distilled by boiling them in water in the common manner. Plants differ so much, according to the soil and season of which they are the produce, and likewise according to their own ages, that it is impossible to fix the quantity of water to be drawn from a certain weight of them to any invariable standard. The distillation may always be continued as long as the liquor runs well flavoured off the subject, but no longer. In the distillation of essential oils, the water, as was observed in the foregoing section, imbibes always a part of the oil. The distilled liquors here treated of, are no other than water thus impregnated with the essential oil of the subject; whatever smell, taste, or virtue, is communicated to the water, or obtained in the form of watery liquor, being found in a concentrated state in the oil. All those vegetables, therefore, which contain an essential oil, will give over some virtue to water by distillation: but the degree of the impregnation of the water, or the quantity of water which the plant is capable of saturating with its virtue, are by no means in proportion to the quantity of its oil. The oil saturates only the water that comes over at the same time with it: if there be more oil than is sufficient for this saturation, the surplus separates, and concretes in its proper form, not miscible with the water that arises afterwards. Some edoriferous flowers, whose oil is in so small quantity that scarcely any visible mark of it appears, unless fifty or an hundred pounds or more are distilled at once, give never theless as strong an impregnation to water as those plants which abound most with oil. Many have been of opinion, that distilled waters may be more and more impregnated with the virtues of the subject, and their strength increased to any assigned degree, by cohobation, that is, by re-distilling them repeatedly from fresh parcels of the plant; experience, however, shews the contrary. A water, skilfully drawn in the first distillation, proves, on every repeated one, not stronger, but more disagreeable. Aqueous liquors are not capable of imbibing above a certain quantity of the volatile oil of vegetables; and this they may be made to take up by one, as well as by any number of distillations: the oftener the process is repeated, the ungrateful impression which they generally receive from the fire, even at the first time, becomes greater and greater. Those plants which do not yield at first waters sufficiently strong, are not proper subjects for this process. The mixture of water and oil which comes over, may either be separated immediately, by means of a separatory, or after it has been put into large narrow-necked bottles, and placed in a cool place, that the portion of oil which is not dissolved in the water, may rise to the top, or sink to the bottom, according to its specific gravity. It is then to be separated, either by a separatory, or by means of a small glass syringe; or by means of a filter of paper; or, lastly, by means of a woollen thread, one end of which is immersed in the oil, and the other lower end in a phial: the oil will thus pass over into the phial by capillary attrac tion, and the thread is to be squeezed dry. Most distilled waters, when first prepared, have a somewhat unpleasant smell, which, however, they gradually lose it is therefore advisable to keep them for some days after their preparation in vessels but slightly covered; and not to cork them up until they lose that smell. That the waters may keep the better, about one-twentieth part of their weight of proof spirit may be added to each after they are distilled. I have been informed by a respectable apothecary, that if the simple distilled waters be rectified by distilling them a second time, they will keep for several years without the addition of any spirit, which always gives an unplea sant flavour, and is often objectionable for other reasons. Distilled waters are employed chiefly as grateful diluents, as suitable vehicles for medicines of greater efficacy, or for rendering disgustful ones more acceptable to the palate and stomach: few are depended on, with any intention of consequence by them. selves. To the chapter on simple distilled wa ters, the London college have annexed the following remarks. "We have ordered most of the waters to be distilled from the dried herbs, because fresh are not ready at all times of the year. Whenever the fresh are used, the weights are to be increased. But, whether, the fresh or dried herbs be employed, the operator may vary the weight according to the season in which they have been produced and collected." Herbs and seeds kept beyond the space of a year, become less proper for the distillation of waters. To every gallon of these waters add five ounces, by measure, of proof spirit. The Edinburgh college order half an ounce of proof spirit to every pound of the water, which is nearly the same. But the Dublin college order five ounces of proof spirit to be added to each pound, which is probably a typographical error. them closely in cans with common salt. Water itself is ordered to be distilled, to CLASS VIII. Two pounds of