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 



I 



a 

 5 



4 5 6 7 8 9 10 11 

 Average number of foreign particles per field 

 FIG. 123. 



12 13 



11 



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. 1 



To facilitate counting an eyepiece with net micrometer is 



1 Chamot, Seventh International Congress Applied Chemistry, Section VIIIc 

 (1009), 249. 



