142 ELEMENTS OF APPLIED MICROSCOPY. 



be supposed from a perusal of its earliest exposition, 

 published by Harting in 1866. Lehmann, Behrens, and 

 others have since shown that many dynamic properties, 

 melting and volatilization for example, as well as the 

 typical chemical reactions, may often be observed to 

 great advantage under the microscope. The use of 

 minute quantities of material (one-tenth of a milligram 

 often sufficing), the rapidity with which residts may be 

 obtained, and the simplicity and compactness of the ap- 

 paratus needed are general advantages of the microchem- 

 ical method, which apply in all maimer of analyses. On 

 the whole, few chemists who take the trouble to familiarize 

 themselves with the use of the microscope wiU fail to find 

 it at times a valuable aid in their work. In the study 

 of certain closely related organic compounds it furnishes 

 at once information which can otherwise be attained, 

 if at all, only by the expense of a vast amount of labor. 



2. The Study of Typical Crystals. — ^It will be well for 

 the student of microchemistry to familiarize himself 

 first with the most important characteristics used in the 

 identification of crystals, by the examination of certain 

 typical forms. The actual process of deposition should 

 be studied and those differences observed which occur in 

 the formation of crystals under different conditions, 

 as, for instance, from alcoholic and aqueous solutions, 

 and by slow spontaneous drying on the one hand and 

 rapid evaporation by heat on the other. Crystals formed 

 in a mother-liquor of the same composition show their 

 characteristics with special distinctness. 



The linear dimensions and the relative proportions of 



