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whicli contains an ingredient Whicli, When insulated, assumesthe aeriat state, is more easy of decomposition, und the de composition is more complete, than a compo d, the ingredietits of whicli are taed ; sor ille tenden cy to elastici ty in
the volatile ingredient counieracis the mutuat assinity ; and when, by the application of heat, Or the operation os a su perior attraction, any portion os it is displaced, it is immo diately Withdra vii Doni the Sphere of action, by assuming the elastic forin, and ceaSes to oppose any obstacte by ses amnity or quantity to the progress of the decomposition. Elasticio too, by countei acting attraction, places limits to the proportions in Which bodies combino. 4th, Tho last circumstance insueucing attraction is TEM FERATURE, or the state of a b y ivitii regard to hoat or
hination. The cause of temperature is a peculiar subito power Ox principi in modern chemicat langvago denominated Caloric), cap te of bcing commmaicaled to bodios, and of bcing in part withdrawn froin them. Iis immediato tendency is to est listi a repulsion botri ocu their particlos hence it gives Piso to expansion OP enlargement of volume, greater m each body according to the quantity of calorie introducod. This progressive augmentation os distanco, ni uch the particios ure placed by it S. steti0n, is accomonieci
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with a proportiones diminution in the sorco os coiresion ; ipe Pied, there re, to a certain extent, that larco is so sat modifled, that the particles hecomo cap Ie of moving easily with xsgard to eauli other, a state M hicli constitutes sui dity ; and, is the commimication of calorio be continued, theexpansion stili continuing, the particles are at longili placedat such distances, that the attraction is entirely overcome, and they repet each other a state whicli constitutes theaurial or gaSeous form. The operation os calorio in influ- Encmg chemicat attraction, appears to depend on the changesit occasiones in the cohesion and elasticity of hodies ;-it favonus combination by dimitatShing cohesion, it counieracis orsi veris it by communicating or increasing elasticity; and these effecis are osten produced together, and modisy each
Froin the disserences of the sorces of affinity among bo- dies, or Dona the operation of thoso circumstances by whichinnity is modi Led, iis power is osten suspended Or oVercome, and substances which have been combined are separated. This forms what in Chemisto is named Decomposition, andit presenis resulis equalty important with those froin Combi-
The dccomposition may be simple, that is, a compound may be resolved into iis constituent paris, each of whicli is insulated. This is in generat essected by the agency of heat.
Within a certain range os temperature, the assinity Whicli has combine I two hodies continues to operate; but whon the temperature is rat sed, and when the hodies differ in their volatilily, or tho tendeney they have to assume the clastic. forni, the olasticity of the moro volatile one is so fur lavom
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tity on chemicat attraction, frequently retians a portion ortho other combined with it. Decomposition is more complicated wheu it is producod by the introduction of a thita substance, whicli exeris an attraction to one of the ingredients of a compo d. Whenthis is effective, the b0h added combines with this ingredient, seming a new compsurid, and it is only the other ingredient of ille original compound that is obtained insulate i.
A crati stili more complicated is, where two compotand sub- StanCes are brought to aci ori each other, and the principies of the ono meri innities to those of the other ; so that an intercliange inlaes place, the two colapo undes are decompos od, and two new ones are formedi The former case used tobe named by chemista single elective attraction ; the lalter duubie elective attraction ; and both were considered as thexesulis of the relative forces os attraction among the hodies concerned. Lut there is sonae reason to helleve, that therarise honi the operation os cohesion, elasticity, and the other fomes that inquence attraction ; and that hut for the operation os illese sorcos, three or more bodies presented to ea liother ivould enter into simultaneous union, instead os passinginto binary combinationS. Galvanism, as weli as Caloric, infitiences chemical aT-nity, and, by the attractive as weli as by the repulsive forceit exeris, is even more powerfui in producing decomposition. It scarcely admits, hora over, of being applied to any pha
Tho OPERATIONs of Pharmacy are generalty dependenton these chemical powers ; they consist os arrangements of circumstances, with the vieiv either of promoting their ex- Pylion, or ol obtaining the producis of chemicat action. QDme prelimina operations aro frequently had recoursoto os a mechanicia nature, to diministi Hie cqhesion os hodies,
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the rubbing being facilitated by the interposition os a fluid,
in whicli the solid is not soluble. Αs by any of these operations, the powder must consist os particles os unequat Sige, the siner are separased froni the coarser by Sisting or waShing. Sisting is passing the powder over a Sieve, the interstices of wllicli are so minute as to allow only thoe sineP particles to
pou der is diffused through a quantity of that fluid, and the
mixture is allowed to. remala at rest. The co Ser partici
quickly subside, and the finer remala suspended. The fluidis then decanted ossi, the powder is allowed to subside, andis afterwariis desed. These methods of reduc g hodies topo der, can be applied to very law of the metais, their forceos cohesion being too strong. They are mechanical ly divid-ed by xasping, or by benig beat tuto leaves, or they are granulated,--an operation performed by melling the metes, and when it is cooled doum as far as it can be without hecomingsolid, potaring it into water : it passes to the Sol id State, assuming the granular forna.
