a famous sect of the Jews, who distinguished themselves by their zeal for the traditions of the elders, which they derived from the same fountain with the written word itself; pretending that both were delivered to Moses from Mount Sinai, and were therefore both of equal authority. From their rigorous observance of these traditions, they looked upon themselves as more holy than other men: and therefore separated themselves from those whom they thought sinners or profane, so as not to eat or drink with them; and hence, from the Hebrew word pharis, which signifies to separate, they had the name of Pharisees or Separatists.
Their pretences to extraordinary piety drew after them the common people, who held them in the highest esteem and veneration. They held a resurrection from the dead, and the existence of angels and spirits; but, according to Josephus, this was no more than a Pythagorean resurrection, that is, of the soul only, by its transmigration into another body, and being born anew with it. From this resurrection they excluded all who were notoriously wicked, being of opinion that the souls of such persons were transmitted into a state of everlasting punishment; but as to lesser crimes, they imagined that they were punished in the bodies which the souls of those who had committed them were sent into. According to this notion it was, that Christ's disciples asked him concerning the blind man, "Who did sin, the man or his parents, that he was born blind?" With the Essenes, they held absolute predestination; and with the Sadducees, free will: but how they reconciled these doctrines, we are nowhere informed.
PHARMACY
Is the art of compounding natural and artificial substances for the purposes of medicine, in such a manner as is most suitable to the respective properties of each, and may best answer the indications of cure.
This art, which in some way or other must have been coeval with medicine itself, has for a long time been divided into the chemical and galenical. No rational principles of distinction, however, were preserved; and those which were ranked among the chemical medicines in one dispensatory, have been ranked among the galenical ones in another. Hence the London college rejected the division altogether; and Dr Lewis reckons pharmacy, in its full extent, to be no other than a branch of chemistry; and the most simple pharmaceutical preparation is chemical, in as far as it has any dependance on the properties of its materials.
The theory of pharmacy therefore is the same with that of chemistry; as are also the operations, which remain to be discussed here only in as far as they are made subservient to the medicinal art, distinct from that which is purely chemical. The objects of pharmacy, however, are much more limited than those of chemistry: the latter comprehending, in the utmost latitude of the word, almost every substance in nature; while pharmacy regards only such bodies in the vegetable, animal, and mineral kingdoms, as, by their effects on the human frame, tend to preserve health, or to restore it when lost. PART I. ELEMENTS OF PHARMACY.
CHAP. I. A general view of the Properties of medicinal substances, and their relations to one another.
SECT. I. Of Vegetables.
1. The medicinal virtues of vegetables differ very considerably according to the different circumstances of the plant, such as its age, the season of the year, and the soil in which it grows.
2. This is exemplified in herbs, some of which contain most odoriferous matter when young, while others have little or none till they have attained a considerable age:—In fruits, some of which contain an astringent acid, afterwards changed into a sweet by maturation; others, such as the orange, at first contain a strong aromatic, and then an acid:—In roots; some of which, during the summer, contain a thin watery juice; but, if wounded early in the spring, yield rich balsamic juices, concreting into solid gummy resins, some of which, from our indigenous plants, are superior to those brought from foreign countries:—In aromatic and in fetid plants; the former of which grow stronger and more fragrant in open exposures, dry soils, and fair warm seasons; while the latter lose their smell in such circumstances. Regard must therefore be had to these and other similar circumstances in the collecting of plants for medical purposes.
3. The different parts of the same plant are very often different in quality from one another. Thus, the leaves and flowers of wormwood are intensely bitter, while the root is aromatic. The capsule including the seeds of poppy has a narcotic virtue, but the seeds themselves have none.
4. The active parts of vegetables are generally capable of being extracted, without any alteration of their qualities, by some operations of a very simple nature; but by others, of a nature seemingly as simple, their nature may be entirely changed. The operations of fermentation, and of fire, are of this nature; for by means of them, the products of vegetables may be converted into substances having quite different properties from what they have naturally. Of the changes produced by these operations we shall therefore now take notice.
Art. 1. Of the Changes produced in Vegetables, or their Juices, by Fermentation.
5. All juices, or infusions, which are either simply sweet, or have a sweetness mixed with acidity, throw off by fermentation a great quantity of gross feculent matter; and are converted into a vinous liquor, affording by distillation an inflammable spirit.
6. The effects of the products just now mentioned on the human body are directly opposite to those of the juices from which they were produced. The latter attenuate the animal fluids, and relax the solids, in such a manner as in some cases to prove useful aperient medicines, and, if taken to too great excess, to produce dangerous fluxes; but the former always thicken the fluids, and constringe the solids.
7. In consequence of the different qualities of the juices or infusions, there are differences among the vinous liquors produced from them; but the spirit, when pure, is always found to be the same, from whatever substance it is produced.
8. Besides the gross matter thrown off during the fermentation, there is separated from several wines an acid saline substance named tartar; of a reddish or white colour, according to the wine which produces it. The red colour is not essential to the salt; for red tartar may be purified by solution in water, and then the tartar of all wines is found to be the same.
9. In fermentation there is also separated from the fermenting substance a great quantity of incoercible vapour, formerly known by the name of gas, but now discovered to be one of the component parts of our atmosphere, and the same with that which is called fixed air; concerning which see the articles Air, Fixed Air, Gas, &c.
10. Many substances, not susceptible of fermentation by themselves, may yet be brought into that state by an admixture of artificial ferments, or even of those which admit of a spontaneous fermentation, together with a proper quantity of water. This method is sometimes followed with vegetable matters intended for distillation, on a supposition that a slight fermentation will unlock their texture, and give out their principles more freely than otherwise; but it is much to be doubted whether this is really the case. The operation of fermentation is the same from first to last; and if its last effects are to convert the whole, or a great part, of the essential oil and saline parts of the vegetable into ardent spirit, it may reasonably be thought that its first effects must be to convert a part of these substances into the same spirit. At any rate, it is universally agreed, that when fermentation is employed with the abovementioned view, it must be continued only for a very short time.
11. The juices of fruits, though very susceptible of fermentation in their natural state, yet, when boiled till they become thick, are found to be indisposed to ferment; and this not only in their thick state, but when diluted again with water; though there appears to be scarcely any other alterations produced in them by the boiling. Hence liquids, prone to fermentation, may thus be preserved. How far this diminution of their fermentability may affect their medical virtues, is not as yet clear.
12. The degree of the species of fermentation, by which wines and inflammable spirits are produced, is called vinous fermentation. If the process is further protracted, more gross matter is thrown off, and new changes succeed, but in a slower and less tumultuary manner than before. The heating inebriating wine becomes by degrees a cooling acid vinegar, which seems to counteract the effects of the other: the more the wine abounded with inflammable spirit, the more does the vinegar abound with uninflammable acid.
There are, however, certain qualities of vegetables, which are not completely subdued even by this second stage of fermentation; some vinegars being apparently Elements. ly more coloured, and containing more of an oily and viscid matter than others. By adding to the fermentable liquor subjects of other kinds, the qualities both of wines and vinegar may be still further diversified, so as to adapt them to particular medicinal uses.
13. It is observable, that though the acetous fermentation will always succeed the vinous, unless industriously prevented, yet it is not always preceded thereby; for many, perhaps all, fermentable liquors may be made to pass to the acetous state, without any intermediate period of true vinosity.
14. If the process is still further continued, further changes takes place. The matter putrefies: and at length what little liquor remains unevaporated, is found to be mere water, and the solid substance at the bottom appears to be the same with common mould.
15. This is reckoned by the chemists one of the stages of fermentation, and distinguished by the name of the putrefactive stage: it is far more general in its object than the other two; every vegetable matter being susceptible of putrefaction, but some particular kinds only being adapted to vinous or acetous fermentation.
16. Putrefaction discovers one difference in vegetables, which seems worthy of being remarked. The generality of vegetables rot and turn to mould, without yielding any very offensive smell from the beginning to the end of the resolution: but there are some which emit, throughout the whole process, a strong fetor, very nearly of the same kind with that which accompanies the putrefaction of animal-substances. See the articles Fermentation and Putrefaction.
Art. 2. Productions from Vegetables by Fire.
17. Fire, the other grand agent in the resolution of bodies, produces in vegetables decompositions of a different kind. Its general effects are the following:
18. Vegetable substances, burnt in the open air, are reduced partly into ashes, and partly into flame and smoke; which last, condensed in long canals, forms a nauseous black foot. In the burning of most vegetables, an acid vapour accompanies the smoke; but the foot is never found to partake of it.
19. Vegetables urged with a red heat in close vessels (the vessel containing the subject being made to communicate with another placed beyond the action of the fire for receiving the matters forced out by the heat) give over a watery liquor called phlegm; an acid liquor called spirit; an elastic incenseable vapour, which appears to be partly fixed and partly inflammable air; and to which an exit must be occasionally allowed lest it burst the vessels or blow off the receiver; a thin oil, at length a very thick dark-coloured oil, both which are of an acrimonious taste, and a burnt fetid smell, whence they are called empyreumatic oils. There remains behind a black coal, not dissoluble in any kind of liquors, not susceptible of putrefaction, not alterable by the most vehement degree of fire so long as the air is excluded, but which, on admitting air to it, burns without flaming, and with little or no smoke, and leaves a very small quantity of white ashes.
Vol. VIII. to the fire; for the most mild and insipid oils receive the same qualities on being urged with the same degree of heat: the acid, which is likewise naturally contained in vegetable subjects, proves always tainted in the present process with the ill smell and taste of the oil that accompanies it; but whether the acid itself suffers any change in its nature, is unknown.
29. When chemistry began first to be formed into a rational science, and to examine the component parts and internal constitution of bodies, it was imagined, that this resolution of vegetables by fire, discovering to us all their active principles, unclogged and unmixed with one another, would afford the surest means of judging of their medicinal powers. But, on prosecuting these experiments, it was soon found, that they were insufficient for that end; that the analyses of poisonous and eculent plants agreed often as nearly with one another as two analyses of one plant: that by the action of a burning heat, the principles of vegetables are not barely separated, but altered, transposed, and combined into new forms; infomuch that it was impossible to know what form they existed in, and what qualities they were endowed with, before these changes and transpositions happened.
Art. 3. Substances naturally contained in Vegetables, and separable by Art without Alteration of their native Qualities.
I. Gross oils abound chiefly in the kernels of fruits, and in certain seeds; from which they are commonly extracted by expression, and hence are distinguished by the name of expressed oils. They are contained also in all the parts of all vegetables that have been examined, and may be forced out by vehemence of fire; but here their qualities are greatly altered in the process by which they are extracted or discovered.
