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Phosphas calcis, Edin, magnesia usta, in transparent, brilliant, hexagonal crysLond. burnt on calcined magnesia. tals, terminated by an oblique hexagonal

Sulphas aluminæ exsiccatus. Edin. dried plane, and soluble in about four hundred sulphate of alumine. burnt alum. Lond. and eighty times its weight of water. The

crystallized carbonate of magnesia conIn the Dublin process for making mag

sists of fifty acid, twenty-five magnesia, nesia, there is a mutual decomposition of

and twenty-five water; the sub-carbonate the two salts employed. The potash

consists of forty-eight acid, forty magneunites itself to the sulphuric acid, while

lite sia, and twelve water; and the carbonate the carbonic acid combines with the mag

of commerce of thirty-four acid, forty-five nesia. The large quantity of water used

a magnesia, and twenty-one water. It is

magnesia, and is necessary for the solution of the sul- decomposed by all the acids, potash, sophate of potash formed; and the boiling da, baryte, lime, and strontian, the sulis indispensably requisite for the expuls phate, phosphate, nitrate, and muriate of sion of a portion of the carbonic acid, alumina, and the super-phosphate of lime. which retains a part of the magnesia in solution. Sulphate of potash may be obtained from the liquor which passes

Class IV. SULPHUREA. through the filter, by evaporation. This is not pure, however, but mixed with un The preparations under this head are decomposed carbonate of potash; for one few; we need only enumerate the two hundred parts of crystallized carbonate of following: potash are sufficient for the decomposi- Sulphur lotum, Lond. washed flowers tion of one hundred and twenty-five parts of sulphur. of sulphate of magnesia; and as the car. Sulphur præcipitatum, Lond. precipi. bonate of potash of commerce contains a tated sulphur. larger proportion of alkali than the crys. In preparing this last, instead of distallized carbonate, a still less proportion solving sulphuret of potash in water, we should be used. From these quantities may gradually add sublimed sulphur to a about forty-five parts of carbonate of mag- boiling solution of potash, until it be sanesia are obtained.

turated. When the sulphuretted potash The ablutions should be made with very is thrown into water, it is entirely dissolvpure water; for nicer purposes, distilled ed, but not without decomposition, for it water may be used, and soft water is in is converted into sulphate of potash, hy. every case necessary. Hard water for this droguretted sulphuret of potash, and sulprocess is peculiarly inadmissible, as the phuretted hydroguret of potash. The two principle in waters, giving the property last compounds are again decomposed on called hardness, is generally a salt of the addition of any acid. The acid comlime, which decomposes the carbonate of bines with the potash, sulphuretted hydromagnesia, by compound affinity, giving gen flies off in the form of gas, while sulrise to carbonate of lime, while the mag. phur is precipitated. It is of little consenesia unites itself to the acid of calca- quence what acid is employed to precipireous salt, by which the quantity of the tate the sulphur. The London College carbonate is not lessened, but is ren order the sulphuric; while the Dublin dered impure by the admixture of carbo- College use nitrous acid; probably be. nate of lime. Another source of impurity cause the nitrate of potash formed is is the silica which the sub-carbonate of more easily washed away than sulphate potash generally contains. It is most of potash. easily got rid of by exposing the alkaline Precipitated sulphur does not differ solution to the air for several days before from well-washed sublimed sulphur, ex. it is used. In proportion as it becomes cept in being much dearer. Its paler saturated with carbonic acid, the silica is colour is owing to its more minute divi. precipitated, and may be separated by sion, or, according to Dr. Thomson, to filtration.

the presence of a little water; but from The carbonate of magnesia thus prepar. either circumstance it derives no supeed, is a very light, wlite, opaque sub. riority to compensate for the disagreestance, without smell or taste, effervescing ableness of its preparation. with acids. It is not, however, saturated These are all the more simple prepara. with carbonic acid. By decomposing sul. tions of sulphur in common use.". There phate of magnesia by an alkaline carbo- are various preparations into which sulnate, without the application of heat, car. phur enters as an ingredient; but such as bonate of magnesia is gradually deposited, constitute compounds of the general cipitate.

nature of metals, alkalies, oils, &c. will Submurias hydrargyri præcipitatus, be found under those classes.

