246 C. B. and J. B. Bhaduri — On Double Thiosulphates [No. 1, 



of the little discrepancy noticed between the thiosulphuric acid deter- 

 mined by direct titration (method B) and that obtained from the total 

 sulphur calculated as thiosulphuric acid. 



The yellow salt described before dissolves easily in dilute hydro- 

 chloric acid without any apparent change. Concentrated hydrochloric 

 acid on the other hand precipitates a white crystalline salt which settles 

 down at once. After a while, however, sulphur dioxide is given off freely 

 from both, and the supernatant liquid turns brown. The white salt if 

 washed immediately with a little water and finally with alcohol is a 

 rather stable one. It can in fact be heated in steam chamber without 

 decomposition. In contact with the mother liquor containing strong 

 hydrochloric acid it decomposes so soon that the washing of the salt 

 becomes difficult and at times impracticable. Besides in presence of a 

 large quantity of strong hydrochloric acid a proportionally large 

 quantity of sodium chloride is precipitated and cannot therefore be com- 

 pletely removed by alcohol. If instead of hydrochloric acid, acetic acid 

 be used, sodium acetate is formed and can be easily removed by washing 

 and filtration with dilute alcohol in which menstruum it is rather freely 

 soluble. We accordingly prepared at first a saturated solution of 

 copper chloride in dilute acetic acid and then gradually added to it a 

 strong solution of sodium thiosulphate, when a perfectly white salt was 

 precipitated. Subsequent experience proved that even acetic acid is 

 not necessary, and the white salt is obtained when a strong solution 

 of sodium thiosulphate is gradually added to an equally strong solution 

 of copper chloride. The precipitate is obtained in fine impalpable 

 powder whieh settles down easily and can therefore be filtered and 

 washed without any considerable difficulty. The result of the analysis 

 of the different samples is given in the annexed table. From the mean 

 atomic ratio Cu : Na : S : CI : O : H 2 = 3 : 301 : 4'68 : 1-29 

 10-78: 1'91 the salt with the formula 9 Cu 2 S 2 3 . 5 Na S 2 3 8 Na 01 

 12 H 2 is obtained having the following percentage composition: — 

 Cu = 31-46 S = 24-78 O = 2876 

 Na = 11-45 CI = 7-85 H 2 = 597 



If strong solutions of copper sulphate or acetate and sodium thio- 

 sulphate be mixed nearly in the proportion of one molecule of the 

 former to two molecules of the latter and allowed to remain for some 

 time as in other cases, no yellow salt separates out. If on the other 

 hand a large excess of concentrated acetic acid be added to the mixture 

 a white or faintly yellowish white precipitate is obtained which is more 

 soluble in water than the yellow salt. Copper acetate should therefore 

 be used in preference to copper sulphate. It can then be washed with 



