Memoir on various Combinations of Gold. 4] 1 



of gold, mixed with phosphoric acid. A second portion of 

 pliosphoretted hydrogen, not sufficient to precipitate all the 

 metal, would again giTe a similar result. 



But if the precipitate be not suffered to form, and the gas be 

 still passed through the liquid, the colour becomes blackish, and 

 a black precipitate is formed Avhich does not appear to contain 

 gold in a metallic state. This precipitate with nitro-muriatic 

 acid yields a solution of gold and of phosphoric acid ; exposed 

 to heat it inflames, and leaves a residue of" metallic gold, retaining, 

 probably, a little phosphorus. When this precipitate has all 

 subsided the liquid is left colourless, and contains only muriatic 

 and phosphoric acids. This precipitate should be considered as 

 a true phosphuret, since it has a colour never obtained by mix- 

 ing gold and phosphorus; when agitated in water, is always 

 homogeneous ; when heated in water, at a temperature which 

 would melt phospliorus, none of this substance is separated in 

 globules ; and lastly, when exposed for days to the atmosphere, 

 gives no white fumes and does not appear to change. 



To a«;sure myself by other means of what took place in this 

 case, I poured a very small quantity of muriate of gold into water 

 charged with phosphoretted hydrogen: the water assumed a 

 blackish colour, like that of tlie liquid from which I obtained 

 phosphorus. Into muriate of gold, on the other hand, I poured 

 phosphoFetted hydrogen water, leaving an excess of muriate: 

 the liquid took a fine purple colour, like that from which gold 

 was precipitated in a metallic state, 



Phosphuret of gold, Hke phosphorus, has the property of pre- 

 cipitating the gold of its solutions in a metallic state. 



It results from these experiments, that while any gold remains 

 in solution, the phosphoretted hydrogen will precipitate it only 

 in a metallic state; but that, in the course of the operation, 

 this gold acting in a state of suspension, upon the phosphoretted 

 hydrogen, passes to the state of phosphoret, and gives a preci- 

 pitate entirely homogeneous. 



Precipitation of Gold by the Mkalies, 

 The phenomena in precipitating solutions of gold by the al- 

 kalies are so different, according to the circumstances under 

 which they are effected, that it is not surprising that chemists 

 should differ in their opinions on the oxides of this metal. 



Proust says that potash precipitates from the solution of gold 

 a yellow powder, which is violet when operated on in a large 

 •piantity of water, but black when washed : excess of alkali, sa- 

 turation, the heat of ebullition, arc none of them sufBcient, he 

 says, to render him master of this preparation : this precipitate 



>vashed. 



