in chemistry, one of the general divisions of salts, comprehending that class of chemical elements which, by their union with acids, form perfect neutrals, in opposition to the salts formed of acids with metals or earths, which are called imperfect.
Alkaline salts are divided into two kinds, the fixed and volatile; and the former into two species, vegetable, and mineral or fossil. All of these possess some properties in common, and some peculiar to each. Those which they have in common are, 1. An acrid and pungent taste, which, when the salts are very pure and strong, degenerates into absolute causticity, and would entirely destroy the organ of sensation if long applied to it. 2. A tendency to dissolve animal substances, and reduce them to a gelatinous substance, which all of them will do when very strong. 3. An attraction for acids, with a power of separating earths and metals from them, though previously combined with the same. 4. They change the blue vegetable juices to green; the green to yellow; the yellow to orange; the orange to red; and the red to purple. 5. They unite with oils, and destroy or cause to fade almost all kinds of colours that can be put upon cloth, whence their use in bleaching, &c.
The properties common to both kinds of fixed alkalies are, 1. They resist the action of fire to a great degree, so that they can easily be reduced to a solid form by evaporating any liquid in which they happen to be dissolved. 2. By an intense fire, they flow into a liquid which concretes into a hard and solid mass in the cold. 3. When mixed in certain proportions with those earths or stones called vitrifiable, they melt, in a heat still more intense, into glass. 4. Mixed with ammoniacal salts, with animal substances, or with foot, they extricate a volatile alkali.
The volatile alkali differs from the other two in being unable to resist the fire, and being entirely reducible into an invisible and permanently elastic fluid, called by Dr Priestley alkaline air. In consequence of this volatility, it always affects the olfactory nerves very perceptibly, and its smell is the general criterion by which its strength may be judged of. Its attraction for acids, power of changing colours, &c., are also considerably weaker than those of the fixed alkalies.
Though two sorts of volatile alkali are commonly sold under the names of spirits of hartshorn and of sal ammoniac, the one differs from the other only in its degree of purity. The former is so called from its being originally made from the horns of deer; but this material has long been laid aside, and the bones of horses, the flint, as they are called, of the horns of cattle, the parings of hoofs, &c., have been substituted in their stead. This kind, however carefully prepared, always contains a portion of animal oil, the smell of which is very perceptible; the other, prepared from pure sal ammoniac, is totally free of any empyreumatic smell, and is as pure as it can be obtained by any means whatever.
Effervescence with acids was formerly supposed to be a distinguishing property of alkalies, though it was always known that by a mixture with quicklime they might be deprived of this property. Dr Black, however, has shown, that the effervescing with acids is not a property of pure alkali, but is occasioned only by the escape of fixed air from it; of consequence, when quicklime is added, which attracts the whole or greatest part of the fixed air, no effervescence can be perceived. In the state in which the fixed alkalies are commonly met with, indeed, effervescence with acids may be said to be an essential property; but this is entirely owing to the cause just mentioned, viz., a quantity of fixed air, to which they are united during the process by which they were originally formed. The quantity of this air, however, is never so great as to saturate them entirely; on the contrary, their alkaline properties are always very perceptible, and they are commonly said to be in a mild state. But the truth is, that now they are in a kind of intermediate state between what may be called perfectly mild and perfectly caustic. In their perfectly mild state, they are united with such a large quantity of fixed air as entirely overpowers their alkaline properties; and therefore they are no more entitled to the name of alkalies in this state, than when combined with the marine, nitrous, or any other acid; in which case the compounds are called neutral salts. But it is a much more laborious and tedious process to saturate an alkali completely with fixed air than with any other acid; nor does it very easily retain the aerial acid after it has once been combined with it. Hence the caustic taste and properties of the alkali almost always predominate, and the salt contains a portion of pure and caustic alkali, to which alone its virtues are to be ascribed.
Vegetable alkali is obtained in its greatest purity by preparing deflating niter with charcoal, provided we make use of the very best of the latter than is barely sufficient to decompose the nitrous acid. It is, however, a very difficult matter to adjust this proportion with sufficient accuracy; for if we employ too much charcoal, the salt will be considerably phlogisticated; if too little, some part of the niter will remain undecomposed. Burnt tartar, therefore, purified by solution and filtration, may be looked upon as the best alkali we have. The common alkalies, or ashes as they are called, and said to be obtained from the ashes of vegetables, are always mix- ed with much phlogiston, and sometimes with lime, salt, or other heterogeneous matters; for which reason they are not to be employed in the nicer chemical experiments, without being purified by solution in water, by filtration, and crystallization. The purest of all these salts is that called the blue pearl, imported from Hungary.
