BARTOW: MICROSCOPIC COMPARISON OF WHITE ARSENIC. 257 



40 per cent of crystals. From these differences I concluded that 

 the arsenic in the suspected sample could not have had the same 

 source as that found in the milk and the whiskey. 



In order to be sure that my separation of the various slides into 

 groups was not due to my familiarity with them, I submitted these 

 slides, together with slides prepared from arsenic from other 

 sources, to Professor S. W. Williston, to Professor W. C. Stevens, 

 and to Professor E. Haworth. Each had no difficulty in separat- 

 ing the slides submitted into groups, always putting those from the 

 same source into the same group, and never classifying the sus- 

 pected sample with the specimens from the milk and the whiskey, 

 thus confirming my own conclusions. 



All the comparisons were made directly from the slides, and, in 

 fact, a better judgment can be formed by observing a considerable 

 portion of each slide. I have, however, had a number of micro- 

 photographs made by Mr. F. E. Marcy the university phcto- 

 grapher. These show the crystals magnified seventy-five diameters 

 and give a very good illustration of the variations in the various 

 samples. I have added also photographs of samples from speci- 

 mens of white arsenic in the chemistry (Fig. 5) and pharmacy 

 laboratories (Fig. 6) of the university, because they show a great 

 variation in the percentage of crystals, though the particles are 

 nearly of the same size. 



