338 



3 OF THE AMERICAN ACADEMY. 



SERIES D. 

 Distillation bIbthod. 



To show the calculation of the analysis, one example will sufl 



N .. of 

 An ilysis. 



26 



Volume (Trine 

 taken. 



c.c. 

 200 



Vollllll;' of 



Solution 



c.c. 

 60 



Voln 



Bolution taken. 



I'd of 



Mirror. 



c.c. 



5 



Dig. 



a) 0.025 



b) 



l: iding of 

 kCrror, Average. 



mg. 



Amount in solution taken, 10 X 0.028 = 0.28 mg. 



Less correction lor lid 0.24 •■ 



■inn per liter urine, 5 X 0.24 =1.2 " 



Comparison of Methods. In order to compare more fairly the distil- 

 lation method with the method of evaporation, the latter was slightly 

 modified tit secure the most favorable conditions for the recovery of 

 the arsenic. 200 cc. urine were evaporated to about 50 c.c, ami then 

 treated with •_'."> o.o. concentrated nitric arid and ."> <•.<•. sulphuric acid. 

 Evaporation was continued until the fumes of sulphuric arid appeared, 

 which lefl a dark residue containing a large amount of organic matter. 

 By successive addition of small amounts of nitric acid and heating, 



