are soluble in alcohol. Of this kind are oil of cloves, spike, &c. The oil of ants is an example in the animal kingdom.

3. Empyreumatic. These are obtained by a considerable degree of heat, and possess an acrid taste and burnt-like flavour, as oil of hartshorn. They are soluble in spirit of wine.

4. Fossil oils. These are found in the earth in their native state; and are called, when pure, naphtha; which is of an acrid taste, and extremely volatile, not miscible with alcohol. A great many inflammable fossils contain this, as bitumens, pit-coal, &c.

I. SULPHUR OR BRIMSTONE. This is a dry friable substance, not miscible with water. It is found in many mineral substances, metallic ores, &c. but is for the most part met with in pyrites. Great quantities of it are found in the neighbourhood of volcanoes.

II. ALCOHOL OR ARDENT SPIRITS. This is a fluid of an acrid and volatile nature, miscible with water; obtained from fermented vegetable juices by distillation; as from the juice of the grape, malt-liquors, rice, &c.

V. CHARCOAL. The residuum of most inflammable matters after undergoing distillation with a strong fire. A black substance, acted upon with difficulty by acids; soluble in hepatic-fulphuris, and entirely dissipable into inflammable air by a very violent heat. Of great use as fuel, and essentially necessary in metallurgy and other arts.

V. WATER.

A colourless insipid fluid well known. It is either simple or mineral.

1. Simple, or pure rain-water, as it is called, though the most homogeneous fluid of this kind with which we are acquainted, is not perfectly pure, but always contains a portion of mucilaginous matter, which can never be perfectly separated. It is supposed to consist of dephlogisticated and inflammable air condensed.

II. MINERAL waters are these spring-waters impregnated with saline substances; the diversity of which is exceeding great; but they all agree in having an acid joined with them. The most common sorts are impregnated with iron and sulphur.

VI. AIR.

An invisible and permanently elastic fluid, is of the following kinds: Dephlogisticated, phlogisticated, fixed or fixable, inflammable, nitrous, vitriolic acid air, marine acid air, dephlogisticated marine acid, alkaline air, hepatic air, atmospheric air.

1. Dephlogisticated. An elastic fluid naturally extricated in the process of vegetation; artificially procured from nitre, minium, manganese, water, &c. eminently capable of supporting flame and animal life. One of the component parts of our atmosphere. 2. Phlogisticated. Produced in great quantities during the putrefactive fermentation; obtained also in the calcination of metals and other phlogistic processes. Destroys animal life, and extinguishes flame, but is very friendly to vegetation. Is another of the component parts of our atmosphere.

3. Fixed, or fixable. Has its name from the property of adhering to certain bodies, and fixing itself in them. Consists of dephlogisticated air united to charcoal. Is obtained by fermentation, and in all phlogistic processes. Manifests the properties of an acid; extinguishes flame, and destroys animal life.

4. Inflammable. Consists wholly of charcoal and a little water rarefied by heat; is remarkable for being the lightest of all gravitating substances. Is produced naturally in mines, and from putrid waters; artificially procured from certain metallic solutions, by passing the steam of water over red-hot iron; by distilling wood, pit-coal, &c., with a strong heat; or by exposing charcoal to the heat of a burning lens in vacuo. It extinguishes flame unless it be mixed with a certain proportion of atmospheric or dephlogisticated air; in which case it explodes violently, destroys animal life, but is friendly to vegetation.

5. Nitrous. Procured artificially in dissolving metallic or other substances in the nitrous acid. On mixture with dephlogisticated air both the fluids lose their elasticity, and a small quantity of nitrous acid is produced. It instantly kills animals, and extinguishes flame. By union with some metals is converted into volatile alkali. In some cases it may be made to support flame, and even animal life. Its property of condensing along with dephlogisticated air renders it a test of the salubrity of the atmosphere.

6. Vitriolic acid air. The same with volatile or sulphureous vitriolic acid.

7. Marine acid air. The same with marine acid reduced into vapour, and deprived of most of its water.

8. Dephlogisticated marine acid. Supposed by some to be the marine acid deprived of its phlogiston; by others, to be the same acid with an addition of pure air. It destroys many kinds of colours; whitens linen, and with inflammable air regenerates common marine acid.

9. Alkaline air. The same with pure volatile alkali; is formed by an union of phlogisticated and inflammable air.

10. Hepatic air. Produced from the decomposition of liver of sulphur by acids, or in the common atmosphere. It is inflammable, but does not burn with explosion.

11. Atmospheric air. Composed of dephlogisticated and phlogisticated air; and thus supports both animal life and vegetation.

TABLE, showing the several Combinations that the simple chemical elementary bodies admit of with one another; the Compound resulting from that Mixture; and the Manner in which the Union is effected: With some Account of the principal Uses to which these are applied in Arts or Manufactures.

N.B. This mark*, put above any word, denotes that there is some difficulty in the process, or that the union is not very complete.

VITRIOLIC ACID may be combined with the following Substances, viz.

ACIDS.

Nitrous Acid. A mixture which readily inflames oils. By solution, generating heat.

Muriatic, Vegetable, and all other Acids yet known. By solution, generating heat. But these mixtures are applied to no particular use in medicine or arts.

Vegetable. Nitrum vitriolatum. A vitriolated tartar, obtained by distilling from nitre with the vitriolic acid.

Sal polychrestum. By deflagrating nitre with sulphur. There are many other kinds of vitriolated tartar, known formerly by different names, and supposed to be possessed of particular properties, but they are now neglected.

Fossil. Glauber's salt. By solution and crystallization. Much used in medicine as a gentle purgative.

Volatile. Secret ammoniac. By solution. Formerly supposed a most powerful menstruum for metals, &c., but without any just foundation.

ALKALIES.

A corroded calx. By simple corrosion. This when perfectly edulcorated with water is found to be a true gypsum.

Selenites. By precipitation from a very dilute solution of chalk in the nitrous acid, by means of the vitriolic acid.

Terra ponderosa. With this it unites in preference to alkalies, forming a very heavy and insoluble substance called spathum ponderosum.

Cyphum or Paris-plaster. Often found in a native state. May be artificially formed by precipitating from a solution of chalk in a very concentrated nitrous acid. Used as a cement; for taking impressions from medals, &c.

Talc, asbestos, &c. A native production which cannot be perfectly imitated by art. Used for holding objects in microscopes, making incombustible cloth, &c.

Magnesia. Epilom, or magnesia Glauber's salt. By solution and crystallization. Much used in medicine for the same purposes as real Glauber's salt.

EARTHS. CHEMISTRY

EARTHS.

Earth of Alum. Alum. By solution, crystallization, &c. Used by dyers as a preparatory for taking on the colours, papermakers, goldsmiths, &c.

Earth of Animals, Osteocella, &c. By solution. The mixtures of these are not applied to any particular use.

Clay. Alum. By digesting pure clay for some time in this acid, and exposing it for some time to the air, an alum is produced; and if the clay is precipitated from this aluminous concrete, it is found to be a pure earth of alum, soluble in all acids.

Flint. A thickish coagulum. By digesting the liquor silices in the vitriolic acid.

Gold*. Imperfectly. By a particular process after being separated from aqua-regia.

Silver*. By solution, after it has been precipitated from the nitrous acid by alkalies. The fumes which arise in this solution are inflammable.

Copper. Blue vitriol. This is sometimes a native production, but in this way it is never pure. It is artificially prepared by solution in a very concentrated acid, and crystallizing it.

Green vitriol or copperas. Obtained at large by particular process from pyrites; or by solution, &c. in a diluted acid. This is the basis of all black dyes, ink, &c. as it strikes a black colour with vegetable astringents.

Iron. Salt of steel. By calcining the crystals of green vitriol till they are converted into a white powder.

Calcium of vitriol. By continuing the calcination till it affumes a brown colour.

Lead. Saturnus vitriolicus. A solution in a boiling heat, but is again precipitated when cold.

An indissoluble concrete. By precipitation from the nitrous acid.

Tin. Jupiter corrosive. By a boiling heat in a concentrated acid.

Mercury. Ignis Geleme, or infernalis of Paracelsus. By a boiling heat, and repeated coctions with fresh acid when it is evaporated.

Turpeth mineral, or mercurius precipitatus flavus. By evaporating to dryness, and then washing with water.

Antimony*. A metallic salt. By elective attraction from butter of antimony.

Zinc. White vitriol. Often found in its native state. Artificially made by solution and crystallization in a diluted acid. Used by painters for drying.

Bismuth. A corroded calx. By solution in a concentrated acid.

Arsenic. By ditto.

Cobalt. A rose-coloured mixture. By solution. If this is precipitated by a fixed alkali, and again dissolved, the liquor appears of a beautiful red.

Expressed. A blackish gummy-like mass. By solution, generating a considerable heat. Native gums are supposed to owe their origin to a mixture of this kind.

Essential. A dark-coloured resinous mass. A great heat and violent effervescence being produced by this mixture. Native resins supposed the same.

Empyreumatic. Little known. By solution.

Fossil. A substance resembling amber. By solution.

SULPHUR*. Here there is no proper union of substances; but if sulphur is boiled in this acid, it becomes less inflammable and more fixed than any ordinary sulphur.

Vitriolic ether. By careful solution and distillation, the ether being separated by the addition of water.

Spiritus vitrioli dulcis. By solution and distillation.

Oleum dulce. By continuing the heat after the ether has arisen.

Oleum anodynum minarale. By redistilling the residuum of the last with alcohol. A medicine much celebrated by Hoffman.

Sulphur. By pushing the heat after the oil comes over. It is to be observed that this is produced in every combination of this acid with inflammables or metals.

WATER. An acidulated water. Sometimes, though seldom, found issuing along with native springs. Applied to no particular use.

NITROUS ACID may be combined with the following Substances, viz.

ACIDS.

Vitriolic, as above.

Muriatic. Aqua regia. By solution. This is the only proper menstruum for gold; and it is a solution of tin in this menstruum which is the basis of the scarlet dye.

Vegetable, and all others. By ditto. These compounds have no particular names, nor are applied to any particular uses in medicine or arts.

Vegetable. Common nitre. A native production. Made artificially by solution and crystallization. This deflagerates with oily or metallic bodies, and is the foundation of gun-powder.

Fossil. Cubic nitre. By solution.

Volatile. Nitrous ammoniac. By solution. This differs from all the other ammoniacal salts, by being soluble in alcohol.

ALKALIES.

Calcaceous. Deliquescent crystals. By ditto and crystallization.

Bullock's phosphorus. By ditto and evaporating to dryness.

Earth of Alum, and all other absorbent earths. By solution. The compounds have no names nor any remarkable properties hitherto discovered.

Crystalline Earths*. By solution after precipitation from the liquor silices.

METALS. METALS.

GOLD*. Slightly impregnated. By a boiling heat in close vessels, after the ordinary method of separating silver from gold by the nitrous acid. It spontaneously subsides in the air.

A fluid solution. By solution. This when diluted with water stains hair and bones black; as also marble, agate, jasper, &c. of different colours.

SILVER. Sal metallorum. By solution and crystallization.

Catharticum lunare, lunar caelicus, or lapis informatus. By inspissating the solution to dryness.

COPPER. A green-coloured solution. By solution.

IRON. A greenish solution, if a diluted acid is employed; if otherwise, it is of a yellowish colour: evaporated to dryness, it deliquesces in the air.

LEAD. A yellow solution. By dissolving in a diluted acid. If much water is added, the metal is precipitated.

Saturni fulminans. By inspissating the solution. This explodes when put upon the fire with greater force than nitre, and has been proposed to be used as an ingredient in gun-powder to augment its force.

TIN. A solution or corroded calx. By a careful solution without heat it remains suspended; if otherwise, it falls down in form of a calx. This is commonly supposed to be the composition used in dyeing scarlet; but by mistake: for it is a solution of tin in aqua-regia that communicates that fine colour to cochineal. The same solution is the basis of the powder which tinges glas of a ruby colour. It is the precipitate of gold from aqua-regia by means of tin.

MERCURY. A limpid solution, intensely corrosive. By solution.

Red precipitate. By evaporating the solution to dryness, and then calcining till it becomes red.

Mercurius corrosivus fusus. By precipitating from the nitrous acid by fixed alkali.

White precipitate. By ditto with the volatile alkali.

BISMUTH. A greenish solution. By using a concentrated acid. This might be applied in some cases in the art of dyeing; but is not yet come into general use.

Magister of bismuth. By precipitating from the solution by means of water. This has been employed as a cosmetic, but is inefficacious and unsafe. If mixed with pomatum, this stains hair of a dark colour without injuring it.

ZINC. A corroded solution. By the ordinary means.

SEMIMETALS.

ANTIMONY. A colourless calx. By simple corrosion.

Bezoaric mineral. By distilling from butter of antimony, after having added the nitrous acid.

Antimonium diaphoreticum. By adding nitre to crude antimony, and deflating.

Cerula antimonii. By deflating regulus of antimony with nitre.

COBALT. A red liquor. By solution either in its calcined or metallic state.

Rose-coloured crystals. By adding muriatic acid, and allowing it to crystallize.

Green sympathetic ink. By dissolving these crystals in water. The solution is red when cold, and green when warm; when wrote with, it disappears when dry; but when held to the fire it becomes green, and again disappears when cold.

NICKEL. A green-coloured liquor. By solution.

OILS.

EXPRESSED. A thick bituminous-like substance. Upon the mixture a considerable degree of heat is generated, and sometimes, though very seldom, actual flame is produced.

ESSENTIAL. Ditto. A more violent heat is generated upon the mixture with these oils than any other, and with many of them an actual flame is produced.

EMPYREUMATIC. This mixture has no name, nor is it applied to any remarkable use in arts.

FOSSILE. Ditto.

ALCOHOL.

Nitrous ether. By digesting; the ether arising to the surface.

Spiritus nitri dulcis. By digesting a little, and then distilling.

WATER.

Acidulated water. By solution.

ACIDS.

The MURIATIC ACID may be combined with the following substances, viz.

VITRIOLIC, and NITROUS. As in the former part of this Table.

VEGETABLE, and all others yet known. By solution; but as none of these mixtures are applied to any particular purpose, we take no notice of them.

ALKALIES.

VEGETABLE. Digestive salt. By solution and crystallization.

Common salt. Commonly obtained by evaporating sea-water to dryness; or artificially made by mixing the acid and alkali, and crystallizing.

FOSSE. Sal gem. A native fossile salt, found in mines in Poland, Spain, &c. of the same nature as common salt, but more pure.

VOLATILE. Common ammoniac. Obtained at large by a particular process from root. Artificially made by mixing the acid and alkali, and crystallizing.

EARTHS.

CALCAREOUS. Liquid shell. By solution. A substance whose effects in medicine have been greatly extolled.

Oil calcis per deliquium. By evaporating liquid shell to dryness. It naturally deliquesces.

Fixed ammoniac. By solution and crystallization. This sometimes appears luminous in the dark when struck with a hammer.

OSTEOCELLA, MAGNESIA, and other absorbents. By solution; but the properties or uses of these are not known.

METALS: CHEMISTRY

GOLD*. A yellow liquor. By boiling a calx of gold (in whatever way obtained) in this acid. It does not act upon it in its metallic state.

SILVER*. A fluid solution. By dissolving the ore of silver in this acid. It does not act upon pure metallic silver.

PLATINA*. A fluid solution. With difficulty effected, after having been precipitated from aqua regia by alkalis.

COPPER. A green deliquescent inflammable salt. By solution and inspissating to dryness.

IRON. Tinctura martis aurea. By solution. The iron is in some measure rendered volatile by this operation.

LEAD. A limpid solution. By a boiling heat, and frequent cohabitations with fresh acid.

Cornea Saturni. By precipitation from the nitrous acid.

TIN*. A corroded powder. By simple corrosion.

Butter of tin. By distilling from corrosive sublimate.

A colourless crystalline mass, extremely acrid. By corrosion, employing the fumes of a very concentrated acid.

Mercur. corrosif. albus. By precipitation from the nitrous acid.

MERCURY*. Corrosive sublimate. By subliming from sal ammoniac, common salt, or many other bodies.

Mercurius dulcis. By redistilling corrosive sublimate with more quicksilver.

Mercurial panacea. By subliming corr. sub. nine times, and digesting for some time in spirit of wine.

BISMUTH*. A solution very slightly impregnated. By employing a very concentrated acid.

ZINC. A solution of a very slight yellow colour.

ARSENIC*. Butter of arsenic. By distilling corrosive sublimate with arsenic; the arsenic uniting with the acid, and leaving the mercury.

COBALT. A reddish solution. By the ordinary means. It becomes green by a gentle heat.

NICKEL. A green solution. By the ordinary means.

OILS*. By solution. The union here is but imperfect, nor have they any particular name.

ALCOHOL. Spiritus salis dulcis. By digestion, and afterwards distilling. The acid here is never totally dulcified.

WATER. Acidulated water. Generating heat by mixture.

VINEGAR may be combined with the following substances, viz.

VITRIOLIC, NITROUS, and MURIATIC, as in the above table. It likewise unites with all other acids, generating heat; but the properties or uses of these are not known.

ALKALIES.

VEGETABLE. Regenerated tartar. By solution and crystallization.

FOSSILE. Polychrest of Rochelle. By ditto.

VOLATILE. Spiritus Mindererii. By solution.

CALCAREOUS EARTHS. Earthy salts. Not known in medicine or arts.

MAGNESIA. Dr Black's purging salt. By solution. It unites with all the other absorbent earths; but the properties of these mixts are unknown.

METALS.

COPPER. Verdigris. By solution and crystallization; or at large, by stratifying copper plates with the husks of the grape.

IRON. Sal maris aperiens. By solution and crystallization.

LEAD. Cerulea. By exposing, in certain circumstances, thin plates of lead to the fumes of vinegar.

Saccharum Saturni. By solution and crystallization.

TIN*. This is not properly dissolved; but the acid is evidently impregnated. By the ordinary means of solution.

MERCURY*. A fluid solution. By employing a precipitate of mercury from the nitrous acid by alkalies.

A red calx. By long digestion with fluid mercury.

ZINC. A colourless solution of a sweetish taste. By digesting for some time.

ANTIMONY*. Vinum benedictum. This is not a proper solution of the metal, but the acid is impregnated.

SEMIMETALS.

with an emetic quality.

ARSENIC. Vinum arsenicum. By ditto. A curious phosphoric liquor.

BISMUTH. An austere styptic liquor. By strong coction.

OILS*. The union here is imperfect, nor have any of them obtained particular names.

ALCOHOL. A mixture much used for anointing sprains, &c.

WATER. Acidulated water.

ACID OF TARTAR may be combined with the following substances, viz.

ALKALIES.

VEGETABLE. Cream of tartar with excess of acid.

Soluble tartar, when completely saturated.

FOSSILE. Rochelle salt.

VOLATILE. A salt very difficult of solution with excess of acid.

A beautiful and soluble salt when perfectly saturated. CHEMISTRY.

EARTH. CALCAREOUS. An indissoluble selenite. METALS. COPPER. A fine green colour for painting. IRON. A green astringent liquid. Chalybeated tartar. SEMIMETAL. REGULUS OF ANTIMONY. Emetic tartar.

ACID OF URINE may be combined with the following Substances, viz.

ACIDS of all kinds. The nature of these not known. ALKALI. FIXED VEGETABLE. A salt not easily crystallized, the nature of which is not known. FOSSILE. A fine crystallized salt used in medicine. VOLATILE. A glaas-like saline substance called microcosmic salt. The acid is always found in this state by evaporating urine.

VITRESCENT EARTHS. Glaas of different sorts. By fusion. LEAD. An inflammable malleable mass. By calcining the dry salt with lead. TIN. A mass resembling zinc; and inflammable. By ditto. IRON. A true phosphorus. By ditto. COPPER. A bluish solution. By employing a watery solution of the acid. MERCURY. A semi-opaque mass. By fusion with the acid in its solid form. ZINC. A corroded powder, soluble in water. By solution in the acid in a watery situation. SEMIMETALS. ANTIMONY. A solution in the ordinary way. BISMUTH. A brilliant striated mass. By fusion with the dry acid. ARSENIC. A whitish semitransparent deliquescent mass. By fusion. COBALT. A reddish tincture. By solution.

OILS. Baldwin's phosphorus. By distilling with substances that contain oils or inflammable matters.

FLUOR ACID may be combined with the following Substances, viz.

ALKALIES. FIXED VEGETABLE. A gelatinous saline mass which cannot be crystallized. Great part of it is also dissipated by evaporation to dryness. FOSSILE. A substance similar to the foregoing. VOLATILE. Lets fall a quantity of siliceous earth, and forms a crystallizable ammoniacal salt. LIME. MAGNESIA. A gelatinous matter. EARTHS. EARTH OF ALUM. Siliceous Earth. After long standing, crystals of quartz. SILVER. The calces of these metals partially dissolved; but the properties of the solution unknown. QUICKSILVER. Copper. The calx easily soluble, and affording blue crystals; the metal only partially so. IRON. Dissolved with violence with the emission of inflammable vapours into an uncrystallizable liquor.

ACID OF SUGAR may be combined with the following Substances, viz.

ALKALIES. FIXED VEGETABLE. A salt scarce capable of crystallization when perfectly neutral. FOSSILE. A salt difficultly soluble in water. VOLATILE. An ammoniacal salt shooting into quadrangular prisms. LIME. A kind of selenite from which the acid cannot be separated but by a burning heat. EARTHS. TERRA PONDEROSA. A salt formed into angular crystals, scarce soluble in water. MAGNESIA. A white powder insoluble without an excess of acid. EARTH OF ALUM. A yellow pellucid mass incapable of crystallization, and liquefying in the air.

METALS. GOLD. SILVER. The calces of all these metals dissolved, but the nature of the solutions unknown. PLATINA. QUICKSILVER. IRON. Dissolved in great quantity, and forming a yellow prismatic salt easily soluble in water.

SEMIMETAL. COBALT. A yellow-coloured salt forming a sympathetic ink with sea-salt. INFLAMMABLES. ALCOHOL. An ether which cannot easily be set on fire unless previously heated, and burning with a blue flame.

ACID OF BORAX, or SEDATIVE SALT, may be combined with the following Substances, viz.

ALKALIES. FOSSILE. Borax. A native substance, which may be imitated by art. It is of great use in promoting the fusion of metals and earths. VOLATILE. An ammoniacal salt shooting into small crystals, and melting by an intense heat into a greyish coloured glass. EARTHS. MAGNESIA. A salt crystallizable in vinegar and acid of ants. Decomposed by other acids and spirit of wine. EARTH OF ALUM. In certain proportions a salt difficult of solution; in others a hard mass resembling putty, yet partially soluble in water. CHEMISTRY

Iron. An amber-colored solution yielding crystals of a yellow color.

Arsenic. A crystallizable compound shooting into pointed ramifications, or forming a greyish, white, or yellow powder.

Alcohol. A solution with a considerable heat, which burns with a green flame.

Water. A solution in a considerable heat. The other mixtures with this acid not known.

ACID OF AMBER may be combined with the following Substances, viz.

Fixed Vegetable. A transparent and crystallizable salt, but deliquescent.

Fossil. A crystallizable salt not deliquescent.

Volatile. An ammoniacal salt shooting into acicular crystals.

Lime. A crystallizable salt, difficult of solution and not deliquescent. Decomposed by common sal ammoniac.

Magnesia. A gummy deliquescent saline mass, not crystallizable.

Earth of Alum. A prismatic salt incapable of decomposition by alkalies.

Silver. A salt shooting into thin oblong crystals obtained from the precipitate; but no solution of the perfect metal.

Copper. A crystallizable salt of a green color.

Iron. A crystallizable salt of a brown color.

Tin. A crystallizable salt from the precipitate, scarce to be decomposed by alkalies.

Lead. A crystallizable salt from the precipitate.

Zinc. A crystallizable salt.

Bismuth. A crystallizable salt from the precipitate, not to be decomposed by alkalies.

Regulus of Antimony. A solution of the precipitate.

ACID OF ANTS may be combined with the following Substances, viz.

Fixed Vegetable. A crystallizable salt, deliquescent in the air.

Fossil. A salt of a similar nature.

Volatile. An ammoniacal liquor, crystallizable with difficulty.

Chalk of Coral. A crystallizable salt which does not deliquesce.

Magnesia. A saline liquor scarcely crystallizable.

Terra Ponderosa. A crystallizable salt which does not deliquesce.

Earth of Alum. Unites with difficulty, and scarcely to the point of saturation. The nature of the compound not known.

Silver*. By solution. The calx of silver precipitated from aquafortis by alkalies; but does not act upon it in its metallic state.

Copper. Beautiful green crystals. By dissolving and crystallizing calcined copper. It acts slowly upon it in its metallic state.

Iron. A crystallizable salt. It dissolves this metal with great facility.

Lead*. A salt resembling saccharum saturni. By dissolving the red calx of lead. But it does not act upon it in its metallic state.

Zinc. Elegant crystals. By the ordinary means.

The effects of this acid upon other bodies, or the uses to which these combinations might be applied, are not yet sufficiently known.

ACID OF ARSENIC may be combined with the following Substances, viz.

Fixed Vegetable. A ponderous salt shooting into fine crystals by superfaturation with acid.

Fossil. A salt crystallizable when perfectly neutral.

Volatile. A peculiar kind of ammoniacal salt parting with the alkali, and decomposing some of it in a strong fire.

Chalk. A crystallizable salt scarcely soluble.

Magnesia. A gelatinous mass which cannot be crystallized.

Terra Ponderosa. An insoluble white powder.

Copper. A green-colored solution.

Iron. A very thick gelatinous solution.

Lead. A solution which cannot be crystallized.

Tin. A gelatinous solution in the moist way. A mixture taking fire in close vessels in the dry way.

Zinc. A solution in the moist way, and in the dry, a mixture taking fire in close vessels.

Bismuth. A partial solution.

Regulus of Antimony. A partial solution.

Cobalt. A partial solution of a red color.

Manganese. A partial solution in its natural state. When the manganese is phlogisticated, a crystallizable salt may be obtained.

Charcoal. A mixture taking fire and subliming when heated in close vessels.

Oil of Turpentine, &c. A thick black substance after some days digestion.

Sulphur. A red sublimate.

ALKALIES. ACID of MOLYBDÆNA may be united with the following Substances, viz.

ALKALIES. { Fixed Vegetable. A crystallizable salt. { Volatile. A neutral salt, the nature of which is unknown.

ACID of MILK may be combined with the following Substances, viz.

ALKALIES. { Fixed Vegetable. A deliquescent salt soluble in alcohol. { Fossil. A salt of a similar nature. { Volatile. A deliquescent salt parting with much of the alkali by heat.

EARTHS. { Calcareous and Argillaceous. Deliquescent salts. { Magnesia. A salt more easily crystallized, but deliquescent.

METALS. { Copper. A blue solution, which cannot be crystallized. { Iron. A brown solution, with the emission of inflammable air, yielding no crystals. { Lead. An astringent sweetish solution, which does not crystallize.

SEMIMETAL. Zinc. A crystallizable salt, with the emission of inflammable air during the solution.

ACID of SUGAR or MILK may be combined with the following Substances, viz.

ALKALIES. { Fixed Vegetable. A salt very difficult of solution. { Fossil. A salt more easily soluble. { Volatile. A peculiar kind of ammoniac.

EARTHS. { Absorbent and Argillaceous. Insoluble salts.

ACID of APPLES may be combined with the following Substances, viz.

ALKALIES. { Fixed Vegetable, Fossil, and Volatile. Deliquescent salts. { Calcareous. A salt difficult of solution unless the acid prevail. { Magnesia. A deliquescent salt. { Earth of Alum. A salt very difficult of solution.

METAL. Iron. A brown solution, which does not crystallize.

SEMIMETAL. Zinc. A fine crystallizable salt.

ACID of FAT may be combined with the following Substances, viz.

ALKALIES. { Fixed, Vegetable, and Fossil. Neutral salts of a particular nature. { Volatile. A concrete volatile salt. { Calcareous. A crystallizable salt of a brown colour. { Magnesia. A gummy mass, which refuses to crystallize.

EARTHS. { Silver. A solution of the calx. { Platina. The calx copiously dissolved, and even the perfect metal attacked by distillation to dryness. { Copper. A green solution, which cannot be crystallized. { Iron. A crystallizable salt, which does not deliquesce. { Lead. An astringent solution of the red calx called minium. { Tin. A solution in small quantity. { Mercury. A solution by being twice distilled from the metal.

SEMIMETALS. Zinc. Dissolved in its metallic state. { Bismuth. A solution of the precipitate. { Regulus of Antimony. A crystallizable salt, which does not deliquesce. { Manganese. A perfect and clear solution.

ACID of BENZOIN may be combined with the following Substances, viz.

ALKALIES. { Fixed Vegetable. A salt shooting into pointed feathery crystals. { Fossil. A salt procurable in larger crystals. { Volatile. A deliquescent salt scarce crystallizable.

EARTHS. { Calcareous. A crystallizable salt not easily soluble. { Magnesia. A crystallizable salt easily soluble.

The FIXED ALKALI, whether VEGETABLE or FOSSIL, can be united with the following Bodies; but the Vegetable is best known.

ACIDS: Vitriolic, Nitrous, Muriatic, Vegetable; and acid of Urine, of Amber, of Ants, of Borax, &c. as in the former part of this Table.

ALKALIES of all sorts. The uses of these mixtures are not known.

EARTHS. { Crystalline. By fusion with twice their weight of alkalies. { Glass. By fusion with a much smaller proportion of alkali. This is the composition of crystal glass, and all others commonly used.

METALS. { Absorbents. Argillaceous, and all kinds of earths. Glass. By fusion; differing in quality according to the nature of the ingredients. Glass is likewise produced with it in fusion with metals.

GOLD*. After having precipitated it from aqua-regia, it dissolves it if the alkali has been calcined with mal substances.

SILVER*. After having precipitated it from the nitrous acid, it dissolves it if the alkali has been calcined in contact with the flame.

No. 76. CHEMISTRY.

METALS.

Tin. A corroded powder. By the ordinary means of solution.

Copper. By ditto.

Lead. A fluid solution. By ditto. This stains hair black.

Iron*. A blood-colored solution. By dropping a solution of iron in the nitrous acid, into an alkaline lixivium.

Mercury*. A fluid solution. After precipitating it from acids; if the alkali is in too large proportions, it then dissolves it, especially if the alkali has been calcined in contact with the flame.

Zinc*. By solution, after having precipitated it from the nitrous acid.

Bismuth*. By solution, after having precipitated it from the nitrous acid.

Antimony.

Kermes mineral. By dissolving antimony in an alkaline lixivium, filtering, and allowing it to stand in a cool place till it precipitates.