The vegetable alkali when thus purified, and containing near one half its weight of fixed air, is of a white colour when dry, with a very hot and caustic taste, possessing in an eminent degree all those qualities which have been ascribed to the alkaline salts in general. It runs per deliquium when exposed to the air; and is usually incapable of being crystallized, though it acquires this property after being employed in the rectification of ardent spirit. It adheres more closely to acids than any substance hitherto discovered; though, from some experiments, Bergman was induced to believe that pure terra ponderosa attracted acids still more powerfully. But this has been discovered to be a mistake by Dr Withering, who, in a paper published in the 7th volume of the Philosophical Transactions, shows, that unless where the earth is united with vitriolic acid, not only the vegetable, the fossil, but even the volatile alkali in its pure or caustic state, will separate it from any other with which it may be combined. Terra ponderosa, therefore, will always decompose vitriolated tartar, Glauber's salt, or vitriolic ammonia; whence the mistake of this celebrated chemist probably has proceeded. After this alkali has been once united with marine acid, it appears to have undergone some change; for the salt then produced, by combining it with the vitriolic acid, resembles Glauber's salt almost as much as it does vitriolated tartar. It seems therefore to have made some approach towards the nature of fossil alkali; but chemists have not inquired what would be the consequence of repeated combinations of this kind.
The fossil alkali differs from the vegetable in having a smaller attraction for acids, in being more easily fusible by itself, and forming a more soluble compound with the vitriolic acid. It is also easily crystallizable, even without the addition of more fixed air than it naturally contains; and experience has determined it to be more proper for glass or soap manufactures than the vegetable alkali; for which reason the demand for it is very considerable.
The fossil alkali was anciently called natron or nitre, and is spoken of by Pliny and Tacitus as an ingredient in glaas, &c. and the scriptures inform us that it was used in baths. The knowledge of this salt was lost in the general obscuration of science which took place on the decline of the Roman empire; nor do we find it mentioned till the time of the Hon. Robert Boyle; and, even since that time, though M. du Hamel gave an accurate account of it in a memoir for the year 1736, little farther notice was taken of it till very lately.
We are now certainly informed that the fossil alkali is found native in many parts of the world, which never is the case with the vegetable alkali. The places where it abounds most are, Egypt, the country of Tripoli in Barbary, the peak of Teneriffe in one of the Canary islands, Hungary, several of the provinces of Russia, some parts of Asia, particularly the neighbourhood of Smyrna, &c. though it has not hitherto been found in any of the western countries of Europe, excepting in the neighbourhood of volcanoes, or in mineral waters; and in these last only in very small quantity.
The great source of the mineral alkali, however, and is the basis from whence it is not improbable that the places already mentioned have been supplied by some unknown natural operation, is the water of the ocean. Fossil alkali is the natural basis of sea-salt; and could any method of readily procuring it from this salt be fallen upon, it would no doubt be a most valuable secret. Hitherto, however, all the methods used with any success by the chemists may be reduced to two. 1. By mixing the nitrous acid with sea-salt in a retort, in the proportion, according to Dr Vogel, of four of the acid to one of the salt, and distilling off the muriatic acid, or rather aqua regia, which will be produced in the process. The residuum will afford a cubical nitre by crystallization, from whence the alkali may be obtained pure by deflating with charcoal. 2. By addition of vitriolic acid the spirit of sea-salt will be expelled much more easily, and at a cheaper rate, than by the nitrous acid. The residuum affords Glauber's salt in great plenty: this being melted in a crucible with a sufficient quantity of charcoal-dust, forms a heap sulphuris; which being decomposed by means of the vegetable acid, the latter may be destroyed by force of fire, and the alkali obtained in purity. For a further explanation of both these methods, see the article Chemistry, Index.
