Maclaukin. — Action of Potassium-Cyanide upon Gold. 699 



In this expression r is the radius and I the length of a capillary 

 tube through which a volume v of the liquid of sp. gr. s flows, 

 under a pressure jj in unit of time. In the following table the 

 results found by this method are given under z. Under Au/0 

 are shown the values found, and also those calculated by the 

 aid of Maclaurin's theorem — that is to say, by the formula 

 Au/0 = a+ bz + &c., where a = 0-33 and h = -0-9. The 

 close agreement of the values found by these two methods is 

 sufficient to prove that the true explanation of the smaller 

 solubility of the gold relatively to the oxygen in the more con- 

 centrated solutions is to be found in the greater viscosity 

 of these solutions. 



Table IV. 



Similar experiments are recorded in the papers above 

 referred to with regard to silver, and precisely the same 

 results were obtained with this metal. 



The following is a summary of results : — 



1. Oxygen is necessary for the solution of gold in potas- 

 sium cyanide, and no gold is dissolved in its absence. 



2. The ratio of the gold dissolved to the oxygen required 

 for its solution is 196 : 8, as demanded by the equation — 



4Au + 8KCN + 0, + 20H, = 4AuCNKCN + 4K0H. 



3. The rate of solution of gold in potassium-cyanide solu- 

 tions varies with the strength of the solution, being small for 

 concentrated solutions, increasing as the solution becomes 

 more dilute, reaching a maximum at 0-25 per cent, of cyanide, 

 and then again diminishing. 



4. The rate of solution of silver in potassium cyanide 

 varies in the same way, and the maximum is reached at the 

 same degree of dilution. 



5. The ratio of the amount of gold dissolved by any given 

 cyanide solution to that of the silver dissolved by the same 

 solution is nearly the ratio ot their atomic weights. 