31. These oils, in their common state, are not dissoluble either in vinous spirits or in water, though, by means of certain intermedia, they may be united both with one and the other. Thus a skilful interposition of sugar renders them miscible with water into what are called lobochs and oily draughts; by the intervention of gum or mucilage, they unite with water into a milky fluid; by alkaline salts they are changed into a soap, which is miscible both with watery and spiritous liquors, and is perfectly dissolved by the latter into an uniform transparent fluid. The addition of any acid to the foamy solution absorbs the alkaline salt; and the oil, which of course separates, is found to have undergone this remarkable change, that it now dissolves, without any intermedium, in pure spirit of wine.
32. Expresssed oils, exposed to the cold, lose greatly of their fluidity; some of them, in a small degree of cold, congeal into a consistent mass. Kept for some time in a warm air, they become thin and highly rancid; their soft, lubricating, and relaxing quality, is changed into a sharp, acrimonious one: and in this state, instead of allaying, they occasion irritation; instead of obtunding corrosive humours, they corrode and inflame. These oils are liable to the same noxious alteration while contained in the original subject; hence the rancidity which the oily seeds and kernels, as almonds, and those called the cold seeds, are so liable to contract in keeping. Nevertheless, on triturating these seeds and kernels with water, the oil, by the intervention of the other matter of the subject, unites with the water into an emulsion or milky liquor, which, instead of growing rancid, turns sour on standing. The rancidity also to which the oils are subject, appears to be owing to the impurities contained in them; for pure oil is found to be quite incorruptible.
33. In the heat of boiling water, and even in a degree of heat as much exceeding this as the heat of boiling water does that of the human body, these oils suffer little distillation of their parts. In a greater heat, they emit a pungent vapour, seemingly of the acid kind; and when suffered to grow cold again, they are found to have acquired a greater degree of consistence than they had before, together with an acrid taste. In a heat approaching to ignition, in close vessels, greatest part of the oil arises in an empyreumatic state, a black coal remaining behind.
34. II. Gross sebaceous matter. From the kernels of some fruits, as that of the chocolate-nut, we obtain, instead of a fluid oil, a substance of a butyraeous consistence; and from others, as the nutmeg, a solid matter as firm as tallow. These concretes are most commodiously extracted by boiling the subject in water; the sebaceous matter, liquefied by the heat, separates and arises to the surface, and resumes its proper consistence as the liquor cools.
35. The substances of this class have the same general properties with expressed oils, but are less disposed to become rancid in keeping than most of the common fluid oils.
36. III. Essential oils are obtained only from those vegetables, or parts of vegetables, that are considerably odorous. They are the direct principle, in which the odour, and oftentimes the warmth, pungency, and other active powers of the subject, reside; whence their name of essences or essential oils.
37. Essential oils unite with rectified spirit of wine, and compose with it one homogene transparent fluid; though some of them require for this purpose a much larger proportion of the spirit than others. Water also, though it does not dissolve their whole substance, may be made to imbibe some portion of their more subtle matter, so as to become considerably impregnated with their flavour: by their admixture with sugar, gum, the yolk of an egg, or alkaline salts, they are made totally dissoluble in water. Digested with volatile alkalies, they undergo various changes of colour, and some of the less odorous acquire considerable degrees of fragrance; whilst fixed alkalies universally impair their odour.
38. In the heat of boiling water, these oils totally exhale: and on this principle they are commonly extracted from subjects that contain them; for no other fluid that naturally exists in vegetables is exhalable by that degree of heat, except the aqueous moisture, from which greatest part of the oil is easily separated. Some of these oils arise with a much less heat, a heat little greater than that in which water begins visibly to evaporate. In their resolution by a burning heat, they differ little from expressed oils.
39. Essential oils, exposed for some time to a warm air, suffer an alteration very different from that which the expressed undergo. Instead of growing thin, rancid, and acrimonious, they gradually become thick, and at length harden into a solid, brittle concrete, with Elements. a remarkable diminution of their volatility, fragrancy, pungency, and warm stimulating quality. In this state they are found to consist of two kinds of matter; a fluid oil, volatile in the heat of boiling water, and nearly of the same quality with the original oil; and of a groser substance which remains behind, not exhaleable without a burning heat, or such a one as changes its nature, and resolves it into an acid, an empyreumatic oil, and a black coal.
40. The admixture of a concentrated acid instantly produces in essential oils a change nearly similar to that which time effects. In making these kinds of com-mixtures, the operator ought to be on his guard; for when a strong acid, particularly that of nitre, is poured hastily into an essential oil, a great heat and ebullition ensue, and often an explosion happens, or the mixture bursts into a flame. The union of expressed oils with acids is accompanied with much less conflict.
41. IV. Concrete essential oil. Some vegetables, as roses and elecampane roots, instead of a fluid essential oil, yield a substance possessing the same general properties, but of a thick or sebaceous consistence. This substance appears to be of as great volatility and subtlety of parts as the fluid oils; it equally exhales in the heat of boiling water, and concretes upon the surface of the collected vapour. The total exhalation of this matter, and its concreting again into its original consistent state, without any separation of it into a fluid and a solid part, distinguishes it from essential oils that have been thickened or indurated by age or by acids.
42. V. Camphor. This is volatile like essential oils, and soluble both in oils and inflammable spirits; it unites freely with water by the intervention of gum, but very sparingly and imperfectly by the other intermedia that render oils miscible with watery liquors. It differs from the sebaceous as well as fluid essential oils, in suffering no sensible alteration from long keeping; in being totally exhaleable, not only by the heat of boiling water, but in a warm air, without any change or separation of its parts, the last particle that remains un-exhaled appearing to be of the same nature with the original camphor; in its receiving no empyreumatic impression, and suffering no resolution, from any degree of fire to which it can be exposed in clofe vessels, though readily combustible in the open air; in being dissolved by concentrated acids into a liquid form; and in several other properties which it is needless to specify in this place.
43. VI. Refin. Essential oils, indurated by age or acids, are called refin. When the indurated mass has been exposed to the heat of boiling water, till its more subtle part, or the pure essential oil, that remained in it, has exhaleed, the groser matter left behind is likewise called refin. We find in many vegetables refins analogous both to one and the other of these concretes; some containing a subtle oil, separable by a heat of boiling water; others containing nothing that is capable of exhaling in that heat.
44. Refins in general dissolve in rectified spirit of wine, though some of them much more difficultly than others: it is chiefly by means of this dissolvent that they are extracted from the subjects in which they are contained. They dissolve also in oils, both expressed and essential; and may be united with watery liquors by means of the same intermedia which render the fluid oils miscible with water. In a heat less than that of boiling water, they melt into an oily fluid; and in this state they may be incorporated one with another. In their resolution by fire, in clofe vessels, they yield a manifest acid, and a large quantity of empyreumatic oil.
45. VII. Gum differs from the foregoing circumstances in being uninflammable: for though it may be burnt to a coal, and thence to ashes, it never yields any flame. It differs remarkably also in the proportion of the principles into which it is resolved by fire; the quantity of empyreumatic oil being far less, and that of acid far greater. In the heat of boiling water, it suffers no diffusion; nor does it liquefy like resins; but continues unchanged, till the heat is so far increased as to scorch or turn it to a coal.
46. By a little quantity of water it is softened into a viscous adhesive mass, called mucilage: by a larger quantity it is dissolved into a fluid, which proves more or less glutinous according to the proportion of gum. It does not dissolve in vinous spirits, or in any kind of oil; nevertheless, when softened with water into a mucilage, it is easily miscible both with the fluid oils and with resins, which by this means become soluble in watery liquors along with the gum, and are thus excellently fitted for medicinal purposes.
47. As oily and resinous substances are thus united to water by the means of gum, so gums may in like manner be united to spirit of wine by the intervention of resins and essential oils; though the spirit does not take up near so much of the gum as water does of the oil or resin.
48. Acid liquors, though they thicken pure oils, or render them consistent, do not impede the dissolution of gum, or of oils blended with gum. Alkaline salts, on the contrary, both fixed and volatile, though they render pure oils dissoluble in water, prevent the solution of gum, and of mixtures of gum and oil. If any pure gum be dissolved in water, the addition of any alkali will occasion the gum to separate, and fall to the bottom in a consistent form: if any oily or resinous body was previously blended with the gum, this also separates, and either sinks to the bottom, or rises to the top, according to its gravity.
49. VIII. Gum-refin. By gum-refin is understood a mixture of gum and resin. Many vegetables contain mixtures of this kind, in which the component parts are so intimately united, with the interpolation perhaps of some other matter, that the compound, in a pharmaceutical view, may be considered as a distinct kind of principle; the whole mass dissolving almost equally in aqueous and in spirituous liquors; and the solutions being not turbid or milky, like those of the groserer mixtures of gum and resin, but perfectly transparent. Such is the astringent matter of bistort root, and the bitter matter of gentian.
50. IX. Saline matter. Of the saline juices of vegetables there are different kinds; the sweet and the acid ones are the most plentiful, and those which are the most known.
51. These juices, exposed to a heat equal to that of boiling water, suffer generally no other change than the evaporation of their watery moisture; the saline matter remaining behind, along with such of the other not volatile parts as were blended with it in the juice; from many, after the exhalation of great part of the water, the saline matter gradually separates in keeping, and concretes into little solid masses, leaving the other substances dissolved, or in a moist state; from others, no means have yet been found of obtaining a pure concrete salt.
52. These salts dissolve not only in water like other saline bodies, but many of them, particularly the sweet, in rectified spirit also. The grofs oily and gummy matter with which they are almost always accompanied in the subject, dissolves freely along with them in water, but is by spirit in great measure left behind. Such heterogeneous matters as the spirit takes up are almost completely retained by it, while the salt concretes; but of those which water takes up, a considerable part always adheres to the salt. Hence essential salts, as they are called, prepared in the common manner from the watery juices of vegetables, are always found to partake largely of the other soluble principles of the subject; whilst those extracted by spirit of wine prove far more pure. By means of rectified spirit, some productions of this kind may be excellently freed from their impurities; and perfect saccharine concretions be obtained from many of our indigenous sweets.
53. There is another kind of saline matter, obtained from some resinous bodies, particularly from benzoin, of a different nature from the foregoing, and supposed by some of the chemists to be a part of the essential oil of the resin, coagulated by an acid, with the acid more predominant or more disengaged than in the other kinds of coagulated or indurated oils. These concretes dissolve both in water and in vinous spirits, though difficulty and sparingly in both: they show some marks of acidity, have a considerable share of smell like that of the resin they are obtained from, exhale in a heat equal to that of boiling water, or a little greater, and prove inflammable in the fire.
General observations on the foregoing principles.
