334 PROCEEDINGS OF THE AMERICAN ACADEMY. 



arsenic in the acid (B), probably about 0.002 mg. in 100 c.c. or 

 0.02 mg. per liter. 



5. 300 c.c. urine were evaporated to 30 c.c. and distilled with 100 c.c. 

 hydrochloric acid (A) into 25 c.c. nitric acid. One half of the solu- 

 tion from the evaporated distillate gave a mirror equal to 0.02 mg. 

 arsenic ; the other half, a color band (Gutzeit) equal to 0.02 mg. The 

 amount of arsenic per liter is therefore 0.4 mg., which confirms the 

 results of analyses 1 and 2, and the test shows the urine to be free 

 from arsenic. 



6. 200 c.c. urine were evaporated to 30 c.c, and distilled with 100 c.c. 

 acid (B) into 25 c.c. nitric acid. The distillate, evaporated with a 

 little more nitric acid, gave a mirror which, as nearly as could be 

 judged, was equal to 0.002 mg. This confirms, within the limits of 

 reading, the results of analyses 3 and 4, and enables us to fix the cor- 

 rection for 100 c.c. of this acid at 0.002 mg. This has been since 

 confirmed by the analysis of the acid by the Gutzeit method. The 

 correction is only appreciable, as will be seen from Series B, below, when 

 the entire solution gives a very low mirror, and entirely disappears 

 when the miiTor, even if a low one, is obtained from a small part of the 

 solution (see Series C). 



The third grade of hydrochloric acid (C), which will hereafter be 

 used in all urine work in this laboratory, was tested as in analyses 2 

 and 4. After reduction of the residues from two lots of 100 c.c. with sul- 

 phurous acid, color bands were obtained equal to 0.3 and 0.5 micro-milli- 

 grams (0.001 milligram) of arsenic. This is equivalent to 0.004 mg. 

 arsenic per liter. The correction for 100 c.c. of this acid, 0.0004 mg., 

 would be practically inappreciable under ordinary conditions of the 

 Marsh procedure, even if the mirror was obtained from the entire solution. 



Analyses. For use in the subsequent analytical work, a solution of 

 arsenious acid was made as follows : One gram of pure arsenious oxide, 

 twice resublimed, was dissolved in a small amount of sodic hydroxide 

 free from arsenic. After acidification with sulphuric acid, this solu- 

 tion was made up to a liter. Of this, 10 c.c. were diluted to a liter, 

 giving a solution containing 0.01 mg. arsenious oxide to the cubic 

 centimeter. 



7. 150 c.c. urine, to which had been added 0.025 mg. arsenic, were 

 evaporated to 25 c.c and distilled with 100 c.c. hydrochloric acid con- 

 taining 0.035 mg. arsenic. The total amount was 0.06 mg. 25 c c. 

 of distillate were collected in 25 c.c. nitric acid, and from this was ob- 

 tained a mirror equal to 0.06 mg. 50 c.c. more of the distillate were 

 collected in 15 c.c. nitric acid, and from this no mirror was found. 



