The new dispensatory: containing I. The elements of pharmaceutical chemistry. II. The materia medica ... III. Pharmaceutical preparations. IV. Medicinal compositions ... Being an attempt to collect and apply the later discoveries to the Dispensatory published by W. Lewis ... / By gentlemen of the Faculty of Edinburgh [i.e. C. Webster and R. Irving].

Date:
1786
    this water varies in different falts : In fome of them, as in Glauber s fait, alum, and copperas, it makes up about one halfof their weight; in others, as in nitre, common fait, and efpccially fclenite.-*, it is in very unail quan- tity. As falts unite to the water of their cryftallifation by their attrac- tion for water alone, we accordingly find that this water is perfectly' pure, and contains* in complete cryltals, no fubftance foreign to the fait. Salts not only differ in the quantity of water neceffary to their folution, but fome of them alfo (though by no means generally) are foluble with equal facility in cold as in hot water. Sometimes, then, we employ evapora- tion ; fometimes cooling; and at other times both thefe expedients aie ufed alternately, to feparate different falts difTolved in the fame liquor. It is obvious, then, that thole which are nearly, or equally foluble in cold as in boiling water, can only be cryftallifed by evaporation; thofe again, Much are much more foluble in boiling than in cold water, are to be fe- parated by cooling. Of the firft of thefe is common or marine fait: of the latter is nitre or falpetre. It remains, then, that we fhould know how to feparate thefe two falts, when both of them happen to be diffolved In the fame water: this method confifls in alternate evaporation and cool- ing. If in fuch a folution a pellicle appears in the boiling liquor before cryftals can be formed in the cooling, we then conclude that the com- mon fait predominates: In this\cafe we evaporate the water, and feparate the common fait as fait as it is formed, till the liquor on cooling Ihows cry- ftals of nitre : we then allow the nitre to cryftallife by cooling. After all the nitre which had been diffolved by the heat alone has now feparated by cooling, we refume the evaporation, and feparate the common lalt till the cooling liquor again (hows cryltals of nitre. We thus repeat the fame fcrics of operations, by which means thefe two falts may be alternately cryftallized ; the one by evaporation, the other by cooling, till they are perfeftly feparated from each other. * If in the beginning of the opera- tion the liquor had, upon trial, given cryftals of nitre by cooling before any pellicle appeared on its furface when boiling, this would have indicated that the nitre was predominant in the folution: the nitre in this cafe, would have been cryftallifed, firft by cooling, till the quantity of nitre ex- ceeding that of the common fait having been feparated, the common fait would next have cryftallifed in its turn by evaporation. The example we Lave now given may be applied to other falts, or to a number of falts which may happen to be diffolved in the fame liquor. For though there are few fo completely foluble in cold water as common fait, and few fo fcantily as nitre ; yet there arc fcarcely two falts which either precifely (how the fame folubility or the fame appearance oi their cryftals. It is obvious, too, that by crvftallifation wc difeover the peculiar predominanqfalt in any fo- lntion of mixed faline matter; but as one lalt always takes down a fmall portion of another, it is neceffary to rediffolvc the firft produ&s, and re- peat the cryftallifiuion, in order to render the fcpaiation complete. u We fee, then, that though the cryftal appearance and form does not alter the fait itfelf, vet that this procef: affords an elegant method of dif- covering compound folutions of falts, of judging of their purity, and, laitly, of feparating different falts very completely from one another. Cryftallifation, then, is ojje of the moft important agents in pharmacy, and ought to be well underilood. We fh»ll attempt t,o explain the parti-
    Chap. 3- Precipitation• *n e come to treat cular management in cryftallifing particular falts, when w of each of them apart.” SECT. v. Precipitation. BY this operation, bodies are recovered from their folutioat, by means of the additton of feme other fubftance, with which either the men! urnum, or the body dilfolved, have a greater affinity than they hay- with one another. 1 * Precipitation, therefore, is of two kinds ; one, where the fubftance fuperadded unites with the menftruum, and occafions that before diffolved to be thrown down ; the other, in which it unites with the diffolved body and falls along with it to the bottom. Of the firft, we have an example *n the precipitation of fulphurfrora alkaline lixivia by the means of acids • of the fccond, in the precipitation of mercury from aquafortis by fea-falt’ or its acid. 1 * The fubje&s of this operation, as well thofe which are capable of be- ing precipitated as thofe which precipitate them, will readily appear from infpedhon of the Table of Affinity. The manner of performing it is fo fimple, as not to Hand in need of any particular diredions; no more be- ing required, than to add the precipitant by degrees, fo long as it conti- nues to occafion any precipitation. When the whole of the powder has fallen, it is to be well edulcorated^ that is, waflted in feveral frefh parcel? of water, and afterwards dried for ufe. Where metals are employed as precipitants, as in the purification of martial vitriol from copper by the addition of frefh iron, they ought to be perfectly clean and free from any rufly or greafy matter ; otherwife they will not readily, if at all, diffolve, and confequently the precipitation will not fuccecd; for the fubftance to be precipitated feparates only by the additional one diffolving and taking its place. The feparated powder, oftentimes, inflead of falling to the bottom, lodges upon the precipitant £ from which it mull be occaiionally ffiaken off, for reafons Efficiently ob- vious. Though, in this operation, the precipitated powder is generally the part required for ufe, yet fome advantage'may frequently be made of the li- quor remaining after the precipitation. Thus when fixed alkaline fait is diffolved in water, and fulphur diffolved in this lixivium; the addition of acids feperates and throws down the fulphur, only in virtue of the acid uniting with, and neutralizing the alkali by which the fulphur was held diffolved : confequently, if the precipitation is made with the vitriolic acid, and the acid gradually dropt in till the alkali is completely fatiated, that is, fo long as it continues to occafion any precipitation or turbidnefs, th& liquor will yield, by proper evaporation and cryftallifation, a neutral fait, compofcd 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 fait cal- led fpiritus fulls viarini coagulatus ; and if with the acid of vinegar, the fal diureticus. £E SECT.