Golden sulphur of antimony. By dissolving a crude antimony in an alkaline lixivium, and precipitating by an acid.

Hepar antimonii. By deflating crude antimony with nitre.

Crocus metallorum. Is hepar antimonii pulverized and edulcorated with water.

Diaphoretic antimony. By deflating regulus of antimony with nitre.

Antimonated nitre. By dissolving diaphoretic antimony in water, and allowing it to crystallize.

Magistery of antimony. By precipitating a solution of diaphoretic antimony by adding vinegar.

Regulus antimonii medicinalis. By fusing crude antimony with alkali. This is not properly a compound of alkali and antimony, but of another kind. But as it is a term much used, it was proper to explain it.

Arsenic*. A metallic arsenical salt. By a particular elective attraction from regulus of antimony and nitre.

Expressed. Soap. The best hard soap is made of olive-oil and fossil alkali. The ordinary white soap of this country is made of tallow and potash; black soap with whale-oil and potash.

Essential. Saponaceous mats. Best made by pouring spirit of wine upon caustic alkali and then oil, digesting and shaking.

ILS.

Empyreumatic. This mixture dissolves gold when precipitated from aqua regia; and is the basis of the fine color called Prussian blue; and has various other properties, as yet but little known.

Fossil. This has no name, nor are the properties well known; but from some observations that have been made on native foamy waters, it is probable that it would keep linen much longer white than any other kind of soap.

SULPHUR.

Hepar sulphuris. By injecting alkalis upon melted sulphur.

Lac sulphuris. By dissolving sulphur in an alkaline lixivium, and precipitating by an acid.

Alkaline lixivium, when caustic, or even the ordinary solution of mild alkali, is a fluid of great power in washing, blacking, &c.

WATER.

Fixed. Mild alkali. This is the general state in which alkalis are found; but if they are rendered caustic by means of quick-lime or otherwise, they again absorb it from the air, or from many other bodies, by elective attraction. When perfectly mild, this alkali may be made to assume a crystalline form.

The VOLATILE ALKALI, or SPIRIT of SAL AMMONIAC, can be united with these Bodies, viz.

ACIDS: Vitriolic, Nitrous, Muriatic, Vegetable; of Urine, of Amber, of Ants, &c.

ALKALI, as above.

METALS.

Gold*. Aurum fulminans. A powder obtained by precipitating it from aqua regia by volatile alkalis.

A liquid solution. By adding a large proportion of alkali after it has been precipitated from aqua regia. This deposits the gold when long exposed to the air. The curious vegetation called arbor Diane is formed by adding mercury to this solution. A violently fulminating powder obtained by digestion.

Silver*. A solution. After it has been precipitated from the nitrous acid. A fulminating powder by digestion.

Platina*. By solution, after having precipitated it from aqua regia.

Copper. A blue-colored solution. By the ordinary means. This when evaporated to dryness, and mixed with tallow, tinges the flame green.

Venus fulminans. By evaporating the solution to dryness.

Aqua cerulea sapphirina. By mixing sal ammoniac, quick-lime, and thin plates of copper, with water, and allowing them to remain a night.

Iron. By ordinary solution.

Lead. By ditto.

Tin. The mixts that are produced by these metals are little known.

Bismuth*. By solution, after having precipitated it from the nitrous acid.

Antimony.

Cobalt. A reddish liquor. By solution.

Nickel. A blue liquor. By ditto.

Expressed. Has no name. By solution.

Essential. Sol volatilis oleum. By ditto with some difficulty, unless the alkali is in a caustic state.

Empyreumatic. A pungent oily substance, of great power in medicine. The principal one of this kind in use is spirit of hartshorn.

Fossil. A particular kind of foamy substance.

SULPHUR. SULPHUR. Smoking spirit of sulphur. By distilling sal ammoniac, quick-lime, and sulphur.

ALCOHOL*. By distilling alcohol from volatile alkalies, it acquires a caustic fiery taste; but the union is not complete. This solution might be of use in washing or bleaching; but, unless in particular cases, would be too expensive.

WATER. It coagulates with alcohol.

AIR. Fixed. Mild volatile alkali. The usual state in which it is found; nor has any method yet been discovered of rendering it solid but in this state.

EXPRESSED OILS may be combined with the following Substances, viz.

ACIDS: Vitriolic, Nitrous, Muriatic, Vegetable, of Urine, of Amber, as in the foregoing part of this Table.

ALKALIES: Fixed and Volatile, as above.

CALCAREOUS EARTHS. A kind of plaster. By mixture when in a caustic state.

METALS. Tin*. Ditto. By solution when the tin is in the state of a calx.

Lead*. Ditto. By boiling the calx of lead in oils. This is used for cements in water-works. The common white paint is a mixture of this less perfect.

SEMIMETALS. Zinc*. Ditto. By ditto.

OILS: Essential, Empyreumatic, and Foible. By mixture; but their uses are not much known.

SULPHUR. Balsam of Sulphur. By solution in a boiling heat.

ALCOHOL. After expressed oils are freed from soap or plasters, they are soluble in alcohol; but not in their ordinary state.

ESSENTIAL OILS may be combined with the following Substances, viz.

ACIDS: Vitriolic, Nitrous, &c. as above.

ALKALIES: Fixed and Volatile, as above.

METALS. Copper. By solution.

Lead. By ditto.

OILS of all kinds. By solution or mixture.

SULPHUR. A balsam of sulphur. By solution, imperfectly; better by adding essential oils to the solution made by expressed oils or hepatic sulphuris.

ALCOHOL. Imperfect mixture. By solution.

Aromatic waters. By distillation.

WATER. Distilled water of the shops. By distilling recent vegetable substances with water.

EMPTYREUMATIC OILS may be combined with the following Substances, viz.

ACIDS: Vitriolic and Nitrous, as above.

ALKALIES: Fixed and Volatile, as above.

OILS of all kinds. By mixture.

ALCOHOL. By solution. By repeated distillations the oils are rendered much more subtle.

FOSSILE OILS may be combined with the following Substances, viz.

ACIDS: Vitriolic and Nitrous, as above.

ALKALIES: Fixed and Volatile, as above.

OILS of all kinds. By mixture.

SULPHUR. With some difficulty, by solution.

ALCOHOL. By ditto.

SULPHUR may be combined with the following Substances, viz.

ACID*: Vitriolic; with the phenomena above described.

ALKALIES: Fixed and Volatile, as above.

METALS. Silver. A mass of a red-like colour. By adding sulphur to red-hot silver, and fusing; found also with it in the state of an ore.

Lead. A sparkling friable mass, hardly fusible. By deflagrating sulphur with lead. This in a native state forms the ore of lead called galena.

Copper. A black brittle mass, easily fused. By adding sulphur to red-hot copper, or stratifying with sulphur and fusing. Naturally in some yellow pyrites.

Iron. A spungy-like dross, easily fusible. By putting sulphur to red-hot iron. This is also found naturally in the common yellow or brown pyrites.

A fulminating compound. By mixing filings of iron with sulphur, moistening them with water, and pressing them hard, they in a few hours burst out into flame. This composition has been employed for imitating earthquakes.

Crocus martis. By deflagrating with iron.

Crocus martis aperiens. By calcining the crocus martis in the fire till it assumes a red appearance.

Crocus martis africensis. By pushing the heat still further.

Tin. A dark-coloured mass, resembling antimony. By fusion.

Ethiops mineral. By heating flowers of sulphur, and pouring the mercury upon it, and stirring it well. Its natural ore is called cinnabar.

Falsilious cinnabar. By applying the mercury and sulphur to each other in their pure state, and subliming.

Cinnabar of antimony. By subliming corrosive sublimate and crude antimony; or the residuum, after distilling butter of antimony.

SEMIMETALS. Bismuth. A faint greyish mass, resembling antimony. By fusion. If in its metallic state, the sulphur separates in the cold; but not so if the calx has been employed.

Antimony. Crude antimony. By fusion.

Zinc*. A very brittle, dark-coloured, shining substance. With some difficulty, by keeping it long in a moderate fire, and covering it several times with sulphur, and keeping it constantly stirred.

Yellow arsenic. By fusing it with \( \frac{1}{4} \)th its weight of sulphur.

Red arsenic. By ditto with \( \frac{1}{8} \)th its weight of sulphur.

Arsenic. Ruby of sulphur, or arsenic, or golden sulphur. By subliming when the proportions are equal.

Orpiment. A natural production; not perfectly imitable by art; composed of sulphur and arsenic.

Much used as a yellow paint.

Nickel. A compound; compact and hard as lead; of a bright metallic appearance; internally yellow. By fusion.

Oils: Expresed, Essential, and Fossil, as above.

Water. Gas fulviflare. By receiving the fumes of burning sulphur in water. This ought rather to be called a union of the volatile vitriolic acid with water.

Alcohol may be combined with the following substances, viz.

ACIDS: Vitriolic, Nitrous, Muriatic, Vegetable, and of Borax, as above.

ALKALI*: Volatile, as above.

METALLIC calces, in some particular cases.

OILS: Expresed, Essential, Empyreumatic, and Fossil, as above.

WATER. By solution.

Gold may be combined with the following substances, viz.

ACIDS: Vitriolic*, Nitrous*, and Muriatic*. In the circumstances and with the phenomena above described.

ALKALIES: Fixed*, and Volatile*, as above.

Silver. By fusion. And the same is to be understood of all the combinations of metals, unless particularly specified.

Platina. Ductile, and of a dusky colour. This has been employed to debase gold, as it is of the same specific gravity, and is not discoverable by the usual tests for discovering the purity of gold.

Lead. A very brittle mass. Gold is rendered pale by the least admixture with this.

Tin. A brittle mass when the tin is added in considerable quantity; but the former accounts of this have been exaggerated.

Copper. Paler and harder than pure gold. This mixture is used in all our coins, the copper being called the alloy.

Iron. Silver-coloured, hard and brittle; very easily fused.

Mercury. Soft like a paste called an amalgamum. By solution; it being in this case called amalgamation; and the same is to be understood of the solution of any other metal in quicksilver.

Zinc. A bright and whitish compound, admitting of a fine polish, and not subject to tarnish; for which qualities it has been proposed as proper for analysing specula for telescopes.

Arsenic. Brittle; and the gold is thus rendered a little volatile.

Antimony. A fine powder for staining glass of a red colour. By calcination.

Bismuth*. A brittle whitish regulus; volatile in the fire.

Cobalt.

Nickel. White and brittle.

Silver may be combined with the following substances, viz.

ACIDS: Vitriolic*, Nitrous*, Muriatic*, Vegetable*, and Acid of Ants*, as above.

ALKALIES: Fixed* and Volatile*, as above.

Crystalline Earths and other vitreous matters. A fine yellow opaque glass. The finest yellow paint for porcelain is procured from a glass mixed with silver.

Gold, as above.

Platina. Pretty pure and malleable. Difficult of fusion; and in part separates when cold.

Lead. Very brittle.

Tin. Extremely brittle, as much so as glass.

Copper. Harder than silver alone. Used in small proportions as alloy in coins.

Iron. A hard whitish compound.

Mercury* By amalgamation with silver-leaf, or calx of silver precipitated by copper, but not by salt.

This is used for silverizing on other metals, in the same way as the amalgamum of gold.

Zinc. Hard, somewhat malleable, and of a white colour.

Antimony. A brittle mass.

Bismuth. A white semi-malleable body.

Arsenic. Brittle; the silver being rendered in part volatile.

Cobalt.

Sulphur, as above.

Lead may be combined with the following substances, viz.

ACIDS: Vitriolic, Nitrous, Muriatic, Vegetable, of Urine, of Ants, as above.

ALKALIES: Fixed and Volatile, as above. CRYSTALLINE EARTHS. A thin glass. By fusion in a moderate heat.

METALS. Gold and Silver, as above. Platina. Of a leafy or fibrous texture, and purplish or blue colour, when exposed to the air. If a large proportion of platina is used, it separates in the cold. Tin. A little harder than either of the metals, and easily fused; hence it is used as a folder for lead; and it forms the principal ingredients of pewter. If the fire is long continued, the tin floats on the surface. Copper*. Brittle and granulated, like tempered iron or steel when broke. By throwing pieces of copper into melted lead. The union here is very slight. Iron*. An opaque brownish glass. By a great degree of heat if the iron has been previously reduced to the state of a calx; but never in its metallic state. Mercury*. By amalgamation. Effected only in a melting heat, unless some bismuth has been previously united with the mercury. Zinc. Hard and brittle. By pouring zinc on melted lead. If the zinc is first melted, and the lead injected upon it, it then deflagrates. Antimony*. Bismuth. A grey-coloured semi-malleable body, easily fused; and thence used as a folder for lead or tin. Arsenic. A grey-coloured brittle mass, easily fused, and extremely volatile. A hyacinth-coloured glass. By fusion in a considerable heat. This glass is easily fused; and is a much more powerful flux than pure glass of lead. Cobalt. The nature of this compound is not known. Nickel. A brittle metallic body.

SEMIMETALS. OILS: Exprefsed* and Essential, as above. SULPHUR, as above.

ACIDS: Vitriolic*, Nitrous*, Muriatic, Vegetable*, of Urine, as above. ALKALIES: Fixed and Volatile, as above.

CRYSTALLINE EARTHS or other vitreous matters. An opaque white vitreous mass, which forms the basis of white enamels.

METALS. Gold, Silver, and Lead, as above. Platina. A coarse hard metal which tarnishes in the air. Copper. A brittle mass. When the copper is in small proportions, it is firmer and harder than pure tin. Iron. A white brittle compound. By heating filings of iron red-hot, and pouring melted tin upon them, a metal resembling the finest silver is made of iron, tin, and a certain proportion of arsenic. Mercury. This amalgam forms foils for mirrors; and forms the yellow pigment called aurum masticum. By being sublimed with sulphur and sal ammoniac. Zinc. Hard and brittle. When the zinc is in small proportions, it forms a very fine kind of pewter. Antimony*. Regular venereal. By elective attraction from copper and crude antimony. Bismuth. Bright, hard, and sonorous, when a small proportion of bismuth is used. This is very easily fused, and employed as a folder. Arsenic. A substance in external appearance resembling zinc. Cobalt. By fusion. Nickel. A brittle metallic mass.

SEMIMETALS. OIL: Exprefsed*, as above. SULPHUR, as above.

COPPER may be combined with the following Substances, viz. ACIDS: Vitriolic, Nitrous, Muriatic, Vegetable, of Urine, of Amber, of Ants, as above. ALKALIES: Fixed, and Volatile, as above.

METALS. Gold, Silver, Lead*, and Tin, as above. Platina. A white and hard compound, which does not tarnish so soon as pure copper, and admits of a fine polish. Iron. Harder and paler than copper. Easily fused. Mercury*. A curious amalgam. Soft at first, but afterwards brittle. By triturating mercury with verdigris, common salt, vinegar, and water.

SEMIMETALS. Zinc. Prince's metal, pinchbeck, and other metals resembling gold. By employing zinc in substance in small proportions. The best pinchbeck about 1-4th of zinc. Spelter. A native substance, found in Cornwall, consisting of zinc and copper, and used as a folder. Antimony. By fusion. Bismuth. A palish brittle mass. Somewhat resembling silver. Arsenic. White copper. By pouring arsenic, fused with nitre, upon copper in fusion. If too large a portion of arsenic is used, it makes the compound black and apt to tarnish. Cobalt. White and brittle. Nickel. White and brittle, and apt to tarnish.

OIL: Essential, as above. SULPHUR, as above. Table.

IRON may be combined with the following substances, viz.

ACIDS: Vitriolic, Nitrous, Muriatic, Vegetable, of Urine, of Amber, of Ants, as above.

ALKALIES: Fixed*, and Volatile, as above.

VITRESCENT EARTHS. A transparent glass. In general blackish; but sometimes yellow, green, or blue. The colour is influenced by the degree of heat as well as nature of the ingredients.

METALS.

{Gold, Silver*, Lead*, Tin, and Copper, as above, {Platina. With cast iron it forms a compound remarkably hard, somewhat ductile, and susceptible of a fine polish.

ZINC. A white substance resembling silver.

ANTIMONY. The magnetic quality of the iron is totally destroyed in this compound.

BISMUTH. In a strong heat, this emits flames.

SEMIMETALS.

{Arsenic. A whitish, hard, and brittle compound. By fusing with soap or tartar. A metal resembling fine steel is made by fusing cast iron with a little arsenic and glass.

COBALT. A compound remarkably ductile. By fusion in a moderate heat.

NICKEL. A brittle mass.

SULPHUR, as above.

MERCURY may be combined with the following substances, viz.

ACIDS: Vitriolic, Nitrous, Muriatic, Vegetable*, of Urine, as above.

ALKALI: Fixed*, as above.

METALS.

{Gold, Silver*, Lead*, Tin, and Copper, as above, {Platina. The compound resulting from this mixture is not known.

ZINC. An amalgam. Soft or hard, according to the proportions employed.

ANTIMONY. By melting the regulus, and pouring it upon boiling mercury. By frequently distilling from this amalgam, the mercury is rendered much more pure, and is then called animoted mercury.

BISMUTH. A silvering for iron. By putting this amalgam upon iron, and evaporating the mercury, it has much the appearance of silver.

COBALT. By mixing first with nickel, and then adding mercury.

SULPHUR, as above.

ZINC may be combined with the following substances, viz.

ACIDS: Vitriolic, Nitrous, Muriatic, Vegetable, of Urine, of Amber, of Ants, as above.

METALS.

{Gold, Silver, Lead, Tin, Copper, and Iron, as above. {Platina. A hard substance.

MERCURY, as above.

SEMIMETALS.

{Antimony. This mixture is applied to no particular use.

{Arsenic. A black and friable mass.

COBALT. The particular nature and properties of this mixt is not known.

OIL: Expressly*, as above.

SULPHUR*, as above.

ANTIMONY may be combined with the following substances, viz.

ACIDS: Vitriolic*, Nitrous, Vegetable*, and Urinous. With the phenomena, and by the means above described.

ALKALIES: Fixed and Volatile, as above.

VITREOUS EARTHS. A thin penetrating glass; which is a powerful flux of metals.

METALS.

{Gold, Silver, Lead, Tin*, Copper, and Iron, as above. {Platina. A hard mass.

MERCURY, and Zinc, as above.

BISMUTH. A mass resembling regulus of Antimony.

SEMIMETALS.

{Arsenic. The nature and qualities of this mixt are not known.

COBALT. Nature unknown.

NICKEL. Ditto.

SULPHUR, as above.

BISMUTH may be combined with the following substances, viz.

ACIDS: Vitriolic, Nitrous, Muriatic, Vegetable, and Urinous; with the phenomena, &c. above described.

ALKALIES: Fixed*, and Volatile*, as above.

VITREOUS MATTERS. A yellow glass. The ore of Bismuth affords with these a blue glass; but this is probably owing to some mixture of Cobalt with it.

METALS.

{Gold, Silver, Lead, Tin, Copper, and Iron, as above. {Platina. This mixture changes its colour much on being exposed to the air.

MERCURY, as above.

ANTIMONY, as above.

{Arsenic. Nature not known.

SEMIMETALS.

{Cobalt*. By mixing first with nickel or regulus of antimony, and then adding cobalt; but it cannot be united by itself.

NICKEL. This mixt is not known.

SULPHUR, as above.

ARSENIC may be combined with the following substances, viz.

ACIDS: Vitriolic, Muriatic*, Vegetable*, and Urinous; with the phenomena, &c. above mentioned.

ALKALIES: ALKALIES: Fixed, and Volatile; with the phenomena, and by the means mentioned above.

VITREOUS MATTERS. A glass which greatly promotes the fusion of other substances. The arsenic must first be prepared by dissolving and precipitating from alkalies.

METALS. { Gold, Silver, Lead, Tin, Copper, and Iron, as above. Platina. Zinc, Antimony, and Bismuth, as above.

SEMIMETALS. { Cobalt. Nickel. The phenomena attending these mixtures have not been as yet particularly observed.

SULPHUR, as above.

PLATINA may be combined with the following Substances, viz.

ACIDS: Muriatic*; with the phenomena, &c. mentioned above. ALKALI: Volatile, as above.

METALS: { Gold, Silver, Mercury, Tin, Copper, and Iron, as above. Zinc, Bismuth, and Arsenic, as above.

SEMIMETALS. { Cobalt. Nickel. The phenomena attending these mixtures not yet observed.

COBALT may be combined with the following Substances, viz.

ACIDS: Vitriolic, Nitrous, Muriatic; and Urinous; with the phenomena, &c. as above described. ALKALI: Volatile, as above.

EARTHS. { Calx of Flint. Saffire. By mixing calcined cobalt with calx of flint, and moistening them with water, and pressing them close in wooden tubs.

METALS: { Gold, Silver, Platina, Mercury*, Lead, Tin, Copper, and Iron, as above. Zinc, Antimony, Bismuth*, and Arsenic, as above.

SEMIMETALS. { Nickel. The properties of this compound not known.

NICKEL may be combined with the following Substances, viz.

ACIDS: Nitrous, and Muriatic; with the phenomena, &c. as mentioned above. ALKALI: Volatile, as above.

METALS: Gold, Platina, Lead, Tin, Copper, and Iron, as above.

SEMIMETALS: Antimony, Bismuth, Arsenic, and Cobalt, as above.

SULPHUR, as above.

ABSORBENT EARTHS may be combined with the following Substances, viz.

ACIDS: Vitriolic, Nitrous, Muriatic, and Vegetable; with the phenomena, and by the affinities above mentioned.

EARTHS. { Crystalline. By this mixture they are both much easier melted into glass than by themselves, but not without the addition of some alkali. Argillaceous. This mixture easily runs into a glass without any addition.

WATER. Lime-water. By solution. It is sometimes found flowing out of the earth in springs; and as it always quits the water when exposed to the air, it is there depoed on the banks of the streams, forming the stony incrustations called petrifications. And filtering through the pores of the earth, and dropping through the roofs of subterraneous caves, it forms the curious incrustations found hanging from the roof of such places; sometimes assuming forms stupenduously magnificent.

AIR. Flint. Lime-stone. It is from the quality that quick-lime has of absorbing its air, and again with it refusing its stony consistence, that it is fitted for a cement in building; and the great hardness of the cements in old buildings is owing to the air being more perfectly united with these than in newer works.

CRYSTALLINE or VITRESCENT EARTHS may be combined with the following Substances, viz.

ACIDS: Vitriolic*, and Nitrous*; with the phenomena, &c. as above mentioned. ALKALI: Fixed, as above.

ABSORBENT EARTHS: as above.

ARGILLACEOUS EARTHS. A mass running into glass in a moderate heat.

METALS: Lead, Tin, Copper, and Iron, as above.

WATER. Although this is not soluble in water by any operation that we are acquainted with; yet, from its crystalline form, it is probable that it has been once suspended; and certainly it is so at this day in those petrifying springs whose incrustations are of the crystalline sort.

SEMIMETALS: Antimony, Bismuth, Arsenic, and Cobalt, as above.

ARGILLACEOUS EARTH may be combined with Absorbent and Crystalline Earths, as above. With water it only unites into a paste of a mechanical nature. Absolute heat, defined, no. 37. Difference of the absolute heat of different fluids, 46. Absorption of heat the universal cause of fluidity, 119. Vapour produced by the absorption of latent heat, 120.

Attention of Humberg's pyrophorus explained, 1418.

Acetous acid, its specific gravity, 400. This acid and its combinations, particularly treated of, 867. Produced by a particular kind of fermentation, ib. Of its combination with alkalies, 868. With earths, 872 sqq. With metallic substances, ib. Whether tin be soluble in it, 879. Of its concentration, 881. May be crystallized in form of a salt, 882. May be reduced into an acetal form, 883. Its combination with inflammable bodies, 884. Produces a greater quantity of ether than the vitriolic acid, ib. Acid of milk seems to be of the aceticus kind, 978. Whey may be converted into an acetic acid, 979. May be almost entirely destroyed by fire, 1001. Requisites for bringing it nearer to the state of tartar, 1002. Wellumb's unsuccessful attempt to do so, 1003. Dr Crell's opinion of the possibility of this transmutation, 1004. Method recommended by him for trying the experiment, 1005. His experiments proving that all the vegetable acids may be reduced to the aceticus, 1006, &c. sqq. Manganese soluble with difficulty in it, 1369. Procurable from the refuse of vitriolic ether, 272. Best prepared from sugar of lead and oil of vitriol, 882. Mr Dolfus's method of making the aceticus ether readily, 884. How to prepare it from vinegar of wood, ib. The aceticus acid has an affinity with that of ants, 1504. How to crystallize its combination with the volatile alkali, 1515. Particular description of the salts formed by combining it with calcarious earth, 1516. With magnesia, 1517. Its phenomena with zinc, 1518. With arsenic, 1519. Supposed to be an antidote against that poison, 1520. Produces a curious phosphoric liquor with it, 2957, 1521. Its effects on silver, 1523. Gold, 1524. Inflammable substances, 1525. Dissolves gums, gum-resins, the flesh and bones of animals, &c., ib. Various methods of concentrating it, 1526. Of its crystallization, 1527. Difference between common aceticus acid and radical vinegar, 1528. Mr Keil's opinion concerning them, 1529. How to obtain it from terra-folata tartari, ib.

Alkali's method of making crucibles from the calx of platinum, 587.

Alkaline phenomena attending the solution of a metal in one, 180. The nitrous most violent in its operation, 181. Vitriolic acid next to it, 182. The marine acid much weaker than either, except when dephlogisticated, 183. The other acids still weaker, 184. Why the nitrous acid precipitates a solution of tin or antimony, 180. Pure vitriolic acid cannot be reduced into an acetal state but by combination with phlogiston, 202. The nitrous acid finds more remarkably changeable such a combination, 203. The marine acid capable of affording an acetal state by reason of the phlogiston it naturally contains, 205. Table of the quantity of acid taken up by various salves, 268. The vitriolic acid contains more fire than the nitrous or marine, 278. On the expulsion of the nitrous by the diluted vitriolic acid, 280. By the same concentration, 281. By a small quantity of dilute vitriolic acid, 282. On the expulsion of the marine acid by the concentrated vitriolic acid, 283. On the decomposition of vitriolated tartar by nitrous acid, 285. This salt cannot be decomposed by dilute nitrous acid, 287. Of its decomposition by marine acid, 288. Requisites for the success of the experiment, 289. Why the marine acid cannot decompose vitriolated tartar previously dissolved in water, 290. The decomposition of vitriolic ammoniac and Glauber's salt by this acid never complete, 291. Nitrous salts decomposed by it, 292. Marine salts decomposed by the nitrous acid, 293. Selenite cannot be decomposed by marine acid, and why, 294. Why the vitriolic acid refuses on evaporation the basis it had left, 295. An excess of acid requisite to make metals soluble in water, 297. Nitrous acid attracts silver more than fixed alkali, 321. Solution of lead in nitrous acid decomposed by fats containing the marine acid, 312. Vitriol of mercury decomposed by marine acid, 313. Precipitation of corrosive sublimate by concentrated vitriolic acid explained, 315. Of the excess of acid in the solution proper for making experiments on metallic precipitates, 334. Iron and zinc, the only metals dissolved by vitriolic acid, 337. Nitrous acid dissolves all metals, though it has less affinity with them than the vitriolic or marine, 338. Why it cannot dissolve them when very concentrated, 339. In what cases marine acid can dissolve iron, and when it cannot, 340. A triple salt formed by marine acid, iron, and regulus of antimony, 366. Another by the same acid, regulus of antimony, and copper, 367. Bismuth precipitates arsenic from the nitrous acid, 369. Copper precipitates it from the marine acid, 370.