54. 1stly, Essential oils, as already observed, are obtainable only from a few vegetables, and camphor from a much smaller number: but grofs oil, resin, gum, and saline matter, appear to be common, in greater or less proportion, to all; some abounding more with one, and others with another.
55. 2dly, The several principles are in many cases intimately combined, so as to be extracted together from the subject by those dissolvents, in which some of them, separately, could not be dissolved. Hence watery infusions, and spiritous tinctures of a plant, contain, respectively, more than water or spirit is the proper dissolvent of.
56. 3dly, After a plant has been sufficiently infused in water, all that spirit extracts from the residuum may be looked upon as consisting wholly of such matter as directly belongs to the action of spirit. And contrariwise, when spirit is applied first, all that water extracts afterwards may be looked upon as consisting only of that matter of which water is the direct dissolvent.
57. 4thly, If a vegetable substance, containing all the principles we have been speaking of, be boiled in water, the essential oil, whether fluid or concrete, and the camphor and volatile essential salt, will gradually exhale with the steam of the water, and may be collected by receiving the steam in proper vessels placed beyond the action of the heat. The other principles not being volatile in this degree of heat, remain behind; the grofs oil and sebaceous matter float on the top; the gummy and saline substance, and a part of the resin, are dissolved by the water, and may be obtained in a solid form by straining the liquor, and exposing it to a gentle heat till the water has exhaled. The rest of the resin still retained by the subject may be extracted by spirit of wine, and separated in its proper form by exhaling the spirit. On these foundations most of the substances contained in vegetables may be extracted, and obtained in a pure state, however they may be compounded together in the subject. By this operation, however, some very considerable change is undoubtedly produced by the fire; since, by pouring back the liquor which has arisen in distillation upon that which remains in the still, we shall never be able to recompone a liquor like that before it was distilled.
58. 5thly, Sometimes one or more of the principles is found naturally disengaged from the others, lying in distinct receptacles within the subject, or extravasated and accumulated on the surface. Thus, in the dried roots of angelica, cut longitudinally, the microscope discovers veins of resin. In the flower-cups of hypericum, and the leaves of the orange-tree, transparent points are distinguished by the naked eye, which, on the first view, seem to be holes; but, on a closer examination, are found to be little vesicles filled with essential oil. In the bark of the fir, pine, larch, and some other trees, the oily receptacles are extremely numerous, and so copiously supplied with the oily and resinous fluid, that they frequently burst, especially in the warm climates, and discharge their contents in great quantities. The acacia tree in Egypt, and the plum and cherry among ourselves, yield almost pure gummy exudations. From a species of ash is secreted the saline sweet substance manna; and the only kind of sugar which the ancients were acquainted with, appears to have been a natural exudation from the cane.
59. 6thly, The foregoing principles are, so far as is known, all that naturally exist in vegetables; and all that art can extract from them, without such operations as change their nature, and destroy their original qualities. In one or more of these principles, the colour, smell, taste, and medicinal virtues of the subject, are almost always found concentrated.
60. 7thly, In some vegetables, the whole medicinal activity resides in one principle. Thus, in sweet almonds, the only medicinal principle is a grofs oil; in horseradish root, an essential oil; in jalap-root, a resin, in marshmallow-root, a gum; in the leaves of fennel, a saline acid substance.
61. 8thly, Others have one kind of virtue residing in one principle, and another in another. Thus Peruvian bark has an astringent resin and a bitter gum; wormwood, a strong-flavoured essential oil, and a bitter gum-resin.
62. 9thly, The grofs insipid oils and sebaceous matters, the simple insipid gums, and the sweet and acid saline substances, seem nearly to agree in their medical small quantity, but of an exceedingly strong diffusive smell.
69. The vesicating matter of cantharides, and those parts of sundry animal-substances in which their peculiar tastes reside, are dissolved by rectified spirit, and seem to have some analogy with resins and gummy resins.
70. The gelatinous principle of animals, like the gum of vegetables, dissolves in water, but not in spirit or in oils; like gums also, it renders oils and fats miscible with water into a milky liquor.
71. Some insects, particularly the ant, are found to contain an acid juice which approaches nearly to the nature of vegetable acids.
72. There are, however, sundry animal-juices, which differ greatly, even in these general kinds of properties, from the corresponding ones of vegetables. Thus animal-juice, which appears analogous to vegetable gummy juices, has this remarkable difference, that though it mingles uniformly with cold or warm water, yet, on considerably heating the mixture, the animal-matter separates from the watery fluid, and concretes into a solid mass. Some have been apprehensive, that the heat of the body, in some distempers, might rise to such a degree as to produce this dangerous or mortal concretion of the serous humours: but the heat requisite for this effect is greater than the human body appears capable of sustaining, being nearly about the middle point between the greatest human heat commonly observed and that of boiling water.
73. The soft and fluid parts of animals are strongly disposed to run into putrefaction; they putrefy much sooner than vegetable matters, and when corrupted prove more offensive.
74. This process takes place, in some degree, in the bodies of living animals, as often as the juices stagnate long, or are prevented, by an obstruction of the natural emunctories, from throwing off their more volatile and corruptible parts.
75. During putrefaction, a quantity of air is generated, all the humours become gradually thinner, and the fibrous parts more lax and tender. Hence the tympany which succeeds the corruption of any of the viscera, or the imprudent suppression of dysenteries by astringents; and the weakness and laxity of the vessels observable in scurvy, &c.
76. The crassamentum of human blood changes by putrefaction into a dark livid-coloured liquor; a few drops of which tinge the serum of a tawny hue; like that of the ichor of sores and dysenteric fluxes, and of the white of the eye, the saliva, the serum of blood drawn from a vein, and that which oozes from a blister in deep scurvy, and in the advanced state of malignant fevers.
77. The putrid crassamentum changes a large quantity of recent urine to a flame-coloured water so common in fevers and in the scurvy. This mixture, after standing an hour or two, gathers a cloud resembling what is seen in the crude water of acute distempers, with some oily matter on the surface, like the scum which floats on septic urine.
78. The serum of blood deposits, in putrefaction, a sediment resembling well-digested pus, and changes to a faint olive green. A serum, so far putrefied as Elements, to become green, is perhaps never to be seen in the vessels of living animals; but in dead bodies this serum is to be distinguished by the green colour which the flesh acquires in corrupting. In salted meats, this is commonly ascribed to the brine, but erroneously; for that has no power of giving this colour, but only of qualifying the taste, and in some degree the ill effects, of corrupted aliments. In foul ulcers, and other sores, where the serum is left to stagnate long, the matter is likewise found of this colour, and is then always acrimonious.
79. The putrefaction of animal-substances is prevented or retarded by all saline matters, even by the fixt and volatile alkaline salts, which have generally been supposed to produce a contrary effect. Of all the salts that have been made trial of, sea-salt seems to resist putrefaction the least: in small quantities, it even accelerates the process. The vegetable bitters, as chamomile-flowers, are much stronger antiseptics, not only preserving flesh long uncorrupted, but likewise somewhat correcting it when putrid: the mineral acids have this last effect in a more remarkable degree. Vinous spirits, aromatic and warm substances, most of the diaphoretic drugs, and the acrid plants falsely called alkalescent, as scurvy-grass and horse-radish, are also found to resist putrefaction; and some of the absorbent earths, as chalk, to promote it.
80. It is observable, that notwithstanding the strong tendency of animal-matters to putrefaction, yet broths made from them with the admixture of vegetables, instead of putrefying, turn sour. Dr Pringle finds, that when animal-flesh in substance is beaten up with bread or other farinaceous vegetables, and a proper quantity of water, into the consistence of a pap, this mixture likewise, kept in a heat equal to that of the human body, grows in a little time sour; whilst the vegetable matters, without the flesh, suffer no such change. See the Appendix to his Observations on the Diseases of the Army.
81. Animal-substances, burnt in the open air, are resolved, like vegetables, into foot and ashes; but with this difference, that no fixt alkaline salt can be obtained from the ashes, and that no acid vapour accompanies the smoke. They emit, during the burning, a fetid smell of a peculiar kind, by which animal-substances may be distinguished at once from all those of the vegetable kingdom. In close vessels, they give over, after the watery moisture, a volatile alkaline salt, which either concretes into a solid form, or dissolves in the water, and thus composes what is called spirit; together with an empyreumatic oil, of a more fetid kind than the oils of vegetables, without the least footstep of acid throughout the whole process. A black coal remains, which, in the open air, burns into white ashes void of saline matter.
82. It was observed in the preceding section, that some few vegetables, in this resolution of them by fire, discover some agreement in their matter with bodies of the animal kingdom, yielding a volatile alkaline salt in considerable quantity, with little or nothing of the acid or fixed alkali which the generality of vegetables afford. In animal-substances also there are some exceptions to the general analysis: from animal-fats, instead of a volatile alkali, an acid liquor is obtained, and their empyreumatic oil wants the peculiar offensiveness of the other animal-oils.
Sect. III. Minerals.
Art. 1. Oils and Bitumens.
83. In the mineral kingdom is found a fluid oil, called naphtha or petroleum, floating on the surface of waters, or issuing from clefts of rocks, particularly in the eastern countries, of a strong smell, very different from that of vegetable or animal oils, limpid almost as water, highly inflammable, not soluble in spirit of wine, and more adverse to union with water than any other oils.
84. There are different sorts of these mineral oils, more or less tinged, of a more or less agreeable, and a stronger or weaker smell. By the admixture of concentrated acids, which raise no great heat or conflict with them, they become thick, and at length congeal; and in these states are called bitumens.
85. These thickened or concreted oils, like the corresponding products of the vegetable kingdom, are generally soluble in spirit of wine, but much more difficulty, more sparingly, and for the most part only partially: they liquefy by heat, but require the heat to be considerably stronger. In a proper degree of heat they give out a fluid oil, greatly resembling the native petrolea, a small quantity of a black coaly matter remaining behind. Their smells are various; but all of them, either in their natural state, or when melted or set on fire, yield a peculiar kind of strong scent, called, from them, bituminous.
Art. 2. Earths.
86. In treating of vegetables and animals, we forbore to speak of their earthy matters, that the distinguishing characters of the several classes of earthy bodies might be the easier apprehended, by having them placed here in one synoptical view: the little impropriety, of joining the vegetable and animal earths to the mineral, must be overlooked for the sake of that advantage. Under the mineral earths are included stones, these being no other than earths in an indurated state. The different kinds of these bodies hitherto taken notice of, are the following.
