Skey, — On the Oxidation of Gold. 381 



Art. LIV. — Further Results obtained in sujjport of my 

 Theory as to the Oxidation of Gold in presence of Air 

 and Water. 



By William Skey. 



[Read before the Wellington Philosophical Society, 15th February, 1893.] 



Just recently, in a contested patent case in connection with 

 Macarthur Forrest's patent process for the extraction of gold 

 from its matrices, I had to devise experiments to rapidly 

 decide as to whether or no chlorine and bromine, when added 

 to cyanide solution in suitable quantity, hasten the extrac- 

 tion of whatever gold is present. 



The way I adopted for this was to prepare from Swedish 

 filter-paper and a standard gold-solution a gold- test paper 

 containing gold in quantity so minute that one square inch of 

 it would only contain ^^ of a grain of this metal. 



Using this test-paper I was enabled in a few seconds to 

 show to the local manager here for this company the effect of 

 the cyanide process as compared with the chloro-cyanide or 

 bromo-cyanide processes. 



This method for determining the relative solvent powers 

 of substances upon gold being so successful, I at once adopted 

 it to enable me to take up and complete the further investiga- 

 tion upon the effects of air and water upon gold that I pro- 

 mised in volume viii. of the Transactions. It may perhaps 

 be remembered that I there stated that the effect of acetic 

 acid in rendering gold amalgamable that had been oxidized 

 by contact with air and water was so singular that it re- 

 quired investigation, especially when such a strong reducing- 

 agent as the protosulphate of iron had no such effect upon 

 it. This was an anomaly, I said, that wanted an expla- 

 nation. 



In thinking this over, it first occurred to me that, as acetic 

 acid renders oxidized gold amalgamable by dissolving the oxide 

 of gold off its surface, it would dissolve gold when in presence 

 of air and water — that is, it would dissolve the oxide formed, 

 and so ultimately take up the whole of any minute film 

 or deposit in a few hours. However, on performing the ex- 

 periment, I was unable to detect any removal of gold by this 

 acid, though I allowed fourteen days for the operation. 



It appears, then, to me that the oxide of gold, or possibly 

 the carbonate of oxide of gold, that has formed on the gold 

 as a film protecting it from the mercury, has been converted 

 into acetate of gold by the acetic acid, and, this being easily 

 decomposed by the mercury (while the oxide or carbonate is 

 not), amalgamation proceeds. That hydrochloric acid also 



