SANGER AND BLACK. — DETERMINATION OE ARSENIC IN URINE. 333 



cupric sulphate in order to retain any hydrogen sulphide which may 

 be formed. 



The sulphuric acid is from the Baker and Adamson Chemical Com- 

 pany, and has never shown a trace of arsenic when tested in greater 

 quantity and for a longer time than in a single determination. In the 

 constant generator it is used at a dilution of 1 to 8 ; in the reduction 

 bottle somewhat more dilute (1.5 normal). 



The hydrochloric acid is also obtained of the Baker and Adamson 

 Company. Two grades 19 have been used : the ordinary chemically 

 pure acid (A), which was found by repeated trials to contain 0.4 mg. 

 arsenious oxide per liter ; and a second (B), in which we have determined 

 by careful analysis an amount equal to 0.02 mg. per liter. 



The nitric acid is an ordinary, chemically pure acid, tested in large 

 quantity after evaporation with sulphuric acid and found to be entirely 

 free from arsenic, both by the Marsh and Gutzeit tests. 



Utensils. All glass and porcelain vessels were new, and, after freedom 

 from arsenic was assured by blank tests, were reserved for this purpose 

 alone. 



Analytical Results. 



Blank Tests. 1. 100 c.c. hydrochloric acid (A) were diluted with 

 35 c.c. water and distilled into 25 c.c. nitric acid. From the evaporated 

 distillate a mirror was obtained equal to 0.04 mg. arsenic. 20 Amount 

 per liter, 0.4 mg. 



2. 100 c.c. acid (A) were added, drop by drop, to 50 c.c. hot nitric 

 acid in a porcelain dish. The mixture evaporated with sulphuric acid 

 gave a mirror equal to 0.04 mg. arsenic. Amount per liter, 0.4 mg. 



3. 100 c.c. hydrochloric acid (B) were diluted with 35 c.c. water and 

 distilled into 25 c.c. nitric acid. The evaporated distillate gave a 

 mirror which was judged to be about 0.003 mg. arsenic. 



4. 200 c.c. acid (B) were added, drop by drop, to 100 c.c. hot nitric 

 acid and the resulting mixture evaporated with sulphuric acid until 

 the nitric acid was expelled. From this was obtained a mirror which 

 was read as 0.002 mg. arsenic. 



From analyses 3 and 4 it was evident that there was a trace of 



19 A third grade (C) has been obtained from the same source since the comple- 

 tion of the analytical work on this paper. In this acid, which is of exceptional 

 purity, the amount of arsenic is not over 0.004 mg. per liter. 



20 In these analyses " arsenic," unless otherwise specified, means arsenious 

 oxide. 



