700 Transactions. — Chemistry. 



6. The variation in the rate of sokition of gold in cyanide 

 sokitions is not directly influenced by the amount of cyanide 

 in solution, except in the case of very dilute solutions, but is 

 mainly due to the solubility of oxygen in these solutions, 

 the amount of gold dissolved being nearly proportional to the 

 absorption coefficients of oxygen in such solutions. 



7. The rate of solution of gold is, however, not exactly 

 proportional to the above-mentioned coefficients, but is rather 

 less than it should be for the more concentrated solutions. 



8. The explanation of this diminishing ratio of the gold 

 dissolved to the oxygen available, as the concentration of the 

 solution increases, is to be found in the increasing viscosity of 

 the solutions as the quantity of cyanide augments. 



9.- The explanations given in 6, 7, and 8 are equally ap- 

 plicable to the solution of silver in potassium-cyanide solu- 

 tions. 



Eeturning to Mr. Skey's paper, to which I have already 

 referred, I give the following extract in order to show the 

 position he takes up. He says, " Why very weak cyanide 

 solutions act as swiftly as they do, while strong solutions do 

 not act upon gold to a degree or at a speed in any way cor- 

 responding to what we expect, is a problem that has not, 

 I think, been solved. To account for this it has been as- 

 sumed that strong solutions of the cyanide do not dissolve 

 oxygen or are not permeated by it as readily as weak solu- 

 tions are. But that there is a plentiful supply of oxygen in 

 these solutions is made manifest by the results of the follow- 

 ing experiments : — 



"1. A newly-made cyanide solution of greatest strength 

 is poured into a shallow vessel, and at the bottom of it a 

 small slip of gold leaf gummed on paper is placed. A long 

 slip of the same is then placed so that one end rests upon the 

 bottom of the vessel while the other end projects out of the 

 solution. In a few minutes it may be seen that the whole of 

 the gold on the long slip has been dissolved, while the piece 

 that is wholly immersed in the fluid does not appear to be at 

 all affected. 



"2. In the same solution place a slip of gold leaf coupled 

 with platina, so as to lie also at the bottom of the vessel, when 

 in a short time it may be shown that the gold has entirely 

 dissolved, wdiile the gold leaf that was not paired with any 

 negative substance has not been afi^ected. With chalcopyrites 

 for the negative pole the solution of the gold was far more 

 rapid than in the former experiment, when platinum was 

 used for this purpose, showing the advantage there is in pair- 

 ing the gold with a substance that is strongly electro-negative 

 to it. 



" I think the results of these experiments clearly prove 



