PHARMACEUTIC METHODS 13 



to the action of some solvent in whicli 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, ignition, 

 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. This is a process exactly similar to distillation 

 with the exception that solids are used instead o'f liquids. Usually 

 the air is sufiicient to cool and condense the vapors. (Benzoic acid, 

 camphor, iodine.) 



Desiccation. The object of desiccation is to drive off some 

 undesired volatile substance from a solid, the fixed residue being 

 the portion desired. If the heat is not sufficient to change the chemi- 

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



drying. 



Carbonization. This is the process of heating organic sub- 

 stances under the exclusion of air. Its object is to change the 

 chemical composition without oxidation. (Charcoal.) 



Ignition. This is the process of strongly heating a substance, 

 usually in a crucible, with full access to air, so as to complete oxida- 

 tion. Nothing but ashes is left. 



Torrefaction. This means roasting. The object is to employ 

 sufficient heat to alter some of the constituents without affecting 

 others. (Coffee, peanuts.) , _ i x x 



Evaporation. This consists in vaporizing a solvent Irom a 

 solution. The object is concentration of the desired dissolved sub- 



Solution This may be defined as the process of incorporating 

 a solid into a liquid state of molecular subdivision, the result be- 

 ing a clear' homogeneous fluid. In this case the molecules of the 

 solid are diffused throughout the liquid, and are so widely sepa- 



