ox gold: its formation in our reefs. 165 



electrical manifestations which are always the concouiitants of 

 chemical action. 



Taking two plates of gold, chemically pure, I placed one of 

 them in a cell cliarged with sea-water, and the otlier in a porous 

 cell charged with sulphide of ammonium, which cell I partially 

 immersed in the first. These gold plates I connected voltaically 

 at points quite clear of the liquid, and inserted a delicate 

 galvanometer in the circuit, when I found the needle was 

 vigorously deflected over an arc of 20° to 30', indicating, of 

 course, that a strong current of electricity was l^eing generated. 

 The direction of this current, as shown by the needle, was from 

 the inner to the outer cell. The gold in the sulphide solution, 

 therefore, was the positive element of the pair. 



Electric currents of equal strength were also developed by 

 charging both cells with sea-water, or with a solution of potash or 

 ammonia, and administering sulphuretted hydrogen to the gold 

 plate in either cell. The direction of these currents was constantly 

 from the cell to which the gas was supplied. By charging one of 

 the cells with potash or ammonia, and the other with sea-water, 

 a current of electricity was also produced, but this was of very 

 feeble intensity, and might well be owing to traces of sulphur in 

 the alkaline solutions. 



The currents thus developed by gold, and in the same manner 

 by platinum, in sulphide solutions soon ceased, but they wei'e so 

 well marked, and had such an apparent intensity, that I was 

 induced to try if they had any effect upon certain metallic 

 solutions, and on trial, I found that, in the case of that obtained 

 by the use of gold plates in contiguous solutions of potash and 

 sulphide of potassium, a degree of intensity was reached sufficient 

 to decompose solutions of copper, silver and gold, and to deposit 

 these several metals in adherent films upon proper electrodes. 

 The same results were afterwards obtained with platinum. 



This capability of gold and platinum to generate electrical 

 currents under these circumstances — currents of such intensity as 

 to exhibit true electrolytic eftects — when taken along with the 

 results of my former expei'iments on this subject, appear 

 conclusive evidence in favour of the sulphurization of these 

 metals being, as has been already urged, the result of chemical 

 action. 



OXIDATION OF GOLD. 



I shall now proceed to a description and explanation of the 

 phenomena, which I have discovered, when gold and silver are 

 allowed contact with air and water, and which I was partly 

 prepared for, by the results described above. 



I shall treat, first of all, with silver. Placing a slip of silver, 

 thox'oughly cleaned, in ordinary spring water, and a second in 

 distilled water, I kept them therein for twelve hours, and then 