Edin. mild muriated quicksilver, Lond.

Cals hydrargyri alba, Lond. white preClass V. Metallica. METALLINE PRE

Hydrargyrus calcinatus, Dub. Lond. PARATIONS.

calcined quicksilver.

Oxydum hydrargyri rubrum, Edin, red The metalline preparations are very precipitate. numerous, especially those of antimony Subsulpbas hydrargyri flavus, Edin. vi. and quicksilver.

triolated quicksilver, Lond. Sulphuretum antimonii præparatum, Sulphuretum hydrargyri nigrum, Edin. Edin. prepared antimony.

æthiops mineral, turpeth mineral. Oxidum antim. cum sulphure per nitra Hydrargyrum sulphuratum nibrum, tum potassæ, Edin, crocus of antimony, Lond. Dub. factitious cinnabar. Lond.

Acetis plumbi, Edin. acetite of lead, suOxidum antimonii, cum sulphure, vi- gar of lead. trificatum, vitrified antimony, Lond. glass Aqua lythargyri acetata, Lond. extract of antimony.

of lead. Sulphuretum antimonii præcipitatum, Cerussa acetata, Lond. acetated ceruse. precipitated sulphuret, or sulphur of an Stanni pulvis, Lond. powder of tin. timony, Lond.

Oxydum zinci, Edin. oxide of zinc, calMurias antimonii, Elin, muriated anti- cined zinc, Lond. mony, Lond. butter of antimony.

Carbonas zinci, Edin. impurus præparaOxidum antimonii cum phosphate cal. tus, prepared calamine. cis, Edin. pulvis antimonialis, Lond. anti Oxydum zinci impurum præparatum, monial powder.

Edin. prepared tutty. Tartris antimonii, tartarised, or tartrite Sulphas zinci, Edin. vitriolated zinc, of antimony.

Lond. Vinum tartritis antimonii, Edin, tartar. The antimonial powder of the London emetic, antimonial wine, Lond.

College is supposed to be nearly the same Nitras argenti, Edin. argentum nitra with the celebrated nostrum of Dr. James, tum, Lond. nitrate of silver, lunar caustic, the composition of which was ascertained

Ærugo præparata, Lond. Dub. prepared by Dr. Pearson of London, to whom we verdigrise, or carbonate of copper. are also indebted for the above formula.

Solutio sulphatis cupri composita, Edin. By burning sulphuret of antimony and styptic water.

shavings of hartshorn in a wbite heat, the Ammoniaretum cupri, Edin, ammonia sulphur is entirely expelled, and the antical copper.

mony is oxydized, while the gelatine of Aqua cupri ammoniati, Lond. water of the hartshorn is destroyed, and nothing is the same.

left but phosphate of lime, combined with Ferri limatura purificata, Edin. purified a little lime. Therefore the mass which iron filings.

results is a inixture of oxide of antimony Carbonis ferri, Edin. rubigo ferri, Lond. and phosphate of lime, which corresponds, carbonate, or rust of iron.

at least as to the nature of the ingredients, Sulphas ferri, Edin. vitriolated iron, with James's powder, which, by Dr. PearLond. sulphate of iron.

son's analysis, was found to consist of 43 Tinctura muriatis ferri, tincture of mu- phosphate of lime, and 57 oxide of antiriate of iron, Lond.

mony. Another excellent chemist, M. Murias ammoniæ et ferri, martial flow. Chenevix, bas lately proposed a method ers, ammoniacal iron, Lond.

of forming the same combination in the Tinctura ejusdem, tincture of the same. humid way, with the view of obtaining a

Tartris ferri, tartrite of, or tartarised, preparation always similar in its composiiron, Lond.

tion and properties. He was led to this Vinum ferri, Lond. wine of iron.

proposal, by considering the uncertainty Hydrargyrus purificatus, Lond. purified of the application, and the precarious na. quicksilver.

ture of the agency of fire, by which means Acetis hydrargyri, Edin. acetite of a variable portion of the oxide of antiinony quicksilver.

may be volatilized, and that which remains Murias hydrargyri, Edin. Lond. muriate may be oxydized in various degrees. of quicksilver, corrosive sublimate.

