1898.] of Copper and Sodium. . 241 



method A. This proves that the whole of the copper is present in the 

 cuprous state, otherwise the iodine required for direct titration would 

 be less, owing to the liberation of iodine by the cupric salt from potas- 

 sium iodide. The little discrepancy between A and B will be explained 

 later on. 



Another important point should be mentioned here in connection 

 with the determination of water. It will be seen on going through the 

 table that when the water is estimated by heating the substance at 

 temperatures up to 250° 0. in a current of carbon dioxide and causing 

 the sulphur dioxide evolved to be absorbed by lead dioxide, we get 

 9 # 46 °/ of water. On the other hand when it is heated rather strongly 

 and the evolved sulphur dioxide is absorbed by red hot lead chromate, 

 the result is 10*5 °/ . It was further noticed that the major portion of 

 the water was liberated before the evolution of any considerable amount 

 of sulphur dioxide began. During the decomposition of the salt a 

 small quantity of sulphuric acid is formed which with the sodium 

 sulphate, another product of decomposition, may form sodium hydrogen 

 sulphate, thus accounting for the increased percentage of water at a 

 very high temperature. We propose to take up the subject in a future 

 communication in connection with the decomposition of the salt. 



It may hence be concluded that the substance is a double thio- 

 sulphate of copper and sodium having the formula 7 Cu 2 S 2 3 5 Na 2 S 2 3 

 16 H 2 with the following percentage composition : — 



Copper = 32-24 %. Sulphur = 27-95 %. 



Sodium = 8-37 °/ . Oxygen (for complete oxidation) = 3205 °/ . 

 Water = 10-48 %. 



The salt with the composition as given above should however take 

 32'04 % oxygen for complete oxidation of the salt to copper sulphate 

 and sodium sulphate. There seems to be a slight difference between 

 the calculated percentage of oxygen and that obtained as a mean of 

 several analysis. This difference however disappears if the result of 

 the analysis of the last preparation, the most stable in the batch, is 

 considered. 



V. Hauer says that an acid cuprous thiosulphate of the formula 

 Cu 2 H 4 (S 2 3 ) 3 may be obtained by adding a concentrated solution of 

 copper sulphate to a strong solution of sodium thiosulphate until the 

 colour is deep yellow and gently heating the mixture, as yellow pris- 

 matic crystals. We have repeatedly tried to prepare the salt, but as 

 often have we failed. The crystals obtained, invariably contained 

 sodium thiosulphate, and when the heating was carried beyond 35-40 Q C. 

 the mixture in some cases changed colour from yellow to a dark reddish 

 J. u. 31 



