320 Browning and Howe — Detection of Sulphides, etc. 



B. 



1 



o-i 



10 



Faint 



Abundant 



No sulphur sepa- 

 rated in 1 miu. 



2 



o-oi 



10 



None 



Abundant 



No sulphur sepa- 

 rated in several 

 minutes. 



3 



o-ooi 



10 



None 



Distinct 



No sulphur. 



4 



0-0005 



10 



None 



Faint 



No sulphur; SnCl, 

 necessary. 



5 



o-oooi 



10 



None 



Very faint 



No sulphur; SnCl, 

 necessary. 



From these experiments the advantage of the use of acetic 

 acid becomes apparent, as does also the use of stannous chloride 

 in increasing the delicacy of this indication, so that a small 

 fraction of a milligram may easily be detected. 



If relatively large amounts of thiosulphate are present with 

 small amounts of sulphite, we have sometimes found it advan- 

 tageous to manipulate so that even the slow decomposition of 

 the thiosulphate by acetic acid may be avoided by first 

 attempting precipitation with barium chloride in a dilute 

 ammoniacal solution. By this method the barium sulphate 

 and sulphite are separated from the thiosulphate and identi- 

 fied — the sulphate by its insolubility in dilute hydrochloric 

 acid, and the sulphite by the action of iodine upon the acid 

 filtrate from the barium sulphate. After filtering, the thio- 

 sulphate may be detected in the filtrate by the use of iodine 

 and bromine as described above. Table IV gives some results 

 by this treatment. 



Table IV. 



(1) 

 (2) 

 (3) 

 W 



As will be seen, the test for the thiosulphate by this method 

 of treatment is not so delicate, probably on account of me- 

 chanical holding of the barium thiosulphate by the precipi- 

 tated sulphate and sulphite. 



Having determined the limits of accuracy -of the method as 

 applied to the sulphite and thiosulphate taken separately, our 

 next experiments were directed toward an investigation of the 



Na 2 S 3 3 

 taken, 

 grm. 



BaS0 4 



precipitated 



by iodine. 



BaS0 4 

 precipitated 

 by bromine. 



Remarks. 



o-i 



None 



Abundant 





o-oi 



None 



Good 





o-ooi 



None 



Fair 



SnCl 2 necessary. 



0-0005 



o-oooi 



None 

 None 



Faint 

 None 



SnCl 2 necessary. 