The demand in this country for fossil alkali is supplied from the ashes of kali and other sea plants, from which it is separated in the same manner as the vegetable alkali from the ashes of other plants. The purest kind of ashes containing this salt is called soda or barilla, and is imported chiefly from foreign countries; that which is obtained from the sea-weed growing on our own coasts, and known by the name of kelp, is excessively impure, and scarce admits of being thoroughly analysed according to the rules of chemistry.
Both these alkalis may be deprived of their fixed properties, and thus rendered pure and caustic, by the addition of quicklime. In this state the difference between them is much less perceptible than in any other, though the addition of fixed air, or any other acid, always shows that no essential change has taken place in either. In this highly caustic state they destroy the parts of animals in a manner similar to that of fire; whence they are called potential cauteries, as the former is called the actual cautery. M. Morveau informs us, that on digesting a piece of beef in a solution of caustic vegetable alkali, the liquor soon became red, and the flesh assumed the form of a semitransparent jelly, in which, however, one could easily perceive the ramifications of the smallest fibre; and, after standing some months, it emitted but very little smell. The vegetable alkali is commonly made use of as the material for the common caudic or lapis infernalis of the shops; for the preparation of which, see Chemistry, Index. Both alkalis attract moisture from the air when reduced to a solid form in their caustic state, though neither the fossil alkali nor its combinations do so in any other case. In their caustic state also they only unite with oils, or dissolve in spirit of wine; which last they have been supposed to purify, though it is more than probable that they decompose and communicate disagreeable qualities to it.
The volatile alkali, when procured immediately by the distillation of any substance capable of yielding it, is obtained in a state similar to that in which the alkalis are usually met with, viz. half mild and half caustic. By exposing the liquid alkali to a great quantity of fixed air, we may at last have it perfectly mild and neutralized; in which state it appears as a white salt extremely volatile, though less so than the pure caustic alkali. It dissolves very readily in water; but unless some caustic spirit, or some lime or fixed alkali be added, in order to abstract part of the fixed air, it will scarcely exhibit the characteristic of volatile alkali, viz. a pungent and urinous smell. The addition of fixed air, however, makes very little difference with regard to the chemical combinations of this salt; for as fixed air has a very slender power of acidity, it is expelled by every other acid with the greatest ease, and the same combinations formed as though it had not been present. The only difference is, that when a mild alkali is added to an acid, a strong effervescence takes place by reason of the escape of the fixed air through the liquid, while with the caustic alkali the mixture is made quietly and without disturbance.
The various combinations of the alkaline salts with the different acids, and the neutral compounds thence resulting, are exhibited in the following table.
1. Vegetable fixed alkali combined with
| Vitriolic acid | Nitrous acid | Marine acid | Acetous acid | |---------------|--------------|-------------|--------------| | Acid of tartar | Acid of borax | Acid of phosphorus | Saccharine acid, &c. | | Aerial acid |
2. Fossil or mineral fixed alkali combined with
| Vitriolic acid | Nitrous acid | Marine acid | Acetous acid | |---------------|--------------|-------------|--------------| | Acid of tartar | Acid of borax | Acid of phosphorus | Saccharine acid, &c. | | Aerial acid |
3. Volatile alkali combined with
| Vitriolic acid | Nitrous acid | Marine acid | Acetous acid | |---------------|--------------|-------------|--------------| | Vitriolic ammoniac, or Glauber's secret sal ammoniac | Nitrous ammoniac, or volatile nitre. | Common sal ammoniac | Spiritus mindereri. |
Volatile alkali combined with
| Acid of tartar | Acid of borax | Acid of phosphorus | Saccharine acid, &c. | |----------------|---------------|-------------------|---------------------| | Aerial acid |
Forms
- A salt whose properties have not been investigated; which floats into fine long crystals, and does not deliquesce in the air. - An anomalous salt. - Microcosmic salt, or essential salt of urine. - Anomalous salts. - Volatile sal ammoniac, or salt of hartshorn.
Besides their attraction for acids, the alkalis have attractions also an attraction for oils, sulphur, and spirit of wine, of the alka in the moist way, when the salts are deprived of their porous fixed air; and in this, as well as the dry way, with glances, several metals, and vitrifiable earths and stones, as has been already mentioned.