Method of finding the quantity of pure acid contained in frit of salt, 376. In other acid liquors, 378. Quantities of acid, water, and alkali, in digestive salt, 379. Mr Kirwan's method of saturating an acid exactly with an alkali, 381. Quantity of mild and caustic vegetable alkali saturated by a given quantity of marine acid, 382. Pure nitrous acid cannot be made to assume an acetal state, 383. How to determine the quantity of pure acid in frit of nitre, 384. Proportion of acid in pure nitrous acid in frit of nitre, 385. To find the specific gravity of the pure nitrous acid, 386. To determine its mathematical specific gravity, 388. Of the quantity of real acid contained in it, 389. Quantity of acid, water, and alkali, in nitre, 391. Experiments on the specific gravity, &c., of vitriolic acid, 395. Dilution of the concentrated acid necessary for these experiments, 396. How to find the specific gravity of pure vitriolic acid, 397. Quantity of acid, water, and alkali, in vitriolated tartar determined, 398. Specific gravity of the aceticus acid, 400. Why the precipitates of alum and mercury contain a part of the acid, 408. How to determine the quantity of pure acid in any substance, 410. Exact computation of the quantity of pure acid taken up by mild vegetable alkali, 418. Of the quantities of acid and water in frit of nitre, 426. Quantity of pure acid taken up by various substances, 428. Quantity of vitriolic acid necessary to saturate mineral alkali, 430. Of the same alkali saturated by dephlogisticated nitrous acid, 432. By marine acid, 433. Quantity of marine acid saturated by calcareous earth, 438. Alum always contains an excess of acid, 448. Proportion of the pure earth of alum taken up by nitrous acid, 449. By marine acid, 450. Qua. tity of iron taken up by the vitriolic acid, 453. Why vitriolic acid is produced by dissolving iron in concentrated vitriolic acid, 455. Of the solution of the calca of iron in vitriolic acid, 456. Proportion of iron dissolved by the nitrous acid, 458. Vitriolic acid acts on iron in a much more dilute state than the nitrous, 461. Proportion of this metal taken up by the marine acid, 462. Calces of iron precipitated of a reddish colour from the marine acid, 493. Of the quantity of copper dissolved in the vitriolic acid, 494. Flammable and vitriolic acid obtained by dissolving copper in this acid, 495. Why the dilute vitriolic acid will not act upon copper, 496. Quantity of copper dissolved in nitrous acid, 498. In marine acid, 499. Effect of the vitriolic acid on tin, 470. Of the nitrous acid, of the marine acid, of the vitriolic acid, on lead, 474. Of the nitrous acid, 476. Scarse soluble in dilute vitriolic acid, 475. Effects of the marine acid upon lead, 477. Of the vitriolic acid on silver, 478. Of nitrous acid on the tame, 479. Of the diffusion of silver in marine acid, 480. The nitrous acid cannot, according to Mr Kirwan, dissolve gold, 484. Effects of the vitriolic acid on mercury, 485. Of the nitrous acid, 486. Of the marine acid, 486. Of the vitriolic acid on zinc, 487. Of nitrous acid upon it, 488. Lack of this fermentative power is concentrated than by dilute nitrous acid, 499. Effects of the marine acid on zinc, 499. Vitriolic acid can scarcely dissolve bismuth, 497. Nitrous acid dissolves it easily, 492. Marine acid scarcely affects upon it, 493. Effects of vitriolic acid on nickel, 493. Of nitrous acid, 494. Of marine acid, 495. Of the vitriolic acid on cobalt, 496. Of nitrous acid, 497. Of the marine acid, 498. Of vitriolic acid on regulus of antimony, 499. Of nitrous acid, 500. Of marine acid, 501. Of vitriolic acid on regulus of arsenic, 502. Of nitrous acid, 503. Of marine acid, 504. Quantity of sulphur contained in it, 509. Why the marine acid acts so weakly, 510. How to dilute acid spirits, 575. Luting proper for them, 577. Of the vitriolic acid and its combinations, 612, &c. See Vitriolic. A mistake of Mr Morveau concerning the excess of acid contained in alum detected by Mr Kirwan, 624. This excess is necessary to render alum soluble in water, 643. Too great an excess prevents the crystallization of the salt, 651. This excess best remedied by the addition of pure clay to the liquor, 652, &c. The fulminous acid might be advantageously diluted, 658. Nitrous acid and its combinations, 722, &c. See Nitrous. Experiment on the transmutation of vitriolic into nitrous acid, 724. In conclusion, 725. Marine acid and its combinations, 723, &c. This acid may be dephlogisticated by frit of nitre or manganese, 790. Mr Scheele's method of doing it by means of dephlogisticated marine acid, 792. A mistake of Stahl concerning its conversion into nitrous acid accounted for, 793. See Marine Fluor acid discovered by Mr Morgenstern, &c., 826, &c. Marine acid proved to be different from that of fluor, 833. And likewise the vitriolic, 836. See Fluor. Of the acid of borax and its combinations, 858-866. See Borax and Sol sediments. Of the acetic acid and its combinations. See Acetous. Of the acid of tartar, 885—895. See Tartar. Of the acid of sugar, 896—903. See Sugar and Saccharine. Of the phosphoric acid, 904—907. See Phosphoric. Of the acid of ants, 907—908. See Ants. Of the acid of amber, 909—915. Purified by marine acid, 911. Effects of spirit of nitre on it, 912. Of oil of vitriol, 913. Of the acid of arsenic, 916, &c. Nitrous acid decomposes arsenic, 918. As does also dephlogisticated marine acid, 919. See Acidic. Of the acid of molybdæna, 938, &c. Effects of the arsenical acid on molybdæna, 959. Nitrous acid acts violently upon it, 960. See Molybdæna. Of the acid of lapis ponderosa, tungsten or wolfram, 967, &c. See Tungsten. Difference between the acids of molybdæna and tungsten, 971. Why Bergmann supposes both these to be metallic earths, 972, 973. Of the acid of milk, 974, &c. Contains the acids of tartar and faeces, 975. Of the acid of sugar of milk, 980, 981. See Milk. Of the acid of human calculus, 982. See Calculus. Of the acid of benzoin, 984, &c. See Flowers and Benzoin. Whether the acid of sugar or tartar is the basis of the anomalous vegetable acids, 990. Dr Crell's method of crystallizing the acid of limes, 997. The crystallized fat cannot be converted into acid of sugar, 999. Product of the acid of tartar by dry distillation, 1000. Acetous acid almost entirely destructible by fire, 1001. Of the transmutation of the vegetable acids into the acetous acid, 1002—1015. See Acetous. Phenomena resulting from the mixture of acid spirits with one another, 1040. Solution of acids promoted by vitriolic acid, 1048. Terra ponderosa usually found in a state of combination with this acid, 1049. Effects of marine acid on aerated terra ponderosa, 1053. See Terra Ponderosa. White matter contained in the vitriolic acid known to be gypsum, 1056. Vitriolic acid easily discoverable by solution of terra ponderosa, 1058. Marmor metallicum soluble in very concentrated vitriolic acid, 1063. Why the fluor acid will not dissolve flint directly, 1073. Why the siliceous earth sometimes cannot be precipitated by an acid without the affluence of heat, 1079. Earth of flints precipitated by fluor acid, 1083. Neither the nitrous nor marine acid necessary for the preparation of aurum fulminans, 1117. Vitriolic acid partially dissolves arsenic, 1271. Marine acid dissolves it totally, 1271. Phlogisticated alkali precipitates arsenic from its solution in marine acid, and from that only, 1273. Arsenic decomposed by dephlogisticated marine acid, 1274. Phenomena of arsenic with nitrous acid, 1280. Butter of arsenic can scarcely be made to unite with marine acid, 1282. Regulus of arsenic converted by the vitriolic acid into white arsenic, 1292. Phenomena of cobalt with vitriolic acid, 1300. With nitric acid, 1301. With marine acid, 1302. With the acid of borax, 1303. Effects of the nitrous acid on nickel, 1313. Dephlogisticated marine acid the only solvent of platinum, 1319. Solution of that metal in an aqua regia composed of nitrous acid and nitrite of salt, 1323. In one composed of marine acid and nitre, 1324. Solution of calc of platinum in marine acid lets fall a crystalline powder on the addition of vegetable alkali, 1325. But not that in the nitrous acid, 1326. Phenomena of manganese with vitriolic acid, 1360. Phlogisticated vitriolic acid entirely dissolves it, 1361. And likewise the phlogisticated nitrous acid, 1363. Effects of it on marine acid, 1364. Entirely dissolved by this acid without addition, 1365. Fluor acid can scarcely dissolve it, 1366. Or phosphoric acid, 1367. Acid of tartar partly dissolves manganese, 1368. Acetous acid effects a solution with difficulty, 1369. Acid of lemons entirely dissolves it, 1370. As does also water impregnated with acetic acid, 1371. Nitrous acid can dissolve manganese after it has lost its phlogiston, 1375. Why the concentrated vitriolic acid dissolves it without addition, 1378. Why the volatile ful, hircus acid dissolves it, 1379. Effects of the nitrous acid on it explained, 1380. Existence of phlogiston proved in the marine acid, 1381. Explanation of the effects of acid of tartar and of lemons, 1382. And of fluor acid, 1383. Effects of dissolving manganese and volatile alkali with nitrous acid, 1393. An acid supposed to occasion the taste of essential oils, 1420. A new one discovered by Mr Homburg, ad 825. See Acids. See also Vitriolic, Nitrous, Marine, Acetous, Trinitary, Flower, &c. Acids, one of the principal classes of salts, 169. Divide into mineral, vegetable, and animal, ib. Their different action compared with that of alkalies, 171. Unite with alkalies into neutral salts, sometimes with, and sometimes without, effervescence, 172. Change the blue colour of vegetables to red, 173. Different degrees of their attraction to alkalies, 174. The vitriolic strongest in a liquid state, ib. Marine acid strongest in a state of vapour, ib. The fixed acids strongest when the subjects are urged with a violent heat, ib. Attraction of the different acids for phlogiston, 175. The acids are capable of forming an union with metals or earths, 176. Will leave a metal to unite with an earth, 176, 177. And an earth to unite with a mild volatile alkali, ib. Will leave a volatile, to unite with a fixed alkali, ib. Some will leave a fixed alkali to unite with phlogiston, 175, 178. Exceptions to these rules, 179. Why precipitates are sometimes thrown down by them, 221. Explanation of the decompositions effected by acids alone, 266. Quantities of the different acids taken up by various bases, 268. This quantity expressed by the quantity of attraction they have for each of these bases, 269. Vitriolic salts decomposed by the nitrous and marine acids, 275. Acids unite with alkalies by giving out fire, and quit them by receiving it, 286. Theatrical experiments of acids to metals difficult to be determined, 296. Proportions of the different metallic substances taken up by the different acids, 298 Metals have a greater affinity with acids than alkalies, 299, 303. Explanation of the table of the affinities to the different metallic substances, 316. An equal quantity of all the mineral acids taken up by vegetable fixed alkali, 402. Quantity of this alkali requisite to saturate the several acids, 403. Acids can never totally dephlogisticate metallic earths, 407. Concentrated acids phlogisticated by alkalies, 409. Of the time required by mixtures of the mineral acids with water to attain their utmost density, 422. Of the alterations of their densities by various degrees of heat, 423. Acids cannot dissolve calcined magnesia without heat, 442. Phenomena of different acids with inflammable substances, 513. Metals soluble in acids, 540. Calculation and increase of their weight by acids, 543. How to dilute the mineral acids, 573. Vitriolic, phosphoric, and acetous acids, found in the resin extracted from the refuse of vitriolic ether, ad 221. Nitrous, marine, and phosphoric acid, capable of expelling the fluor acid, ad 850. Acids of fulminating nitrates and nitre expelled by salt of amber, 910. Of the anomalous vegetable acids, and the resemblance which vegetable acids in general bear to one another, 984, &c. How the anomalous vegetable acids are divided, 993. Of the essential acids, 994. Empyrumatic acids, 995. Whether the acid of sugar or of tartar be the basis of the vegetable acids, 996. Dr Crell's proofs that all the vegetable acids may be reduced to one, which is contained in the purest spirit of wine, 1066. Phenomena attending the dissolution of vitriolic salts in nitrous or marine acid, 1041. Nitrous or marine acids are not necessary for the preparation of aurum fulminans, 1117. Copper undergoes a change by combination with vegetable acids, 1121. Colouring matter of P. Linnæus blue expelled by acids, and then taken up by the atmosphere, 1177. Phenomena of arsenic with different acids, 1275. Manganese becomes insoluble in pure acids, by losing its phlogiston, 1275. See Acids, Phosphoric, Marine, Vegetable, &c. Acids and Alkalies: inaccuracy of the common tests for trying them, 1469. Mr Watt's experiments on this subject, ib. His method of preparing a test from cabbage and other plants, 1550, &c. Absorb air during their formation, 1543. Adopters, or Alkalis, described, 579. Aerated terra ponderosa, analyzed by Dr Withering, 907. Aerial acid, the conversion of dephlogisticated air into it by means of charcoal, a proof of the identity of phlogiston and charcoal, 151. Description of the terra ponderosa combined with the aerial acid, 1051. Aerial acid and phlogiston supposed to exist in the colouring matter of Prussian blue, 1196. See Fix'd air. Affinities, dissimilar and dissimilar, described, 467. Table of the affinities of the three mineral acids to the different metals, 298. Explanation of this table, 310. Table of the proportional affinities of the metallic calces to phlogiston, 339. Dr Black's general table of affinities, 559. Affinity of the different metals to phlogiston, how determined, 348. Agents in chemistry, how distinguished from the objects of it, 22. Air supplies inflammable bodies with the heat they emit during combustion, 157. To great a quantity of air will diminish the heat of a fire, or even put it out entirely, and why, 159. Only a small quantity of air can be obtained from metals when calcined, 191. Different kinds of it produced during the distillation of metals, 201. Specific gravity of the different kinds of air according to Fontana, 375. Exposure of luminous ores to the air some times has the same effect with roasting them, 663. Vitriol deprived of its phlogiston by exposure to the air, 687. Lixivium farnæi gains loses its colouring matter by exposure to the air, 1172. This colouring matter taken up by the air after it has been expelled by acids, 1177. Absorbed during the formation of acids, 1543. Air-butter produced in water during the act of congelation, occasion its expansion and prodigious force, 109. They are extricated by a part of the latent heat discharged from the water at that time, 110. Alchemists' labours were of some advantage to chemistry, 13. Alchemy first mentioned by Julius Firmicus Maternus, a writer of the 4th century, 8. Supposed to be first derived from the Arabians, 10. The pretenders to it very numerous in the beginning of the 16th century, 12. Alchemists' experiments on the effects of mixing tin with gold, 1092, &c. Alombe, derivation of that word, 5. Alombrath fal, made by fulminating equal quantities of corrosive sublimate and sal ammoniac, 1047. Said to dissolve all the metals, 15. Convertible by repeated distillations into a fluid that cannot be raised into vapours by the strongest heat, ib. Algarab's powder, prepared by precipitating butter of antimony with water, 821. The most proper material With volatile alkali, ib. Acid of arsenic with vegetable fixed alkali, 925. With mineral alkali, 927. With volatile alkali, 928. Vegetable alkali capable of being reduced into crystals by means of spirit of wine, 1017. Without any addition into dilute effervescent crystals, ib. Mineral alkali always affumes a crystalline form, ib. Change on the vegetable alkali by being united with spirit of fat, 1018. Difference between the vegetable and mineral alkali, 1019. The former has a greater attraction for acids, ib. Both of them composed of a caustic alkali and fixed air, 1020. Of the volatile alkali, 1030. Of the method of distilling it, 1031. Of its rectification, 1032. Combined with fixed air, 1033. Combined with metals, 1034. With inflammable substances, 1035. With expressed oils, ib. With essential oils and spirit of wine, 1036, 1037. With sulphur, 1038. Solutions of calcareous earth decomposed by mild volatile alkali, 1046. Caustic fixed alkali thrown down an insoluble precipitate from solution of terra ponderosa, 1056. Vegetable alkali precipitates marmor metallicum unchanged from concentrated vitriolic acid, 1064. Volatile alkali precipitates siliceous earth more completely than any other, 1074. A trifle left formed by precipitating this earth with fixed alkali, 1075. Siliceous earth dissolved by boiling in solution of alkali, 1076. A remarkable attraction between fixed alkali and siliceous earth in the dry way, 1077. The use of volatile alkali only lately known in the preparation of aurum fulminans, 1106. This alkali the cause of the explosion, 1121. It exhibits a flash when thrown into a crucible by itself, 1122. Used in the preparation of fuming vinegar, 1139. Phlogisticated alkali loses its peculiar properties, 1168. Colouring matter of Prussian blue unite with volatile alkali, 1182. Forms a kind of ammonical salt with it, 1186. Volatile alkali produced by distilling Prussian blue, 1197. Phenomena on distilling metallic precipitates thrown down by Prussian alkali, 1198. Volatile alkali capable of uniting with fixed alkali and phlogiston so as to be capable of furnishing a great degree of heat, 1202. Phlogisticated alkali cannot precipitate arsenic except from marine acid, 1273. Effects of volatile alkali on nickel, 1314. Mineral alkali capable of decomposing crystals of platinia, but not the vegetable alkali, 1322. Or flaxseed powder precipitated from solution of calx platinia in marine acid, by means of vegetable alkali, 1325. Burnt from the fuming acid, 1326. Whether mineral alkali can decompose solutions of platinum, 1328. Fifty-five times as much of it required for this purpose as of vegetable alkali, 1329. Effects of the volatile alkali on solutions of platinum, 1330. Volatile alkali destroyed by manganese attracting phosphogitton, 1334. See Alkalies. Wiegels account of the phenomena attending the distillation of copper in it, 1335. Its effects on dephlogisticated spirit of salt, 1485. Higgins first discovered its constituent parts, 1533. Procured it from nitrous acid and tin, ib. Effect of the electric spark on a mixture of it and dephlogisticated air, 1555. True composition of it, 1556. Alkalies; one of the general classes of salts, 169. Divided into fixed and volatile, 170. The former subdivided into vegetable and mineral, ib. Difference between their action and that of acids, 171. Neutral salts form them by being united with acids, 172. Vegetable blues changed green by them, 173. Different degrees of attraction between them and acids, 174. Phenomena attending the precipitation of metals by them, 220. Volatile alkalies particularly apt to form triple salts, 274. Why they precipitate the metals, 300. Metals have a greater affinity with acids than alkalies, though the latter separate them from acids, 299. Why luna cornea cannot be reduced without loss by alkaline fats, 314. Alkalies phlogisticate concentrated acids, 409. Proportions of the different ingredients in volatile alkalies, 436. Stone ware vessels corroded by caustic fixed alkalies, 595, 596. Advantages of using clay rather than alkalies for absorbing the superfluous acid in aluminae liquor, 683. Solution of filter decomposed with difficulty by alkalies, 756. How the alkalies are procured, 1016. Differences between the vegetable and mineral alkalies, 1019. Combinations of them with sulphur, 1021. With expressed oils, 1026. With essential oils, 1027. With phlogiston, 1028. Differences between the fixed alkalies obtained from different vegetables, ib. Solution of terra ponderosa in marine acid precipitated by all the alkalies, whether mild or caustic, 1034. Alkalies dissolve lead by boiling, 1216. Effects of arsenic on alkalies, 1290. Test for them and acids, 1549. See Alkali, acid, and acids. Alkaline fats. See Alkali and Alkalies. Alkaline ley prepared for extracting the flowers of benzoin, 898. Affon Moor in Cumberland, a kind of aerated terra ponderosa found near that place, 1051. Alkalies, or Adaptors, described, 579. Alum; cannot form Glauber's salt by being dissolved in water along with common salt, 272. Mistake of Dr Croll on this subject corrected, ib. Nor blue vitriol by boiling it with copper filings, 349. Why its precipitate retains part of the acid, 408. Its earth contains 26 per cent. of fixed air, 446. Portions of the ingredients in it, 447. The salt always contains excess of acid, 443. Proportion of the earth of alum taken up by nitrous acid, 449. By marine acid, 450. Alum of the ancients different from ours, 637. The name of Rock-alum derived from Racoa, a city of Syria, 638. First made in Europe in the middle of the 15th century, in Italy, 639. Made in Spain in the 16th century, 640. In England and Sweden in the 17th, ib. Its component parts first discovered by Boulloud and Geoffroy, 641. Found to contain an excess of acid, ib. This denied by Mr Moreau, 642. His mistake discovered by Mr Kirwan, ib. Insoluble in water when deprived of its superfluous acid, 643. Easily calcinable in the fire; after which it is called burnt alum, ib. Bergman's method of finding the proportion of the ingredients it contains, 644. Difficulty of obtaining the earth of alum in a pure state, 645. Mr Bergman's account of the proportion of the ingredients, 646. Whether earth of alum be a pure clay or not, 647. Dr Lewis's experiment, tending to show that clay undergoes some change by being converted into earth of alum, 649. Quantities of alum soluble in warm and in cold water, 650. Bergman's account of the Swedish ores of alum, 651. Component parts of the aluminous schist, 652. How changed by roasting, 653. Preference of pyrites the only requisite for the production of alum, 654. Ores containing alum ready formed only to be met with in volcanic countries, 655. Ores of alum at Solifata in Italy, 656. Analyzed by Mr Bergman, 657. Heffian, Bohemian, and Scanian, ores, 658. Alum, sulphur, and vitriol extracted from the same ore, 659. Alum slate found at York in England, 660. Bergman's directions for the preparation of alum, 661. Uses of roasting the ore, 662. Exposure to the air sometimes has the same effect with roasting, 663. Earthy ores unfit for either purpose, 664. Method of roasting the ore in Sweden, 665. How often the operation is to be repeated, 666. Danger of increasing the heat too much, 667. Rhman's method of roasting the ore at Garphyttan, 668. Method of burning the hard ores at Tolfa in Italy, 669. Method of dissolving the burned ore at Garphyttan, 670. Heat and cold water used for this purpose in different places, ib. Different methods of extraction, 671. Singular circumstance by which the alum is said to be delayed, 672. Of the proper length of the lixivium before it is commenced to evaporate, 673. Confinement of the evaporating vessel, 674. How far the liquor ought to be evaporated, 675. Of the first crystallization, 676. Depuration of the crystals, 677. Bergman's remarks on the proper form of the coolers, 678. They ought to be of a conical shape, ib. Aluminous ley contains Ambergrease yields a product on distillation similar to that of amber, 1446.

America: method of making nitre there, 736.

Ammoniac, vitriolic, decomposed by solution of silver, 366. How to prepare this kind of sal ammoniac, 633. Erroneously said to have powerful effects on the diffusion of metals, ib. Mr Pett's experiments on it, ib. Nitrous ammoniac, how prepared, 743. Is soluble in spirit of wine, ib. Deliquescent without any addition, ib. The principal ingredient in Ward's white drops, 746. Common sal ammoniac prepared from marine acid and volatile alkali, 759. Diffuses fumes according to Mr Gelbert, ib. Its volatility diminished by repeated sublimations, ib. A small quantity producible by distilling sea-foam with charcoal, &c., ib. Originally prepared in Egypt, 760. A method of making it described, ib. Vegetable ammoniac formed of the acetum acidi and volatile alkali, 870. Can scarcely be procured in a dry state, ib. Acid of common sal ammoniac extracted by acid of amber, 910. And by the arsenical acid, 923. Volatile sal ammoniac, how prepared, 1333. Common sal ammoniac not decomposed by regulus of cobalt, 1334. Effects of it on nickel, 1312. Solution of it precipitates a solution of platinum, 1332. The precipitate fusible by a strong forge heat, 1333. This fusion supplied by Mauguet not to be perfect, 1334. Effects of manganese on it, 1392.

Ammoniacal salts, formed by the union of the colouring matter of Prussian alkali with volatile alkali, 1366.

Ammonium earth, very insoluble in acids, and infusible in the fire, 515. Earth of the soft parts more soluble than that of the hard, ib. This earth erroneously supposed to contain phosphoric acid, ib. Animal fats analyzed, 1428. Yield a great quantity of oil by distillation, ib. A particular kind of acid produced from tallow, 1429. How to rectify the empyreumatic oil of animals, 1427. Of animal and vegetable substances, 1451.

Anomalous earths, 513. Anomalous vegetable acids, how divided, 993.

Antimony: why nitrous acid precipitates a solution of it, 200. Precipitates of it by common and phlogisticated alkalies, 246. Of its precipitates with other metals, 365. A triple salt formed by regulus of antimony, marine acid, and iron, 366. Another with the regulus, marine acid, and copper, 367. Of the solution of the regulus in vitriolic acid, 409. Of its combination with that acid, 709. Corroded by the nitrous acid, 768. Regulus of antimony combined with marine acid, 821. Of the amalgamation of it with mercury, 1237. Renders bismuth capable of uniting with cobalt, 1231. The regulus particularly treated of, 1253, et seq. Has the appearance of a star on its surface when well made, 1252. Sublimes into flowers, 1253. Different methods of preparing the regulus, 1254. Considerable differences in the regulus, according to the different substances used to absorb the sulphur, 1255. Of the regulus made with caynck, 1256. This fundamental easily miscible with mercury, 1255. Enters into the composition of specular and printing types, 1256. Was the basis of many medicinal preparations, now diluted on account of their uncertain operation, ib. Glairs of antimony, how prepared, 1357. More volatile in its effects than the regulus itself, ib. Preparation of chemic tartar from glairs of antimony and pulverized alizarin, 1358, &c. See Tartar and Alizarin. Preparation of golden fulminic acid, 1363. Diaphoretic antimony, 1364. Crocus metallosum, 1365. Butter of Mr Dolbeau's method of preparing it, 821.

Antiphlogistic: their absurd way of explaining the explosion of fulminating silver, 1144.

Arsenic: yield an acid by distillation or infusion in water; 2d 927. Its nature and properties, 908. Acids, acid of, combines an ammoniacal liquor with volatile alkali which cannot be reduced to a dry salt, 908. Crystallizes with fixed alkalies, ib. With chalk or quicklime, ib. Dissolves calcined copper, and forms beautiful crystals with it, ib. Makes a peculiar kind of fuscinum tarturini with muriatic acid, ib. Its effects on other metals, ib. Different methods of procuring their acid, 1502. Properties of the pure acid, 1503. Has an affinity with the acetous, 1504. Its effects on metals, 1505.

Apples, their acid treated of, 1506. Its properties, 1509, 1511. How procured in perfect purity, 1510. Produced from sugar by means of nitrous acid, 1512. Mr Keir's opinion concerning its nature, 1514.

Aquafortis: procured by means of arsenic of a blue colour, 719.

Aquae regiae, best kind for it for dissolving gold, 481. Quantity of gold taken up by it, 482. How prepared from nitric acid and common salt, 788. Of the solution of gold in aqua-regia, 1099. Solution of platinum in an aqua-regia composed of nitrous and marine acids, 1333. In one made with marine acid and nitre, 1324. Various methods of preparing it, 1488. Differences between the liquors prepared by these methods, 1489. How to deprive it of its volatility, 1548.

Aquila alba, a name for mercurius dulcis, 814.

Arabians, the first broachers of alchemy, 10.

Arbor Diane, how made, 754.

Ardent spirits, dissolve camphor in great quantity, 1285.

Argand's lamps, used for lamp-furnaces, 611. Doubtful whether they be preferable for this purpose to Lewis's or not, ib.

Argentine flowers, formed of regulus of antimony, 1253.

Argillaceous earth, in what it differs from the calcareous, 512. Tobacco-clay the purest earth of this kind, 1b. Absorbs colours, ib. Refills the empty violence of fire by itself, but melt by a mixture with chalk, ib. Combination of the argillaceous earth with vitriolic acid, 637, &c. See Alum.

Argonauts, origin of the fable of them, 9.

Arsenic: Of its distillation and precipitation, 243, 365. Calculation of the quantity of phlogiston contained in regulus of arsenic, 318. Precipitated by bismuth from the nitric acid, 369. And by copper from the marine, 370. Quantity of vitriolic acid taken up by regulus of arsenic, 502. Of nitrous acid, 503. Of marine acid, 504. Compounded of a particular kind of acid and phlogiston, 548. Unites with sulphur, ib. Is soluble in water, ib. Expels the acid of nitre, ib. Reason of this decomposition, ib. Phenomena on distillation with the vitriolic acid, 711. Phlogisticated by the nitrous acid, 770. Of the adulteration of corrosive sublimate by arsenic, 818. Oil and butter of arsenic, 823. Formed by subliming arsenic with corrosive sublimate, ib. Of the arsenical acid, 916, et seq. See Arsenic, acid of. A fling grain of regulus of arsenic destroys the malleability of an ounce of gold, 1095. Has a great affinity with tin, 1219. Methods of separating arsenic from tin, 1220. The crackling noise of tin bending supposed to arise from arsenic, 1221. Arsenic found in some places of Germany in a metallic form, 1266. The regulus easily convertible into common white arsenic by distilling part of its phlogiston, 1267. Why the arsenical calx may be mixed with other metals which will unite with it in its reguline state, 1268. Of the solution of the calx in water, 1269. In spirit of wine, 1270. Forms a very insoluble and fixed salt with vitriolic acid, 1271. Dissolves in large quantity in the marine acid, and forms a more volatile salt with it, though difficultly fusible in water, 1272. Resemblance of this solution to butter of arsenic, ib. Phlogisticated alkali precipitates arsenic from marine acid, and from that only, 1273. Arsenic decomposed by phlogisticated marine acid, 1274. Phenomena exhibited by it with other acids, 1275. Liver of arsenic formed by combining it with fixed alkali, 1276. A fenic unites with some metals, and crystallizes with iron and zinc, 1277. Unites readily with sulphur, 1278. Compounds thence resulting, ib. 1279. Phenomena exhibited by mineralized arsenic with nitre, 1280. Butter Butter of arsenic, 1281. This substance can scarce be made to unite with marine acid, 1282. Of the oil of arsenic, 1283. Of the mineralization of arsenic by sulphur, 1284. How to prepare pure regulus of arsenic, 1285. A native regulus called mipiclet, 1286. This contains a large quantity of iron, which will not obey the magnet till the regulus is distillated, ib. Great variability of the regulus of arsenic, 1287. It destroys the malleability of the metal with which it unites, 1288. May be expelled by heat from all of them except platinum, 1289. Volatilizes all of them except platinum, ib. Effects of arsenic upon alkaline salts and nitre, 1290. Decomposes corrosive sublimate, 1291. The regulus converted into white arsenic by vitriolic acid, 1292. Effects of it on metallic solutions, 1293. Platinum may be melted by means of arsenic, 1349. Effects of it on manganese in conjunction with nitre, 1391. Phenomena on distillation with manganic, 1395.

Arsenic, acil of, first discovered by Mr Scheele, 976. Two methods of procuring it, 977. By means of nitrous acid, 978. By dephlogisticated spirit of salt, 979. This acid equally poisonous with the white calx, 980. Easily refines its phlogiston, 921. Takes fire and sublimes instantaneously into regulus with charcoal, 922. Becomes black and thick with oil of turpentine, 923. With sulphur, 924. Crystallizes into a neutral salt with vegetable alkali, 925. This salt decomposed and forms a regulus with charcol, 926. Forms a crystallizable salt when perfectly saturated with mineral alkali, but requires an excess of acid to make it crystallize with the vegetable alkali, 927. Forms likewise a crystallizable salt with the volatile alkali, 928. Expels the vitriolic acid from vitriolated tartar and Glauber's salt, 929. And likewise those of nitre and common salt, 930, 931. Phenomena on distilling it with sal-ammoniac, 932. Decomposes sulphur pondofera and gypsum; but cannot expel the fluor acid, 339, 934. Precipitates lime-water, 935. Forms a crystalline salt with chalk, 936. But refines to crystallize with magnesia, 937. Or with earth of alum, 938. Does not dissolve white clay, 939. Dissolves terra ponderosa, 940. Has no effect on gold or platinum, 941, 942. Dissolves silver in the dry way by a violent heat, 943. Fixes quicksilver, 944. Produces corrosive sublimate by distillation with mercurius dulcis, 945. No butter of arsenic obtained by this process, 946. Dissolves copper, 947. Forms a very thick gelatinous solution of iron, 948. Dissolves lead in the dry way, 949. And likewise tin, 950. Dissolves zinc with effect, 951. But cannot dissolve bismuth, 952. Nor regulus of antimony, 953. Dissolves cobalt partially, 954. But not nickel, 955. Dissolves a small quantity of manganese, 956. Converts regulus of arsenic into the white arsenical calx, 957. Strange phenomena from it and the acetous acid, 2d 957, 1521. M. Pelletier's method of procuring the acid of arsenic, 1496. Differences concerning the weight of the acid to procure, ib.

Abras of different vegetables, Dr Gmelin's account of their colours, &c., 1089.

Attraction: Fire retained in bodies partly by it and partly by the pressure of the surrounding fluid, 55. Of chemical attraction, 162. This kind of attraction not equally strong between all bodies, ib. Different degrees of it between the different acids and alkalies, 174. Attraction of phlogiston supposed to be the cause of capillarity, 219. Kirwan's definition of chemical attraction, 260. Difference between it and cohesion, 261. Geoffroy's rule for determining the degrees of chemical attraction, 262. True method of ascertaining the quantity of attraction each of the acids has for the different bases, 265. This quantity expressed by that of the bases taken up by the different acids, 269. Attraction of metallic calces to phlogiston determined, 316.

Attractive powers of different substances best expressed by numbers, 264. Difficulties in determining the attractive powers of the different acids to metallic substances, 296.

