ARSENIC. 187 



ties of bromide given in the third column are proportional 

 to 100 parts of silver : 



8.3246 grm. AsBfj = 8.58 grm. Ag. 97-023 



4.4368 " 4-573 " 97-022 



5-098 " 5-257 " 96.970 



Mean, 97.005, zb .012 



Hence As = 74.046, ± .058. Why this value should be 

 so much lower than that from the chloride is unexplained. 



The volumetric work done by Kessler,* for the purpose 

 of establishing the atomic weights of chromium and of 

 arsenic, has already been described in the chromium chap- 

 ter. In that investigation the amount of potassium dichro- 

 mate required to oxidize 100 parts of AsoOg to As^Og was 

 determined, and compared with the quantity of potassium 

 chlorate necessary to produce the same effect. From the 

 molecular weight of KCIO3, that of KaCr^O; was then 

 calculable. 



From the same figures, the molecular weights of KCIO3 

 and of KoCrjO; being both known, that of AsjOg may be 

 easily determined. The quantities of the other compounds 

 proportional to 100 parts of AsoOg are as follows: 



K^Cr^O,. KCIO,. 



98.95 41-156 



98.94 41. 116 



99.17 41.200 



98.98 41-255 



99.08 41.201 



99.15 41.086 



41.199 



Mean, 99.045, ± .02} 41.224 



41. 161 



41-193 

 41.149 

 41.126 



Mean, 41.172, rh .009 



* Poggond. Annal., 95, 204. 1855. Also 113, 134. 1861. 