I. Earths soluble in the nitrous, marine, and vegetable acids, but not at all, or exceeding sparingly, in the vitriolic acid. When previously dissolved in other acids, they are precipitated by the addition of this last, which thus unites with them into insipid, or nearly insipid concretes, not dissoluble in any liquor. Of this kind are,
87. [1.] The mineral calcareous earth: distinguished by its being convertible, in a strong fire without addition, into an acrimonious calx called quicklime. This earth occurs in a variety of forms in the mineral kingdom. The fine soft chalk, the coarser limestones, the hard marbles, the transparent spars, the earthy matter contained in waters, and which, separating from them, incrustates the sides of caverns or hangs in icicles from the tops, receiving from its different appearances different appellations; how strongly forever some of these bodies have been recommended for particular medical purposes, are at bottom no other than different forms of this calcareous earth; simple pulverization depriving them of the superficial characters by which they are distinguished in the mass. Most of them contain generally a greater or less admixture of some of the Elements. the indissoluble kinds of earth; which, however, affects their medicinal qualities no otherwise than by the addition which it makes to their bulk. Chalk appears to be one of the purest, and is therefore in general preferred. They all burn into a strong quicklime: in this state, a part of them dissolves in water, which thus becomes impregnated with the astringent and lithontriptic powers that have been erroneously ascribed to some of the earths in their natural state.
88. [2.] The animal calcareous earth: burning into quicklime, like the mineral. Of this kind are oyster-shells, and all the marine shells that have been examined; though with some variation in the strength of the quicklime produced from them.
89. [3.] The earth of bones and horns: not at all burning into quicklime. This kind of earth is more difficult of solution in acids than either of the preceding. It is accompanied in the subject with a quantity of gelatinous matter, which may be separated by long boiling in water, and more perfectly by burning in the open air: the earth may be extracted also from the bone or horn, though difficulty, by means of acids; whereas vegetables, and the soft parts of animals, yield their pure earth by burning only.
II. Earths soluble with ease in the vitriolic as well as other acids; and yielding, in all their combinations therewith, saline concretes soluble in water.
90. [1.] Magnesia alba: compounding with the vitriolic acid a bitter purgative liquor.
91. [2.] Aluminous earth: compounding with the vitriolic acid a very astringent liquor.
III. Earths, which by digestion in acids, either in the cold or in a moderate warmth, are not at all dissolved.
92. [1.] Argillaceous earth: becoming hard, or acquiring an additional hardness, in the fire. Of this kind of earth there are several varieties, differing in some particular properties: as the purer clays, which when moistened with water form a very viscous mass, difficultly diffusible through a large quantity of the fluid, and slowly subsiding from it; boles, less viscous, more readily miscible with water, and more readily subsiding; and ochres, which have nothing of the viscosity of the two foregoing, and are commonly impregnated with a yellow or red ferruginous calx.
93. [2.] Crystalline earth: naturally hard, so as to strike sparks with steel; becoming friable in a strong fire. Of this kind are flints, crystals, &c. which appear to consist of one and the same earth, differing in the purity, hardness, and transparency of the mass.
94. [3.] Gypseous earth: reducible by a gentle heat into a soft powder, which unites with water into a mass, somewhat viscous and tenacious while moist, but quickly drying and becoming hard. A greater heat deprives the powder of this property, without occasioning any other alteration. Such are the transparent selenite; the fibrous stony masses improperly called English tate; and the granulated gyptia, or plaster of Paris stones.
95. [4.] Talky earth: scarcely alterable by a vehement fire. The masses of this earth are generally of a fibrous or leafy texture; more or less pellucid, bright, or glittering; smooth and unctuous to the touch; too flexible and elastic to be easily pulverized; soft, so as to be cut with a knife. In these respects some of the gypseous earths greatly resemble them: but the difference is readily discovered by fire; a weak heat reducing the gypseous to powder, while the strongest makes no other alteration in the talky, than somewhat diminishing their flexibility, brightness, and unctuosity.
Art. 3. Metals.
96. Of metals, the next division of mineral bodies, the most obvious characters are, their peculiar bright aspect, perfect opacity, and great weight: the lightest of them is six, and the heaviest upwards of 19 times heavier than an equal bulk of water.
97. They all melt in the fire, except platinum; a metallic body which has not been applied to any medicinal use, and which is therefore excluded from this general view of medicinal subjects.
98. Gold and silver, how long soever they are continued in fusion, remain unchanged and undiminished. The others, if air is admitted to them, are gradually converted, with different degrees of facility, into a powdery or friable substance called calx, destitute of the metallic aspect, and much lighter in proportion to its bulk than the metal itself. This change in their obvious properties is generally accompanied with a notable alteration in their medicinal virtues: thus quicksilver, which, taken into the body in its crude state and undivided, seems inactive; when calcined by fire, proves, even in small doses, a strong emetic and cathartic, and in smaller ones a powerful alternative in chronic disorders; while regulus of antimony, on the contrary, is changed, by the same treatment, from a high degree of virulence to a state of inactivity.
99. Calces of mercury and arsenic exhale in a heat below ignition: those of lead and bismuth, in a red or low white heat, run into a transparent glass: the others are not at all vitreifiable, or not without extreme vehemence of fire. Both the calces and glasses recover their metallic form and qualities again, by the skillful addition of any kind of inflammable substance that does not contain a mineral acid.
100. All metallic bodies dissolve in acids; some only in particular acids, as silver and lead in the nitrous; some only in compositions of acids, as gold in a mixture of the nitrous and marine; and others, as iron and zinc, in all acids. Some likewise dissolve in all alkaline liquors, as copper; and others, as lead, in expressed oils. Fused with a composition of sulphur and fixed alkaline salt, they are all, except zinc, made soluble in water.
101. All metallic substances dissolved in saline liquors have powerful effects in the human body, tho' many of them appear in their pure state to be inactive. Their activity is generally in proportion to the quantity of acid combined with them: thus lead, which in its crude form has no sensible effect, when united with a small portion of vegetable acid into cerus, discovers a low degree of the styptic and malignant quality which it so strongly exerts when blended with a larger quantity of the same acid, into what is called succarum saturni: and thus mercury, with a certain quantity of the marine acid, forms the violent corrosive sublimate, which, by diminishing the proportion of acid, becomes the mild medicine called mercurius dulcis.
Art. 4. Acids.
102. The mineral acids are distinguished by the names of the concretes from which they have been principally Elements. cipally extracted; the vitriolic from vitriol, the nitrous from nitre or saltpetre, and the marine from common sea-falt. They are all highly corrosive, in somuch as not to be safely touched, unless largely diluted with water, or united with such substances as obtund or sup-press their acidity. Mixed hastily with vinous spirits, they raise a violent ebullition and heat, accompanied with a copious discharge of noxious fumes: a part of the acid unites intimately with the vinous spirit into a new compound void of acidity, called dulcified spirit.
It is observable, that the marine acid is much less disposed to this union with spirit of wine than either of the other two: nevertheless, many of the compound salts resulting from the combination of earthy and metallic bodies with this acid, are soluble in that spirit, while those with the other acids are not. All these acids effervesc strongly with alkaline salts, both fixed and volatile; and form with them neutral salts, that is, such as discover no marks either of an acid or alkaline quality.
103. We have already taken notice of two kinds of alkaline salt; the volatile alkali of animals, and the fixed alkali of vegetables. In the mineral kingdom, another species of fixed alkali, different in several respects from the vegetable, is found sometimes in a detached state, but more plentifully in combination with the marine acid, with which it composes sea-falt. From the coalition of the different acids with these three alka-likes, and with the several soluble earths and metallic bodies, result a variety of saline compounds, the principal of which will be particularized in the sequel of this treatise.
104. The vitriolic acid, in its concentrated liquid state, is much more ponderous than the other two, emits no visible vapours in the heat of the atmosphere, but imbibes moisture therefrom, and increases in its weight: the nitrous and marine emit copious corrosive fumes, the nitrous yellowish red, and the marine white ones. If bottles containing the three acids are stopped with cork, the cork is found in a little time tinged black by the vitriolic, corroded into a yellow substance by the nitrous, and into a whitish one by the marine.
105. It is above laid down as a character of one of the classes of earths, that the vitriolic acid precipitates them when they are previously dissolved in any other acid: it is obvious, that on the same principle this particular acid may be distinguished from all others. This character serves not only for the acid in its pure state, but likewise for all its combinations that are soluble in water: if a solution of any compound salt whose acid is the vitriolic, be added to a solution of chalk in any other acid, the vitriolic acid will part from the sub-stance it was before combined with, and join itself to the chalk, forming therewith a compound, which, being no longer dissoluble in the liquor, renders the whole milky for a time, and then gradually subsides.
106. This acid may be distinguished also in compound salts, by another criterion not less strongly marked: if any salt containing it be mixed with powdered charcoal, and the mixture exposed, in a cloze vessel, to a moderately strong fire, the acid will unite with the directly inflammable part of the char-coal, and compose therewith a genuine sulphur. Com-mon brimstone is no other than a combination of the vitriolic acid with a small proportion of inflammable matter. With any kind of inflammable matter that is not volatile in cloze vessels, as the coal of vegetables, of animals, or of bitumens, this acid composes always the same identical sulphur.
107. The nitrous acid also, whatever kind of body it be combined with, is both distinguished and extricated therefrom, by means of any inflammable sub-stance brought to a state of ignition: if the subject be mixed with a little powdered charcoal, and made red-hot, a deflagration or fulmination ensues, that is, a bright flame with a hissing noise; and the inflammable matter and the acid being thus consumed or dissipated together, there remains only the substance that was before combined with the acid, and the small quantity of ashes afforded by the coal.
108. This property of the nitrous acid, deflagra ting with inflammable substances, and that of the vitriolic of forming sulphur with them, serve not only as cri-teria of the respective acids in their various forms and disguises, but likewise for discovering inflammable matter in bodies, when its quantity is too small to be sensible on other trials.
109. If a fixed alkaline salt be united with a vege-table acid, as that of vinegar, into a neutral salt; on adding to this compound some marine acid, the acetic acid will be disengaged, so as to exhale totally in a moderate heat, leaving the marine in possession of the alkali; the addition of the nitrous will in like manner dispossess the marine, which now arises in its proper white fumes, though without such an addition it could not be extricated from the alkali by any degree of heat: on the addition of the vitriolic acid, the nitrous gives way in its turn, exhaling in red fumes, and leaving only the vitriolic acid and the alkali united to-gether.
110. Again, if any metallic body be dissolved in an acid, the addition of any earthy body that is disso-luble in that acid will precipitate the metal: a vola-tile alkaline salt will in like manner precipitate the earth, and a fixed alkali will dislodge the volatile; which last being readily exhaled by heat, the remain-ing salt will be the same as if the acid and fixed alkali had been joined together at first, without the interven-tion of any of the other bodies.