Aurum fulminans, its nature and properties, 1103. Was known in the 15th century, 1104. The first directions for its preparation given by Basil Valentine, 1105. The use of volatile alkali for this purpose but lately known, 1106. Different accounts of the increase of weight in the metal by being converted into aurum fulminans, 1107. Explodes with incredible force, 1108. Twenty grains of it more than equivalent to half a pound of gun-powder, ib. Does not explode in clothe vessels, 1109. The utmost caution necessary in managing it in the open air, ib. Dr Lewis's account of the heat necessary to make it explode, 1110. Explodes by friction scarce sufficient to occasion any heat, 1111. Terrible accident occasioned by it, 1112. The force of the explosion directed every way, 1113. Particulars relating to the explosion, ib. Will not explode when moist, 1114. Quantity of elastic vapour produced during the explosion, ib. Cause of the explosion attributed to a false principle, 1115. This opinion shown to be erroneous by Mr Bergman, 1116. Why the fulminating property is derived by trituration with fixed alkali, ib. The explosion rendered more violent by boiling with fixed alkali, ib. Why the fulminating property is destroyed by boiling with too strong a solution of alkali, or with concentrated vitriolic acid, ib. Neither the presence of nitrous or marine acids necessary for the production of fulminating gold, 1117. The explosion is not occasioned by fixed air, 1118. How the fulminating calx may be prepared, 1119. The calx most readily thrown down by volatile alkali, ib. A fulminating calx produced from solution of gold in dephlogisticated spirit of salt, ib. Mr Bergman's theory of the cause of the explosion, 1120. Volatile alkali the true cause of it, 1121. Great quantity of elastic fluid generated by the explosion of aurum fulminans, 1123. Why a flight calcination destroys the fulminating property, 1124. Why the calx will not explode in clothe vessels, 1125.

Aurum fulminans, or Myseum, how prepared, 1224.

Bacon (Lord), his opinion of heat, 28, 29. See Verdun.

Baldwin's phosphorus prepared from solution of calcareous earth in spirit of nitre, 749.

Balsamum, or band-bath, described, 578.

Balsams of sulphur, how prepared, 1401. Vegetable balsams whose procured, 1432. May be considered as essential oils thickened by the diffusion of some of their more volatile parts, ib. Analysis of them exemplified in turpentine, 1437.

Barclaytente, a name for the marmor metallicum, or combination of terra ponderosa with vitriolic acid, 1030.

Basil Valentine, the first who gave directions for the preparation of aurum fulminans, 1105.

Beauvais's observations on gypsum, 636. His account of the formation of sedative salt ill founded, 862. Vitrifies a calx of platinum, 1352.

Beausart's observations on phosphoric, 1085.

Bell-metal, composed of copper and tin, 1150. Its specific gravity greater than that of either of the metals singly, 1156.

Bellows, when to be used in chemical operations, 608.

Bell, Reaumur's hint concerning an improvement in their shape, 1211.

Benzoic, yields a fragrant acid fat by sublimation, 984. The same obtained by liquefaction, 985. Quantity obtained by both these methods, 986. Mr Scheele's experiments in order to procure all the flowers benzoic is capable of yielding, 987, &c. Boiling with chalk, 988. Or with alkaline, &c., 989. Boiling with lime the best method, 990. Scheele's receipt for preparing the flowers of benzoic by this method, 991. The flavour of these flowers destroyed and reproduced at a distance, 992. The gum analyzed, 1430. Acid of, investigated by Mr Lichtenstein, 1530. Effects of nitrous acid upon it, 1531. Procured from Peruvian balsam and from urine, 1531.

Bergman's account of the cause of chemical solution, 193. Differences between him and Kirwan accounted for, 435. His method of finding the proportion of ingredients in alum, 614. His account of the quantity of these ingredients, 646. His account of the Swedish ores of alum, 651. His analysis of the ores at Tolfa in Italy, 657. His directions for the preparation of alum, 661. His remarks on the proper form of the coolers for alum, 678. Considers the laps ponderosus or tungsten as a metallic earth, 697. His opinion concerning the acids of tungsten and molybdena, 972. Denies the fusibility of fibrous earth in acids, 1070. Forms crystals of flint artificially, 1072. Shows the error of those who imagine the explosion of aurum fulminans to be occasioned by a false principle, 1116. His theory of the explosion, 1120. His opinion concerning the fulmination of other calces, 1126. His opinion concerning the composition of nickel, 1316. His experiments on platinum, 1321. Letter to Moreau on the subject of a new nomenclature, 1359.

Berthollet's opinion of heat, 56. His division of it into fixed and volatile, 57. See Heat.

Berthollet differs fulminating filter, 1118. Procures the marie acid in a fluid state, 785. His new fulminating mixture, 2d 793. How to procure this talk in quantity, 1487.

Bichloride's tincture of iron, 2d 803. Mistakes of chemists concerning it, 3d 808. True method of preparing it, 4th 808. Supposed to absorb phlogiston from the fluid says, 5th 808.

Bile: Some of its properties affirmed by blood when mixed with the nitrous acid, 1477.

Bismuth: Of its precipitation from acids, 241. Copper and bismuth precipitate one another alternately from the nitrous acid, 357. Is scarcely soluble in vitriolic acid, 401. Increases the fusibility of tin and lead, 543. A compound of this kind fusible in boiling water, 544. Dissolved in great quantities by nitrous acid, 765. Volatile alkalies, after precipitating the metal take it up again, ib. The same thing happens with fixed alkalies calcined with inflammable matter, ib. Mixture of bismuth prepared by adding water to the nitrous solution, 766. Neuman's observations concerning this preparation, ib. Effects of acid of arsenic upon it, 952. Is convertible into hydride and glass, 1348. Occupies less space when in fusion than when in a solid state, 1350. Mixture with all the metallic substances except cobalt and zinc, 1351. Promotes the fusion of all the metal with which it is mixed, 1351. Plaster may be alloyed with it, but without any advantage, 1348.

Bitumen: A kind of fat prepared from it, frequently supersedes the use of the true Glauber's salt, 632. How to to procure the marine acid from it, 736.

Bitumens particularly treated of, 1441. Whether they are of a vegetable or mineral origin, ib. Macquer's opinion; that they are only vegetable refined, ib. Dr Lewis's reasons for being of a contrary opinion, ib.

Black, Doctor, his theory of heat, 35. Experiments by which he was led to the discovery of latent heat, 41. His method of calculating the quantity of heat produced by the condensation of vapour, 44. Difference between his calculations and those of Dr Crawford, 51. Expansive force of water in freezing explained by Dr Black's theory of latent heat, 108. His experiments on the conversion of water into vapour, 121. His observations on chemical vessels, 557. His directions for performing the operation of solution, 565. Description of his portable furnace, 2d 602. How it is adapted to the various operations of chemistry, 603. Of the lining proper for the inside of this furnace, 604. Method of applying the lute, 605. His account of the preparation of nitre, 724. His conclusions concerning the nature of that salt, 732. His method of making nitrous ether, 775. Shows a method of making it without any spirit of wine, 777.

Black lead, a valuable material for some chemical vessels, 602.

Bleaching, how performed by means of dephlogisticated spirit of salt, 1484.

Blood, strangely altered in its properties by mixture with nitrous acid, 1477.

Boerhaave's experiments to produce a change on mercury by keeping it long in a gentle heat, and by repeated distillations, without success, 1220, 1230.

Bolzenia: Bergman's account of the aluminous resin in that country, 618.

Boiling-point of water in vacuo determined by Mr Boyle, 122. And by Mr Robinson of Glasgow, 123.

Bore: camphor converted into an essential oil by distillation with it, 1423.

Bolognian stone, a kind of native phosphorus, 1081. How first discovered, ib. Margraff's account of the appearance of this stone, ib. How rendered luminous, 1082. Seems to be of a gypseous nature, 1081, 1083. Analysis of it, and reason of its shining in the dark, ib.

Borax, composed of a peculiar kind of acid and mineral alkali, 863. How prepared in the East Indies, ib. Of its state when first imported from thence, 864. How refined, ib. Said to be adulterated during this operation, ib. This denied by Dr Black, ib. Simple distillation and filtration all that is necessary, according to him, for the purification, ib. Its purification according to others, 1490. Has a glutinous quality, by which it gives a glost to flaks, ib. Its properties with acids and various salts, 865.

Borax, acid of, found in a kind of mineral in Germany, 858. Procured from the salt either by sublimation or crystallization, 858. Is fixed in the fire, and melts into a kind of glass by a violent heat, 860. Diffuses in spirit of wine, ib. Makes no change on the colour of vegetable juices, ib. Mr Bourdelin's experiments on its nature, 861. Mr Cadet's experiments, 862. M. Beaume's opinion that it is produced by rancid oils unsatisfactory, ib. Of its combination with alkalies, ib. Forms an unknown salt with vegetable alkali, ib. And borax with the mineral alkali, 863. Its effects on cobalt, 1303. Beaume's observation on the method of preparing the lactate salt from it, 1491. Properties of the salt, 1492. Its combinations with volatile alkali, earths, and metals, ib. Experiments with a view to determine the nature of the acid, 1493.

Boulard, M. de Geoffroy, discovers the component parts of alum, 641.

Boullanger's opinion that the fluor acid is no other than the marine combined with an earthy substance, 833. Shown to be erroneous by Mr Scheele, 834.

Bourdelin's experiments on the nature of the acid of borax, 861.

Boyle, Mr, improves the science of chemistry, 17. His opinion concerning the number and nature of the elements, 24. Attempts to prove that fire is not an element, ib. That the solid substance of bodies is converted into air, ib. That water is converted into earth, ib. His arguments inconclusive, ib. His account of the production of heat, 30. Determines the boiling point of water in vacuo, 122. His experiment showing the destructibility of gold, 1098. Curious kinds of mercury prepared by him, 1227.

Brafs, how prepared from copper and calamine, 1154. May be reduced to copper again by a long continued and violent heat distilling the zinc, ib. A compound of brafs and platinum a proper material for speculums, 1344.

Burning: phenomena of it, 516. A great quantity of water produced from oil by burning, ib. Part of this probably from the atmosphere, ib.

Butter of antimony composed of regulus of antimony and marine acid, 821. Becomes fluid by rectification or exposure to the air, ib. Lets fall the pulverized by the direct affusion of water, ib. Formerly used as a caustic, ib. M. Dollfus's method of preparing it, ib.

Butter of arsenic, prepared from regulus of arsenic and corrosive sublimate, 823. Becomes fluid by repeated rectifications, ib. Is not obtained from white arsenic and corrosive sublimated together, 946. May be prepared also by hydrolining orpiment and corrosive sublimate, 1284. Can scarcely be made to unite with marine acid, 1282.

Cabbage, an excellent test for acids or alkalies prepared from it, 1550. Cadet's experiments on the nature of the acid of borax, 862.

Calcineous earths. Decomposition of vitriolated tartar by their solutions explained, 270. Mr Kirwan's experiments on them, 437. Form gypsum with vitriolic acid, 635. Diffuse in the nitrous acid into an acrid liquor which cannot be crystallized, 747. Decomposes this acid by frequent distillations, 784. Are convertible by it into a kind of phosphorus, 749. Form likewise a phosphorus with the marine acid, 797. Their effects on the solution of silver, 756. Form affrangent compounds with the acetic acid, 871. Decompose cream of tartar, 887. Have a great attraction for saccharine acid, 902. Compose fluor spar by being combined with its acid, 831. And tungsten with the acid extracted from it, 971.

Calces of metals; arguments against the existence of phlogiston from the reduction of those of the perfect metals without addition, 140. Reduction of metallic calces by inflammable air, 149. Different colours exhibited by them, 192. Those of some metals, when prepared by nitrous acid, almost totally insoluble after evaporation, 196. Why little or no elastic fluid is produced from them, 213. Of their attraction to phlogiston, 326. How to find the specific gravity of the different metallic calces, 327. Whence their various degrees of affinity to phlogiston may be determined, 328. Calces of copper precipitate dephlogisticated solutions of iron, 343. Solutions of the dephlogisticated calces of iron refuses to crystallize, 457. Calces of iron precipitated of a reddish colour from spirit of fat, 493. Calces of gold soluble in the vitriolic and nitrous acids, 483. Reason of the increase of weight in metallic calces, 524. Bergman's opinion concerning the fulmination of metallic calces, 1126. Erroneous, ib. Effects of the colouring matter of Prussian blue on metallic calces, 1192.

Calcination: quantity of phlogiston lost by metals during that operation, 332. Of the affinity of their calces to the deficient part, 332. Calcination of metals by fire described, 522. Of their calcination and increase of weight by acids, 523. Reason of this increase, 524. Solubility of metals increased by calcination, 545. How to perform the operation of calcination, 583. Why a flight calcination destroys the explosive property of aurum fulminans, 1124. Effects of violent calcination on nickel, 1307.

Calcined metals. See Calcination, Calces, Calcs, and Metal.

Calculus, human; Scheele's experiments on it, 1455. His conclusions concerning its composition, 1456. Is found universally in urine, 1457. Bergman's experiments on it, 1460. Calcareous earth contained in it separated by means of the vitriolic acid, 1402. Red colour of the solution in nitrous acid accounted for, 1400. Mr Higgins's experiments, 1403. His account of its component parts, 1465, 1468. Experiments on the sublimate arising from it on distillation, 1465. Experiments with nitrous acid, 1466. Crystalization of the nitrous solution by exposure to the sun, 1467. Remarks on the remedies proper for diffusing the flores, 1469. Sublimate of calcium met with in consumptive and gouty persons, 1470. Distillation ought not to be attempted when the stone is large, ib.

Calculus of the acid obtained from it, 982. All the calculi produced in the human body of the same nature, ib. Diffused by concentrated vitriolic, and by the nitrous acid, but not by the marine acid, ib. The acid of calculus produces deep red spots on the skin, 983. Assumes a blood-red colour by evaporation, ib.

Calcium, a name given to mercurius dulcis several times sublimed, 814. Repeated sublimation no improvement on the medicine, ib.

Calcs of the diffused metal, with various degrees of phlogiston, contained in metallic solutions, 214. Reasons for believing that metals are reduced to a calx by solution, 215. Increase of attraction between the calx of iron and phlogiston demonstrated, 342. Calx of iron soluble in lixivium funguinis, 1176. But not when highly dephlogisticated, 1176.

Camphor, a volatile substance belonging to the class of essential oils, 1422. Converted into a true essential oil by repeatedly distilling it with hole, 1423. Into an acid by distilling it several times with dephlogisticated spirit of nitre, 1424. Effects of this fat on alkalies and metals, ib. How distinguished from acid of sugar, ib. Account of the method of extracting it from the trees which produce it, its uses, &c., ib.

Cantus's phosphorus, how prepared, 1414. Becomes luminous by exposure to the sun, or the light of an electrical flash, ib.

Capacities of bodies for containing heat; that phrase explained, 52. How they are to be distinguished from the temperature and absolute heat of bodies, 53. The capacity of a body for containing heat the same with the action of heat on the body, 111. Nicholson's account of the capacities of bodies for containing heat, 113.

Cass-iron scarcely decomposes the solution of copper, 345.

Castello's method of purifying ether, ad 722. Shows that pyrophorus is not injured by exposure to light, 1418.

Cavendish supposes heat not to be a distinct substance, 69. His calculation of the quantity of fixed air con- Chemistry

How far on fire by the nitrous acid, 1476.

Chemical attraction particularly treated of, 162; cf. See Attraction. Bergman's account of the cause of chemical solution, 193. Kirwan's definition of chemical attraction, 265. Difference between it and cohesion, 261. Geoffroy's rule for determining the degree of chemical attraction, 262. Chemical decompositions apparently single are often double, 263. Invention of chemical marks and characters, 551. New chemical language invented by the French chemists, 552. Its ridiculous appearance in an attempt to explain the formation of the cells of silver, 1144. Of tables of chemical affinities or attractions, 553. Dr Black's general table of attractions, ib. His observations on chemical vessels, 557. Good and bad qualities of glass as a material for retorts, 558. Of metals, 560. Of earthenware, 561. Of chemical furnaces, 599. See Furnaces.

Chemistry described, 1. High antiquity of the science, 2. Supposed to be founded by Sphærus, an Egyptian, 3. Metes thought to have been well fed in chemistry, 4. Democritus taught chemistry by the Egyptian priests, ib. Chemistry introduced into medicine after his time, ib. Some advantages accruing to chemistry from the labours of the alchemists, 13. History of chemistry from the time of Paracelsus, 15. The science studied by Lord Verulam, 16. Improved by Mr Boyle, 17. Chemistry emerges from its obscurity, 18. Receives considerable advantages from the founding of the Royal Society, and others of that kind, 19. Great improvements made by chemists of various nations, 20. Perfection of chemistry defined, 21. Objects of chemistry how distinguished from the agents, 22. Classification of the objects, 173. How far water is an object of chemistry, 549. Of the different operations in chemistry, 554, et seq.

Chemists, improvements by those of different nations, 18, 19, 20. How divided, 555.

Charcoal proved to be the same with phlogiston, 145. Decisive proofs of their identity from Dr Priestley's experiments, 146. Spirit of wine convertible into charcoal, 147. Charcoal entirely diffused into inflammable air by the heat of a burning lens in vacuo, 148. De-phlogisticated air converted into aerial acid by its union with charcoal, 151. Sulphur produced by distilling concentrated vitriolic acid with charcoal, 715. Or by calcining vitrified tar with the flame, 716. Artificial acid takes fire and sublimates into regulus with it, 922. Neutral artificial salt decomposed by it, 926. Charcoal distilled by liver of fulmin, 1025. Phenomena of distillation with manganese, 1398. Most inflammable matters reduced to charcoal, 1450. Difference between the coals of different substances, ib. Some coals, particularly those of animal substances, can scarce be reduced to ashes, ib. Bullock's blood affords a coal of this kind, ib. Concrete oily substances, or foot, burn with equal difficulty, ib. Some of these coals almost resist the action of nitre, ib. This substance rendered refractory, 1451.

Colouring matter of Prussian blue investigated by Mr Scheele, 1171. This matter flies off from the lixivium fangunius when exposed to the air, 1172. This effect supposed to be owing to fixed air in the atmosphere, 1173. The colouring matter fixed by the addition of some green vitriol to the lixivium, 1174. Calx of iron soluble in the lixivium, 1175. But not when highly de-phlogisticated, 1176. The colouring matter taken up by the air after it has been expelled by acids, 1177. Effects of distilling the lixivium with vitriolic acid, 1178. Attempts to procure the colouring matter by itself, 1179. Neutral salt formed by it for discovering iron in mineral waters, 1180. Effects of distilling this salt with oil of vitriol, 1181. The colouring matter unites with volatile alkali, 1182. How to free it perfectly from any vitriolic taste, 1183. To prevent its escape through the tube during distillation, 1184. The colouring matter neither acid nor alkaline, 1185. Forms a kind of ammoniacal salt with volatile alkali, 1186. Diffuses magna alba, 1187. Very little terra ponderosa, 1188. Diffuses lime, but not clay, 1189. This solution most proper for making experiments on metals, 1190. Precipitates the solutions of silver and quicksilver in nitric acid, and of iron in fixed air, 1191. Its effects on the metallic calces, 1192. On metallic solutions, 1193. Its constituent parts investigated by experiment, 1194. Is of an inflammable nature, 1195. Supposed to contain aerial acid and phlogiston, 1196. Ingredients in its composition, 1199. Unsuccessful attempts to produce it by volatile alkalies in a liquid state, 1200. Successful method with sal ammoniac, salt of tartar, and charcoal, 1201. Its volatility destroyed by manganate, 1204. Can separate only mercury and silver from their solution in nitric acid, 1205.

Colours of vegetables changed by acids and alkalies, 173. Different colours of metallic calces, 192. Colours imparted to various kinds of stones by solution of silver, 753. Colours of various kinds destroyed by de-phlogisticated spirit of salt, 1484.

Comparative heats of bodies defined, 40.

Compounds of two metals sometimes heavier than either of the ingredients, 1156. More fusible than either of them singly, 542. Great fusibility of those of tin and bismuth, 543. Fusibility of these augmented by the addition of lead, ib. One fusible in the heat of boiling water, 544. Platina unites readily with compound metals, 1343.

Concentrated acids phlogisticated by alkalies, 409. Concentrated nitrous-

Index.

tuous acid diffuses less metal than when diluted, 489. How to obtain a very concentrated acetic acid, 881. Violent action of the concentrated nitrous acid upon molybdana, 960. Marmor metallicum soluble in concentrated vitriolic acid, 1065. Precipitated from it unchanged by vegetable fixed alkali, 1064. Why the concentrated vitriolic acid differs from manganic without addition, 1378.

Condensation of vapour produces a great quantity of heat, 43, 125. Dr Black's method of calculating it, 44.

Congealed water, the difficulty with which it melts, a mean of preventing inundations in countries where snow and ice abounds, 88.

Copper, of its precipitates, 238. Why it is dissolved by solutions of silver, mercury, and iron, 336. Why iron and copper precipitate one another, 341. Dephlogisticated solutions of iron precipitated by calces of copper, 343. Dephlogisticates the iron which precipitates it, 344. Its solution scarcely decomposed by calf iron, 345. Why it sometimes cannot precipitate silver, 348. Precipitations of mercury by it, 355. Precipitations of copper by nickel, 360. Copper throws down a white powder from solutions of cobalt, 364. Forms a triple salt with regulus of antimony and marine acid, 367. Precipitates regulus of arsenic from the marine acid, 370. Proportion of it dissolved by the vitriolic acid, 494. Inflammable and vitriolic acid produced from its solution in this acid, 495. Quantity of the metal dissolved by nitrous acid, 498. By marine acid, 500. Forms blue vitriol with the vitriolic acid, 693. Of its solution in nitrous acid, 757. In the marine acid, 804. Forms a beautiful green salt with acetic acid, 872. And with cream of tartar, 894. Combination of arsenical acid with it, 947. Forms a most beautiful blue salt with caustic volatile alkali, 1035. Does not greatly diminish the ductility of gold though previously alloyed with tin, 1094. Its nature particularly confused, 1140. Always lighter than, 1147. Will not strike fire with flint, and therefore of use to make hoops, &c., for gunpowder cakes, ib. Its ductility, tenacity, and specific gravity, ib. Exposed violently to the contact of water, re, in fusion, 1148. How granulated, ib. How calcined, 49. The salts exceedingly refractory, ib. Soluble by acid and the saline substances, and even by water, 1150. More fusible than cold liquids than hot, ib. Undergone few change by combination with vegetable acids, 1151. How amalgamated with mercury, 1152. A curious amalgam formed by mercury and verdigris, 1152. Dr Lewis's methods of amalgamation, 1153. Forms brats, prince's metal, &c., by the addition of calamine or zinc, 1154. Crucible in which these operations are performed tinged of a deep blue colour, ib. Forms bell-metal with a mixture of it, 1155. Lewis's observations on the specific gravity of this and other metallic compounds, 1156. White copper made by fusion with an equal part of arsenic, 1157. A fine gold-coloured metal formed by a mixture of copper and platina, 1341. Phenomena attending the dilution of it in volatile alkali, 1353.

Coppers. See Vitriol.

Corroge fulminate precipitated without any decomposition by oil of vitriol, 315. May be decomposed by silver in dry, but not in the moist way, 356. Of its preparation from quicksilver, 314, &c. Differences of its quality according to the different methods by which it is prepared, 316. Reason of these differences, ib. Method of making it at Amsterdam, ib. Observations on the different methods, 317. Of its adulteration with arsenic, 318. Yields no butter of arsenic by fulmination with that substance, 945, 946. Its use in the preparation of butter of antimony, 821. Of its fulmination with manganic, 1397.

Cramer's artificial compost for making nitre, 728.

Cravatford, Dr, his explanation of Rivin's theory of heat, 36. Differs greatly in his calculations from Dr Cleghorn, 48. His account of sensible heat, 49. Differs from Dr Black, 51. His opinion concerning heat in the abstract, 54. His definition of fire, 59. His method of determining the proportional quantities of heat in bodies, 77. Insufficiency of his method, 78. His solution of a difficulty concerning the seeming disappearance of heat, 86. Insufficient, 91.

Cream of tartar, how prepared, 886. Analyzed by Mr Scheele, 887. Regenerated, 890.

Crell, Dr, a mistake of his concerning the production of Glauber's salt from alum and common salt corrected, 272. His method of crystallizing the acid of lemons, 997. His attempts to bring vinegar nearer to the state of tartar, 1004. His proofs that all vegetable acids are to be derived from one origin, 1006.

Cremum metallorum, how prepared, 1245.

Cronfield discovers the new feminal called nickel, 1306.

Crucibles: of them the proper materials for them, 583. Achard's method of making them from calx of platinum, 587. Mr Pott's directions for making them, 588. Dr Lewis's observations on their construction, 589. Porcelain probably the fittest material for vessels of this kind, 591. Of Reaumur's porcelain as a material for crucibles, 592.

Crypt produced by the fluor acid on the surface of water, 829. Found to be of the nature of filous earth, 829. Scheele's experiments to determine the nature of this earth, 830. The same crypt produced from artificial nitre, 831. Scheele's opinion that the earth is formed by the union of the acid and water, 832. Contested by Meffrs Boullanger, Mommet, &c., 833. Their opinions shown to be erroneous by Mr Scheele, 834. Wiegels's experiments on the origin of it, 839. Found to proceed from the corrosion of the glass-distilling vessel, 840. How to procure the acid free from it, 842. None formed by mixing sand with a salt containing fluor acid, 844. But a great quantity by adding powdered green glass, 845.

Crysaline powder thrown down from solution of calx of platina by vegetable fixed alkali, 1325.

Crysalization, in chemistry: how to perform that operation, 573. Crystallization of alum impeded by vitriolic acid, 681.

Crysalis of one kind of salt contain none of any other, 573. Fulminating crysalis, 1142. Crysalis of platina decomposed by the mineral, but not by the vegetable, fixed alkali, 1322.

Cullen, Dr, his experiments on the production of cold by evaporation, 124.

Cupellation: why lead is useless in that operation, 331. Attempts to refine platina by cupellation, 1355.

Cuprum ammoniacale, how prepared, 1034.

Decompositions, chemical, are often double, though apparently single, 203. Explanation of those effected by acids alone, 266. Decompositions of vitriolic salts supposed to arise from compound forces, 276. Why decompositions are sometimes incomplete, 405, 406.

Dehydration, an operation in chemistry, how performed, 582.

Democritus taught chemistry by the Egyptian priests, 4. Said to be able to imitate the precious stones, particularly the emerald, ib. Was probably only acquainted with the method of making green glass, ib.

Density of mixtures, its increase accounted for, 374. How to determine the accrued density of spirit of nitre mixed with water, 387. Increase of it in compound fulminates, 404.

Dephlogisticated air converted into aerial acid by charcoal, 151. Objection to the existence of phlogiston from the total composition of it in some cases, 152. Little phlogiston consumed by the combustion of iron in this kind of air, 153. Of the dephlogisticated marine acid, 266, 792, &c. Dr Lavoisier's experiments on the dephlogisticated nitrous acid, 432. Solution of dephlogisticated calx of iron cannot be crystallized, 457. Dephlogisticated green vitriol decomposed by clay, 834. Dephlogisticated air a material for the nitric acid, 722. How to prepare the dephlogisticated spirit of nitre, 790, 791. Can scarcely be converted into a liquid, 792, 16, other properties. Acid of arsenic procured by its means, 919, 1274. The only solvent of platinum, 1319. Dephlogisticated spirit of more decomposes cam, ibs, 1424.

Dephlogisticated spirit of salt, expedient method of bleaching linen by means of it, 1434. Effect of it on phosphoric matters, 1485. Differences with caustic volatile alkali, 485. Forms an inseparable with spirit of wine, 1486. Difficulties phlogisticus, ib. Method of procuring a detonating salt in quantity from it, 1487.

Dissoluta metallorum, a name for tin, on account of its bad effects on other metals, 1222.

Disprositive antimony, how prepared, 1204.

Disprosive, Papin's described, 567. Effects of it producible by long boiling, ib.

Distillation, in chemistry, how performed, 565.

Distilled salts: Quantity of ingredients in it, 379, 421. Prepared from vegetable alkali and marine acid, 794.

Diffusion of metals: heat produced by that operation, 190.

Diffusion: how that operation was originally performed, 6. Mr Watt's experiments on the diffusion of water in vacuo, 45. Proper method of performing the operation of distillation, 574. Phenomena on distillation of inflammable substances, 517. Boerhaave's experiments on the distillation of mercury, 1230.

Distilled verdigris, how prepared, 872.

Divalent affinities explained, 207.

Dolful, Mr, his method of preparing butter of antimony, 821. His proof for muriate ether, 824. For acetous ether, 834.

Du Fay supposes all calcareous stones to be phlogistic, 834.

Dyeing: the vitriol formed by precipitating copper with iron less proper for this purpose than that made after the common method, 344.

Earth: water ful poled to be convertible into it, 24. Has not the character of an element, 25. Soluble in acids, 176. Why the metallic earth seldom decomposes salts whose basis is a calcareous earth or alkaline salt, 354. Quantity of earth in vegetable alkali, 413. Difficulty in obtaining the pure earth of alum, 645. Lewis's experiment to show that clay undergoes some change by being converted into this earth, 649. Siliceous earth found in the resin produced from the residuum of vitriolic ether, 2d 722. Quantity of filous earth carried up by fluor acid, 847. Earth of alum combined with arsenical acid, 938. INDEX.

Chemistry.

Silicous earth most completely precipitated by volatile alkali, 1074. Forms a triple salt by precipitation with fixed alkali, 1075. Is dissolved by boiling with alkali, 1076. See Silicous. Vegetable earth supposed by Lewis to be the same with magnesia, 1088. Mr. Gmelin's experiments on it, 1089.

Earth, how divided, 6th 510. Vitriolic acid combined with different earths, 635, et seq. Nitrous acid combined with them, 746. Solution of silver decomposed by calcareous earths, 755. Character curiously marked by the sun's light on the precipitate, 756. Marine acid combined with earths, 797. Flavour acid with them, 82. Acetone acid, 871. Acid of tartar, 893. Of phosphoric earths, 1061. Earths do not attract the colouring matter of Prussian blue, 1169.

Earthenware: of its properties as a material for chemical vessels, 561.

Earthy crust. See Croft.

Eau de luce, how prepared, 1037.

Effervescence attends the solution of metals, 1088.

Edelstahl, a kind of ponderous spar, or marmor metallicum, found near the city, 1001.

Elastic fluids extracted during the solution of metals, 159. Great quantity of elastic fluid generated by the explosion of aurum fulminans, 1123.

Elasticity occasioned by heat, and not by friction, 209.

Electric attractions, in chemistry, defined, 177. Precipitation of metals by one another owing to a double one, 229.