M. Chenevix, therefore, proposes to Submurias hydrargyri, Edin. calomel, prepare a substitute for James's powder, Lond.

by dissolving together equal weights of submuriate of antimony and of phosphate sion or decoction. Heat, by rendering the of lime in the smallest possible quantity oil more limpid, increases very much the of muriatic acid, and then pouring this quantity obtained by expression; but as solution gradually into water sufficient. it renders it less bland, and more apt to ly alkalized with ammonia. For the rea- become rancid, heat is not used in the son mentioned in the preceding article, it preparation of oils which are to be emis absolutely necessary that the muriatic ployed in medicine. When obtained by solution be poured into the alkaline liquor. expression, oils often contain a mixture By an opposite mode of procedure, the of mucilage, starch, and colouring mat. precipitate would contain more antimony ter; but part of these separate in course at first, and towards the end the phos. of time, and fall to the bottom. When phate of lime would be predominant, and oils become rancid, they are no longer. the antimony would be partly in the state fit for internal use, but are then said to of a submuriate. The phosphate of lime effect the killing of quicksilver, as it is is most conveniently obtained pure by called, more quickly. "Decoction is prindissolving calcined bone in muriatic acid, cipally used for the extraction of the and by precipitating it by ammonia. If viscid and consistent oils, which are meltthe ammonia be quite free from carbonic ed out by the heat of the boiling water, acid, no muriate of lime is decomposed. and rise to its surface. M. Chenevix also found that this precipi. Those who prepare large quantities of tate is entirely soluble in every acid which the oil of almonds, blanch them, by steepcan dissolve either phosphate of lime or ing them in very hot water, which causes oxide of antimony separately, and that their epidermis to swell, and separate about 0.28 of James's powder, and at an easily. After they peel them, they dry average 0.44 of the pulvis antimonialis of them in a stove, then grind them in a the London Pharmacopæia, resist the ac. mill like a coffee mill, and lastly, express tion of every acid.

the oil from the paste inclosed in a hemp

en bag. By blanching the almonds, the Class VI. Olea Firata. FIXED Oils. paste which remains within the bag is sold

with greater advantage to the perfumers, These oil are improperly denominated and the oil obtained is perfectly colourexpressed, which is their usual characte- less. But the beat employed disposes ristic name, as in some instances they are the oil to become rancid, and the colour obtained without expression, and in other the oil acquires from the epidermis does instances expression is employed to ob. not injure its qualities. For pharmaceutain volatile oils. The Edinburgh college tical use, therefore, the oil should not be have therefore distinguished these differ expressed from blanched almonds, but ent classes of oils by the terms fixed and merely rubbed in a piece of coarse linen, volatile, which accurately characterize to separate the brown powder adhering them.

to the epidermis as much as possible. Fixed oil is formed in no other part of Sixteen ounces of sweet almonds comvegetables than in their seeds. Some monly give five ounces and a half of oil. times, although very rarely, it is contain: Bitter almonds afford the same propored in the parenchyma of the fruit. Of tions, but the oil has a pleasant bitter this, the best known example is the olive. taste. But it is most commonly found in the In this manner are to be expressed, seeds of dicotyledonous vegetables, some. Oleum amygdalæ, almond oil, from the times also in the fruit of monocotyledo kernel. nous plants, as the cocos butyracea. It Oleum lini, linseed oil, from the bruised has various degrees of consistency, from seeds. the tallow of the croton sebiferum of Chi. Oleum ricini, castor oil, from the seeds na, and the butter of the butter-tree of previously decorticated. Africa, to the fluidity of olive oil.

