28 The Patio and Cazo Process. 



per, chloride of silver and sulphur are produced, or the sub-chloride 

 of copper formed becomes a sulphide. 



Ag a S + 2 On Cl 2 = 2 Ag CI + Cu 2 Cl 2 + S. 

 ' Ag. 2 S + Cu 2 Cl 2 = 2 Ag 01 + Cu 2 S. 

 The liberation of the sulphur is, however, a secondary reac- 

 tion, taking place only to a very limited extent, thus: 



Ag 2 S + Cu Cl 2 = 2 Ag 01 + Cu S 

 Cu S + Cu 01 2 = Cu 2 CI, + 8. 



When the solution is boiled for some time, the sulphur disap- 

 pears and sulphuric acid is formed. The amount of sub-chloride 

 formed, and of sulphur set free, is dependent on the strength of 

 the solvent, which in this case is salt, on the temperature, and on 

 the presence of air. The secondary reaction depends on the power 

 of the solution to dissolve the chloride. If this could be removed, 

 the solvent power of the solution would be to a certain extent 

 regained. The action of the air in facilitating the secondary re- 

 action is due to its converting the sub-chloride into an insoluble 

 ox y- chloride. 



3 0u 3 Cl 3 + 3 H 2 -f 3 O = 3 CuO, Cu Cl„ 3 H 2 + 2 Cu CI,. 



If chloride of copper and sulphide of silver are boiled together 

 the decomposition is complete. 



Ag 2 S + Cu CI, = 2 Ag CI -f- Cu S. 



When sub-chloride of copper and sulphide of silver are mixed, 

 the following reaction takes place: 



Ag, S +Cu 2 CI, = 2 Ag CI + Cu, S. 



When one hundred parts of the sulphide of silver were treated 

 with sub-chloride, in a solution of salt, as much as 7.6 or 8.3 

 per cent, of the silver remains dissolved in the salt solution. 

 When the residue was treated with zinc, the following reaction 

 took place : — 



Ag 2 S + Cu, CI, + Zn = Zn CI, + Cu, S + 2 Ag. 



When a salted solution of sub-chloride of copper is mixed with 

 a saturated solution of chloride of silver in salt, no precipitation 

 takes place, nor can it reduce chloride of silver when it is in pow- 

 der. If sulphide of silver is added to the salt solution of sub- 



