30 The Patio and Cazo Process. 



The chloride solution for this reaction must be kept at a cer- 

 tain strength or the reaction will cease, and anything which 

 causes further dilution will undo a part of the work already ac- 

 complished. 



When chloride of copper and sulphide of arsenic are mixed, 

 rapid decomposition takes place, and a precipitate of sulphide of 

 copper and chloride of arsenic is formed. 



As 2 S 3 + 3 On 01 2 = 3 Cu S + 2 As 01 3 . 



When chloride of copper and sulphide of antimony are mixed, 

 a precipitate containing sulphur, copper, oxygen, chlorine and 

 antimony is formed. Some antimony remains in solution on ac- 

 count of the sulphuric acid formed. When sub-chloride of cop- 

 per is used, most of the copper is precipitated in the metallic 

 state. 



If proustite and pyrargyrite are treated with chloride of copper 

 both are decomposed. All the silver of the pyrargyrite is 

 converted into chloride, while only a part of that in the proustite 

 is so acted on The reaction for proustite is 



4 Ag, As S 3 + 12 Cu Cl a = 8 Ag CI + 2 Ag 2 S + 2 Cu S + 

 As 2 S 3 + 5 Cu 2 Cl 2 + 2 As Cl 3 + 5 S. 

 and for pyrargyrite 



2 Ag 3 Sb S 3 + 4 Cu Cl 2 = 6 Ag CI + Cu 2 01, + 2 Cu S + 

 Sb 2 S 3 + S. 

 In both cases, part of the reagents remain in solution. 



When sub-chloride of copper is dissolved in salt and boiled 

 with pyrargyrite in powder, a black product is formed which 

 contains most of the silver, all the antimony and sulphur, and 

 some copper and chlorine; 7.3 per cent of the silver is dissolved 

 by the salt. 



2 Ag, Sb S 3 + Cu 2 01, = 2 Ag CI + Ag, S + 2 Ag + 2 CuS + 



Sb 2 S 3 . 

 When sub chloride of copper and proustite are treated to- 

 gether, a gray product is formed which contains nearly all of the 

 silver and sulphur, two-thirds of the arsenic, and considerable 

 portions of the copper and chlorine. 



6 Ag, As S 3 + 7 Cu 2 01, = 14 Ag + 4 Ag 01 + 12 Cu S 

 + 2 As, S 3 + 2 Cu 01, + 2 As 01,, 



