6 JOURNAL OF THE 



iiivarial)ly the sulphide. In malvino- his analyses 

 verylikel}^ he determined the copper alone and the per- 

 centag-e of copper in copper oxide and cuprous sulphide 

 is the same. In a subsequent conversation with Dr. 

 Andrews, I haved learned that this was the case. This 

 black residue when thoroug^hly w^ashed free from any 

 sulphuric acid always g-ave off hydrogen sulphide on 

 treatment with hydrochloric acid. 



The composition of the insoluble residue was deter- 

 mined by analysis: 



Found. Calculated for Cu ^ S. 



Sulphur 20.44 20.14 



Copper 79.56 (by difference) 79.86 



100.00 100.00 



In the first of the two primary reactions, 



Cu+2H,SO,-CuSO, + SOo4-2H,0, 

 it is seen that for each atom of copper found as sul- 

 phate, one molecule of sulphur dioxide should be 

 evolved. Calculating- on this basis from the following" 

 table we have the ratio of 2 : 3 between the copper as 

 subsulphide and the copper as sulphate unaccounted 

 for in the production of the sulphur dioxide. 



The formula 



5Cu+4H,SO, = 3CuSO, + Cu„S4-4H,0 

 shows that relation between the two compounds of 

 copper. , 



Second Reactions. — The secondary reactions depend 



1 PickerinfT states (loc. cit.. p. U7) that once at 80° C. he observed that the copper 

 in the two compounds stood in the relation of 2:2.0. I have not been able, however, 

 to have concentrated sulphuric acid act on copper at any temperature from 0° C. to 

 270° C. without the evolution of sulphur dioxide, which is not accounted for at all 

 in case the .second of the primary reactions alone takes place, which he states did 

 take place at 80° C. 



