[210] 



IRotes on tbe S^entiflcation of HlF^aloi^s an^ otber 

 Cvystalline JSoMes I)\? tbe aiC) of tbe /Ibicroscope.* 



By a. Percy Smith, F.I.C, F.C.S. 



Plates 2t, 22. 



THE number of cases in which a crystaUine substance can be 

 identified by the microscope alone is extremely limited ; 

 but as a test of purity, microscopical investigation has a very wide 

 application. When vre are dealing with a substance that, when 

 pure, crystallises in a definite form from any particular solvent, 

 it is manifest that any departure from that form would lead to the 

 suspicion of adulteration. 



Again, if we take such a substance as bark, or opium, it is quite 

 possible to distinguish from each other the various alkaloids which 

 it contains. Besides the form assumed by the free base, it is of 

 importance to convert it into a salt, as there is frequently a marked 

 departure in the form of the crystals — ^.o-,, quinidine and quinidine 

 sulphate ; cinchonidine and cinchonidine sulphate. There may be 

 cases in which the salt and the base possess the same crystalline 

 form. I have recently met with one in cocaine, which, as well as the 

 hydrochlorate, crystallises in long needles radiating from a central 

 nucleus, aggregated at angles of 90°, 180°, 270°^ and 360°. 



Some experience is necessary in selecting the most suitable 

 solvent from which to crystallise an alkaloid, as the duration of 

 the evaporation may have a marked effect upon the form of the 

 crystals. In some cases, evaporation may be accelerated by the 

 aid of heat ; in others, such a proceeding is fatal to success. The 

 addition of alcohol to ether, and of water to alcohol, appears to be 

 the best means of retarding the process when necessary. To take 

 the case of cocaine. From chloroform no crystals are deposited. 

 From ether they are ill defined, but from alcohol, allowing evapo- 

 ration to proceed very slowly, we get the best results. 



I always employ polarised light by which to view the crystals, 



* From the Analyst, by permission of the Editor. 