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Dom belug reduced to illeir minute particles, between whichonly chemicat attraction is exerted. They are theresore inployed, mei ely as preliinina to those operations in Whichsuch a division is obtainud by chemicat means. Os theshthe fit si is So Lurio M. By this is understood that operationin which a solid body c6mbines xvith a fluid in such a maliner that the compound relatiis the quid forna, and is transparent. Transparency is the test os perfeci solution. When the spe
ssuid, it may bo diffused through it, but the mixture is moreor Jess Daque ; and on being hept for . Some time at rest, theheavier hody subsides ; while in solution the particles of the solid are permanently suspended by the state os combinationin whicli illey exist, and arc so minute as not to impair the transparency of the liquid. The liquid has, in this case, been rogarded as tho bodyexerting the active pomer, and has been numed the Solventor Mensiduum ; the solid is considereis as the body dissolved. The attraction, however, Wheiace ille solution procee is, is ieciprocat, and the sortia genetrilly procoetis froin the large quantity of the liquid employed, and Doni the absonce of CO-hesion heing more savourable to the combination proceliling
In generat, a solid can bo dissolved tu a liquid uitly in acertain quantity. I his limitation os solution is named Saturation ; and when the poliat is ronch0d, the liquid is salii tobe satura ted with tho solid. As tho fluid approachos to satiuation, the solution proce iis more stola ly. hon a fluidis saturaled with one hody, iliis doos not provent iis dissolv-ing a portion ol another ; and in this way three, four, or sive hodies may he r rtainod in solution at the Same time by one suid. In these cases, the fluid docs not dissolve so large a pr0portioli of any of these substances, us is it had he u pe
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d in a fluid to any oXtent. Gum Or Sugar, sor CXample, vili dissolve in ivater, and forna a persect 80lution in every proportion. An mCrea se of temperature, in generat, lavoura solution, tho
solution proceo ling more rapidly at a lii O than at a Io v temperatu e; and in those cases in P hicli a certain quantity ion os the solid can be combined with the fluid, a largor quantityis talam up when the temperature is increased. The quantity dissoluod is uot in every case promoted alit e by an in-Crea Se of temperature; water, sor example, having iis Solvent potver, With regaris to nitre, greatly increaSed by ausementation os temperature, while sea-sali is dissolved in nea ly as great a quantity by Water at a low as at a hii temperaturo. This disserenoe in these salis, and in many othera,
depentis on ille differetice in the degree of their fusibility by
expla ined, by considering this operation as depending on chemicat assinity overcoming cohesion in the body dissolved. Agitation lavom s solution, by bringing successively the different paris of the liquid into contact with the solid, and thus preventing the di mished osicct whicli arises Dom the proach to saturation in the portion immediat ly cove gthe solid. The mechanical division of a solid, too, is favou illo to iis solution, principally by cnlarging the sui face Whichis auted ini.
