On the Oxides of Gold, Tin, &c. 7 1 



much diluted in water, have an aqueous transparency when 

 they are well made ; but when mixed together, a fine colour, 

 like that of Malaga wine, is produced ; a circumstance which 

 could never happen, unless the oxygen of the nitro-muriatic 

 solution united v/ith the muriatic solution of tin. If, in a 

 similar mixture, we pour by little and little, stirring it at the 

 same time, the solution of gold with a great excess of acid, 

 and diluted in 130 to 160 parts of water, the intensity of 

 the colour of a similar mixture u ill increase more and more, 

 and latterly present a very fine ]v.irplc tincture, in which all 

 sorts of stuffs may be dyed. By making the nitro-muriatic 

 solution predominate, shades of peach flowers and lilies will 

 be obtained ; and, on the contrary, shades more or less gray 

 are obtained by making the muriatic solution of tin predo- 

 minate. Care must be taken, however, not to employ the 

 latter in too great abundance, because, in powerfully extri- 

 cating the oxygen from the oxide of gold, it will deoxidate it 

 too much, and precipitate it. The precipitate produced in 

 this case is not entirely deprived of oxygen, which hinders 

 it from gilding silver in the cold, like the ashes produced 

 from the combustion of a piece of cloth impregnated with a 

 solution of gold. The longer or shorter preservation of the 

 golden tincture will depend entirely upon the proportions of 

 the two different solutions of tin, more or less overchartrcd 

 with acids, and the solution of gold, in which the acid 

 ought always greatly to predominate. In exposing the 

 purple tincture of gold, of the most jierfcct transparency, to 

 a strong heat, it will decompose itself, and precipitate the 

 colour known by the name of pui-ple of Cassius, the beauty 

 of which will depend more or less on the nitro-muriatic so- 

 iution of tin employed, which, mixed by itself with solution 

 of gold, without the intervention of muriate of tin, produces 

 no change of colour, and preserves itself a long time without 

 forming any precipitate, if the mixture is not too much di- 

 luted with water. The purple tincture of gold is, properly, 

 nothing else than the purple of Cassius, kept in solution by 

 means of the oxygen of the nitro-muriatic solution of tin ; 

 and there is every reason to believe that in the purple of 

 Cassius the oxide of gold is in some measure combined with 

 E 4 the 