With oil the vegetable fixed alkali forms a soap, though less perfect than that made with the caustic mineral alkali. When combined with fixed air they scarcely unite with oils. Boiled with sulphur, or melted with it in their dry state, they unite into a very fetid compound called hepar sulphuris, which is soluble in water, but totally and very quickly decomposed by the contact of air. Vegetable alkali unites with iron, tin, and zinc; corrodes copper, and runs with it into a liquor of a deep blue colour, and joins with lead in fusion. It does not act upon gold in its metallic state; but if a sufficient quantity be added to a solution of gold in aqua regia, the calx of the metal will be first precipitated and afterwards diffused.
Vegetable alkali is a principal ingredient in the powders called fluxes, used for the fusion of metalline ores. It promotes the fusion of earths, and forms glas with the crystalline kind. It is soluble in an equal weight of distilled water; and, when exposed to the air, it soon attracts moisture from it and flows into a liquid. In its caustic state it dissolves in spirit of wine, and forms with it a red tincture called Van Helmont's tincture of salt of tartar, formerly used both as an internal and external remedy, but now fallen into disrepute.
Fossil alkali in its caustic state unites with oil into an harder soap than that made with vegetable alkali. With sulphur it forms a hepar sulphuris in the same manner as the vegetable alkali, and yields a tincture with spirit of wine, which dissolves part of the salt whilst hot, but lets it fall again in a crystalline form when cold. Gold, silver, or quicksilver, are not affected by a solution of this salt; but copper and tin are dissolved by it in the open air. It affects tin, lead, regulus of antimony, and cobalt, slightly; but acts powerfully upon zinc, and forms a kerne mineral with crude antimony. Copper, iron, bismuth, zinc, antimony, and regulus of cobalt, fused with two parts of fossil alkali, are almost entirely dissolved in a very strong heat; but tin, lead, and regulus of antimony, treated in the same manner, only suffer a partial solution.
All the alkalis are of considerable use in medicine, though. though the particular virtues of vegetable and fossil alkali have not hitherto been properly ascertained. It is probable, however, that there must be a considerable diversity in their operations on the human body, as the vegetable alkali shows itself so much more acid and powerful than the fossil. As both of them unite immediately with acids, and change them into mild neutral salts; hence, if any of the strong mineral acids should fall upon any part of the human body, and begin to corrode and give pain, the immediate application of the lixivium tartari, or of a solution of any of those alkaline salts in water, or of the salts themselves in powder, will destroy their causticity, and prevent their doing further mischief: Or if any of these acids should drop on clothes, linen, or other substances, and alkaline salts are immediately applied, they will neutralize the acid, and prevent its further corrosion: Or if a person should, through mistake, swallow any of the mineral acids, or corrosive sublimate, or any other corroding salt which an alkali will decompose, the taking down into the stomach solutions of the alkaline salts, or the salts themselves in proper doses, are the most likely means of affording relief, if not given too late (A).
Both the vegetable and fossil alkali applied externally in a caustic state, first irritate and inflame the skin, and afterwards act as fire in mortifying and destroying it; and therefore have been much used by surgeons for opening buboes and other abscesses, and for eating away proud or fungous flesh that sprouts out from fores. Various formulas of caustic alkalis have been employed for these purposes, of which an account is given under Chemistry and Pharmacy.
The alkaline salts, when much diluted with water, have been used as washes for removing pimples from the face; but if such washes are continued long, they are apt to spoil the skin. The ancients often used to dissolve natron (the fossil alkali) in their baths, and esteemed such baths useful for removing itchings of the skin, the scab, the impetigo, leprosy, and almost all sorts of cutaneous eruptions; and they employed baths of the same kind for promoting sweat, and for curing various disorders. They mixed it likewise with turpentine, with oils, and with stuffs of various kinds, and rubbed or applied such compositions to the skin, for removing different complaints, to heal sores, to strengthen weak or relaxed parts, to destroy the poison of the bite of a mad dog, and of serpents; and they esteemed it as an antidote against many other poisons. It has been proved that alkaline salts preserve animal substances from putrefaction; on which account some practitioners have concluded that they act as strong antiseptic remedies when swallowed as medicines, and are taken up by the lacteal vessels, and by them carried to the splanchnic vein to be mixed with the blood. Experience, however, has shown that they have effects directly opposite, and that by stimulating the vessels and quickening the circulation, they contribute towards the dissolution of the vital fluid; of which Dr Monro says he has seen several instances.