fresh orange-peel, Edin. One pound of sweet fennel seeds bruised, Aqua fœniculi dulcis. Six pounds of the recent petals of the damask rose, Aqua rosæ centifoliæ, Edin. Aqua menthæ piperitæ, Edin. Aqua mentha piperitidis, Lond. Dub. One pound and a half of spearmint, Aqua menthæ sativæ, Dubl. Lond. One pound of cinnamon, (macerated for a day) Lond. Dubl. Aqua lauri cinnamoni, Edin. Aqua cinnamoni, Lond. Dubl. One pound of cassia, Aqua lauri cassiæ, Edin. One pound of bruised dill seeds, Aqua anethi, Lond. Olea Volatilia. VOLATILE These are prepared nearly in the same manner as distilled waters, except that less water is to be added. Seeds, and woody substances, are to be previously bruised, or rasped. The oil comes over with the water, and is afterwards to be separated from it, according as it may be lighter than the water, and swim upon its surface, or heavier, and sink to the bottom. Besides, in preparing distilled waters and oils, it is to be observed, that the goodness of the subject, its texture, the season of the year, and similar causes, must give rise to so many differences, that no certain or general rule can be given to suit accurately each example. Hence, the following is the mode prescribed by the London College. According to these directions are prepar Anise, pimpinellæ anisi, Edin. anisi, Lon. Caraway, carui, Lond. Dub. Fennel seeds, seminum fœniculi dulcis. Juniper berries, juniperi communis, Edin. Pimento, myrti pimentæ, Edin. from the Half a pound of pimento, (macerated for fruit. a day), Lond. Aqua myrti pimentæ, Edin. The virtues of all these waters are nearly alike; and the peculiarities of each will be easily understood by consulting the account given in the materia medica, of the substance from which they are prepared. Mr. Nicholson mentions, that as rose-water is exceedingly apt to spoil, the apothecaries generally prepare it in small quantities at a time from the leaves, preserved by packing Fennel flowers, florum fœniculi dulcis, Rosemary, rorismarini officinalis, Edin. Lavender, lavandulæ spicæ, Edin. laven. dulæ. Lond. Peppermint, mentha piperitæ, Edin. Spearmint, menthæ sativæ, Lond. Dub. Savine, juniperi sabinæ. Edin. sabinæ, Dub. from the flower, or herb in flower. Sassafras, lauri sassafras, Edin. sassafras, Lond, from the root. And, turpentine, pinus picea, from the resin. The residuum, after the oil has been extracted, is the officinal resin (resina flava): and a rectified spirit is obtained by distilling the oil of turpentine with four times its weight of water. The spirit of turpentine, as this essential oil has been styled, is frequently taken internally as a diuretic and sudorific; and it has sometimes a considerable effect when taken to the extent of a few drops only. It has, however, been given in much larger doses, especially when mixed with honey. Recourse has principally been had to such doses in cases of chronic rheumatism, particularly in those modifications of it which are termed sciatica and lumbago; but sometimes it induces bloody urine. The water employed in the distillation of volatile oils always imbibes some portion of the oil; as is evident from the smell, taste, and colour, which it acquires. It cannot, however, retain above a certain quantity; and therefore, such as has been already used and almost saturated itself, may be advantageously employed, instead of common water, in a second, third, or any future, dis. tillation of the same subject. After the distillation of one oil, particular care should be had to clean the worm perfectly before it be employed in the distillation of a different substance. Some oils, those of wormwood and aniseeds for instance, adhere to it so tenaciously, as not to be melted out by heat, or washed off by water; the best way of removing these, is to run a little spirit of wine through it. Volatile oils, after they are distilled, should be suffered to stand for some days, in vessels loosely covered with paper, till they have lost their disagreeable fiery odour, and become limpid; then put them up in small bottles, which are to be kept quite fall, closely stopped, in a cool place. With these cautions, they will retain their virtues in perfection for many years. Most of the oils mentioned above, are prepared by our chemists in Britain, and are easily procurable in a tolerable degree of perfection; but the oils from the more expensive spiceries, though still introduced among the preparations in the foreign pharmacopœias, are, when employed among us, usually imported from abroad. VOL. V. These are frequently so much adulterated that it is not easy to meet with such as are at all fit for use. Nor are these adulterations easily discoverable. The grosser abuses, indeed, may be readily detected. Thus, if the oil be mixed with spirit of wine it will turn milky on the addition of water; if with expressed oils, rectified spirit will dissolve the volatile, and leave the other behind; if with oil of turpentine, on dipping a piece of paper in the mixture, and drying it with a gentle heat, the tur pentine will be betrayed by its smell. But the more subtile artists have contrived other methods of