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The Crystallization of Hippuric Acid. 

 By T. Charters White, F.K.M.S., Hon. Sec. 



( Read December 17th, 1869.) 



In introducing this subject to the Club it will be necessary to call 

 briefly the remembrance of the members to one or two facts fami- 

 liar to all, 



When any soluble substance is dissolved its ultimate atoms are 

 distributed throughout the solvent, and provided the solvent is 

 prevented from evaporating, both solvent and substance remain in 

 the same relation, which is simply that of the most perfect 

 mechanical mixture known, each atom of the substance being im- 

 prisoned in a coating of the solvent. 



Should, however, the solvent be allowed to evaporate, this rela- 

 tion is disturbed ; the substance, if crystallizable, such for instance 

 as Hippuric Acid, is set free to obey certain laws inherent in all 

 salines of forming bodies of definite shapes or crystals ; if this 

 process is allowed to take place slowly we get natural crystals of 

 the salt operated on ; but if crystallization is forced by evaporation 

 at high temperature the solvent is dissipated before the attraction 

 of cohesion of salt can exert its power, and the result is the for- 

 mation of an amorphous mass, or if we are dealing with a small 

 quantity on a glass slide we have a semi-transparent film. The 

 attraction of cohesion of Hippuric Acid acts so readily that no 

 rapidity of evaporation of a hydrous solution can result in any but 

 the natural needle-shaped crystals; we must, therefore, find sol- 

 vents of greater volatility, and those from which I have obtained 

 the best results are the strongest and purest spirits of wine I could 

 procure, and the ordinary methylated spirit which, containing a 

 little varnish, seems to act as a retarding agent in the formation 

 of the crystals, so that they are formed more slowly ; but even 

 with these solvents every care must be taken to promote the 

 most rapid evaporation by warming the slide, the dipper, and 

 the solution, if we would be successful ; the film is then evenly 