Solution is an operation frequently had recoli e to in pharma reutices chemistry, the active principies of many bo-
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OF PHARMACEUTIO CHEMISTRY.dies being dissolved by their proper solvonis. SestS re dis-SolVed in Water, as are also gum, extraci, and other Vegetable producis. Producis of a disserent Lind, as reSin, camplior, and essenties olis, are dissolved in alkohol and wine: and metias are rendered solubie and active by the different acilis. solutions in Water, aikohol, or Wine, possess the Sensibio qualities and medicat viriues of the substance dissolve l. Acid and eskaline liquors change the properties of the hodies whicli they dissolve. In Pharmacy, the operation receiVCS different appellations, according to the nature of the Sol Vent, of the substance dissoluod, and of the mamior in Q hicli it is per med. When a fluid is potired on any Veget te matter, So as to dissolve Onb sonae of iis principies, the operation isnamed EXΤRAcΤ1os, and the part dissolved is sa id to be ex
t te part of the Materia Medica, the aduratages bulonging
l to chemicat action is communicated, is FUSION. It rei qui res inexcly willi rogarit to cach substance, the neceSSarydegree of heat; and whero this is bigh, it is p exsormed
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usualty in crucibies of carthen ware, or sumetimes of blacla leas, or on large scale in iron potS.Chemicat combination is frequently promoted by an eleV tιOn of temperature, though tho heri in V not be so high as to produce fusion, but onb to diministi cohesion to a certain eXtent. CALCINATION, as it used to be named, or metallic idation, is an example of this ; a motui seing heated to abigh temperature, so as to onubio it to combino ivitii theoXygen of the air. DEFLAGRATION is a similar operation, an Inflammabio or metallic substance belug eXp0Sed to a red
Wheu chemicat action has been exert d, other Operationsare Sometimes requirod to olita in the produci, OP Sometimes
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liqiuid evaporating; and in many cases in Pharmacy, particularly in the evaporation of vegetable infusionS Ox tinCtures, the flavoux, and even the more activo qualities of the dissolved substance, are ii te to be injured, especialty to vallis the end of the operation, by a Strong hent. When the object is to obtain the volatile matter by evaporation, the process is of course conducted in close Vesseis, ad ted to condense the vapour and collect the liquid. I his fornas the operation of DISΤILLATION, whicli, with regard todisserent substances, requires to be conducted in xarious
Plen a volatile principie is to be obtainod Doni veget te substances by this process, the dissiculty is to apply the heat sufficiently, without raising it too high. The mode generallyemployod is to heat the veget te matter ivitii Hater, and the distillation is then usualty performed in the common stili. At the beat of boising water, the essentiat Oil of planis, whicli is the clites volatile principie they contain, is VolatiliZed ; it rises with the wateo vapour; is condensed ; istitite ivater has been employed, the greater part of the oti is obtained 'apari; is much has been used, it retains it dissolv-ed, acquiring taste and flavour, and thus sorining the distit ted maters of planis. Is at hol, pure or diluteil, has been themedium os distillation, it always retains the oti in Solution, and fornis What axe amod Distit ted Spiriis. The stili in Whicli the operation is performed avitii these views is of cop- per or iron ; it consists of a body and head, the former de-Si ed to contain the materiais, and to whicli the sire is applied, the lalter to receive the vapour; there issues Dum ita iube, Whicli is connected with a spirat iube, placod in a VeSSel, nam ed the refrigerato , filled with cold water. The V p0ur, in iis progress throui the iube, is condensed, and
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heu metallic matter Would be acted on, by the materiatior the produci os distillation, veSSeis of glass or carthen warctare employed ; the retori, whieli is generalty used, being
densed ; or is the produci is a permanently elastic fluid, whichcamiot be condensed hiat by passing it through Water, a series of botiles connected by tubes, on the principio of Wool 'supparatus, is uSed. When the lar duci obta ined by distilla tion is not persectly pume, it con be frequently pii isted by a second distillation ; the process is then namcd Becti asson ruthen it is Deed frona any superfluous water combined avithit, the operation is named Dephlegni aliun or Concentration. When the produci of volatiligation cis condensed, uot iusto liquid, but in the solid fortia, the process is numed SUBLIMATION, and the produci is a Sublimate. Αs the condensation, in this caSe, tines placo With much more facility, amore simple apparatus is employed, consisting usualty os aconices botile or fiasti vitii a round bottona, thin and equat,named a Cucurbit, in Whicli the materials are contained, heatbeing applied by the medimn of a sand bath. The vapoi condenses in the upper part of the fasti, serming a calae, whicli adheres to it, the orifice being lightly closed to prevent, any part stom heing lost; ox a globular head, With a groovent iis under edge, and a iube to convey 0ff any liquid that
may he condensed, a Lapital as it is named), is applied.
When a solid si stance is throum do via Dom a liquid bychemicat action, it soritis: the operation os PREcIPITATION, and the mattor thrown do via is nam ed a Precipitate. Fxequently the substance precipitaled is ono ivli ich had Mendissolved in illo liquid, and vhicli is separat 'd by a substance added, combining xvith the solvent, or thc. substance Whichrender8 it solubio, and veakeuuag iis attraction. to the ono