364 



All in and Crenshaw — Sulphides of Zinc, 



{'1 percent) sulphide. Concentrated solutions of those reagents 

 change the orange-colored sulphide to a bright yellow color. 

 This is caused by a subdivision of the particles of the latter 

 (see p. 301). Thus 0-1 g. OdSO,.8/3H 4 was dissolved in a 

 little water and enough sodium sulphide was added to make a 

 solution of about 13 per cent concentration. The mixture 

 was then- poured into a platinum tube and the latter was set 

 inside of a larger glass tube, which was then sealed. After 8 

 days at a maximum temperature of 260°, no crystals had been 

 formed. In a similar way about half a gram of the amorphous 

 cadmium sulphide was heated with an excess of 20 per cent 

 sodium sulphide for 7 days at a maximum temperature of 275°. 

 Again no crystals were obtained. We may therefore infer 

 that cadmium sulphide is more soluble in ammonium sulphide 

 than it is in the alkali sulphides, while with zinc sulphide the 

 opposite is true. 



We conclude from the foregoing that no regular form of 

 cadmium sulphide is obtained from alkali sulphide solutions, 

 and that the analogy with zinc does not hold. 



Effect of Sodium thiosulphate on soluble Cadmium salts. 



The crystal form of the precipitate thrown down by sodium 

 thiosulphate from cadmium sulphate solutions was also inves- 

 tigated. The principal reaction with excess of reagent is the 

 same as that with zinc, mei'curic and ferrous salts. There is 

 evidently a secondary reaction producing a little sulphurous 

 acid, and reducing the amount of thiosulphate consumed. The 

 sulphide also sticks obstinately to the glass and occludes a 

 little sulphate, making it difficult to obtain cpiiantitative results, 

 though the latter are good enough to prove that the chie # f 

 reaction with excess of thiosulphate is 4Na 2 S 2 3 + CdS0 4 = 

 4JSTa 2 S0 4 + CdS + 4:S. The following data were obtained in 

 sealed tubes at 100°: 



Table VIII. 

 Action of Na 2 S 2 3 on CdS0 4 . 



Taken 



Na 2 S 2 3 .5H 2 



CdS + S 



CdS 





CdSO.,.8/3H 2 



Na 2 S 2 3 .5H 2 



H 2 



Used up 



Cal. 



found 



Cal. 



found 



Cal. 



1 

 2 



1-000? 



it 



5-006e 



it 



75-1000" 



3-44 

 3-56 



3-87 

 3-87 



0-98 



106 



0-54 



0-56 



