718 



and as mean value was found — 38390 eals. Applying the same 

 principle to the />-7'-values of table 2 we found as the mean value 

 for Q2 in the reaction : 



3 PbS + 2 PbO.PbSO, = 7 Pb + 5 SO, + 5 Q, -- 54324 cal. 



In order to check these tignres we eliminate the unknown heat 

 of formation of the basis sulphate from these equations: 



PbS + 7 PbSO, = 4 PbO . PbSO, + 4 SO, — 4 X 38390 cal. 



6 PbS + 4 PbO . PbSO, ^- 14 Pb + lO SO, — 10 X 54324 cal. 



7PbS + 7PhSO^ =:14Pb + 14 SO, — 696800 cal. 



PbS + PbSO, = 2 Pb + 2 SO, — 99543 cal. 



From the molecular heats ^) 



PbSO,=: 216210 cal. 



PbS= 18420 „ 



SO, = 71080 „ 



the calculation for the above reaction at 20° gives — 92470 cal. 

 The agreement is tolerable. 



Delft. Inorg. and phys. chem. Laboratory 



Technical University. 



1) Landolt. BÖRNSTEIN, Phys. Ghem. Tabelle 1912, 870 and 853. 



(November 27, 1914). 



