2l8 UNIVERSITY OF COLORADO STUDIES 



dissociation of 2H 2 molecules into 2H and 2 OH), forming 2 OH 

 ions. Thus the ions present before solution of the gold are 



4AU+8K+8CN+2H + 2OH + 2O 

 and after the reaction 



8K+4Au(CN) a +40H , 

 or, written in the form of an equation, 



4Au + 8K+8CN + 2H + 20H + 20 = 8k+4Au(CN) a +40H. 

 Oxygen need not necessarily be the carrier of the four negative charges 

 required. Any substance capable of furnishing these charges would 

 cause gold to dissolve in potassium cyanide, or any mechanical means 

 of furnishing these four charges would have the same effect. In this 

 latter case, the equation would be 



2Au+4k+ 4 C / N + 2H + 20H=4k + 2Au(CN) 2 + 20H+H 2 , 

 and gaseous hydrogen would be liberated from the cyanMe solution as 

 the gold dissolved. 



Cyanogen bromide added to a potassium cyanide solution is a very 

 effective gold solvent. The commonly accepted reaction is 



Au 2 + 3 KCN+BrCN=2KAu(CN) a +KBr. 

 Considered electrochemically the reaction is as follows: The solution 

 pressure of the gold sends 2Au ions into the solution, while the solution 

 pressure of the cyanogen bromide sends a Br ion and a CN ion into the 

 solution. The 2Au ions react with the 4CN ions forming 2Au' (CN) 2 

 ions, so that the equation would be written 



2Au + 3k + 3CN+Br + CN=2K + 2Au(CN) 2 +k+Br. 

 It should therefore be possible to set up a cell in which gold and solid 

 cyanogen bromide are the electrodes and potassium cyanide the 

 electrolyte. The current would flow in the cell from the gold to the 

 cyanogen bromide, both being consumed, just as in the gold-oxygen cell 

 the current flows in the cell from the gold to the oxygen, both being 

 consumed. 



