I'elletier on Gold. 121 



Potash has the power of dissolving oxide of gold, inde- 

 pendent of the presence of an alcaline chloride. M. Pelletier 

 boiled magnesia with a solution of the chloride of gold, and ob- 

 tained a precipitate of oxide of gold mixed with magnesia in 

 excess. This precipitate well washed, and deprived of all 

 traces of chloride, being acted on by a solution of potash, had 

 all the gold dissolved ; the presence of the metal in the solu- 

 tion was rendered very sensible by the addition of chlorine or 

 muriatic acid. 



Magnesia and barytes, as well as soda, act in the same 

 manner as potash on the chloride of gold, but with phaenomena 

 less marked, in consequence probably of the slight solubility 

 of the two first substances. 



M. Vaumont has said, that the oxide of gold may be 

 successfully obtained by acting on the chloride by the oxide of 

 zinc. M. Pelletier has found this process to succeed very well ; 

 but the oxide obtained must be washed with nitric acid, to 

 separate any oxide of zinc remaining from the oxide of gold. 



Of the Iodide of Gold. 



No chemist has yet mentioned this combination, M. Pelletier 

 being the first who has described it. He ascertained that gold 

 was not acted on either by iodine or the hydriodic acid ; but 

 the hydriodic acid, containing iodine, easily dissolves gold, and 

 especially when its action is assisted by the addition of a little 

 nitric acid ; it then forms an iodide of gold, which precipitates as 

 a brilliant yellow powder, apparently crystalline. The iodide of 

 gold may also be obtained by other means, as by making the 

 hydriodic acid and the oxide of gold act on each other, or 

 by precipitating the chloride of gold by the hydriodate of 

 potash. 



Whatever process has been employed in procuring the 

 iodide of gold, the compound is identical. It is insoluble in 

 cold water, and boiling water dissolves only a very small quan- 

 tity. The muriatic, nitiic, and sulphuric acids, do not decom- 

 pose it when cold ; when concentrated and boiling, the gold is 

 dissolved by them, and the iodine set free. Heat alone also 



