308 SCIENCE PROGRESS. 



(i) 2Au + 4 KCy+2H 2 + 2 = 2KAuCy 2 +2KOH + H 2 2 

 followed by — 



(2) H 2 2 + 2A11 + 4 KCy = 2 KAuCy 2 + 2KOH. 

 In place of this Bettel 1 suggests the following : — 

 (1) 2 Au + 6KCy + 2 +2H 2 = KAuC) 2 +KAuCy 4 +4KOH 



(2) KAuCy 4 + 2Au + 2 KCy = 3KAuCy 2 . 

 Even if such actions occur, however, it is possible that they 

 are limited to an insignificant part of the whole mass. 



However this may be, it is fully proved that gold 

 cannot directly displace potassium or sodium in alkaline 

 cyanides, the liberation of hydrogen in the liquid never 

 having been observed, whilst conversely the displacement 

 of gold by metallic potassium is readily effected, and is 

 complete. It is necessary that some substance should 

 be present having a strong affinity for potassium, so as to 

 unite with it, in order that gold may be dissolved by cyanide. 

 The usual agent employed is oxygen, but it is not necessary 

 that it should be in the free state, many substances contain- 

 ing it loosely combined being efficient substitutes. Mac 

 Arthur, indeed, has cited experiments 2 to show that gold 

 in ores can be dissolved by potassium cyanide in the absence 

 of oxygen, and Bettel 3 found this to be the case, if the 

 crushed ore contains basic ferric sulphate (a common con- 

 stituent where oxidised pyrites are present), by which 

 potassium ferricyanide is formed, thus : — 



Fe 2 (S0 4 ) 3 + i2KCy = 3K 2 S0 4 + K 6 Fe 2 Cy 12 . 



The addition of other oxidising agents to expedite the 

 action of cyanide has been suggested on all sides, and the 

 results of work in this direction have been the basis of 

 several variations in the original process. Some of the 

 most interesting results are those obtained by Bettel and 

 Marais in 1894. 4 They first removed all solvent power 

 from a cyanide solution by expelling the dissolved oxygen 

 with a current of hydrogen, and then added various oxidis- 

 ing agents and observed the effects produced by them. 

 Under these circumstances, neither potassium bichromate, 



1 South African Mining Journal, 8th May, 1897. 



2 Jour. Soc. Chem. Ind. (1890), p. 7. 3 Loc. cit. ant. 

 4 Proc. Chem. and Met. Soc. of S. Africa, May, 1897. 



