1164 A TREATISE ON METAMORPHISM. 



In the production of the chalcocite from the bomite the reaction for 

 cupric salts in the presence of oxygen may be as follows: 



(11) Cu 3 FeS 3 +CuS0 4 +20=2Cu 2 S+FeS0 4 +SO, 



or, if oxygen be not present, the reaction may be : 



(12) 5Cu 3 FeS 3 +llCuS0 4 +8H,0=13Cu 2 S+5FeS0 4 +8H 2 S0 4 



For cuprous salt in the presence of oxygen the reaction is: 



( 13 ) 2Cu 3 FeS 3 +2Cu 2 S0 4 +20==5Cu 2 S+2FeS0 4 +S0 2 



or, in the absence of oxygen : 



(14) 8Cu 3 FeS 3 +llCu 2 S0 4 +4H 2 0=23Cu 2 S+8FeS0 4 +4H 2 S0 4 



In all of the foregoing reactions the fundamental principle, so far as 

 iron and copper are concerned, is the same. In every case the acid radical 

 of the oxidized copper salt passes to the iron, and the sulphur in the iron 

 unites with the copper, forming copper sulphide, thus producing a greater 

 proportion of copper sulphide in the ore than before the reaction. 



Too much stress must not be laid on the particular chemical reactions 

 written. They are designed to show the nature of the reactions which may 

 occur rather than to assert that the particular reactions written do occur 

 exactly. It is believed that the reactions written are possible, but much 

 experimental work must be done in the laboratory in order to ascertain 

 which of the reactions is most common in an individual case. It is believed 

 that the reactions for the production of rich sulphides of copper by 

 descending waters are often those in which oxygen is present, but doubt- 

 less reactions without oxygen also take place frequently. 



In all cases where S0 2 is regarded as produced by the reactions it may 

 be that instead of this compound sulphuric acid is formed. Indeed, it is 

 well known that S0 2 in the presence of fprric sulphate is oxidized to sul- 

 phuric oxide. In order to modify the equations in which S0 2 appears so as 

 to produce sulphuric acid it is merely necessary to substitute H 2 S0 4 for each 

 S0 2 on the right side of the equation, and add H 2 0+0 on the left side. 

 Probably the reactions in which oxygen is absent also occur in the first 

 concentration of copper in consequence of the reactions of ascending copjter 

 solutions upon previously precipitated lower-grade materials. 