Electric fluid, in winter, the same with the heat sent down from the sun in summer, 99.

Electric spark produces nitrous acid in a mixture of dephtoticated and phlogisticated air, ad 222. Its effect on a mixture of alkaline and dephtoticated air, 1511.

Electrical heat, why so much stronger than that of furnaces, 160. Capable of vivifying platinum, 1335.

Electricity: proofs of the identity of its fluid with fire and light, 96. Connection between it and fire or heat, 97. Elective electricity of the polar regions, 98. Electricity, heat, light, and cold, are to be looked upon as the effects of one universal fluid, 101. Explosion of fulminating fliver probably owing to it, 1146.

Elements: the supposition of them the origin of alchemy, 23. Mr. Boyle's opinion of them, 24. Are in their own nature invisible, 26.

Emetic tartar: different degrees of their strength as commonly prepared, 1248. Pulvis algarth the most proper material for their preparation, 1259.

Empyreumatic acids produced by dry distillation of vegetables are all of one nature, 993. An acid of this kind produced from the liquor in which terebent tartarous is boiled, 1010.

Empyreumatic oils, how rectified, 1426.

England: alum-works when erected there, 640.

Engaging on glass, how performed by means of flour acid, 21837.

Eclipse may sometimes be used for blowing up fires, 629.

Epsom salt: proportion of ingredients in the common land, 443. In nitrous Epsom, 444. Cannot be found in marine Epsom, 445. The true Epsom salt found in the ley remaining after the crystallization of alum, 688. Prepared from the bitter bit of tea leaf, 690.

Equilibrium of heat defined, 75.

Essential oil of lemons, a kind of flavor extracted from ferret, 888. Essential acids produced from the juices of vegetables, their proper uses, 994. Phosphorus combined with essential oils, 1412. Analysis of essential oils, 1419. Their taste supposed to be owing to a disengaged acid, 1420. Why they lose their flavourability, spirit of wine by being frequently distilled, 1421. Converted by strong heat into empyreumatic oils, 16. A considerable quantity yielded by all the kinds of turpentine, 1437.

Ether, vitriolic, produced by a combination of vitriolic acid and spirit of wine, 717. Mr. Beattie's method of making it, 718. Is the lightest of all liquids, 719. Evaporated in vacuo at 20° below 0 of Fahrenheit, ib. Produces a great degree of cold by its evaporation, ib. Dissolves gold, ib. An inflammable tale produced by Wallerius by combining ether with tartar, 722. This thought to be a proof of the transmutation of vitriolic into nitrous acid, ib. The phenomenon otherwise accounted for, 721, 722. Mr. Cavallo's method of purifying ether, ad 722.

Ethyl alcohol produced from the residue of its distillation, affording vitriolic, phosphoric, and acetic acids, Glauber's salt, identical, iron, and earth of flint, ib. Nitrous ether produced by combining that acid with spirit of wine, 775. Dr. Black's method of making it, ib. Mr. Woulfe's process for procuring it in large quantity, 776. Inquiry into the nature of ether, 777. Made by Dr. Black without any spirit, ib. Marine ether how produced, 824. Acetous ether, 884. Saccharine ether, 902. Vitriolic ether crystallizes gold, 1129. Dobbs's method of preparing it with marine acid, 824. With acetic acid, 884. Methods of Pelletier and others for rectifying vitriolic ether, 1471.

Ethereal solution of gold, its properties, 1129.

Evaporating vessel in alum-works described, 674.

Evaporation: Dr. Cullen's experiments on the production of cold by it, 124. Of the method of performing that operation in chemistry, 572. Lead vessels most proper for evaporations in the large way, ib.

Expansion, one of the general effects of heat, 65. That of mercury and some other fluids proportional to the degree of heat, 16. Instruments for measuring the expansion of bodies, 103. Influence of bodies being expanded by col, 103. Expansion of water in freezing occasioned by the extrication of air-bubbles, 109.

Expansive force of water excessive in the act of freezing, 106. Used as an argument for the positive existence of cold, 107. Explained by Dr. Black's theory of latent heat, 108.

Explosion of fulminating gold vastly superior to that of gunpowder, 1108. A final degree of heat sufficient to make this fulminate explode, 1110. Instances of its mischievous effects, 1112. Its force is not entirely directed downwards, 1113. Of the explosion of moist aurum fulminans, 1114. Not occasioned by a failing principle, 1113, 1116. Nor by fixed air, 1118. Mr. Bergman's theory of its cause, 1120. Occasioned by volatile alkali, 1121. Explosion by the vapours of mercury, 1231.

Explosions, violent, occasioned by heat suddenly applied, 732.

Fat, acid of; how procured from feces, 2d 1013. Salts formed by combining it with alkalies, 3d 1013. With caustics, ib. With metals, 4th 1013.

Fats of animals analysed, 1428.

Fermentation: milk capable of a complete one, 979.

Fillings of iron grow hot and take fire spontaneously with sulphur, 1207.

Firmicus Maternus the first writer on alchemy, 8.

Filtering large quantities of water, a scheme for, 569.

Filtration: how to perform that operation in chemistry, 568.

Fire supplied by Mr. Boyle not to be an element per se, 24. The contrary opinion now generally embraced, 32. Two general theories of it in alchemy at present, 33. In what they differ from the theory of Boyle and Newton, 34. Fire retained in bodies partly by attraction and partly by the pressure of the surrounding fluid, 35. Berkenhout's division of fire into fixed and volatile, 57. Pure or volatile fire described, 58. Dr. Crawford's definition of fire, 59. Mr. Kirwan's opinion, 68. Mr. Cavendish's opinion that it is not a distinct substance, 69. Seems destitute of gravity and vis inertiae, 93. Proofs of its identity with light and electricity, 96. Connection between fire and electricity, 97. Vitriolic acid contains more fire than the nitrous or marl, 278. Acids unite to alkalies by giving out fire, and quit them by receiving it, 286, 289.

Fixed air: its specific gravity determined, 411. Of the quantity of it in vegetable alkali, 414. Impure vegetable alkali, 417. Of the quantity contained in mineral alkali, 434. Earth of alum contains a great quantity, 446. Of the quantity of phlogiston in fixed air, 2d 505. Alkaline salts composed of caustic salt and fixed air, 1252. Is not the cause of the explosion of aurum fulminans, 1118. Expels the colouring matter from lixivium funginis, 1173. Water impregnated by it dissolves magnesia, 1371.

Fixed alkali is attracted by nitrous acid and then fixes, 301. Vegetable fixed alkali takes up an equal quantity of all the acids, 402. Exact calculation of the quantity of acid taken up by vegetable fixed alkali, 419. Stone ware corroded by the caustic fixed alkali, 395. Fixed sal ammoniac the fastest with a combination of the marine acid and calcareous earths, 797. Combination of fluor acid with fixed alkali, 4th 850. Fixed alkaline salts how procured, 1004. Vegetable alkali crystallized in various ways, 1017. Changed by combination with marine acid, 1018. Combination of fixed alkalis with sulphur, 1221. With extracted oils, 1226. With essential oils, 1227. With phlogiston, 1038. Differences observed betwixt those obtained from different vegetables, 1039. Precipitate solutions of terra ponderosa, whether in their mild or caustic state, 1054. The caustic fixed alkalies throw down an insoluble precipitate from these solutions, 1056. Marmor metallicum precipitated unchanged from oil of vitriol by mild vegetable alkali, 1064. A triple fats formed by fixed alkalies, filicose earth, and fluor acid, 1075. The mineral, but not the vegetable, fixed alkali decomposes crystals of platinum, 1322.

Flints, earth of, supposed to undergo a transmutation by being dissolved in an alkaline liquor, 1069. This change denied by Mr. Bergman, 1072. The supposed transmutation found to arise from an admixture of clay, 1071. Crystals of fixed plant produced artificially by Mr. Bergman, 1072. Why the fluor acid will not dissolve flint directly, 1073. Earth of flints most completely precipitated by volatile alkali, 1074. Forms a triple salt with fluor acid and fixed alkali, 1075. Diffused by boiling in an alkaline liquor, 1076. Has a remarkable attraction for alkaline salts in the dry way, 1077. Is very rare and porous when precipitated, 1078. Why the alkaline solution sometimes cannot be precipitated by an acid without heat, 1079. Liquor of flint's compound by too great a quantity of water and by fluor acid, 1080. See Silicious earth.

Flores mortales, how prepared, 808.

Flores of Benzoin, how prepared, 984, et seq. See Benzoin. Flowers of zinc prepared by the deflagration of that semimetal, 1241. Dr Lewis's method of reducing them, 1242. An oil supposed to be obtained from them by Mr Homburg, 1943. His mistake detected by Neumann, ib. Another oil by Mr Hellot, 1444. Gold and silver leaf dissolved by this oil, ib. A great proportion of nitre alkalized by the flowers of zinc without any sensible deflagration, 1249.

Flowers: method of preparing tests for acids and alkalis from them, 1552.

Fluids: Dr Cleghorn's proof that heat is occasioned by one, 82. Difficulties concerning the nature and properties of this fluid, 83. Heat most probably the action of an omnipotent fluid, 92. Sensible heat always produced by the conversion of a fluid into a solid, 116.

Fluidity occasioned by the absorption of heat, 115, 119. A proof of this from its being possible to cool water below 32° without freezing, 117.

Fluids differ in the degrees of all soluble heat they contain, 46. The thinnest fluids contain the greatest quantity of heat, 47. Mr Watt's experiments on the evaporation of fluids in vacuo, 126. Fluids part with more heat than solid bodies can, 212.

Fluor acid: why it can be reduced into air without any addition, 207. First discovered by Mr Margraf, 826. Prepared by dissolving fluor spar with oil of vitriol, 827. Forms a white earthy crust on the surface of water put into the receiver, 828, et seq. See Cryst. Fluor acid proved to be distinct from that of sea-falt, 835. And from the acid of vitriol, 836. Quicklime proved to be the basis of fluor spar, 837. Mistake of M. Monner on this subject, 838. Wiegels's experiments on the earth contained in this acid, 839, 840. Mayer's examination of the acid, 841. How to procure the acid free from filious earth, 842. Experiments for this purpose with an iron distilling vessel, 843. A salt containing fluor acid forms no crust by being mixed with sand, 844. But a great quantity with powdered glass, 845. Of the quantity of filious earth which fluor acid carries along with it, 847. Violent action of it upon glass, 848. Mr Wenzel's experiments on the fluor acid in a leaden retort, 850. This acid procurable by means of the acids of nitre, tea-falt, and potash, 850. Appearance and properties of it, 3d 850. Of its combination with fixed alkali, 4th 850. With volatile alkali, 851. With earths, 852. With metals, 853. Glass corroded by it and by the falt, produced by its combination with volatile alkali, 854. Great difficulty of preserving this acid, 855. Golden vessels, or a phial lined with oil and wax, recommended for this purpose, 856. Dr Priestley's method of converting the fluor acid into air, 857. Retreats his opinion of its being only the vitriolic acid altered, ib. Fluor acid cannot be expelled by that of arsenic, 934. Why it cannot diffuse flint directly, 1073. Why it decomposes liquor of flints, 1080. Is scarce capable of dissolving manganese, 1366. Explanation of its action on manganese, 1383.

Fluors: platinum and some of its calces fusible by their means, 1337. Fontaine's account of the specific gravity of different kinds of air, 375. An experiment of his confirming those of Mr Kirwan, 344.

Fusible alkali. See Minerals.

Fourcroy denies that platinum can be amalgamated with mercury, 1380. Incapacity in his account of its hardness, 1351.

Fragility of glass when not well annealed, 559.

France: of the method of making nitre there, 731.

Freezing: of the prodigious expansive power exerted by water during that act, 80.

French makes aurum fulminans explode without any heat, 1111.

Fulminating calx of silver made by Kunckel, 756. Fulminating copper, 1335. Fulminating gold, 1103. See Aurum fulminans. Fulminating silver made by M. Berthollet, 1138. How prepared, 1139. See Silver. Fulminating quicksilver, how prepared, 3d 955.

Fumes: nitrous and sulphurous effervescence with one another, 626. Gold not rendered brittle by the fumes of tin, 1093.

Furnaces, a portable one described, 600. Form of Boerhaave's portable furnace, ib. Another described, ib. Dr Lewis's portable furnaces, 601. Objection to their use in some cases, 602. Dr Black's furnace, 2d 602. How adapted to the various operations of chemistry, 603. Luting proper for it, 604. Method of applying the lute, 605. Melting furnace, 2d 605. Mr Pratt's melting furnace, 606. Why its cavity is made of a roundish form, 607. Lewis's lamp, 611. One constructed on the principles of Argand's lamps, ib.

Furnaces necessary for the operations of chemistry, 599, et seq. Directions for building them properly, 610.

Fusibility of metals increased by mixture, 542. Great fusibility of mixtures of tin and bismuth, 543. Increased by the addition of lead, ib.

Fusion: how to perform that operation in chemistry, 584. Difference between the watery and dry fusion, ib. Of the crucibles necessary for the fusion of chemical subjects, 585, et seq. See Crucibles. Fusion of all metals promoted by bismuth, 1251.

Garfytan, in Sweden: Rinnman's method of burning the aluminoous ore there, 668. Method of dissolving it, 670.

Galls, acid of, how separated from them, 1537. An acid liquor procured from them by distillation, 1538. Its properties, 1539.

Gallip juice of animals contains phosphoric acid, 901.

Geoffry's rule for determining the degrees of chemical attraction, 262. His table of affinities, 553. Investigates the constituent parts of alum, 641. His theory of Prussian blue, 1165.

Germany: method of making nitre in some parts of it, 730.

Glaucous: a kind of apathum ponderatum found in its neighbourhood, 1060.

Glass: method of engraving on it by means of fluor acid, 2d 857.

Glass vessels, when to be used by chemists, 556. Dr Black's remarks on the properties of glasses, 558. After's the filaceous crust observed on that acid on glasses, 848. Corroded by it and by the ammonical falt produced from it, 854. Bismuth convertible into glass, 1250. How to prepare glass of antimony, 1257. A beautiful blue glass produced by the calc of regulus of cobalt, 106.

Glass of lead: of the vessels most capable of resisting its action, 589.

Glass-making: Pliny's account of the origin of it, 7.

Glass, of the materials proper for making them, 580.

Glaucon's falt ammoniac prepared from vitriolic acid and volatile alkali, 633. See Ammoniac.

Glaucon's falt: Dr Croell's mistake concerning its preparation from alum and common falt, 272. Its decomposition by marine acid never complete, 291. Reason of this decomposition explained, 336. Quantity of ingredients in it, 431. Prepared from vitriolic acid and mineral alkali, 632. Dangerous consequences of making crystals of nitre for it, 743. Produced from the resin extracted from the refuse of aluminae, other, 2d 722.

Glauber's spirit of nitre, 734.

Gmelin, Dr, his experiments on the differences between the alkaline salts produced from different vegetables, 1029. On the ashes of different plants, 1059. Method of making dulcified spirit of falt, 1481.

Gold: why its solution is precipitated by green vitriol, 1225. But not by the dephlogisticated kind, 226. Why it is precipitated by foliure of tin, 247. Various precipitates of it, 233. Bisk of aqua regia for dissolving it, 491. Quantity of it taken up by aqua regia, 482. Its calces fusible in the vitriolic and nitrous acids, 483. Kirwan's opinion that it could not in any quantity be dissolved in the nitrous acid, 484. Dr Brandt's experiments showing that it may be in the vessels, 750. Lewis's observation on this experiment, ib. Solution of its calces in spirit of falt, 750. Sublimes along with the acid, ib. The sublimate said to be the material used for the blood of St Janarius, etc. Is not affected in any way by the arsenical acid, 941. Its nature and properties particularly treated of, 1089. Unites readily with all the metals, 1090. Its colour debased by all the metals except copper, ib. Said to lose its malleability remarkably with tin, 1091. Dr Lewis's account of the bad effects of this metal upon it, ib. Mr Alchorne's experiments in opposition, 1092. Gold not rendered brittle by the fumes of tin, 1093. Nor by the addition of the metal itself in small quantities, ib. Nor with the addition of copper, 1094. Malleability of gold entirely destroyed by a small quantity of regulus of arsenic, 1095. Surprising tenacity of its parts, 1096. Is not liable to rot, 1097. Mr Boyle's experiment to show its delustrificatory, 1098. Of its solution in aqua regia, 1099. This solution of a corrosive nature, 1100. May be crystallized, ib. Of the precipitation of the metal from it, 1101. Separated from other metals by green vitriol, 1102. Explodes with prodigious force in some cases, 1103—1125. See Aurum fulminans. Solution of gold by hepatic humus, 1127. Medical virtues of gold entirely imaginary, 1128. Solution in essential oils not permanent, 1128. Dissolved permanently in ether, and crystallizable by its means, 1129. Revived from its solution in aqua regia by mixing it with spirit of wine, ib. A method thus afforded of purifying it from other metals, ib. How to restore its colour when lost, 1130. Mercury fixed by amalgamation with gold, 1244. Whether it be possible to adulterate gold with platina, 1356. How to detect this fraud if it should be committed, 1357.

Golden calf: its dissolution adduced as an instance of Moses's skill in chemistry, 4.

Golden fuligin of antimony, how prepared, 1263.

Golden vessels recommended for keeping the fluor acid, 856.

Granulation of copper, how performed, 1148.

Gravity: the element of fire seems to be defective of it, 93. Of finding the specific gravity of the different metallic calces, 327. How to find the specific gravity of bodies, 371. Of the specific gravity of spirit of tartar, 377. How to find that of the ingredients in digestive falt, 380. Of the pure nitrous acid, 386. Of its mathematical specific gravity, 388. How to construct a table of the specific gravities of spirits of nitre of different strength, 390. How to find the specific gravity of pure vitriolic acid, 397. Of the acetic acid, 400. Of strong vinegar, 401. Of fixed air, 411. Of fixed vegetable alkali, 412. Mr Watson's account of the specific gravity of falt of tartar, 415. Dr Lewis's observations on the specific gravity of bell-metal and other metallic compounds, 1156. INDEX.

Green colour produced from verdigris and cream of tartar, 893.

Gunpowder: its explosive force vastly inferior to that of aurum fulminans, 1108.

Gypsum: proportion of ingredients in the natural kind, 459. Formed of the vitriolic acid and calcareous earth, 635. Some differences between the natural and artificial kinds, ib. Is soluble in some degree by acids, 636. Convertible into quicklime by a strong heat, ib. Poised by a very violent and sudden heat, and likewise by the addition of clay or calcareous earth, ib. Decomposed by fixed and mild volatile alkalies ib. And by the acid of arsenic, 933. Found in the concentrated vitriolic acid, 1059.

Hanover: method of making nitre there, 729.

Hafier: of the aluminium ores found in that country, 638.

Heat, two general theories of, 28. Lord Bacon's definition of it, 29. Mr Boyle's definition, 30. Sentiments of Sir Isaac Newton on the subject, 31. Fire or heat generally allowed to be an element per se, 32. Two other theories instituted, 33. In what they differ from the former, 34. General account of Dr Black's and Dr Lavoisier's theories, 35. Dr Irvine's theory explained by Dr Crawford, 36. Absolute heat defined, 37. Great quantity of heat produced by the condensation of vapour, 43, 125. Difference of the absolute heat of different fluids, 46. Thinest fluids contain the greatest quantity of it, 47. Crawford's account of ferrous heat, 49. Capacities for containing heat explained, 52. Crawford's opinion concerning heat in the abstract, 54. Dr Berkenhout's opinion of its nature, 56. Heat has a tendency to diffuse itself equally over all bodies, 60. Is contained in considerable quantities in all bodies, 61. Its quantity limited in all bodies, 64. Expansion an universal effect of heat, 65. Bodies of the same kind and of equal temperature contain quantities of heat proportional to their quantities of matter, 67. Equilibrium of heat defined, 75. Dr Crawford's method of determining the proportional degrees of heat, 77. His method insufficient, 78. Nicholson's account of the theories of heat, 79. Advantages of the doctrine that heat is caused by vibration, 80. Answer to Mr Nicholson's arguments, 81. Dr Clegg's proof that heat is occasioned by a fluid, 82. Difficulty arises from the supposition that heat diffuses itself equally, 84. Another from the seeming disappearance of heat, 85. Equal dilution of heat promoted by its absorption and evolution, 89. Heat of the torrid zone thus mitigated, 90. Heat most probably the addition of an omnipresent fluid, 92. Diffusion of heat occasioned by the action of the sun, 94. How heat is produced by his rays, 95. Connection between heat and electricity, 97. Heat in summer becomes electric fluid in winter, 99. Solution of the phenomena of heat, 102. Mr Kirwan's theorem for finding the point of total privation of heat, 114. Heat the cause of the softness of bodies, in proportion to fluidity, 115. Absorption of heat the universal cause of fluidity, 120. Heat produced in the burning of inflammable bodies comes from the air, 157. Too much phlogiston prevents the heat of burning bodies from being intense, 158. Why the solar heat and that of electricity are so intense, 165. Table of the various degrees of heat, 167. Heat produced during the diffusion of metals, 190. Heat and not phlogiston the cause of clarity, 209. Heat produced in solution most probably proceeds from the solvent liquor, 211. Argument in favour of the weight of precipitates being augmented by the matter of heat, 240. Experiments to determine the degree of decomposition from the degrees of heat produced by various mixtures, 277. Alteration of the density of acids by various degrees of heat, 283. Strong fluids more expanded by heat than weak and viscid, 444. Distillation of spirit of salt by various degrees of heat, 447. What metals are calcinable, and by what degrees of heat, 530. Violent explosions from the sudden application of heat, 722. Effects of heat on lapis ponderosus, 9. Mercury unalterable by being kept 15 years in a gentle heat, 1229.

Halls procure from flowers of zinc an oil capable of dissolving gold and silver leaf, 1444.

Hepar sulphuris formed by a combination of fixed alkalies and sulphur, 1921. May be made either in the moist or dry way, 1921. Patty decomposed by fixed air, ib. Entirely by acids, 1923. Effects of the inflammable vapours arising during its decomposition, ib. 1924. Its phlogiston very much dispersed to fly off, 1924. Diffuses very many metals, and charcoal, 1925. Solution of gold by its means, 1927. Its effects of it upon nickel, 1509.

Hydric air contains sulphur, 2102.

Herodotus Trismegistus, the same with Siphon, an Egyptian, the founder of chemistry, 5.

Higson, Mr., his experiments on human calculus, 1463, et seq. His observations on the nitrous acid, 1472. Method of obtaining it quite colourless, 1475. Discovers the true composition of volatile alkali, 1553.

Homburg's experiments on specific gravities compared with those of Kirwan, 392. Different results of them accorded for, 393, 399. An oil obtained by Homburg poised to come from the flowers of zinc, 1243. The mistake discovered by Neumann, 1243. How he discovered his pyrophorus, 1415. Best method of preparing it, 1416. See Pyrophorus, Discovers that marine acid corrodes glass, 1482.

House-painting: a yellow colour for that purpose, 696.

Januarius, St., a sublimate of marine acid and gold shown for his blood, 800.

Ice: a quantity of heat lost in the melting of it, 42.

Jelly, the mucilage of animal substances, 1454. All of them reducible to this by long boiling, ib. Is the only true animal substance, ib.

Forms a very strong cement, ib.

Ignited bodies all equally hot, 128.

Ignition an universal effect of fire, 130. Difference between ignition and inflammation, 132.

Ilex aquifolium: the growth of that plant a sign of alumaceous ores in the ground, 639.

Inflammable and vitriolic acid air obtained from solution of copper in vitriolic acid, 465, 471. Inflammable substances, their nature and properties, 516. Principles into which they are reduced by burning, ib. By distillation, 517.

Their phenomena with different acids, 518. Some singular productions, 519. Vitriolic acid combined with them, 712, et seq. Nitrous acid, 771, et seq. Marine acid, 824. An inflammable spirit extracted from sugar of lead, 578. Inflammable vapour arising from the decomposition of sugar fulminis, 1025. Volatile alkalies combined with them, 1035. Of their division and chemical properties, 1308, et seq.

Inflammable air: metallic calces reduced by it, 149. Removal of lead from minium by it, 324. Quantity of inflammable air produced from iron, 454. Why none is produced from the nitrous foliation of iron, 460. Charcoal entirely convertible into it, 1451.

Inflammable spirits produced from radical vinegar, 1344. Sulphurous inflammable vapours produced from it, 1345.

Inflammability difference between it and ignition, 152. Bodies decomposed but not destroyed by inflammation, ib., 153.

Ink: a fine synthetic one produced from fluid of cobalt in spirits of felt, 822. Another by means of volatile mixture of fulphur and saccharum lacteum, 1039. Blue five-pasteurian ink scented from cobalt, 822.

Indelible precipitate thrown down by caustic fixed alkali from solution of terra ponderosa, 1056.

Inundations prevented by the flowers with which congealed water melts, 88.

Iron: objection to the existence of phlogiston from the total consumption of dephlogisticated air in burning it, 152. Little phlogiston expelled from it by this means, 153. The objection inconclusive, 154. Thio-metal not reduced to a calx by burning in dephlogisticated air, 155. Water produced in the reduction of it by inflammable air, 156. Of its precipitates by different substances, 239. Is not an essential ingredient in platinum, 254.

Nor regulus of nickel, 255. Nor cobalt or manganese, 256. Why solutions of iron dissolve copper, 336. Iron and zinc the only metals dissolved by vitriolic acid, 337. Why copper and iron precipitate one another, 344. Increase of the attraction of calx of iron to phlogiston demonstrated, 342. Dephlogisticated solutions of iron precipitated by calcs of copper, 343. Why a saturated solution of silver can scarcely be precipitated by iron, 346. Of the precipitation of zinc and iron by one another, 347. Iron and nickel will fiercely precipitate one another, 359. Cobalt precipitated by iron, 362. A triple salt formed by iron, regulus of antimony, and marine acid, 366. Proportion of iron taken up by the vitriolic acid, 453. Why vitriolic acid is produced by dissolving iron in concentrated vitriolic acid, 455. Solution of the calcs of iron in vitriolic acid, 456. That of the dephlogisticated calces refuses to crystallize, 457. Proportion of iron dissolved in nitrous acid, 458. In the marine acid, 452. Calcs of iron affume a red colour when precipitated from their solution in the marine acid, 463. Produces green vitriol by combination with vitriolic acid, 696, 697. Precipitates spontaneously from the vitriolic acid, 698. Iron contained in the resin produced from the residuum of vitriolic ether, 24722. Cannot be dissolved by concentrated, though it will by diluted, nitrous acid, 759. Diffuses and produces inflammable air with marine acid, 805. Volatilized by this acid, 806. Its solution used in medicine, 807. Combined with acetic acid, 873. With acid of tartar, 895. With the acid of arsenic, 948. Its nature and properties particularly treated of, 1157. Has great tenacity of parts, 1158. Is a combustible substance, 1159. Is the only metal capable of being welded, 1160. Contracts in fusion, and expands again on becoming cold, 1151. Is dissolved by all metals except lead and mercury, 1162. Becomes brittle by being immersed for some time in that fluid, 1162. Can scarce be united to zinc, ib. Has a strong attraction for arsenic, ib. Is the basis of Prussian blue, 1163, et seq. See Prussian blue. Calx of iron soluble in lividum funginis, 1175. Neutral salts for discovering it in mineral waters, 1180. Precipitated by the colouring matter of Prussian blue from its solution by aerial acid, 1191. Nitre alkalized by it, 1206. Its filings take fire spontaneously with fulphur, 1207. Unites with platinum, 1347.

Iron liquor for printing cloth, how prepared, 875.

Irvine, Dr.: general account of his and Dr Black's theory of heat, 35. His theory explained by Dr Crawford, 36.

Italy: first alum-works set up there, 639. Juice, gastric, yields phosphoric acid, 904.

Keir, Mr., his objections to the doctrines of Mr Kirwan, 2d 510. His method of preparing an alkaline standard, 4th 510. Of finding the specific gravity of different liquors, 5th 510. His objections to the opinions concerning the identity of the vegetable acids, 1540.

Kermes mineral, how prepared, 1263.

Kelley, in Shropshire: a kind of spathum ponderofum found there, 1060.

Kilpatrick-bills, near Glasgow: spathum ponderofum found there, 1060.

Kirwan's opinion concerning fire, 68. His theorem for finding the point of total privation of heat, 114. His remarks on some experiments of Dr Priestley, 325. His experiments compared with those of Homburg, 392. Different results of their experiments accounted for, 393, 399. Kirwan's experiments confirmed by one of Pontana, 394. Differences with Mr Bergman and Lavoisier accounted for, 435. Is of opinion that gold cannot be dissolved in nitrous acid, 454. Mistake of Morveau concerning a superabundance of acid in alum accounted for, 642. Objections to his doctrine concerning the specific gravity, &c. of different substances, 2d 510, et seq. To his calculation of the quantity of phlogiston in sulphur, 6th 510.

Kunkel prepares a fulminating calx of silver, 756.

Lamp-furnace: Dr Lewis's described, 611. Is not capable of giving a greater heat than 450° of Fahrenheit, ib.

Language: specimen of a new chemical one, 552. Its strange appearance in attempting to account for the phenomenon of fulminating silver, 1144.

Leptis ponderofum considered as a metallic earth by Mr Bergman, 907. See Tungsten.

Latent heat: experiments by which Dr Black was led to the discovery of it, 41. (This heat cannot be measured, 73. Expansion of water in freezing explained by the theory of latent heat, 103. Air bubbles in ice produced by part of the latent heat of the water, 110. Vapour formed by the abstraction of heat into a latent state, 120.

Lavoisier denies the existence of phlogiston, 1375. His arguments drawn from the increased weight of metals by calcination, 138. His theory of inflammation, 139. The arguments from the reduction of the cost of perfect metals without addition, 141. Dispute between him and Priestley, 141. His differences with Kirwan accounted for, 435. Account of some of his experiments on the increased weight of metallic solutions, 525. Consequences deduced by him from these experiments, 526. Not well founded, 527. Account of the constituent parts of the nitrous acid, 1473. His new nomenclature, 1560.

