1898.] of Copper and Sodium. 237 



a month, the salt in the sealed tube began to change in the course of a 

 few days. It is also important to mention here that the salt does not 

 keep in contact with alcohol as was often noticed during specific gravity- 

 determination. Alcohol therefore appears to have a twofold action 

 when used in washing the moist salt. Firstly, owing to its strong 

 affinity for water, it removes easily the last trace of moisture from the 

 salt, and secondly being in itself very volatile entirely disappears when 

 exposed to the air. 



A series of analysis was made with samples prepared on different 

 occasions under varying conditions, and the result is tabulated on next 

 page. 



From the percentage composition we obtain the following atomic 

 ratio : — 



Cu: Na: S: O = '514 : -369 : '874 : 1984 

 = 14: 1 : 24 : 5'5 



7 : 5 : 12 : 275 



The composition obtained from the analysis of different samples agree 

 so well among one another that there is no reason to assume it to be a 

 mixture. On the contrary it may fairly be assumed to be a compound 

 with definite composition. It has also been found that different crops 

 of the salt obtained from the same mixture at different intervals have 

 identical composition (see samples B. 1 and B. 2). 



On adding caustic soda to a mixture of cupric sulphate and sodium 

 thiosulphate, a blue precipitate is obtained indicating the presence of 

 bivalent copper. If, however, the caustic soda is added after some time 

 when the formation of the yellow salt begins, the yellowish red cuprous 

 hydrate is obtained. On adding caustic soda to the yellow salt sus- 

 pended in water, the latter is decomposed, and the same reddish yellow 

 cuprous hydrate is obtained. This indicates that the first stage of the 

 reaction consists in the reduction of the cupric copper to cuprous 

 copper, and it is during the second stage that the precipitation of the 

 yellow salt commences. The formation of the yellow salt is neither 

 sudden nor rapid, one or two days being sometimes necessary for 

 complete precipitation. It appears as probable that a portion of the 

 copper in solution undergoes oxidation with the reformation of copper 

 sulphate and reproduction of a blue solution. 



The salt thus prepared was subjected to a careful qualitative 

 analysis .for all other possible sulphur compounds, as for instance sul- 

 phuric acid both free and combined, a sulphide, a sulphite, and the 

 thionates. It was found, however, that none of these compounds are 

 present in the salt even as an impurity. But it gave all the reactions 



