SANGER AND BLACK. — QUANTITATIVE DETERMINATION OF ARSENIC. 813 



Hydrogen Sulphide. In a freshly prepared solution of sulphurous 

 acid, which gave no test for arsenic, the amount of sulphur was deter- 

 mined by titration with iodine. A solution was made containing 

 1 mg. of sulphur per cubic centimeter, and from this, in turn, a second 

 containing 0.01 mg. Of this solution amounts corresponding to 10, 

 30, 50, and 70 mmg. sulphur w r ere added to separate reduction bottles 

 aucl the action continued for thirty minutes. Bands of a pale yellow 

 were obtained, slightly darker in shade than those from phosphine. 

 The respective lengths corresponded to those from • 2, 25, 30, and 

 40 mmg. arsenious oxide. Fresh strips of paper were now substituted 

 and each experiment was continued for thirty minutes longer. No 

 additional band was obtained from the first ; from the others the 

 values were approximately 1, 5, and 10 mmg. This shows that under 

 the same conditions and in equal time the band from 50 mmg. sulphur 

 will be of about the same length as that from 30 mmg. of arsenious 

 oxide, and further, that the reduction of the sulphurous acid is not com- 

 pleted in thirty minutes, like the arsenic, but requires a longer time. 



The color of the sulphur band is somewhat brightened by hydro- 

 chloric acid (G N) but not essentially changed, nor was the length 

 increased. Auric chloride produced a dirty light brown. Ammonia 

 on the original band gave also a light brown color. 



Phosphine. A sample of sodic hypophosphite, containing no arsenic 

 on testing, was shown by analysis to contain 28.91 per cent of oxidiz- 

 able phosphorus (theory, 29.23). Of this a solution was made contain- 

 ing 1 mg. of phosphorus per cubic centimeter, from which two others 

 were prepared having 0.1 and 0.01 mg. to the cubic centimeter. Of 

 the last solution, 10, 30, 50, and 70 mmg. were reduced for thirty min- 

 utes in separate bottles. From 10 mmg. no color was obtained, from 

 30 mmg. a very faint indication, and from 50 and 70 mmg. bands cor- 

 responding in length to only about 2 and 10 mmg. of arsenious oxide 

 respectively. After continuing the action for thirty minutes longer, 

 with fresh strips, there was again no color on the first, a faint indication 

 on the second, and about 1 and 10 mmg. on the third and fourth. It 

 was evident that the reduction was very slow. Next were taken 100, 

 300, and 500 mmg. After thirty minutes the length of the first band 

 corresponded to about 2 mmg. of arsenious oxide, the second 30, and 

 the third 50, showing that not over one tenth of the phosphorus had 

 been reduced in the given time. On opening the bottles the odor of 

 phosphine was strong. 



To obtain a band from the hypophosphite equal to that from 

 30 mmg. arsenious oxide in the standard time, an amount equivalent 