sophistication, which elude all trials of this kind. Some have looked upon the specific gra vity of oils as a certain criterion of their genuineness. This, however, is not to be absolutely depended on; for the genuine oils, obtained from the same subjects, often differ in gravity as much as those drawn from different ones. Cinnamon and cloves, whose oils usually sink in water, yield, if slowly and warily distilled, oils of great fragrancy, which are nevertheless specifi cally lighter than the aqueous fluid employed in their distillation; whilst on the other hand, the last runnings of some of the lighter oils prove sometimes so ponderous as to sink in water. As all volatile oils agree in the general properties of solubility in spirit of wine, indissolubility in water, miscibility with water by the intervention of certain intermedia, volatility in the heat of boiling water, &c. it is plain that they may be variously mixed with each other, or the dearer sophisticated with the cheaper, without any possibility of discovering the abuse by any trials of this kind. And, indeed, it would not be of much advantage to the purchaser, if he had infallible criteria of the genuineness of every individual oil. It is of as much importance that they be good, as that they be genuine; for genuine oils, from inattentive distillation, and long and careless keeping, are often weaker both in smell and taste than the common sophisticated ones. The smell and taste seem to be the only certain tests of which the nature of the thing will admit. If a bark should have, in every respect, the appearance of good cin namon, and should be proved indisputably to be the genuine bark of the cinnamon tree; yet if it want the cinnamon flavour, or has it but in a low degree, we reject it; and the case is the same with the oil. It is only from use and habit, or comparisons P with specimens of known quality, that we can judge of the goodness either of the drugs themselves, or of their oils. Most of the volatile oils indeed are too hot and pungent to be tasted with safety; and the smell of the subject is so much concentrated in them, that a small variation in this respect is not easily distinguished; but we can readily dilute them to any assignable degree. A drop of the oil may be dissolved in spirit of wine, or received on a bit of sugar, and dissolved by that intermedium in water. The quantity of liquor which it thus impregnates with its flavour, or the degree of flavour which it communicates to a certain determinate quantity, will be the measure of the degree of goodness of the oil. Medical use. Volatile oils, medicinally considered, agree in the general qualities of pungency and heat; in particular virtues they differ as much as the subjects from which they are obtained, the oil being the direct principle in which the virtues, or at least a considerable part of the virtues, of the several subjects reside. Thus the carminative virtue of the warm seeds, the diuretic of juniper berries, the emmenagogue of savin, the nervine of rosemary, the stomachic of mint, the antiscorbutic of scurvygrass, the cordial of aromatics, &c. are supposed to be concentrated in their oils. There is another remarkable difference in volatile oils, the foundation of which is less obvious, that of the degree of their pungency and heat. These are by no means in proportion, as might be expected, to those of the subject they were drawn from. The oil of cinnamon, for instance, is excessively pungent and fiery; in its undiluted state it is almost caustic; whereas cloves, a spice which in substance is far more pungent than the other, yields an oil which is far less so. This difference seems to depend partly upon the quantity of oil afforded, cinnamon yielding much less than cloves, and consequently having its active matter concentrated into a smaller volume; partly, upon a difference in the nature of the active parts themselves: for though volatile oils contain always the specific odour and flavour of their subjects, whether grateful or ungrateful, they do not always contain the whole pungency: this resides frequently in a more fixed matter, and does not rise with the oil. After the distillation of cloves, pepper, and some other spices, a part of their pungency is found to remain behind: a simple tincture of them in rectified spirit of wine is even more pungent than their pure essett tial oils. The more grateful oils are frequently made use of for reconciling to the stomach medicines of themselves disgustful. It has been customary to employ them as correctors for the resinous purgatives; an use which they do not seem to be well adapted to. All the service they can here be of is to make the resin sit more easily at first on the stomach: far from abating the irritating quality upon which the violence of its operation depends, these pungent oils superadd a fresh stimulus. Volatile oils are never given alone, on account of their extreme heat and pungency; which in some is so great, that a single drop let fall upon the tongue produces a gangrenous eschar. They are readily imbibed by pure dry sugar, and in this form may be conveniently exhibited. Ground