158 



1 — 2° and the thermic effect was vei-y considerable. On an average 

 was found : 457°. The SO^ evolved amounted to a\erafi;e 40 mg. 

 per 25 grams of mixture. 



The ternary eutecticum is, therefore, situated but a little lower 

 than the binary one of mixtures of Cu^S and CuSO, ; the liquidum 

 region in the triangle CujS— CuO— ('uSO^ will exhibit a strongly 

 one-sided situation towards the Cn^S — (!uSO^ side. As the liijuid is 

 very viscous and the evolution of gas a violent one, we have not, 

 up to the present, succeeded in determining the composition of the 

 eutectica. Hence, we can only say this that they will only be 

 permanent under a high SO^-pressure and will, at the ordinary 

 pressure, decompose rapidly witii formation of Cu^O. From our 

 dissociation experiments with mixtures of Cn^S — CuSO, we calculate 

 for the SO,-tension at the initial melting point ± 1.5 atmospheres. 

 A quintuple point between the solid phases Cu^O, CuS, CuSO,, the 

 liquid and the gaseous phase will, therefore, appear at about the 

 above pressure. 



9. Mixtures of CuSO^ and Cii.O will react with formation of 

 the basic sulphate CuO . CuSOj . 



In order to study this reaction more closely, pressure measurements 

 were executed with these mixtures also. In contrast with the former 

 equilibi'ia the pressure rapidly sets in; usually the equdibrium state 

 is attained after 15 — 20 minutes; the adsorption also proceeds 

 rapidly. The values attained from both sides only differed 2 — 3 mm.; 

 hence, the dissociation line is sharply determinable. The SO,-evolution 

 became discernible at ± 480^ ; after evacuation the same pressures 

 were again obtained. The results are given in table IV. 



TABLE IV. 4 CUSO4 + Cu p ^ 3 CuO . CuSOj + SO2 (fig. 3 line IV). 