    SECT. VI. Evaporation. . THIS is a third method of recovering folid bodies from their folu- tions, effeftcd by the means of heat; which evaporating the fluid part, that is, forcing it off in fleam, the matter whkh was diffolvcd therein is left behind in its folid form. “ The general rules for evaporation are, To place the matter in a flat, fhallovv, wide veflel, fo that a large furface of the liquor may be prefented to the air ; for it is only from the furface that evaporation takes place. The degree of heat ought to be proportioned to the volatility of the fub- ftance to be evaporated, and to the degree of fixity of the matter to be left: Thus, the left, fixed the matter to be left is, and the more ffrongly it adheres to the volatile parts, the lefs the degree of heat ought to be ; and in fuch cafes, too, a forcible current of air is fometimes fcarcely ad- mifiible : On the contrary, when the matter to be evaporated is not very volatile, and when the matter to be left is very fixed, and does not ad- here ftrongly to the volatile part, the evaporation may be urged by a flrong heat, aided by a current of air directed upon the furface of the liquor.” This procefs is applicable to the folutions of all thofe fubftances which are lefs volatile than the menflruum, or which will not exhale by the heat requifitefor the evaporation of the fluid ; as the folutions of fixed alkaline falts ; of the gummy, gelatinous, and other inodorous parts of vegetables and animals in water ; and of many refinous and odorous fubftances in fpi- rit of wine. * Water extracts the virtues of fundry fragrant aromatic herbs, almoft as perfectly as rectified fpirit of wine: but the aqueous infuflons are far from being equally fuited to this proctfs with thofe made in fpirit ; water carrying off the whole odour and flavour of the fuhjeft, which that lighter liquor leaves entire behind it. Thus a watery infufion of mint lofes in evaporation the fmell, tafte, apd virtues of the herb ; whilft a tinfture drawn with pure fpirit, yields, on the fame treatment, a thick balfamic liquid, or folid gummy refin, extremely rich in the peculiar qualities of the mint. In evaporating thefe kinds of liquors, particular care mud be had, to- wards the end of the proctfs. that the heat be.very gentle ; otherwife the matter as it grows thick will burn to the veflel, and contraft a difagree- able fmell and tafte : tins burnt flavour i$ called an etnpyreuntci. The li- quor ought to be kept ftirring during the evaporation ; otherwife a part of the matter concretes on the furface expofed to the air, and forms a pel- licle which impedes the farther evaporation. More particular directions for performing this operation to the grtateil advantage, will.be given here- after in the Second Part. J SECT.