Oleum sinapeos, oil of mustard, from Fixed oils are either, 1. Fat, easily con- the bruised seeds. gealed, and not inflammable by 'nitric acid, oil of olives, almonds, rapeseed, Class VII. Aquæ Distillatæ. DISTILLED and ben. 2. Drying, not congrealable, in

WATERS. flammable by nitric acid, oil of linseed, nut, and poppy. 3. Concrete oils, palm Substances which differ in volatility, oil, &c.

may be separated from each other by Fixed oil is separated from fruits and applying a degree of heat capable of conseeds which contain it, either by expres. verting the most volatile into vapour, and VOL, IX.

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by again condensing this vapour in a pro- in rainy seasons, and when growing in per apparatus. Water is converted into moist rich grounds. vapour at 212°, and may be separated by Several chemists have been of opinion, distillation from the earthy and saline mat. that herbs and flowers, moderately dried, ters, which it always contains in a natural yield a greater quantity of essential oil, state. But it is evident, that if any sub. than if they were distilled when fresh. It stances which are as volatile as water be is, however, highly improbable, that the exposed to the same degree of heat, quantity of essential oil will be increased either by immersing them in boiling wa. by drying; on the contrary, part of it must ter, or exposing them to the action of its be dissipated and lost. But drying may steam, they will rise with it in distillation. sometimes be useful in other ways; either In this way the camphor and volatile oils by diminishing the bulk of the subject to of vegetable substances are separated be distilled, or by causing it to part with from the more fixed principles; and as its oil more easily. water is capable of dissolving a certain the choice of proper instruments is of quantity of these volatile substances, it great consequence for the performance of may be impregnated with a great variety this process to advantage. There are of flavours by distilling it from different some oils which pass freely over the aromatic substances. If the subject of swan-neck of the head of the common our distillation coutain more volatile oil still : others, less volatile, cannot easily be than the water employed is capable of made to rise so high. For obtaining dissolving, it will render the water milky, these last, we would recommend a large and afterwards separate from it. It is in low head, having a rim or hollow canal this way that essential oils are obtain round it: in this canal the oil is detain

ed in its first ascent, and thence con· Essential oils are obtained only from veyed at once into the receiver, the adodoriferous substances; but not equally vantages of which are sufficiently obvi. from all of this class, nor in quantity pro- ous. portional to their degree of odour. Some, With regard to the proportion of water which, if we were to reason from analo- to be employed; if whole plants, modegy, should seem very well fitted for this rately dried, are used, or the shavings of process, yield extremely little oil, and woods, as much of either may be put in. others none at all. Roses and chamo. to the vessel, as, lightly pressed, will ocmile flowers, whose strong and lasting cupy half its cavity; and as much water smell promises abundance, are found to may be added as will fill two thirds of it. contain but a small quantity of oil; the When fresh and juicy herbs are to be disviolet and jessamine flower, which per- tilled, thrice their weight of water will fume the air with their odour, lose their be fully sufficient; but dry ones require a sinell upon the gentlest coction, and do much larger quantity. In general, there not afford any oil, on being distilled, un- should be so much water, that, after all less immense quantities are submitted to intended to be distilled has come over, the operation at once; while savin, whose there may be liquor enough left to prevent disagreeable scent extends to no great the matter from burning to the still. The distance, gives out the largest proportion water and ingredients, altogether, should of oil of almost any vegetable known. never take up more than three-fourths of

Nor are the same plants equally fit for the still; there should be liquor enough this operation, when produced in differ to prevent any danger of an empyreuma, ent soils or seasons, or at different times but not so much as to be apt to boil over of their growth. Some yield more oil, if into the receiver. gathered when the flowers begin to fall The subject of distillation should be off, than at any other time. Of this we macerated in the water until it be perhave examples in lavender and rue; fectly penetrated by it. To promote this others, as sage, afford the largesi quan- effect, woods should be thinly shaved tity when young, before they have sent across the grain, or sawn, roots cut transforth any Howers; and others, as thyme, versely into thin slices, barks reduced inwhen the flowers have just appeared. All to coarse powder, and seeds slightly fragrant herbs yield a larger proportion bruised. Very compact and tenacious of oil, when produced in dry soils and in substances require the maceration to be warm summers, than in opposite circum- continued a week or two, or longer; for stances. On the other hand, some of the those of a softer and looser texture, two disagrecable strong-scented ones, as or three days are sufficient; while some wormwood, are said to contain most oil tender herbs and flowers not only stand

in no need of maceration, but are even in- tinued as long as the liquor runs well jured by it. The fermentation which was flavoured off the subject, but no longer. formerly prescribed in some instances is in the distillation of essential oils, the always hurtful.

