218 Gooch and Phelps — Reduction of Arsenic Acid. 



Whenever antimony was introduced intentionally it was 

 taken in the form of antimonic acid produced by oxidizing by 

 bromine in alkaline solution tartar emetic purified by boiling 

 with hydrochloric acid until the distillate contained no trace 

 of arsenic. The stannic chloride employed was similarly puri- 

 fied by boiling in strong hydrochloric acid. 



It will be seen that no indication was given by hydrogen 

 sulphide either in the distillate or residue when the hydro- 

 chloric acid (10cm 3 ) and the potassium bromide (3 grm ) were 

 treated in blank. When the bromide was treated in blank ten 

 times successively no indication was obtained in any individual 

 distillate, but the residue showed a trace of color which was 

 apparently intensified by the action of hydrogen sulphide. 

 This effect was slight and probably due to the prolonged action of 

 the acid upon the rubber. It is not sufficient to interfere with 

 the detection of'O 0001 grm of antimony — as subsequent experi- 

 ments showed. 



A. single distillation, requiring but three or four minutes, 

 proved to be sufficient for the complete volatilization of 

 0*0010 srm of arsenic, two distillations were enough to remove 

 O01 grm , and three 01 grm of arsenic. In handling larger 

 amounts of arsenic, 04 grm or i-s rm 5 it became evident that the 

 presumably pure arseniate actually contained a trace of anti- 

 mony, and the efficiency of the bromide treatment in effecting 

 the detection of a little antimony in presence of a large amount 

 of arsenic is clearly shown. It is plain that while the presence 

 of large amounts of antimony and tin tend to diminish the 

 rapidity of volatilization of the arsenic, the detection of 

 - 0001 grra of arsenic is always sure, and that antimony and tin 

 if originally p resent in appreciable amount will always be dis- 

 coverable in the residue. 



In a comparison of the results of these experiments with 

 those recorded in the former paper describing the reduction 

 by means of potassium iodide, it appears that in general fewer 

 distillations are needed to effect the transfer of the arsenic to 

 the distillate when the bromide is employed — a condition of 

 affairs which is doubtless due to the fact that in the former 

 treatment an insoluble and somewhat refractory precipitate of 

 arsenious iodide is formed when large amounts of arsenic are 

 present, while the bromide causes no precipitation of the 

 arsenic, and interferes in no way with the distillation of the 

 reduced product. 



