SANGER AND BLACK. — DETERMINATION OF ARSENIC IN URINE. 835 



8. By the same procedure as in analysis 7, and also with 150 c.c. 

 urine, 25 c.c. distillate gave 0.06 nig. arsenic, equal to the amount 

 taken. 50 c.c. additional distillate gave no mirror. 



9. With 200 c.c. urine and the same amount of arsenic, the same 

 procedure gave 25 c.c. distillate containing 0.06 mg. arsenic, and 

 50 c.c. additional distillate yielded no further mirror. 



The results of analyses 7, 8, and 9 show that by distilling one half 

 the contents of the flask, according to the method above described, all 

 the arsenic passes over. 



The following series shows that by the former method of destroying 

 the organic matter by evaporation with nitric acid a very large error 

 is made : 



SERIES A. 



Nitric Acid Method. 



In analyses 10 and 11, actual deflagration took place; in Nos. 12 

 and 13 the residues were blackened. 



The next series, B, p. 336, gives the results of a preliminary trial of 

 the distillation treatment, and shows that by the distillation method 

 very small amounts of arsenic can be recovered with practical com- 

 pleteness. As a more severe test of the method, 0.01 mg. arsenic 

 was added to a liter of urine and the analysis carried out as usual, 

 using acid B (Analysis 39). A mirror was obtained fully equal to the 

 standard for 0.01 mg. 



Even with the correction for this acid, we thus recover from 80 to 

 100 per cent of the amount of arsenic taken, which shows that, con- 

 sidering the amount of organic matter involved and the hydrochloric 

 acid used, the method is a delicate one. By the use of an acid of such 

 purity as that of grade C, it will be possible to eliminate entirely the 

 correction for arsenic in the acid, even if the amount of arsenic in the 



