153 



gram of a mixture containing 9 mols CiiS to 4 mols Ca,0 0.1274 

 gram of BaSO^ was olitained in this manner so that the mass, after 

 heating, contains 10.07„ of CnSO^. If the mass had been converted 

 entirely according to 



9 CuS + 4 Cu,0 = 8 Cu,S + CuSO, 

 the CuSO^ content ought to bell.l57„. Hence, it had been converted 

 to a very considerable extent. 



In good agreement herewitli was the fact that a mixture of Cn.jS 

 and CuSO, did not at all change at this temperature; it retained 

 its colour and remained powdery '"). 



Hence, Cu,S — CuSO^ forms the stable, CuS — Cu,0 the metastable 

 phase-pair. 



5. On the strength of the above orientating experiments it seemed 

 probable tiiat we must imagine the stable equilibria in the system 



CajO 



Fig. 1. 



Cu — S — to be as follows. Fig. 1 represents a horizontal projection 

 on the ground plane of a figure in space which holds for a constant 

 temperature and where the vapour pressure p is plotted on the 

 vertical axis. 



Mixtures of CuS and CuSO, will at a given temperature give the 

 highest SOj-pressure, namely the one related to the monovariant 

 equilibrium : 



3 CuS + CnSO, :;! 2Cu,S + 2S0, (I) 



1) This is in contradiction with tlie observations of Schenck and Hempelmann, 

 who record a mell between GuSOi and Gu^S, akeady at 300°. 



