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OF PHARMACE UTIC CHEMISTRY. 69stances, the dissipation of the volatrie matter, and the Oxygenation of the extractive, considerably limit the applicationof this process. Ιt is stili used, however, With a luantage, to extraci the mucilaginous paris os vegetabios, theiae bitter-ness, and Severes others of their peculiar qualities. Alkohol may be applied io vegetabies to dissolve thosa principies whicli are not solubio in Hater, such are theti' essentiat oti, camplior, and resin; and as these are osten the principies ou whicli the viriues of vegetabies depend, these
Eques paris os aikohol and water, in generat, extruct stillinore completely the active matter of planis, as we thus Ob-tain a solution of est those substances Whicli are separateli solubie in cither of these fluids. hen, by the action os one or both of these fluids, a solution of the active pvincipies of a veget te is obtained, it may be evaporated to tho consistenco os a thicla tenacious inass. This fornis What is termed an Extract: it is nam dan Aqueous EXtract when obta ined si om tho aqueous infusionor decoction of a plant, and Spiritous When a Ohol has hceu the solvent. The desim of this preparation is to obtain ille active matter of the vegetable in a finali bulla, and in such astate that it may be preserved without suffering any alteration. It is evidetit, that it is a process ivliich can be pr0perly applied to such planis only as have thoir virtuos dependent on some of their taed principies, and even theSe aieoiten iiij ured by the licat applied, and the si access of the
Distillation is mollior process si pithd to Vegetable sub-Stances, by which ive obiain some of theix activo principies, particularly their essentiat oll. Is the vegetable mattor be
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OF THE GENERAL PRINCIPI ESwith the aqueous vapour : it separates Dona ille water on he..ing allori ed to rema in at rest; a pari of it, however, is also dissolved, and communicates a considerable demee os flavour,und osten also os pungency. This fornis What are nam edDistilled Walers. Is a Mohol bo used instead of water, theessentiat oti is entirely dissolved in it, and we thus obtutu What are termed Distilled Spiriis.
A single example M ill shew the utility of investigations of this Liud, respecting the component principies of veget leproducis, and theiae relations to the more important chemicuingenis. Peruvian barti is one of the most impoliant remedios in the Materia Medica. It is not alwayS, however, practica te to exhibit it in substance with adurentage, aSwhere the stomach is uncommonb irritabie, or ivliere, froni the nature of the disestse, it is necessary to give it in large doses, frequently repented, it is liable to occasion sichnessund Other linea V Sensations, and et en to be rejected by ο- miting. Such inconveniences are attempted to bo obvialed,
hy giving it in the disterent fornas of infusion, decoction,
tincture or intraci, as any of these may be best suiled tothe case. Our knowledge of itS constituent paris can onlylead us to the proper application of theSe proces S. Frona an accurate analysis of iliis bai k, it has been proved that seven paris out os eis it consist of Woody libre, or of a matior inert anil insolubie, Whicli cannot ac t on the system, and
whicli assecis the stomach only by iis wcight anil insolubility. The reminining eighth part is that in xvhicli iJic activity of the medicine resides : it is theres ire evident, ibat is this hooxtracted, without ii tu ing iis activi ty, the medicine could
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'e exhibited with much moro advantage. This is in partuccomptished by the proparations of it that have been mentationed ; but even illese do not convey it in ali iis force. I filio bark be uisused or boiled in a certain quantity of water,
the infusion or decoction is not nearly equat in emcacy to theu hole quantity operated on. It is there re evident, that duxi- either of these operations, the active matter has notbeen enti rely eXtracted, or has suffereti Some change. Andhere Chemistry farther elucidates the peculiar nature of this Eubstance, and the changes producta in se by these processes. It has been Dund, that the matter On whicli the po ver of thisbarla depends is Iiable to oxygenation, and that, during the infusion, and particul ly the docoction of that drug, it sunfers this change frum the action of atmospherio air, and is converted into a substance iusipid and inert. This Ioads tothe 1 provenient of the preparations of this medicino; audexperiments instituted for the purpose hine accordin y prov-
nearly destroyed they are extracted with less i s by a seis minutes' decoction tu covered vesseis. The fame investigations have polated out the nature of the action of sonae ollior substances On bark, sermoly not wed undexstood. Thus, ithad been found by experience, that the eskallies, and more particularly magneSia, ei able P ater to extraci the viriues of bain more completely by infusion, a circumstance elucidatod by the iaci asterwariis discovered, that the extractive matter of the bark, to whicli iis activity is o ving, combines, with facility with these substances, Mid fontis Sesuble Com-
Similar examples might be seven Doni other important vegetable remedies, which Would sussciently prove tho utililyto be derived froni the analysis of the Substances helonging
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insidicines. The account of the analysis of animal substancos, and os thela proximate principies, would, to the Same extent ut leaSt, be foreim to the objects of this skotch, as so sow of these substances are employed in medicino ; aud of those whichare used, the compoSition, and consequently the pharmaceu-tic trea tinent, a re in a great meas ure peculiar to Ench. Their generat chemicat characters aro similar to those of Veget te principies. -Composed os a sexu ultimate elements the disserenoes in their properties arise in a great menSiuesroin the different proportions, or the disserent modos in ri hichthese are combined. And these elements having powerfui reciprocat attractions, and being disposed to enter into combinations almost indefinitely diversified, theso substances areextrem ely susceptible os decomposition, froin the vc-actionos their clemenis, favoured by hiunidity, by the action orthe air, OP by cle 'ation os temperatu e . They are exeumore liable to this thau veget te substances; for the elements existing in simultaneous combination are more numerous, thela innities are there re more nicely adjusted, and of courge ille equilibrium is more easib subvorted.
