Browning and Howe — Detection of Sulphides, etc. 319 



ide, filtering off the sulphate which represents the sulphite 

 originally present, adding bromine in excess to the filtrate and 

 again bleaching with stannous chloride to increase the visibility 

 of the sulphate which now represents the thiosulphate origin- 

 ally present. The details of experiments in which the sulphite 

 was taken alone and oxidized with iodine are given in Table 

 11. 



Table II. 





K 2 S0 3 



Volume 



BaS0 4 precipitated 







taken. 



of water. 



after oxidation 







grm. 



cm 3 . 



with iodine. 



Remarks. 



(1) 



O'l 



10 



Very abundant 



Plainly visible before add- 

 ing SnCl 2 . 



(2) 



0*01 



10 



Abundant 



Plainly visible before add- 

 ing SnCl 2 . 



(3) 



o-ooi 



10 



Distinct 



More distinct after adding 



SnCl 2 . 



W 



0-0005 



10 



. Faii- 



Hardly visible before add- 

 ing SnCl 2 . 



(5) 



o-oooi 



10 



Faint 



Invisible before adding 



SnCL. 



A corresponding series of experiments was made in which 

 hydrochloric acid was substituted for acetic acid and essentially 

 the same results were obtained. 



A similar series of experiments was made to test the effect 

 of treating the thiosulphate in an acidified solution, first with 

 iodine and then after filtration (if a precipitate had formed) 

 with bromine. In the experiments of division A hydrochloric 

 acid (a few drops) was added before treating with barium 

 chloride, and in those of division B acetic acid was used simi- 

 larly. Stannous chloride was employed to bleach the excess of 

 iodine and bromine. 







Table III. 





tfa 2 S 2 0s 



Volume 



BaS0 4 precipi- 



BaS0 4 precipi 





taken. 



of water. 



tated by action 



tated by actioi 



i 



grm. 



cm 3 . 



of iodine. 



A. 

 Distinct 



of bromine. 



Remarks. 



o-i 



10 



Abundant 



Sulphur separated 











in 30 seconds. 



o-oi 



10 



Faint 



Abundant 



No sulphur in 90 

 seconds. 



o-ooi 



10 



None 



Distinct 



No sulphur in sev- 

 eral minutes. 



0-0005 



10 



None 



Faint 



No sulphur ; SnCl f 

 necessary. 



0*0001 



10 



None 



Very faint 



No sulphur; SnCl 3 

 necessary. 



