PHARMACEUTICAL PREPARATIONS 73 



Percolation, or method of displacement, is the process 

 employed in preparing tinctures and extracts, in which a 

 fluid is allowed to percolate through a drug packed in a 

 conical cylinder, carrying with it the soluble constituents of 

 the drug. 



Dialysis is the operation of separating colloid from 

 crystalloid substances in solution. The solution is placed 

 in a dialyser (a cylinder, over the bottom of which is placed 

 a piece of parchment) and the dialyser is immersed in water. 

 The crystalline bodies diffuse into the water through the 

 parchment while the colloid materials remain behind. 



Scaling is the method by which concentrated prepara- 

 tions of drugs are dried upon glass plates in thin films, and 

 then broken up into scales — viz., scale pepsin. 



Other familiar chemical processes employed in phar- 

 macy are : 



Liquefaction, which must not be conducted at too high 

 a temperature if the substance be organic, otherwise charring 

 will occur. 



Evaporation is accomplished usually in a sand or water 

 bath. 



Crystallization is done to purify crystallizable substances. 



Distillation, 



SMimation, 



Fusion. 



Incineration is the combustion of a substance for its ashes. 



Reduction is employed to recover a metal in its purity 

 when in a combined state. 



Pharmaceutical Preparations. 



The '* United States Pharmacopoeia " is an authoritative 

 book, including the drugs of most value with a description 

 of their properties, tests for their purity, and methods for 

 making their preparatious. It is revised each decade by a 

 convention of representative delegates from medical schools 



