The Patio and Cazo Process. 23 



iron are found. It is mixed with insoluble copper ores in 

 order to produce the necessary soluble copper salts. 



Fe 9 3 S0 4 + 3 Cu == 3 Ou S0 4 , + Fe 2 O a . 



The iron is precipitated and the sulphate of copper crystalized. 

 The same result is obtained with malachite. Chloride of iron 

 may also be used to produce chloride of copper. 



Fe a 01, + 3 Cu = 3 Cu Cl 2 + Fe 2 0,. 



With atacamite, a mineral frequently found in these countries, 

 a mixture of chloride and sulphate of copper is formed. 



Cu Cl 2 , 3 Cu + Fe 2 3 S0 4 = Cu Cl 2 + 3 Cu S0 4 , + Fe 2 3 . 



With chloride of iron — 



Cu Cl 2 , 3 Cu + Fe 2 Cl 6 = 4 Cu Cl 2 + Fe 2 3 . 



Decomposing iron pyrites can also be used — 



2 Fe S0 4 + 2 Ou + = 2 Cu S0 4 + Fe 2 0,. 



This last reaction is a little slow; but if roasted pyrites is used, 

 it takes place very quickly. If a little excess of the oxide of 

 copper is added, no iron is left in solution. The mixture should 

 be roasted in such a way as not to decompose any of the sulphate 

 of copper, but all the sulphate of iron should yield its sulphuric 

 acid to the oxide of copper; this it is almost impossible to do. 

 But the heat makes rapid action possible. 



When no sulphate of iron can be had, as in some parts of 

 Peru, sulphate of alumina can be used: 



Al 2 3 S0 4 + 3 Cu 0=3 Cu S0 4 + Al 2 3 . 



The decomposition does not take place so rapidly or so com- 

 pletely as with the sulphate of iron, owing to the pasty condi- 

 tion of the alumina produced. 



On account of the difficulty of obtaining the magistral, whose 

 only efficiency is the amount of sulphate of copper that it con- 

 tains, of the same strength at different times, sulphate of cop- 

 per has been entirely substituted as magistral in many places 

 for the roasted copper pyrites magistral, with great success and 

 greater certainty and celerity of working ; but, in many places, 

 the old magistral is still used, and even when copper pyrites 

 cannot be had, roasted iron pyrites is used. 



