21 



ened with alcohol or water and rubbed with a muller. In rubbing, 

 a circular or figure eight motion should be used. 



Separation. — This is usually the next step in the preparation 

 of drugs. Its purpose is to separate the desired ingredients from 

 the inert or undesired. It may be accomplished in three ways. If 

 the desired ingredients are volatile, they may be driven off by heat. 

 That is by distillation and sublimation. If the substances are not 

 volatile, the separation is usually done by exposing the crude drugs 

 to the action of some solvent in which the desired ingredients are 

 soluble and the undesirable, so far as possible, insoluble. The 

 third method is by mechanical means as in the case of fixed oils 

 where the separation is done by pressure. 



Separation by Heat. — This method can be used whenever the 

 substances to be separated have different boiling points, and are not 

 destroyed by the necessary degree of heat. This process differs as 

 to whether the fixed or volatile portion is desired and if the latter, ac- 

 cording as to whether it is a solid or liquid. The different processes 

 of using heat are; distillation, sublimation, carbonization, igni- 

 tion, desiccation and torrefaction. 



Distillation. — This is the process of converting a liquid into a 

 gas and condensing the gas back again into a liquid. The apparatus 

 necessary is some receptacle for heating the liquid, conducting off 

 and condensing the gas. The ordinary worm still is a good ex- 

 ample. Its purpose is to separate volatile from non-volatile agents 

 and for purifying volatile substances. It may be divided into frac- 

 tional, which means a separation of a mixture of liquids, and destruc- 

 tive where the substances are heated so strongly that they decompose 

 and the volatile products which arise from the decomposition are 

 saved. (Organic bodies as tar). 



Sublimation is a process exactly similar to distillation with the 

 exception that solids are used instead of liquids. Usually the air 

 is sufficient to cool and condense the vapors. (Benzoic acid, cam- 

 phor, iodine.) 



Desiccation. — The object of desiccation is to drive off some 

 undesired volatile substance from a solid. The fixed residue being 

 the portion d'esired. If the heat is not sufficient to change the chemi- 

 cal composition, the process is termed desiccation. It simply means 

 drying. 



