155 



rature and heating the precipitate so obtained, after drying at 200° — 

 250°, in a current of H^S. In order to remove occluded gases it was 

 then again heated in a vacuum at 300° — 350°. It contained 66. 2% 

 of Cu (theory 66.46%). 



The SO, evolution is already perceptible at ± 150°, hut the 

 reaction velocity at this temperature is so trifling, that it is 

 practically impossible to attain -the equilibrium by heating at a con- 

 stant temperature. Hence, the mass was first heated at a higher 

 temperature (usually 220° — 240°) until a considerable quantity of 

 SO2 had evolved and then cooled very gradually until a temperature 

 was reached where adsorption of S0„ occurred. Now, this tempera- 

 ture was kept constant for a considerable time, small quantities of 

 SOj were frequently withdrawn and it was I'ecorded whether an}- 

 further absolution took place or not. In this manner it was possible to 

 restrict the equilibrium })ressure within 20 — 30 ni.m. ; closer limits 

 could not be obtained in this very slowly progressing reaction. 

 Table II represents the results. 



TABLE II. 3CuS + CuSOj ^ 2CU2S + 2S0. (fig. 2 line I). 



These pressures were always again attained after a few evacuations. 

 The reaction product at the end of the measurements was still in a 

 powdery condition, the colour had changed fi'om black to gre}'. 

 CujO could not be detected. The pressures measured will, therefore, 

 relate indeed to the above-cited monovariant equilibrium. 



7. In exactly the same manner the reaction Cu^S -|- 2 CuSO^ ^ 

 2 Cu,0 -\- 3 SOj was investigated. This also jn'oeeeds very slowly at 

 temperatures where the equilibrium pressure is less than 1 atmos- 

 phere, so that it is here also impracticable to attain the equilibrium 

 by heating at constant temperature. Hence, it was necessary to approxi- 

 mate the pressure in the same manner as detailed above. 



As it appeared very soon that our observations differed very much 