Alkalis promote the secretions in general, particularly by the kidneys; but by the help of warm liquors and bed-clothes, their operation may be directed towards the skin. They have also been employed in cases of heartburn, and others where an acid prevails in the stomach and bowels, or where these organs are loaded with viscid phlegm. They are likewise given with a view to assist the operation of the bile when it is too weak and inert, either by themselves, or mixed with purgative or other medicines. The fossil alkali has been alleged to be a more powerful solvent of the human calculus than the vegetable, though perhaps without any just foundation. It is given from 5 to 20 grains three times a-day; and in some cases even to double that quantity. It may be taken in any common liquor, or in clear broth made of lean meat, from which the fat has been skimmed off; or the powdered salts may be made up into pills or boluses mixed with licorice powder, by means of mucilage of gum Arabic or conserve.
The vegetable alkali has long been used as a diuretic of considerable use in dropsies with great success; and Dr Monro informs us, that he has seen a number of cases of anasarca in which the water was carried off by it. As diuretics, it may be taken from ten grains to half a drachm, or more, two or three times a-day, mixed with some diluted water, syrup, broth, or water-gruel, or with two ounces of white-wine, which partly neutralizes the salt. When added to infusions of juniper-berry, broom-tops, horseradish, mustard-feed, winter's-bark, &c. in wine and beer, they prove powerful diuretics; and Dr Monro gives the following formula.
"Take broom-tops, horseradish, and juniper-berries, of each an ounce; bruise them in a stone or marble mortar; put them into a large wide-mouthed bottle, and add to them an ounce of salt of tartar and two quarts of Rhinish wine. Infuse them for four days; decant off the wine, and filter it through paper for use. Two or three ounces may be taken three or four times a-day."
Or, "Take an ounce of canella alba, and as much mustard-feed and juniper-berries; bruise them well in an iron mortar, and add an ounce of purified vegetable alkali with two quarts of porter: infuse for four days, and filter the liquor through paper; let the patient take a wine-glass full every four or six hours."
The diuretic powers of these medicines are sometimes increased by opium, and they have been successfully joined with essential oils and balsams.
The most remarkable property of these salts, however, is that of dissolving the human calculus; for the last solvent discovery of which, Mrs Stephens, in the year 1740, obtained a parliamentary reward of £500. At that time Dr Jurin being afflicted with the stone, tried a number of experiments on these medicines; from which he concluded, that their efficacy depended entirely on the
(A) With regard to the mineral acids, an exception seems to take place if oil of vitriol in its concentrated state should happen to be swallowed; for this contracts such a degree of heat on the contact of any aqueous fluid as would destroy the patient, independent of another cause. An instance we have seen where a person unhappily mistook a bottle of oil of vitriol for water in the night-time. He recovered by swallowing instantly a great quantity of milk. Another recovered by drinking a bottle of Florence oil. the alkaline salts and lime which they contained; and therefore he began to try what effects a soap-ley would have on himself. At first he took only a few drops, but gradually increased his dose till he came to an ounce, and sometimes an ounce and a half, in a proper vehicle, in 24 hours. This produced the discharge of some small calculi, and relieved him of the symptoms of the stone. Dr Hartley, likewise, laboured under this complaint; and believing that the efficacy of Mrs Stephens's medicines depended on the soap, lime, and alkaline salts which they contained, ordered a paste to be prepared for himself, made of eight ounces of soap, one of oyster-shell lime, a drachm of salt of tartar, and as much water as formed the whole into a soft mass; of which he took large quantities, and found himself greatly relieved, though not cured, as a stone was found in his bladder after his death. These and other instances of success soon brought the medicines into general use; but though many found relief from them, others, particularly those who were afflicted with the stone, had all the symptoms of their distemper aggravated, by the salts rendering the blood, and other liquors of the body, particularly the urine, sharp and acrid, so as to irritate and inflame the bladder, which was already in too irritable a state, from the constant friction of the calculus lodged within it. The late experiments of Mr Scheele and Sir Torbern Bergman, however, have made it evident, that the human calculus is composed of a concrete acid joined to a small portion of animal earth. Most people, therefore, who are afflicted with the stone or gravel, wish to try the efficacy of these remedies, rather than submit to the dangerous operation of lithotomy; we shall therefore subjoin, from Dr Monro, the following directions for making and using the soap-ley.