with eight or ten times their weight of sugar they become soluble in aqueous liquors, and thus may be diluted to any assigned degree. Mucilages also render them miscible with water into an uniform milky liquor. They dissolve likewise in spirit of wine; the more fragrant in an equal weight, and almost all of them in less than four times their own quantity. These solutions may be either taken on sugar, or mixed with syrups, or the like. On mixing them with water the liquor grows milky, and the oil separates. The more pungent oils are employed externally against paralytic complaints, numbness, pains, and aches, cold tumours, and in other cases where particular parts require to be heated or stimulated. The tooth-ach is sometimes relieved by a drop of these almost caustic oils, received on cotton, and cautiously introduced into the hollow tooth. Among the volatile oils ought also to be enumerated the empyreumatic oils; for these also are volatile, but have a character peculiar to themselves. The simple volatile oils exist ready formed in the aromatic substances from which they are obtained, and are only separated from the fixed principles by the action of a heat not exceeding that of boiling water. The empyreumatic, on the contrary, are always formed by the action of a degree of heat considerably higher than that of boiling water, and are the product of decomposition, and a new arrangement of the elementary principles of substances, containing at least oxygen, hydrogen, and carbon. Their production is therefore always attended with the formation of other new products. In their chemical properties they do not differ very remarkably from the volatile oils, and are principally distinguished from them by their unpleasant, pungent smell, and rough, bitterish taste. The following are the chief: Oleum petrolei, oil of bitumen, or tar. Oleum succini, oil of amber, which is af. terwards rectified. Oleum animale, animal oil, obtained from hartshorn, which also is rectified by being again distilled with water. same kind prepared by the distiller; the latter being extremely curious in rectifying or purifying the spirits (when designed for what he calls fine goods) from all unpleasant flavour. Spiritus cari carvi, Edin. spirit of caraway. Take of caraway seeds half a pound; diluted alcohol nine pounds. Macerate two days in a close vessel; then pour on as much water as will prevent empyreuma, and draw off by distillation nine pounds. Spiritus carvi, Lond. Dub. spirit of cara CLASS IX. Spiritus Distillati. DISTILLED way. Take of caraway seeds, bruised, half SPIRITS. The flavour and virtues of distilled waters are owing, as observed in the preceding chapter, to their being impregnated with a portion of the essential oil of the subject from which they are drawn. Alcohol, considered as a vehicle for these oils, has this advantage above water, that it keeps all the oil that rises with it perfectly dissolved into an uniform limpid liquor. Nevertheless many substances, which, on being distilled with water, impart to it their virtues in great perfection; if treated in the same manner with alcohol, scarcely give over to it any smell or taste. The cause of this difference is, that alcohol is not susceptible of so great a degree of heat as water. It is obvious, therefore, that substances may be volatile enough to rise with the heat of boiling water, but not with that of boiling alcohol. Thus if cinnamon, for instance, be com mitted to distillation with a mixture of alcohol and water, or with a pure proof spirit, which is no other than a mixture of about equal parts of the two; the alcohol will arise first clear, colourless, and transparent, and almost without any taste of the spice; but as soon as the more ponderous watery fluid begins to arise, the oil comes freely over with it, so as to render the liquor highly odorous, sapid, and of a milky hue. The proof spirits usually met with in the shops are accompanied with a degree of ill flavour, which, though concealed by means of certain additions, plainly discovers itself in distillation. This nauseous flavour does not begin to arise till after the purer spiritous part has come over, which is the very time that the virtues of the ingredients begin also to arise most plentifully; and hence the liquor receives an ungrateful taint. To this cause principally is owing the general complaint, that the cordials of the apothecary are less agreeable than those of the a pound; proof spirit of wine one gallon; (nine pounds, Dub.) water sufficient to prevent empyreuma. Draw off one gallon, (nine pounds, Dub.) In the same manner is prepared the same quantity of spirit from Cinnamon, one pound, Spiritus lauri cinnamomi, Edin. Spiritus menthæ piperitæ, Edin. Spiritus menthæ sativæ, Lond. Spiritus myristica moschata, Edin. Spiritus nucis moschata, Dub. Lond. Pimento, half a pound, Spiritus myrti pimentæ, Edin. Spiritus pimento, Dub. Lond. The rest belonging to this division are obtained from Decoctions and infusions differ chiefly in the employment of boiling or of cold water. At the same time, however, that the increase of temperature in decoctions facili |