first halt at i 100 rn.m. and then a slow rise to 236 m.m. Both 

 pressures are again situated on the above cited [hT-Unes. 



CONCLUSION. 



:I9. Summarizing it thus appears that on abstraction of SO^ from 

 a mixture of PbS and PbSO^, the sulijoined moiiovariant ecpiilibria 

 are successively met with, which are indicated in lig. 3 I) v the regions 

 I, II, III, IV and V. 



PbS— PbSO,— PbO.PbSO, ... I 

 Pb— PbS-Pl:>O.PbSO, .... II 

 Pbb— PbO.PbSO,— (PbO),.PbSO, . Ill 

 Pbe— ,PbO),.PbSO,— (PbO)3.PbSO, . IV 

 Pbd— (PbO)3.PbSO,— PbO ... V 



The lead phase may contain a 

 little PbS in solution. As the con- 

 tent thereof varies in the different 

 equilibria, this difference is repre- 

 sented by the indices a, b etc. 

 Probably, however this sulphide 

 content is very small. 



F'ig. 2 indicates the pressures 

 in these monovariant equilibria 

 and the changes thereof with the 

 temperature. 



//PbO 



Fig. 3. 



The 



ein region A is the existential region of PbS -f- PbSO^ 



B „ 

 C „ 

 D „ 

 E „ 

 F „ 



„ PbSO, + PbO . PbSO, 

 „ PbO . PbSO, + Pb 

 „ (PbO), PbSO, -f Pb 

 „ (PbOj3 PbSO, + Pb 

 „ PbO + Pb. 



Hence, at the temperatures and pressures of region F all the 

 sulphur will have been expelled from the roasting material. 



20. By substituting the values found in table 1 first series in 



Q 

 the equation log p ^= — rn^ ~lT^ "f" ^ ^"^ combining the equations 



thus obtained in pairs, Qi was calculated for the reaction : 

 PbS 4- 7 PbSO, = 4 PbO . PbSO, -f 4 SO, + 4 Q^ 



