Maclaukin. — Action of Potassium-Cyanide upon Gold. 701 



that there is a sufficiency of oxygen present, even iu the 

 strongest sohitions of potassic cyanide, to allow of the rapid 

 solution of gold therein. But why strong cyanide solutions 

 have so little, or so vei'y slow, an efl'ect upon gold as we find 

 is a question that, in the light of these results, appears as yet 

 quite unanswered. For my part, I am inclined to think that a 

 compound forms upon the gold when in strong cyanide solu- 

 tions that is either insoluble or but very slowly soluble in 

 these strong solutions, but is soluble to a considerable extent 

 in weak solutions. It is, I think, very probable that the 

 cyanide of gold that first forms on the gold has to be dis- 

 solved as a simple cyanide before it can be so acted upon 

 by the potassic cyanide as to pass into the comparatively- 

 soluble aurocyanide of potassium." 



It is remarkable that Mr. Skey should make the state- 

 ment, " It has been assumed that strong solutions of cyanide 

 do not dissolve oxygen, or are not permeated by it as readily 

 as weak solutions are," when he had before him my papers 

 proving that oxygen is less soluble in concentrated than in 

 dilute solutions. In the two experiments that follow this 

 statement Mr. Skey shows that gold when partly immersed in 

 the solution or w^hen coupled with platinum is rapidly dis- 

 solved, and concludes " that there is a sufficiency of oxygen 

 present, even in the strongest solutions of potassic cyanide, to 

 allow of the rapid solution of gold therein." It may be as 

 w^ell in the first place to point out that these experiments do 

 not deal with the question of concentration in a satisfactory 

 manner. Whilst it is shown that by partial immersion or 

 contact with platinum the rate of solution of the gold is 

 greatly increased, nothing is given to show the relative effect 

 of solutions of varying concentration in such cases. It is un- 

 necessar}', however, to consider this point further at present, 

 as I shall show that in these particular cases the solution of 

 the gold is not due, as Mr. Skey assumes, to the oxygen in 

 solution, but to electrolytic action. 



Pe}-haps it will be best to consider the question in the 

 successive steps which I took in my investigation. 



Strips of gold leaf (1 to 3, Fig. 1), gummed 



on paper, were gummed on to the inside of 



a beaker, into which a saturated solution of 



potassium cyanide was then poured, until the 



top of No. 3 strip was just covered. In five 



minutes No. 2 was almost entirely dissolved, 



whilst No. 1, which extended partly over the 



bottom of the beaker, required about thirty 



F'^-' minutes. The top of No. 3 was only about 



^in. beneath the surface of the liquid, and yet after standing 



for an hour there was no alteration in its appearance. Nos. 2 



li 