111. The power in bodies, on which these various transpositions and combinations depend, is called by the chemists affinity; a term, like the Newtonian attraction, designed to express, not the cause, but the ef-fect. When an acid spontaneously quits a metal to unite with an alkali, they say it has a greater affinity to the alkali than to the metal: and when, conversely, they say it has a greater affinity to fixed alkalies than to those of the volatile kind, they mean only that it will unite with the fixed in preference to the volatile, and that, if previously united with a volatile alkali, it will forsake this for a fixed one.
112. The doctrine of the affinities of bodies is of a very extensive use in the chemical pharmacy: many of the officinal processes, as we shall see hereafter, are founded on it: several of the preparations turn out very different from what would be expected by a person unacquainted with these properties of bodies; and several of them, if, from an error in the process, or other causes, they prove unfit for the use intended, may be Of the Pharmaceutical Apparatus.
117. Furnaces. One of the principal parts of the pharmaceutic apparatus consists in contrivances for containing and applying fire, and for directing and regulating its power. Of these contrivances, called furnaces, there are different kinds, according to the conveniency of the place, and the particular purposes they are intended to answer. See the article Furnace; and Chemistry, no 98, 99, 101, 102.
118. The most simple pharmaceutical furnace is the common stove, otherwise called the furnace for open fires. This is usually made of an iron hoop, five or six inches deep; with a grate or some iron-bars across the bottom, for supporting the fuel. It either stands upon feet, so as to be moveable from place to place, or is fixed in brick-work. In this last case, a cavity is left under the grate for receiving the ashes that drop through it; and an aperture or door, in the fore-part of this ash-pit, serves both for allowing the ashes to be occasionally raked out, and for admitting air to pass up through the fuel. This furnace is designed for such operations as require only a moderate heat; as infusion, decoction, and the evaporation of liquids. The vessel containing the subject-matter is supported over the fire by a treivet.
119. A deeper hoop or body, cylindrical, parallel-pipedal, widening upwards, elliptical, or of other figures; formed of, or lined with, such materials as are capable of sustaining a strong fire, with a grate and ash-pit beneath, as in the preceding, and communicating at the top with a perpendicular pipe, or chimney, makes a wind-furnace.
120. The greater the perpendicular height of the chimney, the greater will be the draught of air through the furnace, and the more intensely will the fire burn; provided the width of the chimney is sufficient to allow a free passage to all the air that the furnace can receive through the grate: for which purpose, the area of the aperture of the chimney should be nearly equal to the area of the interstices of the grate.
121. Hence, where the chimney consists of moveable pipes, made to fit upon one another at the ends, so that the length can be occasionally increased or diminished, the vehemence of the fire will be increased or diminished in the same proportion.
122. In furnaces whose chimney is fixed, the same advantage may be procured on another principle. As the intensity of the fire depends wholly upon the quantity of air successively passing through and animating the burning fuel, it is obvious, that the most vehement fire may be suppressed or restrained at pleasure, by more or less closing either the ash-pit door by which the air is admitted, or the chimney by which it passes off; and that the fire may be more or less raised again, by more or less opening those passages. A moveable plate or register, in any convenient part of the chimney, affords commodious means of varying the width of the passage, and consequently of regulating the heat.
Vol. VIII.
123. There are two general kinds of these wind-furnaces; one, with the chimney on the top, over the middle of the furnace; the other with the chimney on one side, and the mouth clear.
124. In the first, either the upper part of the furnace is contracted to such an aperture, that the chimney may fit upon it; or it is covered with an arched dome, or with a flat plate, having a like aperture in the middle. As in this disposition of the chimney, the inside of the furnace cannot be come at from above; a door is made in the side, a little above the grate, for supplying fuel, inspecting the matter in the fire, &c.
125. For performing fusions in this furnace, the crucible, or melting vessel, is placed immediately among the fuel; with a flip of brick, or some other like support, between it and the grate, to keep the cold air, which enters underneath, from striking on its bottom.
126. When designed as a reverberatory, that is, for distillation in long necks or coated glass-retorts, two iron bars are placed across, above the fire, for supporting the vessel, whose neck comes out at an aperture made for that purpose in the side. This aperture should be made in the side opposite to that in which is the door above-mentioned, or at least so remote from it, that the receiver, fitted on the neck of the distilling vessel without the furnace, may not lie in the operator's way when he wants to stir the fire or throw in fresh fuel.
127. The other kind of wind-furnace communicates, by an aperture in its back-part near the top, either with an upright pipe of its own, or with the chimney of the room; in which last case, all other passages into the chimney must be closed up. Here the mouth of the furnace serves for a door, which may be occasionally covered with a plate or tile. Of this kind is the furnace most commonly used for fusion in a crucible.
151. Vessels. Of these and other pharmaceutical instruments the principal will be mentioned in the following chapter, in speaking of the several operations, to which they are respectively subservient.
152. Weights. Two different kinds of weights are made use of in this country; one in the merchandize of gold and silver; the other for almost all goods besides. The first we call Troy, the latter Averdupois weight.
153. The goldsmiths divide the Troy pound into 12 ounces; the ounce into 20 penny-weights; and the penny-weight into 24 grains. The Averdupois pound is divided into 16 ounces; and the ounce into 16 parts, called drams.
The pound of the London and Edinburgh dispensatories (which is the only one made use of in this article) is that of the goldsmiths, divided in the following manner:
| The Pound | twelve Ounces. | |-----------|----------------| | The Ounce | contains Eight Drams. | | The Dram | three Scruples. | | The Scruple | twenty Grains. |
The grain is equal to the goldsmith's grain.
154. The medical or Troy pound is less than the averdupois, but the ounce and the dram greater. The Troy pound contains 5760 grains; the averdupois 7000 grains. The Troy ounce contains 480 grains; the averdupois only 437½. The Troy dram 60; the averdupois dram somewhat more than 27. Eleven drams averdupois are equal to five drams Troy; 12 ounces averdupois Elements. averdupois to nearly 11 ounces Troy; and 19 pounds averdupois to somewhat more than 23 pounds Troy.
155. These differences in our weights have occasioned great confusion in the practice of Pharmacy. As the druggists and grocers fell by the averdupois weight, the apothecaries have not in general kept any weights adjusted to the Troy pound greater than two drams, using for all above averdupois. By this means it is apparent, that in all compositions, where the ingredients are prescribed, some by pounds and others by ounces, they are taken in a wrong proportion to each other; and the same happens when any are directed in lesser denominations than the ounce, as these subdivisions used by the apothecaries are made to a different ounce. The mercurial plaster of the late Pharmacopoeia, and the mercurial cerate of the present, if compounded by the averdupois weight, contain about one sixth less quicksilver than if made, as they ought to be, by the Troy. This error prevailed so far as to be received in some former editions of the London Pharmacopoeia itself; but is now happily removed.
156. Measures. The measures employed with us in pharmacy are the common wine-measures.
A Gallon = Eight Pints (librae). The Pint contains Sixteen Ounces. The Ounce = Eight Drams.
157. By a spoonful, in the London dispensatory, is understood, the measure of half an ounce; in the Edinburgh, half an ounce weight in syrups, and three drams in distilled waters.
158. Though the pint is called by Latin writers libra or "pound," there is not any known liquor of which a pint-measure answers to that weight. A pint of the highest rectified spirit of wine exceeds a pound by above half an ounce; a pint of water exceeds it by upwards of three ounces; and a pint of oil of vitriol weighs more than two pounds and a quarter.
159. A table of the weights of certain measures of different fluids may on many occasions be useful, both for assiting the operator in regulating their proportions in certain cases, and for shewing the comparative gravities of the fluids themselves. Dr Lewis has drawn up such a table for a pint, an ounce, and a dram measure of those liquids, whose gravity has been determined by experiments that can be relied on. The wine-gallon contains 231 cubic inches; whence the pint contains 28 7/8; the ounce 1 10 1/2; and the dram 1 1/4 of a cubic inch.
| Inflammable Spirits. | |---------------------| | Ætheral spirit of wine | 11 1 36 | 336 | 42 | | Highly-rectified spirit of wine | 12 5 20 | 380 | 47 1/2 | | Common-rectified spirit of wine | 13 2 40 | 400 | 50 | | Proof-spirit | 14 1 36 | 426 | 53 | | Dulcified spirit of salt | 14 4 48 | 438 | 55 | | Dulcified spirit of nitre | 15 2 40 | 460 | 57 1/2 |
| Wines. | |--------| | Burgundy | 14 1 36 | 426 | 53 | | Red port | 15 1 36 | 456 | 57 | | Canary | 15 6 40 | 475 | 59 1/2 |
| Express Oils. | |---------------| | Oil-olive | 14 0 0 | 420 | 52 1/2 | | Linseed-oil | 14 2 8 | 428 | 53 1/2 |
| Essential Oils. | |-----------------| | Oil of turpentine | 12 1 4 | 364 | 45 1/2 | | of orange-peel | 408 | 51 | | of juniper-berry | 419 | 52 | | of rolfmary | 430 | 54 | | of origanum | 432 | 54 | | of caraway-seeds | 432 | 54 | | of nutmegs | 436 | 54 1/2 | | of savin | 443 | 55 1/2 | | of hyssop | 443 | 55 1/2 | | of cummin-seed | 448 | 56 | | of mint | 448 | 56 | | of pennyroyal | 450 | 56 1/2 | | of dill-seed | 457 | 57 | | of fennel-seed | 458 | 57 | | of cloves | 476 | 59 1/2 | | of cinnamon | 476 | 59 1/2 | | of saffras | 503 | 63 |
| Alkaline Liquors. | |-------------------| | Lixiv. faponarium, Phar. Lond. | 16 0 0 | 480 | 60 | | Spirit of sal ammonia | 17 1 10 | 515 | 64 1/2 | | Strong soap-boilers ley | 17 6 24 | 534 | 67 | | Lixivium tartari | 24 0 0 | 720 | 90 |
| Acid Liquors. | |---------------| | Wine-vinegar | 15 3 44 | 464 | 58 | | Beer-vinegar | 15 6 56 | 476 | 59 1/2 | | Glauber's spirit of salt | 17 4 0 | 525 | 65 1/2 | | Glauber's spirit of nitre | 20 2 40 | 610 | 76 | | Strong oil of vitriol | 28 5 20 | 860 | 107 1/2 |
| Animal Fluids. | |----------------| | Urine | 15 5 20 | 470 | 59 | | Cows milk | 15 6 40 | 475 | 59 1/2 | | Asses milk | 16 0 0 | 480 | 60 | | Blood | 16 1 4 | 484 | 60 1/2 |
| Waters. | |---------| | Distilled water | 15 1 50 | 456 | 57 | | Rain-water | 15 2 40 | 460 | 57 1/2 | | Spring-water | 15 3 12 | 462 | 58 | | Sea-water | 15 5 20 | 470 | 59 |
| Quicksilver. | |--------------| | 214 5 20 | 6440 | 805 |
CHAP. III.