Lead: quicksilver produced from it in certain cases, 12, 762. Water may be made sufficiently hot to melt lead, 131. Why the vitriolic acid cannot act upon it without a boiling heat, 197. Precipitates of lead, 237. Sea-salt decomposed in various ways by means of it, 302. In what cases solution of lead is precipitated by other metals, 309. The solution in marine acid decomposed by vitriolic salts, 310. Revival of lead from mercury by inflammable air, 324. Why it is useful in cupellation, 331. Precipitation of it by nickel, 360. Vessels capable of resisting the glats of lead, 589. Lead vessels most proper for the preparation of oil of vitriol, 627. Cannot be dissolved in the vitriolic acid, 702. A beautiful white for painting in water prepared from litharge, nitrous and vitriolic acids, 703. Diffolves and crystallizes with the nitrous acid, 767. This salt decomposes with great violence in the fire, 762. Becomes fluid like oil by repeated diffusions in aqua-vitae, 762. Combination of lead with marine acid, 811. Plumbum cornucii, 812. Combined with acetic acid, 874. White lead the result of this preparation, 875. Observations on the process for making it, 876. Sugar of lead prepared from acetic acid and white lead, 877. Inflammable spirit procured by distilling this salt, 878. Combination of lead with the acid of arsenic, 949. Great attraction between silver and lead, 1156. Cannot be united to iron, 1162. The metal particularly treated of, 1207, et seq. The least ductile and tenacious of all metals, 1208. Sheet-lead, how cast, 1209. Milled lead scarce to be preferred to this kind, 1210. Rendered famous by being cast into a certain shape, 1211. Of its calcination, 1212. Minium or red-lead, how prepared, 1213. Litharge, 1214. Phenomena with other metals, 1215. Remarkable way of uniting with copper and separating from it again, ib. Soluble in alkalies and oils, 1216. Of its union with platinum, 1348. Lemons, essential oil of, a species of tartar extracted from ferret sold under this name, 858. Dr Croll's method of crystallizing the acid of lemons, 997. This acid cannot be converted into acid of sugar, 999. Entirely dissolves manganese, 1375. Explanation of the action of the acids of tartar and lemons on manganese, 1352.

Legation, a chemical operation, how performed, 599. Reaumur's porcelain recommended for levigating crucibles, ib.

Lenoir, Dr., his observations on the making of crucibles, 590. His experiments on Reaumur's porcelain, 593, 594. Description of his portable furnaces, 601. Objection to their use in some cases, 602. His lamp-furnace described, 611. His experiment to show that clay undergoes some change by being converted into earth of alum, 619. His directions for making turpith mineral, 766. Experiments on the solubility of tin in the acetic acid, 880. His opinion concerning the earth of vegetables, 1088. His methods of amalgamating mercury with copper, 1153. His observations on the specific gravity of bell-metal and other compounds of the metallic kind, 1156. His observation on the cracking noise made by tin in bending, 1221. His detection of an erroneous process in which mercury was supposed to be converted into water, 1236. His method of reducing the flowers of zinc, 1242. His experiments on alloying platinum with other metals, 1338.

Ley, alkaline, why it is unfit for extracting the flowers of benzoin, 698.

Libricus, smoking liquor of, how prepared, 810.

Lichtenstein's experiments on the acid of benzoin, 1530.

Light: proofs of its identity with fire and electricity, 96. The effect of one universal fluid, 101. Characters curiously marked by the sun's light on a precipitate of silver by calcareous earth, 736.

Lime the most proper material for extracting the flowers of benzoin, 991. Crystalization of the acid of lemons prevented by the small left particle of lime, 998. Terra ponderosa convertible into a kind of lime capable of decomposing vitriolic salts, 1055. Dissolved by the colouring matter of Prussian blue, 1159. How prevented from sticking to the bottoms of distilling vessels, 1033.

Lime-water precipitated by the arsenical acid, 935.

Liquid phlogiston, how prepared, 1410.

Litharge prepared in the refining of silver with lead, 1214. Almost always contains some lead in a metallic state, ib. Bifluoride convertible into a substance of this kind, 1250.

Lithophoric acid. See Calomel, acid of.

Lixivium fanginis loses its colouring matter by exposure to the air, 1172. Calx of iron soluble in it, 1175.

Liver of arsenic formed of alkali and arsenic boiled together, 1276.

Lubbock, Dr., his theory of heat, &c., 142.

Luna cornua, why it cannot be reduced without oils by alkaline fats, 314. May be decomposed by mercury, 356. How prepared, 802. Its properties gave rise to the notion of malleable glass, 803. How reduced, 1134.

Lunar cauldle, how prepared, 752.

Lute, proper for lining furnaces, 605.

Luting for acid spirits, 577.

Maceration, in chemistry: how to perform that operation, 595.

Macleay's theory of Prussian blue, 1167. Supposes the fusion of calx of platinum by the methods recommended to be imperfect, 1354.

Magnesia combined with vitriolic acid, 957. Dissolved by the colouring matter of Prussian blue, 1187. Will not dissolve in acids after calcination without heat, 412. Its preparation and properties, 514. Combined with the nitrous acid, 749.

Maglery of bitumen, 766.

Manganese: how to deplogisticate spirit of salt by it for the decomposition of arsenic, 919. Combined with the arsenical acid, 956. Identity of vegetable acids proved from the solution of manganese by the nitrous acid with the addition of acid of sugar, 1011. From its solution by means of vitriolic acid and spirit of wine, 1114. Keeps the colouring matter of Prussian blue from rising, 1204. A new semi-metal afforded, 1359. Common manganese treated with vitriolic acid, 1360. Is entirely dissolved by phlogisticated vitriolic acid, 1361. Precipitate and crystals obtained from the solution, 1362. Dissolved by phlogisticated nitrous acid, 1365. Effects of it on spirit of salt, 1364. See Deplogisticated and Marine acid. Entirely dissolved by marise acid, 1365. Scarce soluble in fluor acid, 1366. Or in that of phosphorus, 1367. Partly dissolves in acid of tartrar, 1368. With difficulty in the acetic, 1369. Entirely dissolved by acid of lemons, 1370. And by water impregnated with fixed air, 1371. Has a strong attraction for phlogiston, 1372. Becomes white by saturation with it, 1373. Contains some phlogiston naturally, 1374. Becomes insoluble in pure acids by losing its phlogiston, 1375. Partial solutions of manganese explained on this principle, 1376. Its fl. own attraction for phlogiston when combined with acids, 1377. Why it is dissolved by the concentrated acid of vitriol without addition, 1378. Why the volatile sulphureous acid dissolves it, 1379. Explanation of the effects of nitrous acid upon it, 1380. Of those of tartrar and lemons, 1382. Of fluor acid, 1383. Pieces of manganese on nitre, 1384. Experiments of manganese united with phlogiston, 1385, et seq. By distillation for 16, 1386. Boiled with oil-olive, 1387. By distillation with charcoal, 1388. With sulphur, 1389. By calcination with nitre, 1390. With the addition of arsenic, 1391. By distillation with sal-ammoniac, 1392. By digestion with pure nitrous acid, 1393. Deliquescent volatile alkaline by attracting its phlogiston, 1394. Effects of distilling it with arsenic, 1395. With cinambar, 1396. With corrosive sublimate, 1397. Used for the rectification of ether, 1471.

Margrave's analysis of all the different INDEX.

Chemistry.

Priesley's observations on marine acid, 785. How procured by means of the vitriolic, 786. Why its distillation with copperas does not succeed, 787. To procure marine acid by means of the nitrous, 788. By distilling common salt per se, 989. Marine acid dephtilicated by that of nitre, or by manganic, 790. Mr Scheele's method of dephtilicating it by manganic, 791. Properties of it when dephtilicated, 792. Marine acid combined with alkaline felses, 793. With vegetable fixed alkali, 794. With mineral alkali, 795. Volatile alkali, 795, 796. Combined with earths, 797. With metallic substances, 799. Dissolves and volatilizes the calx of gold, ib. With silver, 801. Dissolves the red silver ore, ib. Forms luna cornea with this metal, 802, 803. With copper, 804. With iron, 805. Volatilizes this metal, 806. The solution of iron in this acid used in medicine, 807. Sublimate of iron, and ful ammoniac named flores mortuiae, 808. Solution of tin, 809. Of great use in dyeing, ib. Volatilizes the metal, and forms with it the smoking liquor of Labinus, 810. With lead, 811. Forms with it plumbum cornueum, 812. With quicksilver, 813. Forms with it corrosive sublimate, 814, &c. See Corrosive. Volatilizes zinc, 820. With regulus of antimony, 821. See Butter. Forms a fine sympathetic ink with regulus of cobalt, 822. Combined with inflammable substances, 824. Marine ether, 824. Of its attraction for phlogiston, 825. Is not the same with fluor acid, 835. Expels the fluor acid, ad 850. Purifies fats of amber, 911. Phenomena on diffusing vitriolic fats in marine acid, 1041. On mixing them with solutions of calcareous earth in marine acid, 1042. Of the solution of terra ponderosa in it, 1053. Is not necessary for the preparation of aurum fulminans, 1117. Solution of cobalt in marine acid, 1302. Effects of manganese upon it, 1364. Existence of phlogiston in it proved, 1381. Can scarcely unite with butter of arsenic, 1282. Dephtilicated marine acid the only solvent of platinum, 1319. Used for distillation of spirit of nitre, 737. Various methods of making marine ether, 824. Method of distilling the acid with clay, 1480. Effect of it upon phlogistic matters, 1481. Glass corroded by it, 1482. Cause of its yellow colour, 1483. Effect of the dephtilicated acid upon phlogistic matters, 1485. How to make marine ether from the dephtilicated acid, 1486.

Marble, chemical, treated of, 551.

Marinum metallicum, Withering's experiments on it, 1060. Diffuses in concentrated vitriolic acid, 1063. Precipitated from it unchanged by vegetable fixed alkali, 1064. May be decomposed in the dry way by salt of tartar, 1065.

Martial vitriol, procured by precipitating copper with iron, less fit for dyeing than the common, 344.

Marrow analysed, 1430.

Mathematical specific gravity explained, 373. The mathematical specific gravity of spirit of nitre determined, 388.

Mayer's examination of the fluor acid, 841, &c.

Melting furnace described, 2d 605, &c. See Furnace.

Menstruum, a quantity of it retained by some precipitates, 251.

Menstruum fine firepuit, a liquor for dissolving gold, 1119.

Mercurius dulcis, how prepared from corrosive sublimate, 814, 819. Preparation of it in the millet way, 1238.

Mercurius precipitatus per se, how prepared, 1228.

Mercurius Trifugillius, the same with Hermes or Sophas, an Egyptian, the founder of chemistry, 3.

Mercury, of its precipitates, 236. Its solution in nitrous acid decomposed by vitriolic fats, 311. Vitriol of mercury decomposed by marine acid, 313. Why corrosive mercury is precipitated by oil of vitriol, 315. Examination of Dr Priestley's experiment concerning the revival of mercury, 322. Why so much of the metal was revived in the Doctor's experiments, 323. Why copper is dissolved by solution of mercury, 336. Precipitations of mercury by copper, 335. Why mercury and silver precipitate one another from the nitrous acid, 355. Corrosive sublimate cannot be decomposed by silver though mercury can decompose luna cornua, 356. Why precipitates of mercury and alum contain part of the acid, 408. Of mercury divided in vitriolic acid, 485, 704. See Quicksilver. Copper, how amalgamated with mercury, 1152. Dr Lewis's methods, 1153. A curious amalgam with veg. digests, ib. Cannot be united with iron, 1162. May be separated from its solution in nitrous acid by the colouring matter of Prussian blue, 1205. Use of the amalgam of mercury and tin, 1223. The metal particularly deficient, 1225. Is less heavy in winter than in summer, ib. How purified, 1226. Curious mercuries prepared by Mr Boyle, 1247. Is calcined into a red powder, by being exposed to a considerable degree of heat, and to the air at the same time, 1228. Is unalterable by a gentle heat, or by repeated distillations, 1229, 1230. Explosion by its vapours, 1231. Amalgamated with different substances, 1232. Separation of the amalgamated metal, 1233. Becomes fixed by amalgamation with gold, 1234. Supposed to be convertible into water, 1235. The mistake detected by Dr Lewis, 1236. How to amalgamate it with regulus of antimony, 1237. Can scarcely be united with platinum, 1345. Will leave platinum to unite with gold, 1346.

Metallic calces, of their various colours, 192. Metallic solutions contain a calx of the metal with various degrees of phlogiston, 214. Phlogiston the cause of their colour, 218. Some metallic fats decompose others, 224. Advantages to be derived from the examination of metallic precipitates, 253. Metallic fats insoluble in water without an excess of acid, 297. Of the attraction of metallic calces to phlogiston, 326. Of finding their specific gravity, 317. Table of the proportional affinities of metallic calces to phlogiston, 329. They can never be totally dephtilicated by acids, 407. Of their general properties, 519. Are soluble in acids, 520. Composed of an earth and phlogiston, 521. Their calcination and revivification, 522. Increase of weight by acids, 523. Reason of the increase of weight in metallic calces, 524. Combinations of them with acids. See Acid and Metals. Lapis ponderosus supposed by Mr Bergman to be a metallic earth, 967. Why he supposed the acids of molybdana and tungsten to be metallic earths, 973. Chemical properties of the different metallic substances investigated, 1089, &c. Effects of the colouring matter of Prussian blue on metallic calces, 1192. Its effects on metallic solutions, 1193.

Metals may receive a vast quantity of heat more than is sufficient to bring them into a state of fusion, 129. The cases of the perfect ones reducible without addition, a proof of the nonexistence of phlogiston, 140. Why they weigh less in their metallic than in their calcined state, 130. Combine with acids, 176. Separate from them again on the addition of earths or alkaline fats, 177. Phenomena attending their solution in acids, 180. Of their different degrees of solubility, 183. Their solution attended with effervescence, 188. And heat, 190. Yield little air after they have been calcined, 191. Why marine acids act on some of them and not on others, 198. Why some metals are more soluble than others, 197. Their fusions contain a calx of the dissolved metal, 214. Reasons for believing that this calcination takes place, 215. Why the calces of the perfect metals may be reduced without addition, 216. Phenomena attending the precipitation of metals by alkaline fats, 220. Their precipitation on one another owing to a double elective attraction, 229. Variations in the order in which they precipitate one another, 230. They contain different quantities of phlogiston, 238. Difficulties in determining the attractive powers of the metals to acids, 296. Quantities of the different metals taken up by acids, 298. Metals have a greater affinity than alkalies with the acids, 299. Why alkalies precipitate the metals, 300. Why th the metallic earths seldom decompose salts having an earth or alkali for their basis. 304. Explanation of the table of affinities of the acids to the different metals, 316. Of the quantity of phlogiston contained in the different metals, 317. Quantity of it lost by metals during calcination, 331. Why the metals are more dephlogisticated by mutual precipitation than by direct solution, 335. All of them dissolved by nitric acid, 338. In what cases the marine acid can dissolve metals, and when it cannot, 340. Mr Kirwan's experiments on metals, 451. Best method of dissolving them, 452. What metals are calcinable, and with what degrees of heat, 530. Of their fusibility, 541. Their fusibility increased by mixtures, 542. Their solubility increased by calcination, 545. Effects of sulphur on them, 546. Of their division into metals and fementals, 547. Their good and bad qualities as materials for chemical vessels, 560. Vitriolic tal ammonia erroneously supposed to be a great solvent of metals, 634. Effects of vitriolic acid on metals, 691, et seq. Of the nitrous acid, 750. Of the marine acid, 799. Of the fluor acid, 853. Of the acerous, 872. Of the acid of tartar, 894. Of the acid of sugar, 901. Of the phosphoric acid, 906. Of the acid of amber, 915. Acid of molybdæna has no sign of any metal, 964. Metals dissolved by hepar fuliginis, 1025. Combination of volatile alkali with metals, 1034. Their properties particularly treated of, 1090. The fusion of all metals promoted by bismuth, 1231. Of the effects of white arsenic on them, 1277. Effects of regulus of arsenic on other metals, 1283. Combination of metals with sulphur, 1403. Effects of phosphorus on them, 1413. Microscopic salts, how prepared from urine, 1505. Mr Margraaf's experiments on it, 606.

Alkali, of the acids, 974. Acquires its greatest acidity by standing a fortnight, ib. Scheele's method of procuring the pure acid of milk, 976. Properties of this acid, 977. It seems to be of the acerous kind, 978. Milk is capable of complete fermentation, 979. How to procure the acid of sugar of milk, 980. Milled lead; the advantages of using it in preference to sheet-lead precarious, 1270.

Mineral spirits; how to crystallize it, 1515.

Minium, of the revival of lead from it by inflammable air, 324. How to prepare it from the metal, 1115.

Mineral alkali, why preferred as a precipitant by Mr Bergman, 231. Precipitates platinum imperfectly, 234. An equal quantity of all the mineral acids taken up by vegetable fixed alkali. See Acids. How to prepare the mineral alkali for experiments on the precipitation of metals, 429. Quantity of it taken up by the dephlogisticated nitrous acid, 532. Excess of acid in aluminium leys cannot be removed by mineral alkali, 630. Of its combinations with the different acids. See Acids. Marine, Vitriolic, &c. Difference between it and the vegetable alkali, 1019. Whether mineral alkali can separate platinum from its solvent, 1349. Fifty-five times as much of it required to precipitate this metal as of vegetable alkali, 1329.

Mineral acids. See Acids.

Mineral waters; Mr Wulfe's test for them, 1557. See Waters.

Mispickel, a natural regulus of arsenic, 1286.

Mixtures; the attractive powers of acids determined by the various degrees of heat excited by them, 277. Increased density of mixtures accounted for, 374. Time required by mineral acids and water to acquire their utmost density, 432. Phenomena resulting from mixtures of the different acids, alkalies, and neutral salts, with one another, 1040, et seq.

Molybdæna, acid of, examined, 957. How to reduce the substance to powder, 958. Effects of the acid of arsenic on it, 919. Violent action of the concentrated nitrous acid upon this substance, 960. Acid of molybdæna procurable by fire alone, 961. Its chemical properties, 962. Is capable of uniting with phlogiston, 963. Shows no sign of containing any metal, 964. Properties of the acid obtained by nitre, 965. Molybdæna decomposed by uniting its acid with sulphur, 966. Differences between the acids of tungsten and molybdæna, 971. M. Pelletier's experiments on this acid, 1497. Monet's opinions concerning the fluor acid, 833. Shown to be erroneous by Mr Scheele, 834. Mistake of Mr Monet concerning the basis of fluor spar, 838.

Monet's mistake concerning the preparation of Glauber's salt from alum detected by Mr Kirwan, 642.

Molybdæna supposed to be well skilled in chemistry, 4.

Mulchage of vegetables considered, 1452. Of animals the same with jelly or glue, 1454.

Marine. See Marine.

Naphtha, a fine kind of mineral oil described, 1442.

Neumann's observations on the preparation of the magritery of bismuth, 766.

Neutral salts composed of an acid and alkali, 172. One for discovering iron in mineral waters, 1180. Platinum may be partly precipitated by some neutral salts, 1331.

Newton, Sir Isaac, his sentiments concerning heat, 31.

Nicholson's account of the theories of heat, 79. Answer to his argument concerning vibration as the cause of heat, 81. His account of the capacities of bodies for containing heat, &c., 113.

Nickel, a kind of fementinal, of its solution and precipitation, 242. Is precipitated by zinc, 358. Iron and nickel will scarcely precipitate one another, 359. Nickel precipitates copper, lead, and bismuth, 360. Throws down homogeneous matter from cobalt, 393. Of its solution in vitriolic acid, 493. In the nitrous acid, 770. Effects of acid of a fentic tincture, 955. The fementinal particularly treated of, 1360. Discovered by Mr Cronstedt, ib. Effects of calcination with violent heat upon it, 1367. Of sulphur and borax, 1308. Of copper fuliginis, 1309. Of nitre, 1316. This salt separates all the cobalts in the fementinal, 1311. Effects of acid ammonia upon it, 1312. Of nitrous acid, 1313. Of volatile alkali, 1314. Nickel cannot be obtained in a state of purity, 1315. Bergman's opinion of its composition, 1316. Experiments to compose it artificially, 1317.

Nitre; quantity of acid, water, and alkali in it, determined, 391. Why it is so much lighter than vitriolated tartar, 416. The ingredients of which it is composed, 420. Of the preparation of nitre, 724, et seq. Discovered in some places in Podolia in Poland, 725. In Spain and America, 726. Requires for its formation, 727. Cramer's artificial composition for making it, 728. How prepared in Hanover, 729. In other parts of Germany, 730. In France, 731. Dr Black's conclusion concerning its nature, 732. Supposed to be the last effect of putrefaction, 733. How to procure the spirit of nitre by means of vitriolic acid, 735. Of its rectification, 736. Different methods of distilling, 737. Its uses, 738. Prepared from the nitrous acid and vegetable fixed alkali, 740. Cubic nitre formed from this acid and mineral alkali, 741. Enumeration of its properties and uses, 742, 743. Danger of swallowing large quantities of it, ib. Is purified by throwing a little sulphur on its surface while melted, 744. Calcinated nitre, 747. How allayed by charcoal, 779. Clyffus of nitre, 780. Its acid expelled by that of phosphorus, 907. And by that of amber, 910. And by the acid of arsenic, 930. Properties of the acid of molybdæna obtained by nitre, 965. Alkalized by iron, 1206. And by the flowers of zinc, 1249. Effects of regulus of arsenic on nitre, 1290. Effects of it on cobalt, 1303. On nickel, 1310. Is capable of separating all the cobalts from nickel, 1311. Effects of manganese on nitre, 1384. Of phlogisticated manganese upon it, 1390. M. Berthollet's new salt resembling it, ad 793. Method of making it in quantity, 1387. Generated in some cases without putrefaction, 1478.

Nitrous acid, the most violent of any in its operations, 181. Renders the calces of metals almost infusible, 196. Why it precipitates a solution of tin or antimony, 400. Is more obviously changed than vitriolic by the addition of phlogiston, 203. Vitriolic salts decomposed by it, 275. Contains less fire than the vitriolic acid, 278. On the expulsion of it by the vitriolic acid, 280. By a small quantity of dilute vitriolic acid, 281. Receives fire from the vitriolic during its expulsion, 284. Of the decomposition of vitriolated tartar by it, 285. Vitriolated tartar cannot be decomposed by dilute nitrous acid, 287. Nitrous salts decomposed by marine acid, 292. Marine salts by the nitrous acid, 293. Nitrous acid attracts silver more than fixed alkali, 301. Nitrous solutions of mercury decomposed by vitriolic fats, 311. Nitrous acid dissolves all metals, though it has lost affinity with them than the vitriolic or marine, 338. Why mercury and silver precipitate one another from the nitrous acid, 355. Regulus of arsenic precipitated by bismuth from the nitrous acid, 369. This acid, when pure, cannot be made to exist in an aerial form, 385. To find the specific gravity of pure nitrous acid, 386. Quantity of mineral alkali taken up by dephlogisticated nitrous acid, 432. Quantity of ingredients in nitrous fementines, 440. In nitrous Epform, 444. Orpiment earth of alum taken up by it, 449. Of iron dissolved by it, 458. Quantity of nitrous air obtained from this solution, 459. Nitrous acid cannot act upon iron in such a dilute state as the vitriolic, 461. Of copper dissolved by the nitrous acid, 468. Tin dissolved by it, 472. Of lead dissolved by nitrous acid, 476. Silver with nitrous acid, 479. Calces of gold soluble by it, 483. Cannot dissolve gold according to Mr Kirwan, 484. Zinc with nitrous acid, 488. Lead metal dissolved by concentrated than by diluted nitrous acid, 489. Effects of this acid on nickel, 494. On regulus of antimony, 500. On regulus of arsenic, 503. Effervescence between nitrous and sulphurous fumes, 626. Experiment relating to the conversion of the vitriolic into the nitrous acid, 720. Inconclusive, 721. Of its origin, ad 722. Attraction for phlogiston, its distinguishing characteristic, 734. How to extract it by means of the vitriolic, 735. How to purify it from any vitriolic taint, 736. Of distilling it with different substances containing the vitriolic acid, 737. Of its uses, and the method of distilling it in the large way, 738. Procured of a blue colour by means of arsenic, 739. Of its combination with alkaline salts, 740. Forms common nitre with the vegetable alkali, ib. Cubic nitre with the mineral, 741. Nitrous ammoniac with volatile alkali, 745. Of its combination with earths, 747. Forms calcareous nitre with quicklime or chalk, 747. Is decomposed by quicklime, 748. Forms Baldwin's phosphorus with it, INDEX.

629

it, 749. Produces affluing compounds with earth of alum, and purgative ones with magnesia, ib. Of its combination with metals, 750. Is capable of diffusing gold in some cases, 753. Dissolves and crystallizes with silver, 751. Forms lunar caustic with it, 752. Dissolves and crystallizes with copper, 757. Corrodes, and acts violently upon iron, but scarcely dissolves it, 759. Dissolves tin in very small quantity, 760. Forms a violently deprecitating salt with lead, 761. Dissolves quicksilver in great quantity, 763. Purified by distillation from this metal, from vitriolic or marine acids, 764. Readily dissolves bismuth, 765, and zinc, 767. Corrodes regulus of antimony, 768. Dissolves cobalt, nickel, and arsenic, 769, 770. Affords a method of discovering cobalt in ores, 770. Thickens expressed oils, 771. Forms ether with spirit of wine, 773, et seq. Of its decomposition by phlogiston, 778. Takes fire with fine olefiant oils, ib. How to procure marine acid by its means, 788. Dephlogisticates this acid, 790. Fluor acid procured by its means, 2d 850. Effects of it on salt of amber, 912. Arsenic decomposed by it, 918. Violent action of it on molybdena, 960. Effects of dissolving vitriolic salts in it, 1040, 1042. Forms fine crystals with terra ponderosa, 1066. Is not necessary for the preparation of aurum fulminans, 1117. Effects of it on arsenic mineralized by sulphur, 1250. Regulus of cobalt combined with it, 1301. Its effects on nickel, 1313. Explanation of its effects on manganese, 1380. Of digesting phlogisticated manganese with pure nitrous acid, 1393. Camphor decomposed by it, 1424. Precurable by means of spirit of salt, 737. How to procure the dephtogisticated kind, 1738, 1745. Lavoisier's account of the constituent parts of nitrous acid, 1473. Mr Caven- dith's account, 1474. How to set charcoal on fire by means of it, 1476. Remarkable effects of it on blood, 1477. Mr Scheele's experiments with it on various substances, 1513. Volatile alkali prepared from nitrous acid and tin, 1553.

Some late experiments of Dr Priestley have shown, that though nitrous acid is produced from the decomposition of phlogisticated and phlogisticated air, by taking the electric spark in the mixture, it is likewise produced by the more rapid decomposition of combustion, when inflammable air is made use of instead of the phlogisticated kind. In this case, though phlogisticated air should happen to exist in the mixture, it is not in the least affected by the process, but remains after the combustion of the others just as it was; nay, the Doctor observes, that by the addition of phlogisticated air, the quantity of nitrous acid produced is so far from being augmented, that it is much diminished. The acid in these processes always appears to be extremely volatile, inasmuch the fumes part of it constantly escape. No liquor at all was condensed when the explosions were made in quick succession, even though the vessel never became hotter than the hand. In another process, the atmospheric air was perfectly excluded, while the purest phlogisticated air was produced from one of the materials employed, viz. precipitate per se. In this experiment he found, that a considerable quantity of fixed air was produced, and that the water became acid by the absorption of it. He concludes, therefore, on the whole, that a mixture of phlogisticated and inflammable air always produces an acid by combustion; but that, when they are in their nascent state, the aerial acid is generated; when both are completely formed previous to the experiment, the nitrous acid appears.

Nitrous air: Why it does not unite with water, 204. Quantity of it produced by solution of iron in nitrous acid, 459. Quantity of phlogiston contained in it, 505.

Objects of chemistry, how distinguished from the agents, 12. How clasped, 163.

Oil of vitriol precipitates corrosive sublimate from water, and why, 315. Kirwan's experiments on it, 395. Why the dilution of it is necessary in these experiments, 396. Quantity of fixed air in oil of tartar, 414. Why oil of vitriol and iron produce vitriolic air, 455. Combination of oil of vitriol with common oil, 712. Oil of arlene, how prepared, 823. Effects of oil of vitriol on salt of amber, 913. Effects of mixing oil of turpentine with arlene acid, 943. Oil of vitriol by distillation with the salt composed of alkali and the colouring matter of Prussian blue, 1191. Oil supposed by Homberg to be obtained from flowers of zinc, 1243. The mistake discovered by Neumann, ib. Another capable of dissolving gold and silver leaf by Mr Hellor, 1244. Effects of oil-olive on manganese, 1387. Camphor soluble in oil, 1425. Quantity of essential oil obtained from turpentine, 1437. This oil very difficult of solution, 1438.

Oils expressed, thickened by nitrous acid, 771. Essential, fixed by spirit of nitre, 778. Fixed alkalies combined with expressed oils, 1026. With essential oils, 1037. Lead soluble in oils, 1216. Of the combination of phosphorus with essential oils, 1412. Chemical properties of oils treated of, 1419, et seq. Essential oils, ib. Empyreumatic oils, 1420. How to purify rancid oils, 1431.

Operations in chemistry described, with directions how to perform them, 554, et seq.

Ores: Bergman's account of the aluminous ores in Sweden, 654.

Alum, sulphur, and vitriol, extracted from the same, 659. How to discover cobalt in ores by means of the nitrous acid, 770.

Orpiment formed of sulphur and arsenic, 1279.

Oyster-balls, of their phosphoric quality, 1087.

Papin's digester described, 567.

Paracelsus, account of him, 14. History of chemistry since his time, 15.

Peat analysed, 1440.

Pelletier, M. his method of rectifying ether, 1471. His experiments on molybdena, 1497.

Pelican, an obsolete chemical vessel described, 566.

Pentland Hills, marmor metallicum found near them, 1060.

Perfect metals. See Metals.

Perovian bismuth, yields acid of benzoin, 1532.

Petroleum, or rock oil, account of it, 1443.

Phlogisticated ammonia, composed of vitriolic acid and volatile alkali, 633.

Phlogisticated matters: effect of marine acid upon them, 1481.

Phlogisticated alkali, quantity of precipitate obtained from manganese by it, 257. Phlogisticated air an ingredient in the nitrous acid, 24722. How prepared, 1023. Losses its alkaline properties, 1168. Cannot precipitate a-lime except from marine acid, 1273. Phlogisticated nitrous acid dissolves manganese, 1323.

