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 results 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 manner of analyses. On 
the whole, few chemists who take the trouble to familiarize 
themselves: with the use of the microscope will 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 