Of the Pharmaceutical Operations.
SECT. I. Solution.
160. Solution is an intimate commixture of solid bodies with fluids into one seemingly homogeneous liquor. The dissolving fluid is called a Menstruum or Solvent.
161. The principal menstrua made use of in pharmacy, are water, vinous spirits, oils, acid and alkaline liquors.
162. Water is the menstruum of all salts, of vegetable gums, and of animal gellies. Of salts it dissolves only a determinate quantity, though of one kind of salt more than another; and being thus saturated, leaves any additional quantity of the same salt untouched.
163. Experiments have been made for determining the Elements, the quantities of water which different salts require for their dissolution: Mr Eller has given a large set in the Memoirs of the royal academy of sciences of Berlin for the year 1750, from which the following table is extracted.
Eight ounces by weight of distilled water dissolved
| Salt | oz. | dr. | gr. | |---------------------------|-----|-----|-----| | Of refined sugar | 24 | | | | Green vitriol | 9 | 4 | | | Blue vitriol | 9 | | | | White vitriol | 4 | 4 | | | Epsom salt | 4 | | | | Purified nitre | 4 | | | | Soluble tartar | 4 | | | | Common salt | 3 | 4 | | | Sal gemmae | 3 | 4 | | | Sal catharticus Glauberi | 3 | 4 | | | Seignette's salt | 3 | | | | Alum | 2 | 4 | | | Sal ammoniac | 2 | 4 | | | Vitriolated tartar | 1 | 4 | | | Salt of hartshorn | 1 | 4 | | | Sugar of lead | 1 | 2 | | | Cream of tartar | 1 | | | | Borax | 0 | 4 | 20 |
164. Though great care appears to have been taken in making these experiments, it is not to be expected, that the proportions of the several salts, soluble in a certain quantity of water, will always be found exactly the same with those above set down. Salts differ in their solubility according to the degree of their purity, perfection, and dines: the vitriols, and the artificial compound salts in general, differ remarkably in this respect, according as they are more or less impregnated with the acid ingredient. Thus vitriolated tartar, perfectly neutralized, is extremely difficult of solution: the matter which remains in making Glauber's spirit of nitre, is no other than a vitriolated tartar; and it dissolves so difficulty, that the operator is obliged to break the retort in order to get it out; but on adding more of the vitriolic acid, it dissolves with ease. Hence many have been tempted to use an over-proportion of acid in this preparation; and we frequently find in the shops, under the name of vitriolated tartar, this acid soluble salt. The degree of heat occasions also a notable difference in the quantity of salt taken up: in very cold weather, eight ounces of water will dissolve only about one ounce of nitre; whereas, in warm weather, the same quantity will take up three ounces or more. To these circumstances are probably owing, in great part, the remarkable differences in the proportional solubilities of salt, as determined by different authors: it is observable, that common salt is less affected in its solubility, by a variation of heat, than any other, water in a temperate state dissolving nearly as much of it as very hot water; and accordingly this is the salt in which the different experiments agree the best. In the experiments of Hoffmann, Neumann, and Petit, the proportion of this salt, on a reduction of the numbers, comes out exactly the same, viz. three ounces of the salt to eight of water: Dr Brownrigg makes the quantity of salt a little more; Dr Grew, a dram and a scruple more; and Eller, as appears in the above table, four drams more: so that in the trial of six different persons, made probably in different circumstances, the greatest difference is only one-sixth of the whole quantity of salt; whereas in some other salts there are differences of twice or thrice the quantity of the salt. In the experiments from which the table is drawn, the water was of the temperature of between 40 and 42 degrees of Fahrenheit's thermometer, or above freezing by about one-seventh of the interval between freezing and the human heat.
165. Some salts omitted by Eller are here subjoined: the first is taken from Dr Grew, and the other four from Neumann.
Eight ounces of water dissolved
| Salt | oz. | dr. | gr. | |---------------------------|-----|-----|-----| | Of fixed alkaline salt | | | | | Sal diuretics | 8 | | | | Sugar-candy, both brown and white | 9 | | | | Sugar of milk | 0 | 2 | 40 | | Essential salt of ferret | 0 | 1 | 20 |
166. Though water takes up only a certain quantity of one kind of salt, yet when saturated with one, it will still dissolve some portion of another; and when it can bear no more of either of these, it will still take up a third, without letting go any of the former. The principal experiments of this kind that have been made relative to pharmaceutic subjects, are exhibited in the following table, of which the two first articles are from Grew, and the others from Eller.
Water, 32 parts by weight fully saturated with
| Salt | oz. | dr. | gr. | |---------------------------|-----|-----|-----| | Nitre | | | | | Common salt | | | | | Nitre | | | | | Fixed alkali | | | | | Volatile alkali | | | | | Sal ammoniac | | | | | Soluble tartar | | | | | Vitriolated tartar | | | | | Glauber's salt | | | | | Epsom salt | | | | | Borax | | | |
dissolved afterwards
| Salt | oz. | dr. | gr. | |---------------------------|-----|-----|-----| | Sal ammoniac | 10 | | | | Nitre | 10 | | | | Fixed alkali | 7 | | | | Nitre, near | 2 | | | | Nitre | 4 | | | | Common salt | 2 | | | | Nitre | 2 | | | | Fixed alkali | 2 | | | | Nitre | 1 | | | | Sugar | 6 | | | | Fixed alkali | 2 | | |
167. In regard to the other class of bodies which water is a menstruum for, viz. those of the gummy and gelatinous kind, there is no determinate point of saturation: the water unites readily with any proportions of them, forming with different quantities liquors of different consistences. This fluid takes up likewise, when assisted by trituration, the vegetable gummy resins, as ammoniacum and myrrh; the solutions of which, though imperfect, that is, not transparent, but turbid and of a milky hue, are nevertheless applicable to valuable purposes in medicine. It mingles with vinous spirits, with acid and alkaline liquors, not with oils; but imbibes some of the more subtle parts of essential oils, so as to become impregnated with their smell and taste.
168. Rectified spirit of wine is the menstruum of the essential oils, resins and camphor of vegetables; of the pure distilled oils, and several of the colouring and medicinal parts of animals; of some mineral bituminous Elements, tuminous substances, as of ambergris; and of soaps, though it does not act upon the expressed oil and fixed alkaline salt of which soap is composed; whence, if soap contains any superfluous quantity of either the oil or salt, it may, by means of this menstruum, be excellently purified therefrom. It dissolves, by the affluence of heat, volatile alkaline salts; and, more readily, the neutral ones, composed either of fixed alkali and the acetic acid, as the sal diureticus, or of volatile alkali and the nitrous acid, as also the salt of amber, &c. It mingles with water and with acids; not with alkaline lixivias.
169. Oils dissolve vegetable resins and balsams, wax, animal-fat, mineral bitumens, sulphur, and certain metallic substances, particularly lead. The expressed oils are, for most of these bodies, more powerful menstrua than those obtained by distillation; as the former are more capable of sustaining, without injury, a strong heat, which is, in most cases, necessary to enable them to act. It is said, that one ounce of sulphur will dissolve in three ounces of expressed oil, particularly that of linseed; but requires six ounces of essential oil, as that of turpentine.
170. All acids dissolve alkaline salts, alkaline earths, and metallic substances. The different acids differ greatly in the action upon these last; one dissolving only some particular metals; and another, others.
171. The vegetable acids dissolve a considerable quantity of zinc, iron, copper, lead, and tin; and extract so much from the metallic part of antimony, as to become powerfully emetic: they dissolve lead more readily, if the metal is previously calcined by fire, than in its metallic state.
172. The marine acid dissolves zinc, iron, and copper; and though it scarce acts on any other metallic substance in the common way of making solutions, it may nevertheless be artfully combined with them all except gold: the corrosive sublimate, and antimonial caustic of the shops, are combinations of it with mercury and the metallic part of antimony, effected by applying the acid, in the form of fume, to the subjects, at the same time also strongly heated.
173. The nitrous acid is the common menstruum of all metallic substances, except gold and the metallic part of antimony; of which two, the proper solvent is a mixture of the nitrous and marine acids called aqua regia.
174. The vitriolic acid, diluted with water, easily dissolves zinc and iron: in its concentrated state, and assisted by a boiling heat, it may be made to corrode, or imperfectly dissolve, most of the other metals.
175. Alkaline lixivia dissolve oils, resinous substances, and sulphur. Their power is greatly promoted by the addition of quicklime; instances of which occur in the preparation of soap, and in the common caustic. Thus acuated, they reduce the flesh, bones, and other solid parts of animals, into a gelatinous matter.
176. Solutions made in water, and in spirit of wine, possess the virtues of the body dissolved; whilst oils generally sheathe its activity, and acids and alkalies vary its quality. Hence watery and spirituous liquors are the proper menstrua of the native virtues of vegetable and animal matters.
177. Most of the foregoing solutions are easily effected, by pouring the menstruum on the body to be dissolved, and suffering them to stand together, for some time, exposed to a suitable warmth. A strong heat is generally requisite to enable oils and alkaline liquors to perform their office: nor will acids act on some metallic bodies without its assistance. The action of watery and spirituous menstrua is likewise expedited by a moderate heat; though the quantity which they afterwards keep dissolved is not, as some suppose, by this means increased: all that heat occasions these to take up more than they would do in a longer time in the cold, will, when the heat ceases, subside again: this at least is most commonly the case, though there may be some instances of the contrary.
178. The action of acids on the bodies which they dissolve, is generally accompanied with heat, effervescence, and a copious discharge of fumes. The fumes which arise during the dissolution of some metals in the vitriolic acid, prove inflammable: hence in the preparation of the artificial vitriol of iron and zinc, the operator ought to be careful, especially where the solution is made in a narrow-mouthed vessel; lest, by the imprudent approach of a candle, the exhaling vapour be set on fire.
179. There is another species of solution, in which the moisture of the air is the menstruum. Fixed alkaline salts, and those of the neutral kind, composed of alkaline salts and the vegetable acids, or of soluble earths and any acid except the vitriolic, and some metallic salts, on being exposed for some time to a moist air, gradually attract its humidity, and at length become liquid. Some substances, not dissoluble by the application of water in its grosser form, as the butter of antimony, are easily liquefied by this slow action of the aerial moisture. This process is termed Deliquiation.
Sect. II. Extraction.