"Take of tartar, eight ounces; of fresh quicklime, four ounces; of distilled water, a quart; mix them all well together in a large bottle, and let them stand for 24 hours; then pour off the ley and filter it through paper, keeping it in well-stopped vials for use. Of this the dose is from 30 drops to three or four drachms, which is to be repeated two or three times in the day.
"One of the best methods of taking this ley is, to mix the quantity to be used in the day with three pints of plain broth, which has been made with the lean part of veal, with all the fat or oily parts separated from it, by putting it, when made, into a large bowl, and skimming them off with a spoon when cold, and to drink, within an hour, a pint of this broth three times in the day—early in the morning—at noon—and in the evening; and to continue the use of this medicine for three, four, or more months; and, during this course, to live on such things as least counteract the operation of the medicine: to take for breakfast some plain broth, such as has been described, with dry toasted bread or biscuit; or a dish or two of tea or coffee in place of the broth; for dinner, to eat the lean part of plain boiled or roasted meat, or a fowl, with their own gravy or juice for sauce; and to eat only of vegetables which contain but little acid, such as potatoes, &c., and to use for drink toast and water, or water with a very small portion of spirit in it; and to abstain from eating fruit and acetic vegetables, fat meat, butter, or oil; and from drinking wine, beer, cider, punch, and in short from taking anything which is likely to counteract or destroy the effects of the ley."
With regard to the use of the soap-ley, our author observes, "that he has seen a number of people who have taken it, both for gravelish complaints and for the stone; that many of those who had gravel were relieved, and some of them seemed to be cured; that some few of those who had the confirmed stone, received considerable relief for a time from its use; but the complaints afterwards returned; nor can he say that one complete cure was made; though from the accounts given by the late Dr Whytt of Edinburgh, and others, it should appear that this had sometimes happened: that in many cases of stone the ley occasioned pain and irritation, and increased the violence of the symptoms so much, that the patients were obliged to lay it aside; and that this happened most frequently where the bladder seemed to be already diseased from the irritation of the stone; that at all times it is advisable to lay aside this medicine, at least for a time, whenever it irritates and occasions pain, or where there are appearances of its continued use having broken down the crisis of the blood.
Instead of the soap-ley, the following solution of vegetable alkali, fully-saturated with fixed air, has been lately recommended as a powerful solvent of the stone. "Take two ounces of salt of tartar, and dissolve it in two quarts of distilled water, and then saturate it fully with fixed air; and let the patient take eight ounces of it every eight hours. But though many cases have been related in which this medicine is said to have been serviceable, our author says he has seen only one gentleman who had taken it, and who had found considerable relief from it. Soap-ley has likewise been recommended as a solvent of bilious calculi, and has sometimes been of service; but this has probably arisen more from its property of dissolving thick and viscid humours, and afflicting the action of the bile, than by acting on the calculi themselves.
The volatile alkali has many of the virtues of the Medical fixed, but affects animal substances, particularly in its caustic state, less powerfully than they do. It gives a brisk and strong stimulus to the nerves and fibres of living animals; and is therefore employed in diseases where the pulse is low and the circulation too languid; in low fevers, where the patient is in danger of sinking; in apoplectic and lethargic disorders of elderly people of phlegmatic habits, in paralytic cases, fainting fits, &c., where a brisk and stimulating remedy is wanted. It is often used as a diaphoretic and sudorific in cases of rheumatism, in the end of fevers, catarrhs, and other diseases, where a plentiful diaphoresis or sweat is required; and, according to our author, it is principally owing to this quality that the alkalis have obtained their reputation of being efficacious remedies against the bites of serpents and other venomous animals. It is equally efficacious against mineral acid poisons with the fixed alkali.
It now remains only to give some account of the origin of the alkalis, or that process by which they are naturally produced. This subject, however, is very much involved in obscurity; nor has the origin of fixed alkalis, at least, been investigated with such diligence and success as that of the acids. Chemists have been divided in their opinions, whether alkaline salts be natural tural bodies, or formed by the force of fire, uniting the principles of which they consist in the burning or distilling the substances from which they are got. It is generally supposed that they are formed by the force of fire intimately uniting an earth, an acid, and an inflammable matter together, so as to form an alkaline salt, which is supposed to be composed of these principles. In support of this opinion, it has been alleged,
1. That the fixed vegetable alkali is produced by burning vegetables which contain the principles fit for forming these salts; though no vestige of an alkali can be discovered in these vegetables in their natural state.
