CHAPTER VIII. 
QUANTITATIVE ANALYSIS BY MEANS OF THE MICROSCOPE. 
Some of the most difficult problems with which the chemist has 
to deal are those requiring an opinion as to the probable per¬ 
centage composition or amount of adulteration of materials 
which cannot be chemically analyzed. As typical examples of 
these cases may be cited, mixtures of starches, meals, adulter¬ 
ated flours, spices, teas and other food products; mixtures in 
which firsts ” have been sophisticated with an inferior quality 
of the same material; adulterated pigments; mixtures of wood 
pulps, paper pulps, textile fibers, powdered ores, powdered 
materials of all kinds, explosives, etc., etc. 
In the solution of problems of the above type there are several 
possible methods of procedure. That these methods may be 
sufficiently accurate for our purpose the following requirements 
must be met. The components of the mixture must differ suf¬ 
ficiently in their appearance under the microscope to permit 
their easy recognition, or they must be readily differentiated by 
their different behaviors towards stains or reagents; the com¬ 
ponents must not differ materially one from the other in specific 
gravity and must be small enough in size to allow mounting on 
an object slide and covering with a cover-glass; if of different 
specific gravities, their specific gravities must be known. 
Most of these approximate quantitative microscopic methods 
are based upon the fact that in normal powdered materials 
such as meals, ground spices, powdered drugs, etc., in fact all 
vegetable tissues and most powdered material of fairly definite 
composition, characteristic elements are present in numbers 
which bear to each other ratios which vary between fairly narrow 
limits. These ratios having been first ascertained through the 
examination of material known to be normal or of known com¬ 
position, any variation in the ratios thereform is to be inter- 
198 
