100 



A mixdire of equal mols. of lliis basic sulphate and Cu^O yielded 

 the |)ressui-es of table V 2"'' series. As both series of observations 

 entirely agree, we may be sure that they relate to a same mono- 

 variant equilibrium, namely between CuO . CuSOj, Cu,0, CuO and 

 the gaseous phase. As the equilibrium pressure does not alter after 

 withdrawal of SO,, tliat is after variation in the relation of CujO 

 and CuO, the miscibility of these phases, noticed by Wohlkk') at 

 higher temperatures, will be slight in this temperature-range, so that 

 they will both continue to exist. 



Finally, the SO, was withdrawn com])letely, so that only CuO 

 could remain, as we had started from equimolecular quantities of 

 basic sulphate and Cu^O. We have been able to demonstrate that 

 this was really the case by measuring the dissociation hereof in 

 Cu,0 and 0,. Here we found at 944° ... 36 m.m. and at 958° . . . 

 49 m.m., observations which entirely agree with those of Wöhler 

 for pure CuO. 



11. With the above mentioned equilibria in the ternary system 

 Cu-S-0 are connected the dissociation equilibria of pure CuSO^ and 

 CuO . CuSO,. 



These have been determined by Wöhler and his co-workers. 



On a closer scrutiny of. the values given by them it appeared 

 that the p-T-lines that can be construed thereof intersect each other, 

 which would lead to the improbable conclusion that the basic sulphate 

 is only stable above ± 625° and must dissociate below this tem- 

 perature into CuO and CuSO^. Hence, we were obliged to doubt 

 the correctness of their determinations. 



As, however, the accurate knowledge of the dissociation line of 

 the basic salt was of importance to us because — as will be seen 

 in § 14 — the equilibrium pressure of reaction V can be calculated 

 therefrom, we have once more determined the dissociation lines of 

 the normal and of the basic sulphate. The results differ considerably 

 from those of Wohleh. 



Both equilibria can be attained very readily and the pressures 

 obtained by evolution and absorption do not differ more than 2 — 3 m.m. ; 

 after evacuation they accurately resume the same value. By way 

 of a check a series of observations were executed in the dissociation 

 of the normal sulphate where platinum gauze was tied round the 

 porcelain tube with the substance. ^ />;7c»/7 it was probable, however, 

 that even without addition of this catalyst the equilibi'iuni in the 



1) L. VVOHLER, C.S., loC.cit. 