2. That the essential salts of vegetables, which contain an acid and an earth, on being calcined in a crucible with charcoal, yield an alkaline salt.
3. That by alternately allowing the vegetable alkali to run over deliquium, and drying it again, it precipitates a quantity of earth every time it is distilled; so that the whole of the salt is at last reduced to this kind of earth, while the acid, phlogiston, &c., have evaporated, or been destroyed by the repeated application of heat for drying the salt.
4. In like manner the volatile alkali is produced by distilling animal substances which contain the principles fit for producing it, though no marks of a volatile alkali could be discovered in these substances while they were fresh.
On the other hand, it has been asserted, that the alkaline salts obtained by burning vegetables, or distilling animal substances, existed originally in the materials from which they are procured; that they were generated in the plants by the process of vegetation, and freed by the fire from the other principles which disguised them. In support of this opinion the following arguments are made use of by Messrs Weigle, Rosenfeld, Morveau, &c.
1. That they had not been able to procure an alkaline salt by mixing earths, oils, and acids together, and subjecting them to the most intense fire.
2. The crystals of tartar, which were formerly believed to be pure acid salts, have been found by late experiments to contain a vegetable alkali.
3. The vegetable alkaline salt, when purified, is always of the same nature, from whatever substance it is procured; and therefore must have been an original principle or body existing in the vegetables from which it is procured: for had it been produced by art, it would have varied, and we should have had different species of it, according to the principles which the plants contained.
And, 4. The neutral salts which have been found mixed with the ashes of plants, as vitriolated tartar, nitre, and soda-salt, are likewise strong proofs of the original existence of alkali in vegetables.
On this subject Dr Monro observes, that hitherto we have not sufficient evidence to determine positively whether the vegetable alkali be produced by the force of fire, or if it existed originally in the substances from which it is prepared, though he is inclined to favour the former opinion. With regard to the volatile alkali, however, we have abundant evidence of its being produced from substances which could not possibly be supposed to contain it originally. Dr Stahl affirms us, that if any dry fixed alkaline salt be well rubbed in a mortar with such a quantity of oil of turpentine as is sufficient to make it of the consistence of a pulp, and digested for some weeks in a cucurbit or retort, we obtain a volatile alkali. Mr Geoffroy relates, that having placed a large retort in a sand furnace, and adapting a tubulated receiver to it, afterwards heating the bottom of the retort red hot, he put into it, by means of a long tube rising from the upper part of the neck, a powder composed of equal parts of nitre and charcoal, on which there came over into the receiver a liquor highly impregnated with volatile alkali. Cartleufer, in the first volume of his Materia Medica, tells us, that if two parts of salt of tartar be mixed with one of sulphur, and be afterwards distilled, they yield a volatile alkaline salt and spirit. Boerhaave and Maquer have both affirmed, that the vegetative process itself produces a volatile alkali; and that the juices got by bruising mustard-seed and other alkaline vegetables, as they are called, contain a volatile alkali which effervesces with acids; but this is denied by Cartheuer and Vogel, who affirm that they could discover no traces of volatile alkali in these juices by any experiments they made.
But whatever may be concluded from the experience of former chemists, the late discoveries of Dr Priestley and Mr Cavendish have decisively shown, that the volatile alkali is by no means a simple element or natural principle, but a compound, and which may be artificially prepared. Dr Priestley informs us, that by the See Aerol union of nitrous air with iron, a volatile alkali is generated; and Mr Cavendish, that by the action of the electric fluid, or pure elementary fire, upon phlogisticated air, the nitrous acid is produced; the volatile alkali, therefore, must be supposed to consist ultimately of phlogisticated air united to a great quantity of elementary fire. In like manner, we can suppose this subtle element to enter into the substance of any kind of earth in such a manner as to exert its peculiar action when that substance is applied to any other, we may reasonably conclude that the fixed alkalis also are not simple and permanent principles, but capable of artificial composition and decomposition. It is certain that the action of alkaline salts is extremely similar to that of fire; and as we know that this element is combined in a latent state with fluids, there can be no absurdity in supposing it capable of combining also with solids.
or **Sal Kali**, in botany. See **SALICORNIA**.