Phlogiston: Of its existence, 27, 136. Denied by M. Lavoisier, 137. Arguments against it from the increased weight of metals by calcination, 138. From the reduction of the calces of perfect metals without addition, 140. The disputes on this subject must now be entirely decided, 143. Objections from its invisibility and supposed want of gravity, 144. Common charcoal and phlogiston the same, 145. Decisive proofs of its identity from Priestley's experiments, 146. Too much phlogiston prevents the heat of a fire from being intense, 158. Solution sometimes promoted by abstracting part of the phlogiston, 186. But totally prevented by taking away too much, as exemplified in manganese, 187. Hindered by too great a quantity of phlogiston, 194. Is the cause of colour in metallic solutions, 218. Attraction of phlogiston supposed to be the cause of causticity, 219. Metals contain different quantities of it, 258. Of the phlogiston contained in the different metals, 317. Method of calculating this quantity exemplified in regulus of arlene, 318. Table of the quantities of phlogiston in different metals, 319. Of the attraction of metallic calces to phlogiston, 320. Whence their various degrees of affinity to phlogiston may be determined, 328. Table of their proportional affinities to phlogiston, 329. Quantity of it lost by them during calcina-

tion, 331. Their affinity to the deficient part of their phlogiston, 334. Increase of the attraction of the calx of iron to phlogiston demonstrated, 342. Quantity of phlogiston contained in nitrous air, 355. In fixed air, 2d 305. In vitriolic acid air, 506. In sulphur, 507. In marine acid air, 509. Attraction of marine acid for phlogiston, 825. Union of phlogiston with acid of molybdena, 963. Is remarkably disposed to fly off from hepatic fulphuris, 1024. Combined with fixed alkalies, 1028. Supposed to exist in the colouring matter of Prussian blue, 1196. Is strongly attracted by manganese, 1372. Gives a white colour to manganese, 1373. Some phlogiston naturally contained in this substance, 1374. Proof of its existence in the muriatic acid, 1381. Sulphur decomposed by a superabundance of phlogiston, 1401.

Phosphoric acid, found in the residuum of ether, 2d 722. Expels that of fluor, 2d 850. This acid particularly treated of, 904, et seq. Expels the acids of vitriolated tartar, nitre, and fer-fusil, 907. Can scarcely dissolve manganese, 1367. Of phosphoric earth, 1081, et seq. Surprising phosphoric quality of other fluids, 1087. By whom discovered, 904. Found in vast quantities in the mineral kingdom, ib. In vegetables and the galvic juice of animals, ib.

Phosphoric liquor, curious one from a-fenic and vinegar, 2d 957, 1521.

Phosphorus of Baldwin prepared from nitrous acid and calcareous earth, 749. Phosphorus scintillans, of marine acid and calcareous earth, 797. Bolognian phosphorus, 1081. How rendered luminous, 1082. Analyzed, 1083. Phosphorus of urine, 1406. Mr Margraff's process for making it, 1407. Rectification of this phosphorus, 1408. The process for making it sometimes dangerous, 1409. Liquid phosphorus, how prepared, 1410. Experiments with phosphorus on fish of wine, 1411. With essential oils and acids, 1412. Mr Margraff's experiments with it on metals, 1413. Canton's phosphorus, 414. Hauy's phosphorus, 1415, et seq. See also Phosphorus.

M. Pelletier has now discovered a method of uniting phosphorus, without any decomposition, with all the metals, though he cautions against the danger with which the process is attended. Gold is phosphorated by mixing half an ounce of its calx with an ounce of phosphoric glass and about a grain of powdered charcoal; the whole is then put into a crucible, the composition covered with a little powdered charcoal, and a degree of heat sufficient to fuse the gold applied. A great many phosphoric vapours arise, but part are retained and unite with the gold which is left at the bottom of the crucible. The metal by this operation loses its colour, becomes whitish, breaks under the hammer, and has a crystalline appearance.

appearance. By continuing the fire a long time the phosphorus would be entirely distillated. The quantity of phosphoric glaas and charcoal just mentioned is sufficient to phosphorate a whole ounce of platinum. By an hour's calcination in a crucible, the metal is converted into a blackish mass resembling glass, weighing upwards of an ounce, and of which the lower part consists of cubical crystals. Notwithstanding this change, however, the quantity of phosphorus united with the platinum is very inconsiderable; for from 12 ounces of the metal, and as much phosphoric glaas, only 12 ounces and five grains of the phosphorated metallic mass was obtained. It was very brittle, but of considerable hardness; was not attracted by the magnet, and by exposure to a strong fire parted with the phosphorus it had been combined with. He observes, that all the metals lose their malleability by combination with phosphorus, excepting tin and lead; and the refusium of the matter which has once phosphorated a metal, will serve again for the same purpose.

The salt formed by a combination of the phosphoric acid with mineral alkali is found to be an useful purgative, and as such is now brought into practice.

M. de Struve and Marquet are said to have discovered, that the gastric juice of animals is composed of the phosphoric acid and volatile alkali; and Mr. Struve has composed a liquid from these two ingredients which acts in a similar manner on alimentary matters.

Phosphorus analysed, 1447.

Platinum not partly composed of iron, 254. An excellent material for chemical vessels, 87. Mr. Achard's method of making crucibles of the calx, 587. Effects of acid of arsenic upon it, 943. Is the heaviest of all metals, 1318. Insoluble except by dephtogliatified marine acid, 1319. Found in small grains, 1320. Bergman's experiments on it, 1321. Crystals of it can be decomposed by the mineral, but not the vegetable fixed alkali, 1322. Soluble in aqua regia made with nitrous acid and lead-salt, 1323. In one made of nitre and spirit of salt, 1324. Solution of the calx in marine acid lets fall a crystalline powder on the addition of vegetable alkali, 1325. But not the nitrous solution, 1326. This precipitate a kind of triple salt, 1327. Whether mineral alkali can separate platinum from its solvent, 1328. Fifty-five times as much mineral alkali as of vegetable requisite for the precipitation, 1329. Effects of the volatile alkali on the solution, 1330. The metal partly precipitable by neutral salts, 1331. Triple salts formed by this metal, 1332. Platinum the most insoluble substance in the world, 1333. First melted by a burning mirror, 1334. May be vitrified by electric fire, 1335. Its precipitate fusible in a common forge, 1336. This precipitate, or even crude platinum, fusible by the affluence of fluxes, 1337. Alloyed by Dr. Lewis with other metals, 1338. With gold, 1339. With silver, 1340. Copper considerably improved by union with it, 1341. It unites most readily with zinc, 1342. And with the compound metals, 1343. The compound of brass and platinum a proper material for juggling, 1344. It can scarcely be united with mercury, 1345. Is defeated by mercury when gold is added, 1346. May be united with forged and cast iron, 1347. And with tin, lead, or bismuth, 1348. May be melted by means of arsenic, 1349. The possibility of uniting it with mercury denied by Fourcroy, 1350. Insufficiency in his account of its hardness, 1351. Precipitate of platinum vitrified by M. Beaumé, 1352. The precipitate by sal ammoniac fusible in a strong forge heat, 1353. This fusion supposed by Macquer not to be perfect, 1354. Attempts to purify platinum by cupellation, 1355. Of the possibility of adulterating gold with it, 1356. Methods of detecting this fraud if it should be practised, 1357. Platinum most easily discoverable by its great specific gravity, 1358.

Pigging's account of the origin of glazing, 7.

Plumbum: cornuform formed of marine acid and lead, 812.

Petrila, in Poland: nitre found in the earth in that country, 725.

Polar regions: the excessive cold of winter, how mitigated, 98.

Poland: see Petrila.

Pomeron's fp: formed of terra ponderosa and vitriolic or aerial acid, 1051. See Terra ponderosa. Analysis and properties of the aerated kind, 1057.

Portable furnaces, 600, et seq. See Furnaces.

Poveshell's vessels of use in chemistry, 503, 504. Reaumur's porcelain recommended, 592. Dr. Lewis's experiments upon it, 593.

Pot directions concerning crucibles, 588. His melting furnace described, 606. See Furnace. His observations on the composition of nitrous acid by quicklime, 748. His experiments on the fate of amber, 749.

Precipitates, insoluble, thrown down by caustic alkali from solution of terra ponderosa, 1556. Phenomena on distilling metallic precipitates thrown down by Prussian alkali, 1168. Precipitate of platinum vitrified by M. Beaumé, 1352.

Precipitates, why 6 times thrown down by acids, 221. By the perfect neutral salts, 222. By a triple combination, 223. Various precipitates of gold, 535. Of the cause of such great variations in the weights of precipitates, 228. Arguments in favour of the weight of precipitates being augmented by the matter of heat, 249. A quantity of the menstruum retained by some precipitates, 251.

Table of different ones, 259. Why those of mercury and alum contain part of the acid, 408.

Precipitation: phenomena attending that of metals by alkaline salts, 220. Their precipitation by one another owing to a double elective attraction, 239. Use of the tables and calculations for knowing a priori the phenomena of precipitation, 333. Why mutual precipitation dehlogliatifies the metals more than direct solution, 335. Precipitations by lead, 352. Of mercury by copper, 353. Of nickel by zinc, 358. Of copper, lead, and bismuth, by nickel, 360. Of cobalt by iron, 362. Of some heterogeneous matter from cobalt by nickel, 363. Precipitations of, and by regulus of antimony, 365. Of and by arsenic, 368. Of regulus of a fenny acid by bismuth, 369. And by copper, 370. The operation of precipitation described, 370.

Preservatives of wood, 621.

Pressure of the surrounding fluid a mean of retaining life in bodies, 55.

Privilegi: dispute betwixt him and Lavollier, 141. Identity of phlogiston and charcoal given by his experiments, 146. Kirwan's examination of his experiment concerning the revival of mercury, 332. Why so much of the metal was revived in his experiments, 333. Kirwan's remarks on these experiments, 335. His method of procuring the sulphurous vitriolic acid, 712. His observations on marine acid, 755. Experiments on converting the fluor acid into a kind of air, 857. His experiments on the vegetable acid air, 883.

Prevention of heat totally: Mr. Kirwan's theorem for finding the joint of it, 114.

Prussian blue a preparation of iron, 1163. Dr. Woodward's receipt for making it, 1164. Mr. Geoffroy's theory, 1165. Amusing phenomenon in the preparation, 1166. Macquer's theory, 1167. Some blue produced by the common alkalis, 1170. Mr. Scheele's investigation of it, 1171, et seq. Prussian blue yields volatile alkali by distillation, 1197. Appearances on distilling other precipitates thrown down by the Prussian alkali, 1198. Appearances on distilling Prussian blue accounted for, 1203. See Colouring matter.

Pulvis Algaroth, the most proper material for emetic tartar, 1259. Objection to its use, 1260. The objection removed by Mr. Scheele, 1261, 1262. See Algaroth. Pulvis fulminans, how prepared, 1425.

Purification of quicksilver, 834.

Pyrites: how to extract green vitriol from it, 619. Its preference only requisite for the production of alum, 654.

Pyrometer, an instrument for measuring the expansion of bodies, 103.

Pyrophorus of Homberg, 1415. Best formed of alum and sugar, 1416. Is not injured by exposure to light, 1417. Theory of its accension, 1418.

Quadruple salts, how formed, 273.

Quantity of heat, difficulty of determining it, 70. It cannot be used in the common acceptation of the word with regard to fire, 71. It cannot be determined by Dr. Cleghorn's hypothesis, 76. Is impossible to be determined in any way, 117.

Quicklime a calcareous earth deprived of its fixed air, 511. Decomposes spirit of nitre, 748. Is the basis of flour spar, 837. Effects of it on felt of amber, 947.

Quickflour sometimes produced from lead, 72, 762. Its combination with acids. See Mercury. How to obtain a perfectly saturated solution of it in nitrous acid, 1293.

Quickflour, fulminating, 34903.

Quincent affinities defined, 267.

Radical vinegar differs from the common acerous acid, 1248. Inflammable spirit produced from it, 1344.

Rancid oils purified by churning with water, 1431.

Redlead, or red arsenic, prepared from arsenic and sulphur, 1279.

Reaumur's porcelain prepared by cementation of green glaas, 592. Dr. Lewis's observations on the method of making it, 593. An excellent material for chemical vessels, ib. And for levigating planks, 599. His method of rendering lead poisonous, 1311. Him for an improvement of the shape of bells, ib.

Red lead, how prepared, 1213.

Red precipitate of mercury, how prepared, 704.

Reduction of metallic calx, without addition, an argument against the existence of phlogiston, 130. The phenomenon explained, 320.

Regalum. See Antimony, Arsenic, and Cobalt.

Reid, Dr., his observations on the temperatures of bodies, 50.

Relate heat explained, 382.

Refins analysed, 1432. Are only balms thickened by evaporation, ib.

Retort, a chemical vessel, described, 570.

Revivification of metals, how accomplished, 522.

Rinnan's method of burning the ores of alum, 663.

Roasting aluminaous ores, uses of it, 662, et seq. See Alum.

Roasting, Mr. of Glasgow, determines the boiling point of water in vacuum, 123.

Rockburn, whence that name is derived, 638.

Rockburn's form of cream of tartar and mineral alkali, 891. Scheele's method of preparing it, 891.

Roy's Society, when founded, 19.

This and other societies of the kind has been of great advantage to chemistry, ib.

Rufing Index.

**Chemistry**

*Rusting of metals explained*, 541. Tin less liable to this defect than iron or copper, 1223.

*Saccharine acid*, how prepared, 896. Saccharine ether, 902. Is not easily set on fire, and burns with a blue flame, ib.

*Saccharin saturate*, its solution destroys that of green vitriol, 1044, and solution of tin, 1045. How prepared from lead, 877. An inflammable spirit procurable from it by distillation, 878. A particular kind of it obtainable by means of acid of ants, or spirit of verdigris, 908.

*Sal ammoniac*, composed of sal ammoniac and corrosive sublimate. See Ammoniac.

*Sal ammoniac*. See Ammoniac.

*Sal digestive*. See Digestive Salt.

*Sal diuretique*, how prepared from acetic acid and vegetable fixed alkali, 808.

*Sal prunellae*, prepared from nitre and sulphur, 744. Why the fire is thus purified, ib.

*Sal rosenfeldi*. See Rochelle Salt.

*Sal felsianus*. See Borax, acid of.

*Sal volatile oleosome*, a preparation of volatile alkali, spirit of wine, and essential oils, 1036.

*Salam mixture* prescribed in fevers, the same with a solution of soluble tartar, 889.

*Salt of vinegar*, formed from spirit of verdigris, 882. Essential salt of lemons, a kind of tartar extracted from forest soil for it, 888. True salt of lemons cannot be converted into acid of sugar, 999. Neutral salt for discovering iron in mineral waters, 1170. Watson's account of the specific gravity of salt of tartar, 415.

*Saltpetre*. See Nitre.

*Salt*: their general properties considered, 164, et seq. Are either fusible or volatile, ib. Soluble in water and crystallizable, ib. Their solution attended with an emission of air-bubbles sometimes mistaken for an effervescence, 165. Generally soluble in greater quantity in hot than in cold water, ib. Sea-salt an exception to this rule, ib. Of their mixture and separation, 166. Hypotheses concerning their solution, 167. Are destructible by repeated solution and evaporation, 168. Divided into acids and alkalies, 169. See Acid and Alkali.

*Neutral salts* formed by the combination of these two, 172. Perfect and imperfect neutral salts defined, ib. Why the acids and alkalies generally effect each other on mixture, ib. Metallic solutions sometimes disturbed by neutral salts, 222. Triple and quadruple salts, how formed, 273. Vitriolic salts decomposed by the nitrous and marine acids, &c. See Vitriolic.

*Nitrous salts* decomposed by the marine acid, &c. See Nitrous. Why the metallic calces seldom decompose the perfect neutrals, 304. Anomalous salts formed from the acetic acid and earths, 871. Of fixed alkaline salts, 1016. See Alkalies. Neutral salts partly precipitate platinum, 1331.

*Sand* mixed with fluor acid, produces no earthy crust by distillation, 844.

*Sand-guts, fills, &c.* how to get them in furnaces, 610.

*Scamini*, of the aluminous ores found in that country, 658.

*Schelle's method* of dephlogisticating spirit of fat, 791. Discovers the fluor acid, 826. His opinion that the earthy crust formed by this acid proceeds from an union of it with water, 832. Detects the errors of Boullanger and Monet on this subject, 834. Explanation of one of his experiments concerning this crust, 846. His method of analysing cream of tartar and extracting its acid pure, 887. Discovers the acid of arsenic, 916. His method of analysing molybdena, 959. Tungsten, 968. His method of procuring the pure acid of milk, 976. His receipt for preparing the flowers of benzin, 991. For preparing the pulveris argothor, 1262. Distinguishes the nature of the colouring matter of Prussian blue, 1471. Method of preparing Rochelle salt, 891.

*Schiller's method* of preparing the acid of tartar, 888.

*Selby*, aluminoous component parts of it, 652.

*Selby*, decomposed in various ways with lead, 302. Why the diffusion of it does not succeed with copperas, 757. Its acid not the same with that of fluors, 835. Its acid expelled by that of phosphorus, 907. And by acid of arsenic, 931. Whitens silver, 1137. Unsuccessful attempts to decompose it, 1479. Method of distilling its acid with clay, 1480. Effects of the spirit upon phlogistic matters, 1481.

*Sebacic acid*, procured from a variety of substances, 1533. Has a remarkable force of attraction, 1534. Its effects on tin, 1535. On other substances, 1536.

*Secret sal ammoniac*. Glauber's. See Glauber and Ammoniac.

*Secretive salt*. See Borax, acid of.

*Seguinette's salt*. See Rochelle salt.

*Semiflute*, See Cyphus. Found in the residuum of varnish ether, 24722. Why it cannot be decomposed by marine acid, 294. Quantity of ingredients in nitrous fumigate, 440.

*In marine ether*, 441.

*Semiflute tartaricus*, composed of acid of tartar and calcareous earth, 887, 893. The liquor from which it has been extracted affords an empyreumatic acid of tartar, 1010.

*Seminatural*, a new one procurable from tungsten, 1301.

*Semimetal*, one of the general classes of metallic substances, 547.

*Semiflute bent*, Crawford's account of it, 49.

*Select-lead*, how made, 1309. The advantages of milled lead over very dubious, 1210.

*Silica*, found in the residuum of vitriolic ether, ad 712.

*Siliceous earth*, produces a crust on the water into which fluor acid is distilled, 859. See Crep. Of the quantity of siliceous earth carried along with this acid, 847. Most completely precipitated from its solvent by volatile alkali, 1074. Diffused by boiling in fixed alkaline ley, 1076.

*Silver*: Why the vitriolic acid cannot act upon it without a boiling heat, 197. Difficulty concerning its amalgamation followed by Mr Bergman, 217. Precipitates of it, 235. Is attracted more than fixed alkali by nitrous acid, 301. Explanation of the decomposition of vitriolated tartar by solution of silver, 305. Of other vitriolic fats, 306. Its solution always decomposed by marine fats, 308. Experiment explaining the reduction of its calces per se, 323. Why silver is dissolved by solution of silver, 336. Why a saturated solution of silver can scarcely be precipitated by iron, 346. Why copper sometimes cannot precipitate silver, 348. Cannot precipitate copper from vitriolic acid, 355. Why it precipitates mercury from the nitrous acid, 355. Can decompose corrosive sublimate except in the dry way, 356. Of its solution in vitriolic acids, 478. In marine acid, 480, 921. If its combination with vitriolic acid, 691. Has a strong attraction for mercury in this state, ib. Combination with the nitrous acid, 751. Volatilized by uniting with this acid, ib. Colours produced by this solution, 753. The solution decomposed, 753. Is not acted on by the arsine acid, 942. The metal particularly treated of, 1131. Its ductility inferior to that of gold, ib. Its colour and ductility destroyed by sulphur, 1132. Purified by precipitation with lead, 1133. Reduced from its combination with marine acid, 1134, 1135. Has a great attraction for lead, 1136. Whitened externally by common fat and cream of tartar, 1137. Fulminating silver discovered by Kunckel, 756. By M. Berthollet, 1138. How prepared, 1139. Fulminates by the touch of any substance, whether cold or hot, 1140. Dangerous to fulminate more than a grain at a time, 1141. Crystals formed by evaporating the liquor after the precipitation of the calx explode violently by a touch, 1142. Cautious to be used in preparing it, 1143. Afforded theory by which the antiphlogistians attempt to account for this phenomenon, 1144. Remarks on it and others, 1145. Electricity probably the cause of this phenomenon, 1146. Silver precipitated from its solution in nitrous acid by the colouring matter of Prussian blue, 1191, 1205. Combination of it with platinum, 1340.

*Sphinx*, an Egyptian, the founder of chemistry, 3.

*Small* produced from the calx of cobalt and flints, 1205.

*Smoking liquor* of Libavus prepared from corrosive sublimate and tin, 810.

*Soap*, common, prepared by combining fixed alkalies with expressed oil, 1026. Starkey's soap, by combining them with essential oils, 1047. This combination difficult to be effected, ib. M. Beaume's method by long trituration of the ingredients, ib. Dr Lewis's, by heating the alkali red hot, and mixing it with the oil in that state, ib. This soap naturally subject to a decomposition by the efflorescence of a talc, ib.

*Staphylococci* bodies approaching to fungosity caused by heat, 116.

*Star heat*, why far more intense than that of common fires, 160.

*Solidated*, aluminous ores found there as altered by Mr Bergman, 656.

*Solid bodies* do not part with too much heat as fluids, 212.

*Solubility* of different metals, various degrees of it, 185. Their fusibility increased by calcination, 545.

*Soluble tartar*, prepared by combining cream of tartar with vegetable fixed alkali, 889. The same with the saline mixture preferred in fevers, ib.

*Solution of fats in water*, phenomena attending it, 165. Hypothesis concerning it, 167. Salts destructive by repeated solutions, 168. Phenomena attending the solution of metals, 180. Sometimes promoted by abstracting a portion of phlogiston, 186. Totally prevented by taking away too much, 187.

*Solution of metals* attended with effervescence, 188. And the extraction of various kinds of elastic fluids, 189. Bergman's account of the cause of chemical solution, 193. Solution impeded by too great a quantity of phlogiston, 194. Heat produced in solution most probably proceeds from the solvent liquor, 211. Reasons for believing that metals are calcined by solution, 215. Why solution of gold is precipitated by solution of tin, 227. Why solution of calcareous earth decomposes vitriolated tartar, 270. Decomposition of vitriolated tartar by solution of silver explained, 335. This solution always decomposed by marine fats, 308. As also solution of lead, 309. Solution of lead in marine acid decomposed by vitriolic acid, 310. And nitrous solution of mercury, 311. Solution of copper scarcely decomposed by cast iron, 345. Why a saturated solution of silver can scarcely be precipitated by iron, 346. Of the solution of calces of iron in vitriolic acid, 456. That of the dephlogisticated calces refuses to crystallize, 457. Solution of tin in vitriolic acid yields inflammable air, 471.

*How to perform the chemical operation of solution*, 564. Solution of silver in nitrous acid, 751. Shoots into a corrosive tartar, ib. Its crystals form lunar caustic, 752. Stains hair, bones, &c. of a brown or black colour, 753. Imparts various colours to stones, 753. Various vegetations produced from it, 754. Several curious circumstances attending its decomposition, 755, 756. Solution of calces of gold in marine acid, 799. Of tin in aqua regia. This flotation useful in dyeing, ib. Is decomposed by facecharum fatarni, 1045. Calcareous solutions by mild volatile alkali, ib. Solution of fats promoted by vitriolic acid, 1048. Solution of terra ponderosa of tinct of the vitriolic acid, 1053. Solution of flint, 1069. Solution of alkali dissolves siliceous earth, 1076. Solution of gold in aqua regia, 1099. Solution of hepar sulphuris, 1127. Inulinic ether, 1129. Solution of lime by the colouring matter of Prussian blue, the most proper for making experiments on metals, 1195. Effects of this matter on metallic fusions, 1193. How to attain a perfectly saturated solution of quicksilver, 1139. Of the solution of arsenic in water, 1169. Effects of regulus of arsenic on metallic solutions, 1293.

Sorrel, a kind of tartar extracted from it sold for effential salt of lemons, 883. See Sugar.

Spain: when alum was first made there, 642. Nitre, how prepared in that country, 746.

Spar, ponderous, account of Dr Withering's experiments on it, 1057.

Specific gravity. See Gravity.

Specula, materials proper for them: proposed by Mr Hellot from a mixture of gold and zinc, 1246. A mixture of brass and platinum proposed by others, 1344.

Spirit of nitre: how to determine the quantity of pure acid contained in it, 884. Proportion of it to that in f. irie of salt, 885. How to determine the accurate density on mixing spirit of nitre with water, 387. Experiment to determine the real quantity of acid in spirit of nitre, 389. How to construct a table of specific gravities for spirit of nitre, 390. Strong spirit of nitre more expanded by heat than weak, and why, 424. Exact quantity of dilatation of spirit of nitre, 425. Solution of mercury with spirit of nitre, 426. Quantity of bitumine dissolved by it, 492. Of cobalt, 497. Of regulus of arsenic, 504. How to prepare this spirit by means of oil of vitriol, 735. By means of arsenic, 739. Oils fired by it, 778. Effects of it on salt of amber, 912.

Spirit of salt: method of finding the quantity of pure acid contained in it, 376. Of finding its specific gravity, 377. Proportion of acid in spirit of salt to that in spirit of nitre, 385. Dilatation of spirit of salt by various degrees of heat, 427. Effects of it in the way of solution in cobalt, 498. How procured by means of vitriolic acid, 786. By nitrous acid, 788. By distillation of common salt without addition, 789. Diffuses and volatilizes the calces of gold, 799. Arsenic decomposed by dephtlificated spirit of salt, 919.

Spirit of wine yields a great quantity of water by being burned, 134. Convertible into charcoal, 147. Ether produced by its combination with vitriolic acid, 717. Its combination with nitrous acid produces spiritus nitri dulcis and ether, 773, &c. Ether with the marine acid, 824. With the vegetable acid, 885. And with the facecharum acid, 922. Converted into acetic acid by digestion with the acid of tartar, 1013. Enables vitriolic acid to dissolve manganese, 1014. Yields a great quantity of water by distillation with caustic alkali, 1015. Diffuses a small proportion of arsenic, 1270. How it may be made to dissolve sulphur, 1102. Diffuses essential oils, 1241.

Spiritus Minervarii: how to crystallize it, 1151.

Spiritus nitri dulcis, how prepared, 774. Analysis of its residuum by Mr Pott, 781. Affords acetic acids, 1070. And acid of tartar, 1089.

Spiritus volatilis facinatus. See Eau de Cologne.

Stable: a mistake of his concerning the conversion of marine into nitrous acid detected, 793.

Standard Proof: quantity of pure metal contained in it, 321.

Star formed on the surface of regulus of antimony, 1252.

Steel, salt of, the same with green vitriol, 697. How prepared from iron, 1247.

Still: how to set them, 610.

Stone ware corroded by caustic alkalies, 595.

Strasburg: two distilleries described, 1435.

Sublimation, in chemistry, how performed, 581.

Sublimate. See Carbone.

Sugar acid, of the same with that of tartral, ad 903. Acid of apples procured from sugar by means of the nitrous acid, 1512.

The acid procurable from this substance by means of the nitrous acid resembles that of tartar, in being capable of supersaturating the vegetable alkali, and forming with it an acid salt resembling crude tartar. This is found naturally existing in ferret and some other plants. There is, however, another acid obtained from sugar along with an empyreumatic oil by dry distillation, which has been purified and examined by Mr Schrikell. Eight ounces and four scruples of liquid were obtained in this manner from 16 of fine sugar. About six drachms of water came over first; after which the acid passed in white vapours, which condensed in unctuous films on the sides of the receiver. It had a pungent and agreeable smell, and tasted empyreumatic. By repeated distillations from pure clay, its smell became mild, and it acquired an apparent increase of acidity. With vegetable alkali, it formed a salt taking like that of Sylvis, and shooting into needle-like crystals, soluble with difficulty in cold water, but not at all in spirit of wine. It did not deliquesce in the air; but dehydrated in the fire, and did not melt on hot coals. With the mineral alkali yellow crystals were formed resembling Rochelle salt in taste, easily soluble in water, and not deliquitating in the air. Volatile alkali gave a sharp saline liquor, which could not be crystallized, but left a saline mass on evaporation; and a similar saline mass was produced by uniting it with calcareous earth. Magnesia and earth of alum formed gummy compounds. When concentrated, it diffused the cals of gold, and even gold-leaf; but had no effect on silver, mercury, or their calces. With mercury it gave a yellow solution, which shot into oblong white crystals of an astringent taste. A blood-red solution, which shot into green crystals, was obtained from iron. Copper was dissolved into a green liquid, which did not crystallize. Regulus of antimony was also dissolved, and the solution was of a greenish colour. Zinc was partly dissolved into a green liquor, and partly corroded. The precipitates were remarkable. The crystals of iron gave a green precipitate with alkalies, a black or dark blue one with Prussian alkali, and a white one with marine acid. Solution of regulus let fall a yellow precipitate with fixed alkali; with volatile alkali, a powder soluble again in the precipitant; vitriolic and marine acids, and an infusion of galls, threw down a white powder, but no precipitate ensued on adding nitrous acid. Solution of zinc gave a white precipitate with infusion of galls, alkalies of all kinds whether fixed, volatile, or phosphatic, as well as by the nitrous acid. Tin was partially dissolved, and the solution precipitated by alkalies, and an infusion of galls, but not by any of the mineral acids. Lead was precipitated of a white colour by vitriolic and marine acids, and of a grey colour by infusion of galls.

Sugar of lead. See Saccharum and saccharum.

Sugar: whether the acid of sugar or of tartar is the basis of vegetable acids, 996. Identity of vegetable acids proved from the decomposition of this acid, 1008. Nitrous acid enabled by the acid of sugar to dissolve manganese, 1011. Method of procuring the acetic acid from it, 882.

Sugar of milk: how to procure its acid, 680.

Sulphur dephtlificated by nitrous acid, 105. Exists in hepatic air, 210. Quantity of phlogiston in it, 507. Protects me from burning it, 508. Destroys the malleability of metals, 540. How to procure the vitriolic acid from it, 623. Quantity of the acid contained in sulphur, ib. Quantity procurable from it, 624. Methods of obviating the difficulties in the process, 625. Effervescence between the fumes of nitre and sulphur, 626. Extracted from the fumarite ore with alum and vitriol, 659. Prepared by combining the vitriolic acid with phlogiston, 715, 716. Effects of acid of arsenic upon it, 974. Molybdena recomposed by uniting its acid with fulphur, 966. Combined with fixed alkalies, 1031. Its phlogiston disposed to fly off when sulphur is combined with fixed alkalies, 1024. Its combination with volatile alkalies, 1038. Effects of it on silver, 1132. Takes fire spontaneously with iron fillings, 1207. Cannot be united with zinc, 1248. How to separate it from antimony, 1254. Easily united with arsenic, 1278. And mineralizes it, 1284. Effects of it on regulus of cobalt, 1303. Effects of it on nickel, 1308. On manganese, 1389. Its nature and properties particularly considered, 1398, et seq. May be crystallized, 1400. Decomposed by superabundance of phlogiston, 1401. How it may be dissolved in spirit of wine, 1402. Its union with metals, 1403.

