6 MATER i A MEDIC A AND THERAPEUTICS. 



time, so as to deposit a second or finer size of powder, 

 and again decanting ; and repeating the operation 

 indefinitely until an extreme degree of fineness has 

 been reached. 



Lixiviation (lix, a lye) is a process of washing an 

 ash or crude mixture of solids, for the purpose of dis- 

 solving out the constituents in the form of a lye, or 

 water impregnated with salts. 



Maceration and Percolation are described under 

 Tincturce (page 15). 



Characters. This part of the description must be 

 studied practically. Using the Manual as his guide, 

 the student must examine specimens of drugs, and 

 note respecting each article its general appearance to 

 the eye, whether liquid, solid, crystalline, etc.; its colour, 

 its weight, its smell, and its taste (if non-poisonous). 

 If convenient, his examination of the drug should 

 follow the pharmacopoeial account farther, and include 

 the determination of its reaction ; of its solubility in 

 water, alcohol, ether, oils, etc. ; and of the effects of 

 heat on its volatility, fusibility, etc. Other important 

 chemical properties, bearing on its pharmaceutical 

 applications, may have to be studied, especially its 

 incompatibility with other drugs, which prevents their 

 combination in preparations. Along with the charac- 

 ters, in many instances, certain tests are given, which 

 introduce the student to the subject of 



Impurities, and the methods of distinguishing 

 substances so like each other as to be very readily 

 confounded. Impurities may be the result of the 

 imperfect selection, preservation, or preparation of 

 drugs, including chemical decomposition of every 

 kind ; or of fraudulent adulteration. Similarity is, 

 of course, a matter of accident, but may give rise to 

 serious error. 



The tests of purity applied to inorganic drugs 

 are mainly such as are familiar to the student of 



