708 



The mixture was introduced in a porcelain boat. The remaining 

 space in the reaction tube was occupied by a porcelain rod so as 

 to render the gas-vohime as small as possible and thus to accelerate 

 the setting in of tlie equilibrium as much as possible. 



The heating took place in an electric furnace. The temperature 

 was measured with a Pt-PtRh thermocell and a galvanometer. 



8. Although the reacting substances had been previously dried at 

 300° there still was evolved, on heating at 500°, in vacuo, a little 

 moisture, which condensed in the colder part of the tubes and was 

 removed by a repeated evacuation and gentle heating. 



Subsequently the dissociation pressure was measured at different 

 pressures between 500'' — 700^ 



The equilibrium set in very rapidly so that when the tempe- 

 rature had been raised and more gas began to evolve there 

 could generally not be noticed any change in pressure after 20 — 30 

 minutes. Then a further evolution of SO^ was caused by a short 

 heating at a somewhat higher temperature and after cooling to the 

 original temperature the course of the absorption of the SO, was 

 recorded. This also took place very rapidly. The equilibrium was 

 thus attained from both sides and yielded figures which differed 

 from each other at most 2 or 3 in.m. Also the same pressure again 

 set in after an evacuation. The equilibrium is, therefore, independent 

 of the total composition, which was confirmed by a change in the 

 proportions of FbSO^ and PbS. 



The results are contained in table I. (Fig. 2 Curve I). 



TABLE I. 



After the tube had been evacuated a few times and a certain 

 quantity of the dissociation product might thus have been formed, 



