696 Transactions. — Chemistry. 



2. If so, does Eisner's equation represent the true amount 

 of oxygen required ? 



3. \Yhat is the relation between the concentration of the 

 solution and the rate of solution of the gold ; and what is the 

 explanation of the more rapid action of dilute solutions ? 



In seeking for an answer to the first of these questions 

 I made several experiments, using both gold foil and gold 

 paper (filter-paper on w'hich metallic gold is precipitated). 

 A gold plate exposed to the action of a 4-per-cent. solution 

 of potassium cyanide, from which air had been removed as 

 far as possible, lost in twenty-four hours only 0-0002 gram., 

 whilst the same gold plate when exposed to the action of 

 this solution wuth free access of an- lost 0-00835 gram, in 

 the same time. A piece of gold paper containing 000002 

 gram, of gold, and having a distinct pink tint, in the absence 

 of oxygen, did not lose its colour for eight days, whilst, when 

 a similar piece was exposed to the action of the same cyanide 

 solution, saturated with air, the colour faded completely in 

 two minutes. These results can leave no doubt as to the 

 absolute necessity of oxygen in order to bring about the solu- 

 tion of gold. 



2. Amount of oxygen required for the solution of gold. — I 

 exposed a weighed gold plate to the action of potassium- 

 cyanide solution, enclosed with a measured volume of oxygen 

 in a suitable vessel, and after standing for two or three days I 

 reweighed the plate and measured the volume of the oxygen 

 remaining. I could thus calculate the weight of oxygen re- 

 quired to dissolve a given weight of gold, and I found, as the 

 mean of four experiments, that this weight was within 5 per 

 cent, of that calculated from Eisner's equation. It is there- 

 fore evident that Eisner's equation is correct ; or, in other 

 words, two atoms of gold require for solution in potassium 

 cyanide one atom of oxygen. 



3. What is the relation between the concentration of the 

 cyanide solution aiad the rate of solution of the gold, and 

 what is the explanation of the more rapid action of dilute 

 solutions? — After numerous experiments, the following plan 

 was adopted to determine this point : Four circular plates of 

 gold, each 22mm. in diameter, were suspended by cotton so as 

 to hang an inch or two from the bottom of a tall glass vessel 

 holding 500cc. of cyanide. By means of a crank attached to 

 a water- v;heel, the plates were raised and lowered about an 

 inch twenty times a minute. The solution was kept saturated 

 with air by appropriate means. The plates were exposed to 

 this action for an hour, and were weighed before and after the 

 experiment, the loss in weight representing the gold dissolved. 

 The results are given in the following table : — 