180. The liquors which dissolve certain substances in their pure state, serve likewise to extract them from admixtures of other matter. Thus rectified spirit of wine, the menstruum of essential oils and resins, takes up the virtues of the resinous and oily vegetables; as water does those of the mucilaginous and saline; the inactive earthy parts remaining untouched by both. Water extracts likewise from many plants substances which by themselves it has little effect upon; even essential oils being, as we have formerly observed, rendered soluble in that fluid, by the admixture of gummy and saline matter, of which all vegetables participate in a greater or less degree. Thus many of the aromatic plants, and most of the bitters and astringents, yield their virtues to this menstruum.
181. Extraction is performed by maceration or steeping the subject in its appropriated menstruum in the cold, or digesting or circulating them in a moderate warmth; or infusing the plant in the boiling liquor, and suffering them to stand in a covered vessel till grown cold; or actually boiling them together for some time.
182. The term digestion is sometimes used for maceration; and in this case the process is directed to be performed without heat: where this circumstance is not expressed, digestion always implies the use of heat. Circulation differs from digestion only in this, that the steam, into which a part of the liquor is resolved by the heat, is, by means of a proper disposition of the vessels, Elements, vessels, condensed and conveyed back again upon the subject. Digestion is usually performed in a matrafs, (or bolthead), Florence flask, or the like; either of which may be converted into a circulatory vessel, by inverting another into the mouth, and securing the juncture with a piece of wet bladder. A single matrafs, if its neck is very long and narrow, will answer the purpose as effectually, the vapour cooling and condensing before it can rise to the top. In a vessel of this kind, even spirit of wine, one of the most volatile liquors we know of, may be boiled without any considerable loss. The use of this instrument is likewise free from an inconvenience which may, in some cases, attend the other, of the uppermost vessel being burnt or thrown off. As the long-necked matrafs here recommended are difficultly filled or emptied, and likewise very dear, a long glass-pipe may be occasionally luted to the shorter ones.
183. Heat greatly expedites extraction; but by this means proves as injurious to some substances, by occasioning the menstruum to take up their groser and more ungrateful parts, as it is necessary for enabling it to extract the virtues of others. Thus guaiacum or logwood impart little to aqueous liquors without a boiling heat, whilst even a small degree of warmth proves greatly prejudicial to the fine bitter of carduus benedictus. This plant, which, infused in boiling, or digested in feebly hot water, gives out a nauseous taste, so offensive to the stomach as to promote vomiting, yields to the cold element a grateful balsamic bitter, the most elegant stomachic of the shops.
184. As heat promotes the dissolving power of liquids; so cold, on the other hand, diminishes it. Hence tinctures, or extractions made by a considerable heat, deposit in cold weather a part of their contents, and thus become proportionably weaker; a circumstance which deserves particular regard.
Sect. III. Depuration.
185. There are different methods of depurating or purifying liquors from their feculences, according as the liquor itself is more or less tenacious, or the feculent matter of greater or less gravity.
186. Thin fluids readily deposit their more ponderous impurities upon standing at rest for some time in a cool place: and may then be decanted, or poured off clear, by inclining the vessel.
187. Glutinous, unctuous, or thick substances, are to be liquefied by a suitable heat; when the groser feculencies will fall to the bottom, the lighter rising to the surface, to be distillated or scummed off.
188, 189. Where the impurities are neither so ponderous as to subside freely to the bottom, nor so light as to arise readily to the surface, they may be separated in great measure by colature through strainers of linen, woollen, or other cloth, and more perfectly by filtration through a soft bibulous kind of paper made for this use.
190. Glutinous and unctuous liquors, which do not easily pass through the pores of a filter or strainer, are clarified by beating them up with whites of eggs; which concreting or growing hard when heated, and entangling the impure matter, arise with it to the surface. The mixture is to be gently boiled till the foam begins to break, when the vessel is to be removed from the fire, the crust taken off, and the liquor passed through a flannel-bag.
191. Decantation, colature, and filtration, are applicable to most of the medicated liquors that stand in need of purification. Distillation and clarification very rarely have place; since these, along with the impurities of the liquor, frequently separate its medicinal parts. Thus, if the decoction of poppy-heads for making diacodium be solicitously scummed or clarified, (as some have been accustomed to do), the medicine will lose almost all that the poppies communicated; and instead of a mild opiate, turn out little other than a plain syrup of sugar.
192. It may be proper to observe, that the common sorts of filtering-paper are apt to communicate a disagreeable flavour: and hence, in filtering fine bitters, or other liquors whose gratefulness is of primary consequence, the part which passes through first ought to be kept apart for inferior purposes.
Sect. IV. Crystallization.
193.—197. Water, assisted by heat, dissolves a larger proportion of saline substances than it can retain when grown cold. Hence, on the abatement of the heat, a part of the salt separates from the menstruum, and concretions at the sides and bottom of the vessel. These concretions, unless too hastily formed by the sudden cooling of the liquor, or disturbed in their coalescence by agitation or other like causes, prove transparent, and of regular figures, resembling in appearance the natural spring-crystals.
198. Different salts require different quantities of water to keep them dissolved: and hence if a mixture of two or more be dissolved in this fluid, they will begin to separate and crystallize at different periods of the evaporation. Upon this foundation salts are freed not only from such impurities as water is not capable of dissolving and carrying through the pores of a filter, but likewise from admixtures of one another; that which requires most water to dissolve in shooting first into crystals.
Sect. V. Precipitation.
199. By this operation, bodies are recovered from their solutions by means of the addition of some other substance, with which either the menstruum, or the body dissolved, have a greater affinity than they have with one another.
200, 201. Precipitation, therefore, is of two kinds; one where the substance superadded unites with the menstruum, and occasions that before dissolved to be thrown down; the other, in which it unites with the dissolved body, and falls along with it to the bottom. Of the first we have an example in the precipitation of sulphur from alkaline lixivia by the means of the acid; of the second, in the precipitation of mercury from aquafortis by sea-salt or its acid.
189. Where metals are employed as precipitants, as in the purification of martial vitriol from copper, by the addition of fresh iron, they ought to be perfectly clean and free from any rusty or greasy matter; otherwise they will not readily, if at all, dissolve, and consequently the precipitation will not succeed; for the substance to be precipitated separates only by the additional one dissolving and taking its place. The separated separated powder oftentimes, instead of falling to the bottom, lodges upon the precipitant; from which it must be occasionally shaken off, for reasons sufficiently obvious.
203. Though in this operation the precipitated powder is generally the part required for use, yet some advantage may frequently be made of the liquor remaining after the precipitation. Thus when fixed alkaline salt is dissolved in water, and sulphur dissolved in this liquorium, the addition of acids separates and throws down the sulphur, only in virtue of the acid uniting with and neutralizing the alkali by which the sulphur was held dissolved; consequently, if the precipitation is made with the vitriolic acid, and the acid gradually dropped in till the alkali is completely saturated, that is, so long as it continues to occasion any precipitation or turbidness, the liquor will yield, by proper evaporation and crystallization, a neutral salt, composed of the vitriolic acid and fixed alkali, that is, vitriolated tartar. In like manner, if the precipitation is made with the nitrous acid, a true nitre may be recovered from the liquor; if with the marine, the salt called *spiritus falsi marini coagulatus*; and if with the acid of vinegar, the *sal diureticus*.
**Sect. VI. Evaporation.**
204. This is a third method of recovering solid bodies from their solutions, effected by the means of heat; which evaporating the fluid part, that is, forcing it off in steam, the matter which was dissolved therein is left behind in its solid form.
205. This process is applicable to the solutions of all those substances which are less volatile than the menstruum, or which will not exhale by the heat requisite for the evaporation of the fluid; as the solutions of fixed alkaline salts, of the gummy, gelatinous, and other inodorous parts of vegetables and animals in water, and of many resinous and odorous substances in spirit of wine.
206. Water extracts the virtues of sundry fragrant aromatic herbs almost as perfectly as rectified spirit of wine: but the aqueous infusions are far from being equally suited to this process with those made in spirit; water carrying off the whole odour and flavour of the subject, which that lighter liquor leaves entire behind it. Thus a watery infusion of mint loses in evaporation the smell, taste, and virtues of the herb; whilst a tincture drawn with pure spirit yields, on the same treatment, a thick balsamic liquid, or solid gummy resin, extremely rich in the peculiar qualities of the mint.
207. In evaporating these kinds of liquors, particular care must be had, towards the end of the process, that the heat be very gentle; otherwise the matter as it grows thick will burn to the vessel, and contract a disagreeable smell and taste: this burnt flavour is called an *empyreuma*. The liquor ought to be kept stirring during the evaporation; otherwise a part of the matter concretes on the surface exposed to the air, and forms a pellicle which impedes the farther evaporation.
**Sect. VII. Distillation.**
208. In the foregoing operation, fluids are rarefied by heat into steam or vapour, which is suffered to exhale in the air, but which the business of this is to collect and preserve. For this purpose the steam is received in proper vessels, fitted to that in which the subject is contained; and being there cooled, condensed into a fluid form again.
209. There are two kinds of distillation: by the one, the more subtle and volatile parts of liquors are elevated from the grosser; by the other, liquids, incorporated with solid bodies, are forced out from them by vehemence of fire.
210. To the first belongs the distillation of the pure inflammable spirit from vinous liquors, and of such of the active parts of vegetables as are capable of being extracted by boiling water or spirit, and at the same time of arising along with their steam.
211. As boiling water extracts or dissolves the essential oils of vegetables whilst blended with the other principles of the subject without saturation, but imbibes only a determinate, and that a small, portion of them in their pure state; as these oils are the only substances contained in common vegetables, which prove totally volatile in that degree of heat; and as it is in them that the virtues of aromatics, and the peculiar odour and flavour of all plants, reside; it is evident that water may be impregnated, by distillation, with the more valuable parts of many vegetables: that this impregnation is limited, the oil arising in this process pure from those parts of the plant which before rendered it soluble in water without limitation; hence greatest part of the oil separates from the distilled aqueous liquor, and, according to its greater or less gravity, either sinks to the bottom or swims on the surface; that consequently infusions and distilled waters are greatly different from one another: that the first may be rendered stronger and stronger by pouring the liquor on fresh parcels of the subject; but that the latter cannot be in like manner improved by cohobating, or redistilling them from fresh ingredients.
212. As the oils of many vegetables do not freely distil with a less heat than that in which water boils, as rectified spirit of wine is not susceptible of this degree of heat, and as this menstruum totally dissolves these oils in their pure state; it follows, that spirit elevates far less from most vegetables than water; but that nevertheless the distilled spirit, by keeping all that it does elevate perfectly dissolved, may, in some cases, prove as strong of the subject as the distilled water.