Along With carbon, hydrogeia, and oxygen, Whicli are thechiel c0nstituent principies of vegetable matter, nitrogeu, and frequently sulphur and phosphorus, enter into the composition os animal substances. Helice, When decomposed by heat, they afford producis compooed of these, of Whicli ammonia is always the principat; and the re-uction of theso Principies, and the evolution of the producis arising si omthis, seem principalty to forin the serius of cllanges Whicheonstitute putrefaction, the species of spontaneous decompo
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L. ilae vegetable substances, the animal producis consist or artous proximate principies, alid sonae analogy may be tracedhei vestia severat of the vegetable and animal proximate principies. Animal sat has a strict connection in properties and composition withilaed Oil; animal mucus resembles veget leoniicit age ; secula has a similar relation to gelatin ; vegetabluaud animal gluten are ne ly is not enti Pely the Same : n Sul stauce Similax to saccharine matter exigis in milla, and in Some of the other animal secretions : in the bile is sound a principie strictb analomus to resin ; and benZoic, OXali and acetio acides are common to Voth. Hence, generallyspealaing, the sexu antimal substances belonging to the Materia Medica are acted on by the usual solvenis in nearly the samo
manner as Veget te substances, andrare Submitted to similis pharmaceutic processes. The regulis of these are similar
ossicines preparations. Thus, by the action Os aikohol, theactive matter of mussi, Castor, and cantharides is tractei and tinctures of those a13e employed. In Other Ca Ses Waler
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NATURAL substances are not always obtained in that statελ whicli they are best adapted to exhibition as remedies. They a re subjected, theresere, to Various proceSSes, with the View of preparing them for uSe; and to complete this State-ment of the Principies os Pharmaceutio Chemist , the n ture of these is to be inted out . These processes, or at leaSt the greater number, and themost important of them, are chemices, and are dependent therelare on the agencies of those genet ut forces ivliencechemicat changes arise ; they are indeed litile more thun applications of theSe, under peculiar regulations adapted to dita ferent substances. The generat factS, there re, comae ted vitii the operation of these forces, are firSt to bo stated, inso faer as they have any relation to the present subjeci.
