Browning and Howe — Detection of Sulphides, etc. 321 



working of the method when these two acids are found 

 together in solution. Sulphates, almost invariably present 

 with sulphites, are of course quite easily separated by filtration 

 and treating with the barium salt in acid solution. Sulphides 

 if present in the solution would seriously interfere with the 

 working of this method if not removed, being readily oxidized 

 by the iodine or bromine to sulphite, sulphate or, should 

 sulphur also separate, to thiosulphate. We found in course of 

 our work that in attempting to neutralize a mixture of freshly 

 prepared alkaline sulphide together with a sulphite we often 

 obtained a precipitate of sulphur. After the removal of the 

 sulphide and sulphate, we were surprised to find on treating 

 with iodine scarcely a trace of sulphite. On treating with 

 bromine however an abundant indication of thiosulphate was 

 obtained. It is well known of course that thiosulphate may 

 be found by boiling a sulphite with sulphur, but that this 

 reaction should take place so readily and completely seemed to 

 us rather unusual. 



For the removal of a sulphide before proceeding with the 

 tests for sulphite and thiosulphate Grieg Smith recommends 

 the passing of carbon dioxide through the solution until the 

 escaping gas gives no indication of hydrogen sulphide, but 

 Bloxarn* calls attention to the tedious and wholly unsatisfactory 

 character of this method of removal and recommends a mixture 

 of zinc chloride, cadmium chloride, ammonium chloride and am- 

 monia. We have found that the addition of zinc acetate to a faintly 

 alkaline solution accomplishes the same purpose in an entirely 

 satisfactory manner. The sulphide used in our work was freshly 

 made by passing hydrogen sulphide through a dilute solution 

 of sodium hydroxide. When portions of this solution, still 

 alkaline, were treated with zinc acetate in excess, and the zinc 

 hydroxide and sulphide removed by filtration, the filtrate gave 

 no test for either sulphite or thiosulphate by the application of 

 iodine and bromine as described, and the vapor evolved on 

 boiling caused no darkening of lead paper. The following 

 table shows the results of a few experiments in which tests 







Table V. 





K 2 SO s 



Na 2 So0 3 



BaS0 4 precipitated 



BaS0 4 precipitated 



taken. 



taken. 



after oxidation 



after oxidation 



grm. 



grm. 



with iodine. 



with bromine. 



O'l 



0*01 



Abundant 



Good. 



o-i 



o-ooi 



Abundant 



Distinct. 



o-oi 



o-i 



Good 



Abundant. 



o-ooi 



o-i 



Faint 



Abundant. 



o-ooi 



o-ooi 



Fair 



Fair. 



* Chem. News, lxxii, 63. 