213. The apparatus made use of for distilling spirits, waters, and oils, consists of a still, or copper vessel, for containing the subject, on which is fitted a large head with a swan neck. The vapour arising into the head, is thence conveyed through a worm, or long spiral pipe, placed in a vessel of cold water called a refrigeratory; and being there condensed, runs down into a receiver.
214. It may be observed, that as the parts which are preserved in evaporation cannot arise in distillation, the liquor remaining after the distillation, properly depurated and insipidated, will yield the same extracts as those prepared from the tincture or decoction of the subject made on purpose for that use; the object of these operations collecting only the volatile parts, and the the other the more fixed; so that where one subject contains medicinal parts of both kinds, they may thus be obtained distinct, without one being injured by the process which collects the other.
215, 216, 217. The subjects of the second kind of distillation are, the gross oils of vegetables and animals, the mineral acid spirits, and the metallic fluid quicksilver; which as they require a much stronger degree of heat to elevate them than the foregoing liquors can sustain, so they likewise condense without arising so far from the action of the fire. The distillation of these is performed in low glass vessels, called, from their neck being bent to one side, retorts; to the farther end of the neck a receiver is luted, which standing without the furnace, the vapours soon condense in it, without the use of a refrigeratory; nevertheless, to promote this effect, some are accustomed, especially in warm weather, to cool the receiver, by occasionally applying wet cloths to it, or keeping it partly immersed in a vessel of cold water.
Sect. VIII. Sublimation.
218. As all fluids are volatile by heat, and consequently capable of being separated, in most cases, from fixed matters by the foregoing process; so various solid bodies are subjected to a similar treatment. Fluids are said to distil, and solids to sublime; though sometimes both are obtained in one and the same operation. If the subliming matter concretes into a mass, it is commonly called a sublimate; if into a powdery form, flowers.
219. The principal subjects of this operation are, volatile alkaline salts; neutral salts, composed of volatile alkalies and acids, as sal ammoniac; the salt of amber, and flowers of benzoin; mercurial preparations; and sulphur. Bodies of themselves not volatile are frequently made to sublime by the mixture of volatile ones; thus iron is carried up by sal ammoniac in the preparation of the flores martiales.
220. The fumes of solid bodies in close vessels rise but little way, and adhere to that part of the vessel where they concrete. Hence a receiver or condenser is less necessary here than in the preceding operation; a single vessel, as a matras, or tall vial, or the like, being frequently sufficient. The most commodious apparatus for the sublimation of particular substances, and the most advantageous method of conducting the several processes, will be afterwards delivered.
Sect. IX. Expression.
221. The press is chiefly made use of for forcing out the juices of succulent herbs and fruits, and the insipid oils of the unctuous seeds and kernels.
222. The harder fruits, as quinces, require to be previously well beat or ground; but herbs are to be only moderately bruised. The subject is then included in a hair-bag, and pressed between wooden plates, in the common screw-press, as long as any juice runs from it.
223. The expression of oils is performed nearly in the same manner as that of juices; only here, iron plates are substituted to the wooden ones there made use of. The subject is well pounded, and included in a strong canvas-bag, betwixt which and the plates of the press a hair-cloth is interposed.
224. The insipid oils of all the unctuous seeds are obtained, uninjured, by this operation, if performed without the use of heat, which though it greatly promotes the extraction of the oil, at the same time impresses an ungrateful flavour, and increases its disposition to grow rancid.
225. The oils expressed from aromatic substances generally carry with them a portion of their essential oil; hence the smell and flavour of the expressed oils of nutmegs and mace. They are very rarely found impregnated with any of the other qualities of the subject: oil of mustard seed, for instance, is as soft and void of acrimony as that of almonds, the pungency of the mustard remaining entire in the cake left after the expression.
Sect. X. Exsiccation.
226. There are two general methods of exsiccating or drying moist-bodies: in one, their humid parts are exhaled by heat; in the other, they are imbibed or absorbed by substances whose soft and spongy texture adapts them to that use. Bodies intimately combined with or dissolved in a fluid, as recent vegetables and their juices, require the first; such as are only superficially mixed, as when earthy or indissoluble powders are ground with water, are commodiously separated from it by the second.
227. Vegetables and their parts are usually exsiccated by the natural warmth of the air; the affluence of a gentle artificial heat may, nevertheless, in general, be not only safely, but advantageously had recourse to. By a moderate fire, even the more tender flowers may be dried in a little time, without any loss either of their odour or lively colour; which would both be greatly injured or destroyed by a more slow exsiccation in the air. Some plants indeed, particularly those of the acid kind, as horseradish, fennel, grapes, and arum, lose their virtues by this process, however carefully performed; but far the greater number retain them unimpaired, and oftentimes improved.
228. The thicker vegetable juices may be exsiccated by the heat of the sun; or, where this is not sufficient, by that of a water bath, or an oven moderately warm. The thinner juices may be gently boiled till they begin to thicken, and then treated as the foregoing; this process, termed insipillation or evaporation, has been spoken of already. The juices of some plants, as arum-root, briony-root, orris-root, wild cucumbers, &c., separate, upon standing for some time, into a thick part which falls to the bottom, and a thin aqueous one which swims above it: this last is to be poured off, and the first exsiccated by a gentle warmth; preparations of this kind have been usually called faculae; that of the wild cucumber, is the only one which practice now retains.
229. Indissoluble bodies mixed with water into a thick consistence, may be easily freed from the greatest part of it, by dropping them on a chalk-flone, or some powdered chalk pressed into a smooth mass, which readily imbibes their humidity. Where the quantity of fluid is large, as in the edulcoration of precipitates, it may be separated by decantation or filtration.
Sect. XI. Commination.
230. Commination is the bare reduction of solid coherent coherent bodies into small particles or powder. The methods of effecting this are various, according to the texture of the subject.
231. Dry friable bodies, or such as are brittle and not very hard, and mixtures of these with somewhat moist ones, are easily pulverized in a mortar.
232. For very light dry substances, resins, and the roots of a tenacious texture, the mortar may in some cases be previously rubbed with a little sweet oil, or a few drops of oil be occasionally added: this prevents the finer powder of the first from flying off, and the others from coliering under the pestle. Camphor is most commodiously powdered, by rubbing it with a little rectified spirit of wine.
233. Tough substances, as woods, the peels of oranges and lemons, &c. are most conveniently raked; and soft oily bodies, as nutmegs, passed through a grater.
234. The comminution of the harder minerals, as calamine, crystal, flint, &c. is greatly facilitated by extinction; that is, by heating them red hot, and quenching them in water: by repeating this process a few times, most of the hard stones becomes easily pulverizable. This process, however, is not to be applied to any of the alkaline or calcareous stones; lest, instead of an insipid powder, we produce an acrimonious calx or lime.
235. Some metals, as tin, though strongly cohering in their natural state, prove extremely brittle when heated, insomuch as to be easily divided into small particles by dextrous agitation. Hence the officinal method of pulverizing tin, by melting it, and, at the instant of its beginning to return into a state of fluidity, briskly shaking it in a wooden box. The comminution of metals in this manner is termed by the metallurgists granulation.
236. On a similar principle, certain salts, as nitre, may be reduced into powder in large quantity, by dissolving them in boiling water, setting the solution over a moderate fire, and keeping the salt constantly stirring during its evaporation, so as to prevent its particles, disjoined by the fluid, from re-uniting together into larger masses.
237. Powders are reduced to a great degree of fineness by triturating or rubbing them for a length of time in a mortar. Such as are not dissoluble in water, or injured by the admixture of that fluid, are moistened with it into the consistence of a paste, and levigated or ground on a flat smooth marble or iron plate; or where a large quantity is to be prepared at times, in mills made for that use.
238. Comminution, though one of the most simple operations of pharmacy, has, in many cases, very considerable effects. The resinous purgatives, when finely triturated, are more easily soluble in the animal-fluids, and consequently prove more cathartic and less irritating than in their grosser state. Crude antimony, which when reduced to a tolerably fine powder discovers little medicinal virtue, if levigated to a great degree of subtlety, proves a powerful alternative in many chronic disorders.
239. By comminution, the heaviest bodies may be made to float in the lightest fluids, for a longer or shorter time, according to their greater or less degree of tenuity. Hence we are furnished with an excellent criterion of the fineness of certain powders, and a method of separating the more subtle parts from the grosser, distinguished by the name of elutriation, or washing over. See 275, &c.
Sect. XII. Fusion.
240. Fusion is the reduction of solid bodies into a state of fluidity by fire. Almost all natural substances, the pure earths and the solid parts of animals and vegetables excepted, melt in proper degrees of fire; some in a very gentle heat, whilst others require its utmost violence.
241. Turpentine, and other soft resinous substances, liquefy in a gentle warmth; wax, pitch, fulphur, and the mineral bitumens, require a heat too great for the hand to support; fixed alkaline salts, common salt, and nitre, require a red or almost white heat to melt them; and glaas, a full white heat.
242. Among metallic substances, tin, bismuth, and lead, flow long before ignition; antimony likewise melts before it is visibly red-hot, but not before the vessel is considerably so: the regulus of antimony demands a much stronger fire. Zinc begins to melt in a red heat; gold and silver require a low white heat; copper, a bright white heat; and iron, an extreme white heat.
243. One body, rendered fluid by heat, becomes sometimes a menstruum for another not fusible of itself in the same degree of fire. Thus red-hot silver melts on being thrown into melted lead less hot than itself: and thus if steel, heated to whiteness, be taken out of the furnace, and applied to a roll of sulphur; the sulphur instantly liquefying, occasions the steel to melt with it; hence the catalys cum sulphure of the shops. This concrete, nevertheless, remarkably impedes the fusion of some other metals, as lead, which, when united with a certain quantity of sulphur, is scarce to be perfectly melted by a very strong fire; hence the method, described in its place, of purifying zinc, a metal which sulphur has no effect upon, from the lead so frequently mixed with it.
244. Sulphur is the only unmetallic substance which mingles in fusion with metals. Earthy, saline, and other like matters, even the calces and glasses prepared from metals themselves, float distinct upon the surface, and form what is called scoriae or drosses. Where the quantity of this is large in proportion to the metal, it is most commodiously separated by pouring the whole into a conical mould: the pure metal or regulus, tho' small in quantity, occupies a considerable height in the lower narrow part of the cone, and when congealed may be easily freed from the scoriae by a hammer. The mould should be previously greased, or rather smoked, to make the metal come freely out; and thoroughly dried and heated, to prevent the explosion which sometimes happens from the sudden contact of melted metals with moist bodies.
Sect. XIII. Calcination.
245. By calcination is understood the reduction of solid bodies by the means of fire, from a coherent to a powdery state, accompanied with a change of their quality; in which last respect this process differs from comminution.
246. To this head belong the burning of vegetable Part II.