The force principalty productive os chemicat action, is that species of attraction exerted bet veen the particles of hodies, Vhich brings them into intimate union. Is two substances of different hiniis be placed in contact, und with that donee os fluidity whicli admits of the particles of the one movingto those of the other, it osten happens that they unite to-gether, and forni a substance in Which neither can be any lanser recognised, and whicli is homogenesus, and in general
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possessed os nexu properties. This constituteA What, in ille latasturege of chemist , is nainud Combination, and 1t is conceived to arise frum in attraction eXerted belWeen the particles, of the ono body and those of the Other. I his species
of attraction, denominated Chemicat si om being productive of chemices phenomena, somelimes also named ΑTnity, is distinguished froin the other species of attraction by the ph nomena to whicli it sives rise, or by the latus it ob s,froin the attraction of gravitation, by not bring exerted si
Sensibie distances, or on masses of matter, but oesy at in sensibie distances, and on the minute particles of hodies, frona the attraction of aggregation, by being eXerted botweeu 'particles of different kinds, and forming a Substance withnew properties, while that force operates On particles of a similar nature, and unites them into an aggregate in ichthe fame essentiat propertios eXist. It is poSSible, however, that theso sorces, though thus distinguiShed, may be the r sult of the sume power modified br tbe circumstances underi, hicli it actS. The substance formed by chemices combination is nameda Compolind. The Substances united ni o the constituent orcomponent paris Or principies of ilie compo. ind. Whenthese are Separated, the proceSS is named Decomposition. The most minute paris into whicli a body can be resolved without decomposition, ni e named iis integrant paris ; undit is hei vcen these that the force of aggregation is conceivedio bo exerte t. Chemicat attraction is exerted belween the constituent paris. The most important phenomenon attending chemicat combination is a change of properties. In generat, the forna, density, colour, inste, and Other sensit te qualities, as weli usthe fusibili ty, volatilily, tendency to combination, and othorcheini id pr0pertius in the comp0und, a re more or less di
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body acquires merely the liquid forin, with perhaps a Stight change os dens ity, but in hich no important properi y is
number of their constituent principies ; they are abundantam g the productions os nature, and can be sonued also by
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The compounds formed by the exertion Or chemicat attraction have apparintly the fame relation to this potver assimple hodies have : they have a similar tenden to combi nation, unite in different proportions, and with dimerent de-grees of sorce ; aud est these combinations are accompanted by the Same phenomena, and appear to Observe the Samelaws. It has been supposed, howcver, that when Compound substances combiue together, the combination is the result, not of the mutuat attraction belween the integrant particles of these compotinds, hut of the assinities of their ultimate element' modissed by the condition in V hicli they exist In ali cases, attraction is much modi ed, and iis resulis determined, by circumstances soroim to the attractive forceiiseis. The operation of these cireui tances has been est lished with inore precision by the labours of Ecd hollet, and has been proved to be more important than was former bellevia. They require, therei ore, more distinct enuinera tion, especialty as sonae of them give rise to important resulis in the processes of Pharina . Quantity os matter influenCes assinity, an increase mlhe relative quantity of one b0dy with regard to anotherenabling it to act ivitii more sorco ; Or, as the law has been Stated, every substauce having a tendency to inter into combination, acts in the ratio os iis assinity and iis quav- tity.V Hence an effect can bu producta frona tho. mutua Iaction of two hodies, When one is in a certain relative pae portion to the other, which ivili not be obtain d whon ille prop0rtion is changed; a compotin i, for example, may be de CompoSed by a Substance exerting nn attraction to Ono os iis ingredients, when the decomposing substanco is present in
Jarge quantity, while the decomposition will not happen Domais action in a finalter quantity. Heiace, i , decompositionis Osten only partiat, sor in proportion as an ingredient, in
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OF TAE GENERAL PRINCIPI ES consequence of au assinity exerted tu it by any b0dy, is ab-Stracted from another ivith whicli it has been combined, thequantity of the lalter bocoming relatively larger to the por- fion os the former Whicli rematiis, adiis so much to the forco os iis assinity, that it is capable of countei acting the actionos the docomposing substance, of at longili arresting it, and preventing the decomposition froni boing complete. Bothos these circumstances a re of much importunce in Pharmacy, and Pender neceSSary particular attention to vards iu-suring the viii a m strengit, os active preparations.
2d, COHESION, or the state of a both ivitii regni d to the aggregation of iis interamni particles, must obviousty modisy the chemicat action Os auother body upon it, by opposing a
resistance Whicli must be overcome hesore the imion of theirparticles can bo essected; helice the cause, that two solidhodies seldom aci chemicatly on each other, and that fluidit' promoteA Chemicat action. Eut besides this obvious effeci, cohesion, even when it has been overcome, stili modiues tho exertiori os chemicat attraction, by resuming iis force when-over the force of tliat attraction is diminished, and thun somelimes giving Υise to uew combinations ; and sometimestoo, Maen Suddenly eStablislied in Consequence of the assini
lios hecoming eflective, it determines the propoletions iuishicli hodies combine, by insulathng the compound at a certain' stage of the combination. It is thus the most powerfulenuse in placing Iimiis to the exertion os chemicui attractiou. Isso LUBILIΤY is merely the result of the force os cohesion, in i elation to the liquid whicli is the medium os chemices action, aud iis action is of CourSe similar; it counieracis combination, by Withdra ving the insolubie substance Pota thε action os a body exerting an attraction to it'; and by the samo operation, it insulates a compound when it is sermod: isdgreat DLNSITV, or specisc gravity, 50 sar as it infitiences at-