water, as was observed in the foregoing With regard to the fire, the operator section, imbibes always a part of the oil. ought to be expeditious in raising it at The distilled liquors, here treated of, are first, and to keep it up during the whole no other than water thus impregnated process, to such a degree only, that the with the essential oil of the subject : oil may freely distil; otherwise the oil whatever smell, taste, or virtue, is com. will be exposed to an unnecessary heat; municated to the water, or obtained in a circumstance which ought as much as the form of watery liquor, being found in possible to be avoided. Fire communi. a concentrated state in the oil.. cates to all these oils a disagreeable im. All those vegetables, therefore, which pregnation, as is evident from their being contain an essential oil, will give over much less grateful when newly distilled, some virtue to water by distillation : but than after they have stood for some time the degree of the impregnation of the in a cool place : and the longer the heat water, or the quantity of water which the is continued, the greater alteration it pro- plant is capable of saturating with its virduces in them.

tue, are by no means in proportion to The greater number of oils require for the quantity of its oil. The oil saturates their distillation the heat of water strongly only the water that comes over at the boiling; but there are many also which same time with it: if there be more oil rise with a heat considerably less ; such than is sufficient for this saturation, the as those of lemon and citron peel; of the surplus separates, and concretes in its flowers of lavender and rosemary, and of proper form, not miscible with the water almost all the more odoriferous kinds of that arises afterwards. Some odoriferous flowers. We have already observed, that flowers, whose oil is in so small quantity these flowers have their fragrance much that scarcely any visible mark of it apinjured, or even destroyed, by beating or pears, unless fifty or an hundred pounds bruising them ; it is impaired also by the or more are distilled at once, give never. immersion in water in the present pro- theless as strong an impregnation to wacess, and the more so in proportion to the ter as those plants which abound most continuance of the immersion and the with oil. heat; hence oils distilled in the common Many have been of opinion, that dismanner, prove much less agreeable in tilled waters may be more and more imsmell than the subjects themselves. For pregnated with the virtues of the subject, the distillation of substances of this class, and their strength increased to any asanother method has been contrived; in- signed degree, by cohobation, that is, by stead of being immersed in water, they re-distilling them repeatedly from fresh are exposed only to its vapour. A pro- parcels of the plant ; experience, howper quantity of water being put into the ever, shews the contrary. A water, skilbottom of the still, the odoriferous herbs fully drawn in the first distillation, proves, or flowers are laid lightly in a basket, of on every repeated one, not stronger, but such a size that it may enter into the still, more disagreeable. Aqueous liquors are and rest against its sides just above the not capable of imbibing above a certain water. The head being then fitted on, quantity of the volatile oil of vegetables ; and the water made to boil, the steam, and this they may be made to take up by percolating through the subject, imbibes one, as well as by any number of distillathe oil, without impairing its fragrance, tions: the oftener the process is repeatand carries it over into the receiver. Oilsed, the ungrateful impression which they thus obtained possess the odour of the generally receive from the fire, even subject in an exquisite degree, and have at the first time, becomes greater and nothing of the disagreeable scent per- greater. ceivable in those distilled by boiling them Those plants which do not yield at first in water in the common manner.

waters sufficiently strong, are not proper Plants differ so much according to the subjects for this process. soil and season of which they are the pro- The mixture of water and oil which duce, and likewise according to their own comes over may either be separated images, that it is impossible to fix the quan. mediately, by means of a separatory, or tity of water to be drawn from a certain after it has been put into large narrowweight of them to any invariable stand. necked bottles, and placed in a cool place, ard. The distillation may always be con- that the portion of oil which is not dis

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