PHARMACY. 



object is to obtain the soluble substance 

 in a slate of purity, the operation is term- 

 ed lixiviation, and as small a quantity of 

 the menstruum as is possible is used. 

 When, however, it is employed to free an 

 insoluble substance from soluble impuri- 

 ties, it is termed edulcoration, \vhicli is 

 best performed by using 1 a very large 

 quantity of the menstruum. 



Organic products being generally com- 

 posed of heterogeneous substances, are 

 only partially soluble in the different 

 menstrua. To the solution of any of these 

 substances, while the others remain un- 

 dissolved, the term extraction is applied; 

 and when, by evaporation, the substance 

 extracted is reduced to a solid form, it is 

 termed an extract, which is hard or soft, 

 watery or spiritous, according to the de- 

 gree of consistency it acquires, and the 

 nature of the menstruum employed. 



Infusion is employed to extract the vir- 

 tues of aromatic and volatile substances, 

 which would be dissipated by decoction, 

 and destroyed by maceration, and to se- 

 parate substances of easy solution from 

 others which are less soluble. The pro- 

 cess consists in pouring upon the sub- 

 stance to be infused, placed in a proper 

 vessel, the menstruum, either hot or cold, 

 according 1 to the direction, covering it up, 

 agitating it frequently, and, after a due 

 time, straining or decanting off the li- 

 quor, which is now termed the infusion. 



Maceration differs from infusion, in be- 

 ing continued for a longer time, and can 

 only be employed for substances which 

 do not easily ferment or spoil. 



Digestion, on the other hand, differs 

 from maceration only in ti.e activity of 

 the menstruum being promoted by a 

 gentle degree of heat. It is commonly 

 performed in a glass matrass, which 

 should only be filled one-third, and co- 

 vered with a piece of wet bladder, pierc- 

 ed with one or more small holes, so that 

 the evaporation of the menstruum may 

 be prevented as much as possible, with- 

 out risk of bursting the vessel. The ves- 

 sel may be heated, either by means of the 

 sun's rays, of a common fire, or of the 

 sand-bath : and when the last is employ- 

 ed, the vessel should not be sunk deeper 

 in the sand than the portion that is filled. 

 Sometimes when the menstruum employ- 

 ed is valuable, a distilling apparatus is 

 used to prevent any waste of it. At other 

 times, a blind capital is luted on the ma- 

 trass, or a smaller matrass is inverted 

 within a larger one ; and as the vapour 

 which arises is condensed in it, and runs 



back into the larger, the process in this 

 form has got the name of circulation, up- 

 on which we have observed already. 



Decoction is performed by subjecting 

 the substances operated on, to a degree of 

 heat which is sufficient to convert the 

 menstruum into vapour, and can only be 

 employed with advantage for extracting 

 principles \\hich are not volatile, and 

 from substances whose texture is so dense 

 and compact as to resist the less active 

 methods of solution. When the menstru- 

 um is valuable, that portion of it which is 

 converted into vapour is generally saved 

 by condensing it in a distilling appara- 

 tus. 



Solutions in alcohol, if coloured, are 

 termed tinctures, f.nd in vinegar or wine, 

 medicated vinegars or wines. The solu- 

 tion of metals in mercury is termed amal- 

 gamation. The combinations of othei 

 metals with each other form alloys. 



Absorption is the condensation of a gas 

 into a fluid or solid form, in consequence 

 of its combination with a fluid or solid 

 It is facilitated by increase of surface and 

 agitation ; and the power of absorption ii: 

 fluids is much increased by compressior 

 and diminution of temperature, althougl 

 in every instance it be limited and deter 

 minate. Dr. Xooth invented an ingeni 

 ous apparatus for combining gases wit! 

 fluids, and Messrs. Schweppe, Paul, ant 

 Cuthbertson have very advantageousl} 

 employed compression. 



Fluids often become solid by entering 

 into combination with solids, and thi< 

 change is always accompanied by consi 

 derable increase of temperature, as in th< 

 slaking of lime. 



Chemical Decomposition is the separa 

 tion of the elementary parts of bodies 

 which were chemically combined : anc 

 can only be effected by the agency o 

 substances possessing a stronger affinit) 

 for one or more of the constituents of the 

 compound, than these possess for eacl 

 other. 



Decomposition has acquired variou; 

 appellations, according to the phenome 

 na which accompany it. 



Dissolution differs from solution in be 

 ing accompanied by a decomposition, 01 

 change in the nature of the substanct 

 dissolved. Thus, we correctly say, a so 

 lution of lime in muriatic acid, and a dis 

 solution of chalk in muriatic acid. 



Sometimes a gas is separated during 

 the action of bodies on each other. Wher 

 this escapes with considerable violence 

 and agitation of the fluid it is termed ef 