    Chap. 3. Diftillation. *73 SECT. VII. Distillation. IN the foregoing operation fluids are rarefied by heat into fteam or va- pour, which is fuftered to exhale in the air, but which the bufinefs of this is to collect and preferve. For this purpofe the fteam is received in proper veffels, luted to that in which the fubjcft is contained; and being tiiere cooled, condentes into a fluid form again. There are two kinds of diftillation : by the one, the more fubtile and volatile parts of liquors are elevated from the groffer ; by the other, liquids incorporated with folid bodies are forced out from them by vehemence by tire. To the fir ft belong, the diftillation of the pure inflammable fpirit from vinous liquors ; and of fuch of the aftive parts of vegetables as are capable of being extrafted by boiling water or fpirit, and at the fame time of arifing along with their fteam. As boiling water extra&s or diffolves the eflential oils of vegetables, whilft blended with the other principles of the fubjeft, without faturation, but imbibes only a determinate, and that a frnall proportion of them in their pure ftate ; as thefe oils are the only fubftances, contained in com- mon 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, refide : it is evident, that water may be impregnated, by diftillation, with the more valuable parts of many vegetables : that this impregnation is limited, the oil arifing in this procefs pure from thofe parts of the plant which before rendered it foluble in w'ater without limitation ; hence greateft part of the oil feparates from the diftilled aqueous liquor* and, according to its greater or lefs gravity, either finks to the bottom or fwims on the furface : that confequently infufions and diftilled waters are greatly different from one another: that the firft may be rendered ftrong- cr by pouring the liquor on frefh parcels of the fubjeft ; but that the lat- ter cannot be in like manner improved by cobobating, or re-diitilling them from frefh ingredients. See Part II. As the oils of many vegetables do not freely dift ill with a lefs heat than that in which water boils ; as reftified fpirit of wine is not fufceptible of this degree of heat ; and as this menftruum totally diffolves thefe oils in their pure ftate; it follows, that fpirit elevates far lefs from moft vegeta- bles than water; but that neverthelefs the diftilled fpirit, by keeping all that it does elevate, perfectly difTolved, may, in fome cafes, prove as ftiong of the fubjeft as the diftilled water. “ The more gentle the heat, and the flower the diftillation goes on, the volatile parts are the more peifcdtly fe- parated in their native ftate.” _ The apparatus made ufe.of for diftilling fpirits, waters, and oils, con- fift of a Jiill, or copper veffel, for containirig the fubjeft, on which is luted a large head with a fwan-neck• The vapour arifing into the head, is hence conveyed throw a nv<irm, or long fpiral pipe* placed in a \efiel of cold water called a refrigeratory ; and being their condenfed, runs down into a receiver. In the fecond part of this work, we fliall give tome impiovc- ments
    ments in this apparatus for particular purpofes; with directions for per- forming the feveral proceffes to the greateft advantage. It may be obferved, that as the parts which are preferved in evapora- tion cannot arife in diftillation, the liquor remaining after the diftillation, properly depurated and infpiffated, will yield the fame extracts as thofe prepared from the tindbure or decodbion of the fubjedb made on purpofc for that ufe ; the one of theCe operations colluding only the volatile parts, and the other the more fixed : fo that where one fubjedt contains medici- nal parts of both kinds, 'they may thus be obtained diliineb, without one being injured by the procefs which colledbs the other. The fubjedbs of the fecond kind of diftillation are, the grofs oils of ve- getables and animals, the mineial acid fpirits, and the metallic fluid quick- silver ; which as they require a much fbronger degree of heat to elevate them than the foregoing liquors can fuftain, fo they likewife condenfe without arifing fo far from the adbion of the fire. The diftillation of thefe h performed in low glafs veffels, called, from their neck being bent to one fide, retorts ; to the farther end of the neck a receiver is luted, which Handing without the furnace, the vapours foon condenfe in it, without the ufe of a i frigeratoty : neverthelcfs, to promote this effedb, fome arc accuftoroed, efpecially in warm weather, to cool the receiver, by occa- fiooally applying wet cloths to it, or keeping it partly immerfedin a veffel of cold water. I he vapours of fome fubftances are fo fluggifh, or flrongly retained by a fixed matter, a6vfcarce to arift even over the low neck of the retort. Thefe are molt commodioufly diftilied in ftreight-necked earthen veffels, called tor.gr.eck:, laid on their tides, fo that the vapour paffts off laterally with little or no afeent: a receiver is luted to the end of the neck without the furnace. In this manner, the acid fpirit of vitriol is diftilied. The matter which remains in the retort or longueck, after the diftillation, is vulgarly called caput mortwnm. In thefe diilillations, a quantity of elaftic air is frequently generated; which, imlefs an exit is allowed it, blows off or buribs the receiver. The danger of this may in good mcafure be prevented, by flowly railing the" fire j but more cfftdtRally, by leaving a fmall hole in the luting, to be oc- calionally opened or ftopt with a wooden plug ; or inferting at the junc- tuie an upright pipe of fuch a height, that the iteam of the diibilling liquor may not be able to rife to the top : •« but it is ftill better done by fitting to the apparatus other veffels, by which their vapours piay be con- denfed.” SECT. VIII. Sublimation. AS all fluids are volatile by heat, and confequently capable of being leparated, in moil cafes, from fixed matters, by the foregoing pro- ceis ; fo various folid bodies art: fubjedbed to a fimilar treatment. Fluids are faid to dtftill, and foluls to Jubltme ; though fometimes both are ob- tained is one and the fame operation. If the fubliming matter concretes into