8 JOURNAIy OF THE 



Cu,S + 2H,S0, = CuS + CuS0, + S0,+H,0 



explains such a chang-e. 



Another portion of cuprous sulphide was boiled with 

 concentrated acid until it nearly all disappeared. The 

 free sulphur produced was determined. 



Found. Calculated. 



Sulphur 19.71 20.138 



The formula 



Cu,S4-4H,SO,=2CuS04+2SO, + S4-4H,0 

 shows the final result of the continued action of sul- 

 phuric acid on the subsulphide. 



From these data the secondary reactions between 

 copper and concentrated sulphuric acid may be ex- 

 pressed by the two formulas, 



1. Cu,S + 2HoS0, = CuS+CuS04 +S0, +2H2O. 



2. CuS+2H,SO, = S + CuSO,+SO,4-2H,0. 

 The occurrence of sulphur on the sides of the flask 



at the end of the reaction may be said to be due to the 

 sublimation of that element which is produced by the 

 direct decomposition of sulphuric acid without the 

 intermediate formation of hydrog-en sulphide for the 

 following" reasons: 



1. If hydrog"en sulphide were produced by the decom- 

 position of the sulphide, it is natural to expect some to 

 escape in the g-ases which are g-iven off. None could 

 be detected. 



2. As is well known, hydrog-en sulphide is decom- 

 posed by concentrated sulphuric acid. 



3. The deposit of sulphur is first noted on the sides 

 of the flask and not in the delivery tube where the 

 g-ases, hydrog'cn sulphide, and sulphur dioxide, would 

 naturally come into the most intimate relations. 



4. If flowers of sulphur be heated with concentrated 