Sulphurous fumes effervescence with those of spirit of nitre, 626. Volatile sulphurous acid described, 713. How procured by Dr Priestley, 714. Why this acid diffuses manganese, 1379. Sulphurous inflammable vapours procured from radical vinegar, 1345.

Sun distributes the heat on the earth, 94. How heat is produced by his rays, 95. His light blackens the precipitates of solution of silver, 756.

Sunflower contains nitr, 733.

Sweden: when alum was first made there, 640. Method of roasting the aluminous ores there, 665, et seq.

Sympathetic ink of a blue colour, 822.

Table of the different degrees of heat, 161. Of different precipitates, from Mr Bergman, 259. Of the quantity of acid taken up by different bases, 268. Coincidence of this table with experience, 271. Of the quantities of the different metals taken up by acids, 298. Table of the affinities of the acids to the different metals explained, 316. Of the quantities of phlogiston in different metals, 319. Of the proportional affinities of metallic calces to phlogiston, 324. Dr Black's table of affinities, 353.

Tallow analysed, 1429.

Tartar: quantity of fixed air in oil of tartar, 414. Its acid particularly treated of, 883, et seq. Crude tartar described, ib. Purified, and then called cream of tartar, by boiling with some of the finer kinds of clay, 886. Scheele's analysis of cream of tartar, and method of procuring the pure acid, 887. Soluble tartar: formed by uniting the vegetable fixed alkali with cream of tartar, 889. Cream of tartar, how regenerated, 890. Seignette's or Kochette's salt formed by combining the mineral alkali with cream of tartar, 891. Salt formed by the union of cream of tartar with volatile alkali, 892. Combination of the acid of tartar with earths, 893. With metallic substances, 894. Forms a fine green colour with copper, 894. Chalybeate tartar with iron, 895. Whether this acid or that of sugar is the basis of vegetable acids, 990. Product of acid of tartar by dry distillation, 1000. Requires for bringing vinegar nearer the state of tartar, 1002. Weirnub's unsuccessful attempt for this purpose, 1003. Dr Crell's opinion of the possibility INDEX.

penibility of the transmutation, 1004. Method recommended by him for attempting the experiment, 1005. Argument in favour of the identity of vegetable acids from the production of an empyreumatic acid of tartar from the liquor in which tartaraceous selenite is boiled, 1010. From the solution of manganese in a mixture of vitriolic and tartaraceous acids, 1012. Silver whitened by cream of tartar and common salt, 1137. Of the preparation of emetic tartar, 1257, 1258, et seq. See Emetic. Manganese soluble in acid of tartar, 1368. Explanation of its action upon manganese, 1382. Schiller's method of procuring its acid, 888.

Though the acid of tartar has been commonly supposed a product of the vinous fermentation, yet late experiments have shown that this is not the case. It has been found not only in the juice of the grape, but in that of tamarinds, the berries of the rhoea coriaria, and the leaves of the rumex acetosa. In these it is generally combined with the vegetable fixed alkali, or with calcareous earth. Hermann has found it combined with calcareous earth in the juice of the roots of the tritium repens, the leontodon-taraxacum, and China-bark. By the affluence of nitrous acid he obtained it also from the juice of grapes, mulberries, apples, pears, oranges, strawberries, and plums; also from honey, sugar, gum arabic, manna, spirit of wine, beech-wood, and the root of black heliotrope. In these cases, where the nitrous acid is made use of, however, it may justly be supposed that the acid of tartar is partly at least produced from it. In Scheele's process for procuring the pure acid of tartar by means of calcareous earth, it is advisable to make use of quicklime rather than chalk, as by this double the quantity of tartar will be decomposed. A hundred parts of pure tartar contain about 23 of vegetable alkali, 43 parts of acid employed to saturate that alkali, and 34 of superabundant acid. By using oyster-shells well prepared by boiling and powdering, the crystals of the acid may be obtained very white and pure. Some chemists have imagined that the vegetable alkali does not exist ready formed in tartar, but that it is produced by fire or mineral acids. In proof of this Mr. Machi offers the following experiments. On an ounce of cream of tartar were poured to ounces of boiling water, and the mixture allowed to remain in a jar covered with paper and parchment in which a small hole was made with a pin. At the end of three months it was considerably diminished; and contained a quantity of thick, tough, yellow, mucilaginous matter, which neither effervesced with acids nor alkalies, and, when burnt, the ashes were found to contain only a very small quantity of alkali. The experiment was repeated by Mr. Corvinus with some variation. He kept a solution of cream of tartar in a heat between 10° and 30° of Reaumur's scale; removing the saline pellicles which formed on the surface as fast as they appeared, and redissolving them in water. By continuing the digestion for several months, the liquor became at last evidently alkaline; and thus he obtained 216 grains of a brown alkali from two ounces of cream of tartar. Mr. Berthollet exposed for nine months, to the heat of his laboratory, a solution of two ounces of cream of tartar in eight ounces of water; taking care to replace the water which evaporated, but without removing the crusts which formed upon the surface. At the end of this time he found that the liquor was no longer acid, but began to turn the syrup of violets green. In 18 months it became strongly alkaline; and left, when evaporated, an oily residuum which effervesced with acids, and weighed 468 grams. On treating in the same manner a solution of terra foliata tartari, the liquor began to change the syrup of violets green in two months, and in four the decomposition seemed to be complete. At the end of a year he filtered and evaporated the liquor to dryness, by which process he obtained 432 grams of fixed alkali. The same quantity of terra foliata tartari decomposed immediately by distillation, yielded only 36 grams more of alkali. Solution of fats of wood-fellifer offered no decomposition by a similar treatment for two years. The latter he observed to be a much more powerful antiseptic than tartar; for which reason it seems to resist decomposition in a proportionable degree. He supposes oil to be the principal cause of the destruction of these acids; and the obvious deficiency of oil in the facecharine acid, in comparison with tartar, seems to be the cause of the want of capacity in it to undergo the decomposition just mentioned. A remarkable circumstance attends this spontaneous decomposition, viz. that no air is either absorbed or emitted during the whole process. It is also worth noting, that in combining acid of tartar with fixed alkali, the salt is precipitated with acid or cream of tartar is always formed in preference to the other called foliata tartar. Thus, if to a saturated solution of alkali with cream of tartar we add another of pure tartaraceous acid, a white flocculent matter will be precipitated to the bottom; which, on examination, is found to be a true tartar. Any other acid added to the solution of tartarified tartar will in like manner produce a precipitation of tartar, by engaging a part of the alkali with which it was combined; and if the acid of tartar be added to a solution of any neutral salt containing the vegetable fixed alkali, as vitriolated tartar, salt of Sylvius, and nitre, a similar precipitation of tartar will ensue. Hence the acid of tartar may be employed as a test to discover the presence of the vegetable fixed alkali, and to distinguish it from the mineral, which has not that effect. Bergman indeed observes, that Rocheleau tartar will do the same thing; but it must be remembered, that this is prepared with crude tartar, which contains a portion of vegetable alkali, and not with the pure acid.

Temperatures: Dr Reid's observations concerning, 50.

Terra foliata tartari. See Sul diureticus. How to preserve it in a bottle without danger of its deliquifying, 868.

Terra ponderosa combined with acid of arsenic, 940. Usually found united with vitriolic acid, 1049. Dr Withering's experiments upon it, 1050. Its appearance when combined with aerial acid, 1051. Effects of fire upon it, 1052. Phenomena with marine acid, 1053. Is precipitable from it by mild and caustic fixed alkalis, 1054. Convertible into lime capable of decomposing vitriolic salts, 1055. Insoluble precipitate thrown down by caustic alkali, 1056. Analysis and properties of the aerated ponderous tar, 1057. Its solution a test of the presence of vitriolic acid, 1058. Nitrous solution thrown into fine crystals, 1060. A small quantity dissolved by the colouring matter of Prussian blue, 1188.

Tests for acids and alkalies: Inaccuracy of those commonly in use, 1549. How to prepare one from red cabbage and other vegetables, 1550—1552. Mr Woolfe's test for mineral waters, 1557.

Theory of chemistry defined, 21.

Thermometers: its use, 103. Wedgewood's improvement, 104.

Thunder and lightnings: why more common in summer than in winter, 106.

Tin: why nitrous acid precipitates its solution, 200. Why solution of gold is precipitated by solution of tin, 227. The precipitate contains partly of tin, 238. Of its precipitates, 242. Why it cannot be precipitated in its metallic form, 335. Action of the vitriolic acid on tin, 470. Diffused in nitrous acid, 472. Great fusibility of the compounds of tin and bismuth, 543. One soluble in hot water, 544. Of the compound formed by it and vitriolic acid, 701. Its solution in marine acid useful in dyeing, 800. Is volatilized by this acid, and forms the smoking liquid of Llubivus, 810. Of its combination with the acetic acid, 879. Dr Lewis's experiments on this subject, 880. Effects of acid of arsenic upon it, 950. Solution of tin dehydrated by cacchianum tartar, 1045. Said to destroy the malleability of gold remarkably, 1091. Mr Alchone's experiments to determine this point, 1092. Its fumes do not render gold brittle, 1093. Nor the addition of small quantities of tin and copper, 1094. The metal particularly treated of, 1216. May be beat into thin leaves, 1217. Of its calcination, 1218. Its affinity with arsenic, 1219. Arsenic separable from it, 1220. Dr Lewis's observations on this affinity, 1221. Other metals injured by tin, 1222. Tin not liable to rust, 1223. An ingredient in aurum molacrum, 1224. Of its union with sulphur, ib. Readily unites with platinum, 1348. Remarkable effects of the ferraceous acid upon it, 1355. Volatile alkali prepared from a mixture of it with nitrous acid, 1553.

Tinctura martis made from marine acid and iron, 807.

Tobacco naturally contains nitre, 735.

Teffa: method of burning the hard ores of alum there, 669.

Torrid zone: heat of it: how mitigated, 90.

Transmutation of metals not to be credited, 11. A feeling transmutation of vitriolic into marine acid, 784. Transmutation of earth of flints into some other, 1069. The mistake discovered by Mr Bergman, 1070, et seq. See Flint.

Triple and quadruple salts, how formed, 275. Volatile alkali particularly adapted for their formation, 274. Metallic solutions sometimes decomposed by a triple combination, 223. A triple salt formed by marine acid, iron, and regalite of antimony, 366. Another by marine acid, copper, and regalite of antimony, 367. A triple salt formed by precipitating fluoearth with fixed alkali, 773. A kind of triple salt formed by precipitating calx of platinum from the marine acid, 1327. Other triple salts formed by it, 1332.

Tubal-Cains: whether to be accounted a chemist or not, 97.

Yungsten particularly examined, 967, et seq. Confounded as a metallic carbon by Mr Bergman, 967. Scheele's method of analysing it, 968. Effects of heat upon it, 969. Its chemical properties, 970. Differences between the acids of tungsten and molybdenum, 971. Bergman's opinion concerning them, 972. Why he supposed the acids to be metallic earths, 973. Its properties according to M. Luysart, 1498. Of the yellow matter called its acid by Mr Scheele, 1499. No simple acid procurable from the mineral, 1501. A new feminalated made from it, 1501.

Turbitic mineral, how prepared, 705, 706.

Turpentine: Appearance of oil of turpentine with acid of arsenic, 923. Chio turpentine described, 1433. Venice turpentine, 1434. Strasbourg, 1435. Common, 1436. Analysis of turpentine, 1437. Essential oil difficult of solution, 1438.

Vapour formed by the absorption of latent heat, 120. Dr Black's experiments on the conversion of water into vapour, 121. Heat expelled in great quantity by its condensation, 125.

Vegetable colours changed by acids and alkalies, 173. Of vegetable earths, 515, 1089. Supposed by Dr Lewis to be the same with magnesia, 1089. Dr Gmelin's experiments, experiments, ib. Vegetable animalic, 870. Vegetable ether, 884. Vegetable acids produce a remarkable change in copper, 1151. Vegetable substances in general considered, 1451.

The following is a list of the Vegetables from which the industry of the modern chemist has produced different acids, with the names of the discoverers.

1. Agave Americana. The juice exuding from the calyx of this plant yields acid of tartar and apples. Mr Hoffman of Weimar.

2. Alum. Acid of sugar and apples. Mr Scheele.

3. Apples. A peculiar acid called by the name of the fruit. By nitrous acid that of tartar is procured. Mr Scheele and Mr Hermann.

4. Barberry. Acid of apples, and of tartar. By treatment with nitrous acid it yields acid of sugar. Scheele and Hermann—Hoffman denies that it contains any native acid of tartar. By treating it with spirit of wine and manganese he obtained an ether.

5. Bilberry (Vaccinium myrtillus). Equal parts of the acids of citrons and apples. Scheele.

6. Bramble (Rubus chamaemorus). The same with the foregoing. Scheele.

7. Camphor. A peculiar kind of cryallizable acid. M. Kolgen.

8. Cherries. Equal parts of acids of citrons and apples. Saccharine acid by treatment with spirit of nitre. Scheele, Hermann, and Weyrumb. Herrnhaltz says that he found acid of tartar also.

9. Citrons and lemons. A particular kind of cryallizable acid. Scheele.

10. Coffee. The infusion evaporated and treated with spirit of nitre. Acids of sugar and apples. Scheele.

II. Corks. A yellow acid by repeated abstractions of spirit of nitre. With some of the alkalies and earths this acid forms cryallizable salts which do not deliquesce, though others do. That with fixed vegetable alkalies forms needle-like crystals, soluble in water, vitriolic, nitrous, or marine acids, but not in vinegar or spirit of wine. Like the fagacine acid it has a strong affinity to calcareous earth, which it separates from lime-water, and forms a greyish fageline powder, soluble in marine acid, but not in water, nor even in its own acid. It exhibits some appearances with metals, which deserve further examination. Brugnatelli.

12. Cranberry. (Vaccinium oxycoccus). Acid of citrons. Scheele.

13. Currants, red and white. Acids of citrons and apples. Weyrumb. Herrnhaltz says that they contain acid of tartar.

14. Elder berries. Acid of apples. Scheele.

15. Galls. A peculiar kind of acid. Scheele—Mr Keir observes, that from other abstractive matters, especially those used in dyeing, it is probable that similar acids might be obtained. Mr Morveau has obtained from galls a resin which he supposes to be their acidifiable base; and which, along with pure air, forms the acid of galls. When purified, this acid is said to make a fine and durable ink.

16. Geranium acidum. Small acid crystals. Carthager. Said by Hermann to be the acid of sugar.

17. Gooseberries. Acid of apples. Scheele—Herrnhaltz says that they contain the acid of tartar also.

18. Grapes. Their juice well known to contain the acid of tartar partially combined with fixed alkali.

19. Greengages. Saline crystals from the extract of the juice after three months standing. They were soluble in water, and gave an earthy precipitate on mixture with fixed alkali. On abrading the nitrous acid from them, and adding a solution of calcareous earth in vinegar, a precipitate fell, which was found to consist of acid of tartar saturated with lime. Herrnhaltz.

20. Gum Arabic. Acid of sugar and apples. Scheele.

21. Gum tragacanth. Acids of sugar of milk, apples, and sugar.

22. Hau (Citrus auris). Equal parts of acids of citrons and apples.

23. Honey. An acid liquor by distillation; and with spirit of nitre, the acid of sugar. The distilled acid has been said to dissolve gold.

24. Lemon. An acid the same with that of citrons.

25. Lecithon taraxacum. Acid of tartar by treatment with spirit of nitre.

26. Manna. Acid of sugar by treatment with spirit of nitre.

27. Mulberries. Acid of tartar. Herrnhaltz. A cryallizable acid felt by evaporating the juice. Angelus Sala.

28. Oil of olives. A salt which sublimed and cryallized, by repeated and copious abstractions of the nitrous acid. Weyrumb.

29. Peruvian bark. Acid of apples and sugar, by treating the extract with nitrous acid. Scheele.

30. Prunus spinosa et domestica. Acid of apples. Scheele.

31. Prunus padus. Acid of citrons. Scheele.

32. Poppy. Acids of sugar and apples, by treating the juice with nitrous acid. Scheele.

33. Raspberries. Acids of apples and citrons. Scheele. Acid of tartar by saturating the juice with chalk, and then separating the earthy basis by means of vitriolic acid. Herrnhaltz.

34. Rhapontic. Acid of tartar by cryallizing the juice; or sugar by treating it with nitrous acid. Bindheim.

35. Rhubarb. Acids of sugar and apples by treating the infusion with nitrous acid. If a pound of Indian rhubarb be infused in hot water, a powder sublimes, which by washing becomes white, weighing then about nine drachms, and is found to consist of calcareous earth united with the acid of sugar. Scheele.

36. Ribes cynobati. Acid of citrons or lemons. Scheele.

37. Salep. Acids of sugar and apples by treatment with nitrous acid. Scheele.

38. Service (Sambucus aucuparia). Acid of apples. Scheele.

39. Solanum dulcamara. Acid of citrons. Scheele.

40. Sorrel (Ranunculus acerifolius). Crystals of tartar by evaporating and cryallizing the juice; and pure acid of tartar by saturating the acid with chalk, and then expelling it by means of the vitriolic. Herrnhaltz. Other chemists, however, have certainly found it to contain the acid of sugar partly neutralized with alkali, and which is capable of being cryallized. This is generally known under the name of acid of wood-tar, and is manufactured in considerable quantities in Thuringia, Silesia, Switzerland, and the Harz. It is prepared from this plant as well as the osalis acetosella. The plants are bruised in stone or wooden mortars; the juice is squeezed through them; and when cleared by filtering, is to be boiled to a proper consistency, and clarified with the whites of eggs, or with blood. It is to be strained while hot, and then kept in a cold cellar. In a few weeks crystals will be formed, from which the remaining liquor must be poured off, and by further evaporation will yield more salt. Salary obtained only two ounces and a half of salt from 25 pounds of the juice.

41. Strawberry. Equal parts of the acids of apples and citrons. Scheele.

42. Sugar. See the article.

43. Sumach (Rhus coriaria). Cryall of tartar. Professor Trompfholtz and Son.

44. Tamarind. Acid of tartar, tartar itself, with a mucilaginous and saccharine matter. Weyrumb.

45. Vaccinium vitis idaea. Acid of citrons. Scheele.

46. Wood and bark of the birch tree. From 15 ounces of the wood were obtained 17 ounces of rectified acid, which when freed from an amber-coloured oil was to the specific gravity of water as 49 to 48, and of such strength that one ounce of it required 23 of lime-water for its saturation. Chemists of Dijon.—By allowing the acid distilled from the bark to remain at rest for three months, much of its oil was separated; by saturation with fixed alkali a dark-coloured neutral salt was obtained, which was purified by fusion and subsequent filtration and evaporation. On subjecting the purified salt to distillation, an acid arose, which had no longer an empiricumatic smell, but rather a flavour of garlic. Gentling. Vegetation, curious, produced from Tollution of silver, 754.

Venice turpentine. See Turpentine.

Verdigris, how prepared, 872. Distilled, ib. Verdigris distilled, best method of making it, 872.

Verditer, a preparation of copper, 758. Method of making blue verditer generally unknown, ib.

Fermentation made by subliming sulphur and mercury together, 1404. Difficulty in adjusting the proportions of the ingredients, ib. May be made without sublimation from quicksilver and the volatile tincture of sulphur, ib. Or with the addition of sulphur by fixed alkali or quicklime, ib. Is darker or lighter according to the quantity of sulphur, ib.

Verulam, Lord, studies and revives the science of chemistry, 16. His opinions concerning heat, 29.

Vesicles, chemical: of the proper ones to be used, 557, &c. Dr Black's opinion, ib. Of glaas, 558. Of metal, 560. See Chemical, Glass, Metal, Earthen ware, and Porcelain.

Vibration: Nicholson's account of the advantages attending the supposition that heat is occasioned by it, 80. Anfwered, 81.

Vinegar: Its ill gravity of it when strongly concentrated, 101. Why it may be reduced into air without addition, 208. Procured from the residuum of vitriolic ether, 272. L-wi's experiments on the solubility of tin in this acid, 880. Whey convertible into vinegar, 979. Qualities for bringing it nearer the state of tartar, 1002. Weyrumb's attempts for this purpose, 1003. Dr Crell's opinion of the possibility of the transmutation, 1004. Method recommended by him for attempting the experiment, 1005. Supposed to be an antidote against arsenic, 1520. Difference between radical vinegar and common acetic acid, 1528.

Vir inerte: fire seems to be deffute of it, 93.

Vitriol: why solution of gold is precipitated by the green kind, 225. But not by this salt when dephtalicated, 216. That procured by precipitation of copper with iron left fit for dyeing than the common, 344. Blue vitriol cannot be formed by boiling alum and copper filings, 349. Proportion of ingredients in blue vitriol, 467. How to extract green vitriol from pyrites, and to distil the acid from it, 620, &c. Extracted from the faene ore with sulphur and alum, 659. Alum is generally contaminated by dephtalicated vitriol, 684. Perfect green vitriol cannot be destroyed by clay, 686. How to abtract the phlogiston from it, 687. How to prepare blue vitriol, 993. Parts with its acid with more difficulty than the green kind, 694. Its uses, 695. White vitriol, how prepared, 708. Why the distillation of tea-fat with copper does not succeed, 787. Green vitriol decomposed by fagacine faturni, 1044. Fixe the colouring matter of Prussian blue, 1174. How affected by dephtalicated marine gas, 1485.

Vitriol, acid of. See Vitriolic acid.

Vitriolic acid: why it cannot act on lead, silver, &c. without a boiling heat, 197. Cannot be reduced into an aerial form but by a combination with phlogiston, 202. On the expulsion of the nitrous acid by the vitriolic diluted, 280. By the same in a concentrated state, With a small quantity of vitriolic acid diluted, 283. On the expulsion of the marine acid by the concentrated vitriolic, 283. Decomposition of vitriolic ammonia by marine acid never complete, 291. Why the vitriolic acid retinues on evaporation the bases it had left, 285. Decomposition of vitriolic ammonia by solution of silver explained, 306. Of corrosive mercury by concentrated vitriolic acid, 315. Can dissolve no other metals than iron and zinc, 337. Kirwan's experiments on the specific gravity of oil of vitriol, 385. Why it is necessary to dilute the acid in these experiments, 396. To find its specific gravity, 397. Quantity of acid necessary to saturate pure mineral alkali, 430. Why vitriolic acid is produced by dissolving iron in concentrated vitriolic acid, 453. Solution of the calces of iron in vitriolic acid, 456. It acts on iron in a much more dilute state than the nitrous, 461. Proportion of copper dissolved by vitriolic acid, 464. Vitriolic air obtained from this solution, 467. Why this metal cannot be acted upon by diluted vitriolic acid, 466. Action of the vitriolic acid on tin, 470. On lead, 474. On silver, 478. On mercury, 483. Zinc, 487. Bismuth, 491. Nickel, 2d 493. Cobalt, 496. Regulus of antimony, 509. Regulus of arsenic, 502. Quantity of phosphorus in vitriolic air, 506. This acid and its combinations particularly treated of, 612, et seq. Is never found naturally pure, 612. How rectified, 613. Attracts moisture from the airs, 614. Produces cold and heat according to circumstances, 615. Quantity of alkali saturated by it, 616. Its effects on the human body, 617. Difficulty of procuring it by itself, 618. Distillation of it from copperas, 626. Rectification of the acid thus obtained, 622. To procure it from sulphur, 623. Quantity of acid contained in it, 623. Quantity produced from it, 624. Methods of obviating the difficulties in this process, 625. Ought to be made in lead vessels, 627. Of its combination with fixed alkali, 628. With calcareous earth, 635. With argillaceous earth, 637. With magnesia, 690. With metals, 691. With inflammable substances, 710. Bergman's experiments to show that an excess of this acid impedes the crystallization of alum, 681. Procured from the residuum of vitriolic ether, 2d 722. Of its transmutation into the nitrous acid, 720. How to extract the nitrous acid by its means, 734. Whether the marine acid be the same with it, 783. Experiment seeming to prove the transmutation, 784. Expelled by acid of sugar, 998. Effects of it on falt of amber, 913. Diffuses manganese in conjunction with the acid of tartar, 1012. Or with spirit of wine, 1014. Expelled by the nitrous and marine acids, 1041. Promotes the solubility of fats, 1048. Terra ponderosa usually found united with the vitriolic acid, 1049. Unites with this substance more readily than with alkalies, 1055. Its presence readily discovered by terra ponderosa, 1058. The oil of vitriol usually fond contains gypsum, 1059. Effects of it on arsenic, 1371. Converts the regulus into white arsenic, 1292. On regulus of cobalt, 1300.

Vitriolated tartar: its decomposition by calcareous earth explained, 270. On its decomposition by nitrous acid, 285. Cannot be decomposed by diluted nitrous acid, 287. Decomposed by marine acid, 288. Requires for the success of this experiment, 289. Cannot be decomposed in a state of solution by this acid, 290. Explanation of its decomposition by solution of silver, 305. Why it is so much heavier than nitre, 416. Of the quantity of ingredients in it, 419. How prepared, 628, 629. Its uses, 631. Decomposed and sulphur procured from it by calcination with charcoal, 716. Its acid expelled by that of phosphorus, 927. And by the arsenical acid, 929.

Volatil alkali left strongly attracted than metallic earths by acids, 303. May be used to remove the excess of acid in aluminaeous ley, 680. Forms Glauber's sal ammoniac with vitriolic acid, 633. Nitrous ammoniac with the nitrous, 745. Common sal ammoniac with the marine, 795. Vegetable ammoniac with the acetous, 870. A salt forming into elegant crystals with the acid of tartar, 892. Its combination with fluid acid, 851. Glafs corroded by this salt, 854. A great quantity of it saturated by acid of sugar, 900. Forms microcosmic salt with the phosphoric acid, 905. Combined with acid of arsenic, 928. In its mild state decomposes calcareous solutions, 1046. Precipitates filious earth completely, 1074. Its preparation particularly treated of, 1090, et seq. Obtained from various substances, ib. Proper way of distilling it, 1031. How purified, 1032. Volatile sal ammoniac, how prepared, 1033. Volatile alkali combined with metals, 1034. With essential oils and spirit of wine, 1036, 1037. With sulphur, 1038. Volatile tincture of sulphur, 1038. Its use in the preparation of aurum fulminans but lately known, 1106. The cause of its explosion, 1121. Unites with the colouring matter of Prussian blue, 1180. Obtained by distillation from Prussian blue, 1197. May be united with phlogiston and fixed alkali, so as to sustain a great degree of heat, 1202. Effects of it on nickel, 1314. On solution of platinum, 1330. Why the volatile sulphurous acid dissolves manganese, 1379. Volatile alkali destroyed by manganese attracting its phlogiston, 1394.

Volcanic countries only afford ores containing alum ready made, 655. Unguentum citrinum, how prepared, 772.

Urine, how the microcosmic salt is procured from it, 95. Always contains a calculous matter, 1457. Why fresh urine reddens lacmus, 1458. Different salts contained in it, 1459. Affords the acid of benzoin, 1532.

Ward's drop: Nitrous ammoniac the principal ingredient in it, 746.

Water: Its flowlessness melting when congealed, a preventative of inundations, 88. Prodigious force exerted by it in freezing, 106. Remains sometimes fluid though cooled below 32 degrees, 117. Dr Black's experiments on the conversion of water into steam, 121. Its boiling point in vacuo determined by Mr Boyle, 122. And by Mr Robinson of Glasgow, 123. May be made sufficiently hot to melt lead, 131. A great quantity of water yielded by burning spirit of wine, 134. Produced from the deflagration of dephlogisticated and inflammable air, 135. In the reduction of iron by inflammable air, 136. Why it does not unite with nitrous air, 204. Cannot dissolve metallic salts without an excess of acid, 297. Quantity of it in digestive fats, 379. In nitre, 391. In vitriolated tartar, 398. In spirit of nitre, 426. How far it is an object of chemistry, 549. Scheme for filtering large quantities of it, 569. Earthy crust formed on it by fluid acid, 833. See Graft. Neutral salt for discovering iron in mineral waters, 1180. Mercury supposed convertible into it, 1235. The mistake discovered by Lewis, 1236.

Waters, mineral, Mr Woulfe's test for them, 1557.

Watt's experiments on the distillation of water in vacuo, 45. On the evaporation of fluids in vacuo, 126. Test for acids and alkalies, 1549, et seq.

Wedgwood's improvement of the thermometer, 104. His stone ware an improvement in chemical vessels, 597.

Weight of metals increased by calcination, 533, et seq.

Wenzel's experiments on fluor acid, 850. Method of preparing crystals of verdigris, 872.

Wyfryd's analysis of the residuum of vitriolic ether, 2d 722. His attempt to reduce vinegar nearer to the state of tartar, 1003.

Why: chemical properties of it, 970. Convertible into vinegar, 979.

White: a beautiful white colour from lead, 703. White drop of Ward, 746. White copper, how prepared, 1157.

Wiggle's experiments on fluor acid, 839. Account of the distillation of nitrous acid by clay, &c., 737. His new chemical nomenclature, 1561.

Wilkin's experiments on phosphori, 1086.

Winch's method of purifying ether, 2d 722. Waters, how purified, 886.

Withering's experiments on terra ponderosa, 1050.

Wolfram. See Tungsten.

Wood, preservatives for, 621, 700.

Woodward's receipt for making Prussian blue, 1164.

Wulfe's method of procuring nitrous ether in large quantity, 776. Test for mineral waters, 1557.

Yellow colour for house-painting, 699.

York, account of the aluminous ore found near that place, 660.

Zaffire, a calc of cobalt, detribefied, 1294.

Zinc and iron, the only metals dissolved by vitriolic acid, 337. Of their precipitation by one another, 347. Precipitates nickel, 388. Cannot precipitate copper, 389.

Forms white vitriol with the vitriolic acid, 707. Combined with the nitrous acid, 767. With the marine acid, 820. Volatilized by it, ib. Acid of arsenic, 951. Cannot easily be combined with iron, 1162. Its combination with copper, 1154. The metal particularly heated, 1240. Deflagrates violently in a strong heat, ib. Sublimes into flowers, 1241. Dr Lewis's method of reducing them, 1242. Oil suppos'd to be obtained from them by Homberg, 1243. The mistake discovered by Neumann, ib. Another oil by Mr Hellot, capable of dissolving gold and silver leaf, 1244. Combination of zinc with other metals, 1245. Its deflagration with other metals, 1247. Cannot be united with sulphur, 1248. Nitre alkalified by its flowers, 1249. Unites readily with platina, 1342.