5^2 



HISTORY OF GOLD. 



generally been supposed, that the purple powder could be no- 

 thing but an intimate mixture of gold in the metallic state and 

 oxide of tin. 



If, however, we reflect on some properties, which eminently 

 distinguish this purple from a simple mixture of powdered gold 

 and oxide, and in particular the difficulty we find in separating 

 the latter from it, we shall be inclined to suspect, that something 

 jTiore than simple mixture must take place in this precipi- 

 tate. 

 ?reof$ of this. Let us begin with estab-lishing the metallic state of the gold, 

 after which we will examine the degree of oxidation of the tin 

 that accompanies it. 



To analyse the simple powder, we must employ aqua regia, 

 for the nitric or muriatic acid has only a very slow and very 

 imperfect action on it. Scarcely is it wetted with this, before 

 we perceive it lose its colour, yield a solution of gold, and 

 leave the oxide of tin bare. This oxide is heavy, sandy, and 

 transparent as powdered glass, which is the usual charater of 

 the oxide at a maximum. But it may be said, the nitric acid 

 of the solution of gold may have raised it to this degree. I 

 answer, no : for if the purple powder be heated in marine 

 acid, the oxide taken from it is equally vitreous, and its solu- 

 tion no longer precipitates that of gold ; it only gives a yellow 

 colour with hydrosulphurated water. There can be no doubt, 

 therefore, that, if the tin accompanying the gold be at a maxi- 

 mum of oxidation, it is because it has taken to itself the oxigen 

 Corapdnent of the gold as it threw it down. Oxide of tin at a maximum, 

 powder. therefore, and gold, are irrefragably the constitutent parts of the 



purple powder of Cassius. 



Now to begin with showing that this oxide cannot unite 

 with the gold during the precipitation of the purple powder, 

 any farther then a particular affinity attracts it to this metal, I 

 shall here recapitulate some of the properties of the oxide of 

 tin. 

 The oxide of ^^^f passing from a minimum of oxidation to a maximum, 

 tin unites with diminishes in solubility : a fact that has been sufficiently shown 

 chemical affiui- ^^ ™y ^*^^ paper on tin. In this respect, tin follows the law 

 ty. of most of the metals that are susceptible of two degrees of 



oxidation. But this decrease of solubility is not the cause of 

 its precipitation in the present instance ; for, though less solu- 

 ble 



