268 



PROCEEDINGS OF THE AMERICAN ACADEMY 



opportunity to imprison traces of the mother liquor. Crystallization 

 from hot solutions could not be adopted because of the risk of the 

 formation of basic salt.* But even if the true amount of the water 

 of crystallization could have been determined, it would have been of 

 little present use for the determination of the atomic weight of copper, 

 because of the uncertainty in its molecular weight. It is hoped that 

 an investigation of the quantitative relations of water in other com- 

 pounds may be in progress during the coming year at this Laboratory. 



The Atomic Weight of Sulphur. 



It is seen that the ratio between the weights of sodic carbonate and 

 sodic sulphate found in each analysis of cupric sulphate forms a valu- 

 able check upon the purity of the first substance. Conversely, if we 

 assume the purity of each of the substances and the molecular weight 

 of one of them, we obtain data for calculating the molecular weight of 

 the other. Since sulphur is probably the least definitely determined 

 of the elements involved, the figures may be used with advantage for 

 the calculation of its atomic weight. 



Molecular Weight of Sodic Sulphate. 



Weujhts rcdncid to Vacinim. 



* Hampe, loc. cit. 



