QUANTITATIVE ANALYSIS BY MEANS OF THE MICROSCOPE 201 
tides as abscissas. The averages of the counts of these particles 
obtained in each of the three mixtures of known per cent adul¬ 
teration are then marked upon the coordinate paper in their 
proper places, and a line is drawn through the zero and the three 
points; the “ plot ” obtained will be substantially a straight line if 
the work has been properly done. If the points laid out show 
a marked deviation from a straight line the components differ 
Fig. 123. 
materially in their densities, or an error has been made. There 
is thus obtained a device. Fig. 123, by which we can determine, 
from a count of the foreign particles in any similar mixture, the 
per cent of this foreign matter present in material of unknown 
percentage composition.^ 
To facilitate counting an eyepiece with net micrometer is 
1 Chamot, Seventh International Congress Applied Chemistry, Section VIIIc 
(1909), 249. 
