6 RefleSilons on PruJJiats. 



orange colour. This procefs might furnifli another means 

 cf purifying platina. 



A piece of cotton cloth impregnated with a folutton o( 

 gold, containing a fixth part of that metal without excefs of 

 acid, being plunged in a folution of ammonia, furnifhed me 

 with an ochre yellow. This yellow at length became blackifh 

 after being kept in a fheet of paper. As alkaline liquors, and 

 particularly that of the carbonat of pot-a(h or of foda, have a 

 great tendency to diflblve the oxyd of gold, it cannot be ufed 

 for its precipitation on cloth. Cloth coloured yellow by gold 

 dipped in muriat of tin diluted with water, undergoes a change 

 into dark blackifti grey, which becomes brighter in propor- 

 tion as the folution is diluted. I have often obtained violets 

 and lilacs by dipping, without precipitation, the cloth merely 

 imbibed with a folution of gold, in nitro-muriatic folutions 

 of tin prepared with different proportions of the acid. Se- 

 veral fhades of gold colour will be obtained by precipitating 

 oxyd of tin from its nitro-muriatic folution by dilution with 

 water, to which a folution of gold has been added, drop by 

 drop, at different times, with intervals of feveral hours. This 

 niode of operation will furnifh orange colours, while, if you 

 fabftifute oxyd of gold for the folution, you will obtain lilacs, 

 which, approaching more and more to (hades of crimfon, 

 will at laft become orange, if you continue to add to them, 

 from time to time, oxyd of gold. Thefe (hades depend a great 

 deal on the proportion of muriatic acid prefeni in the nitro- 

 jnuriatic folution of tin. If it conlains too great a quantity, 

 the dofe of water muft be augmented to make the oxyd of 

 tin precipitate itfelf, and the gold in that cafe gives a grey 

 colour more or lefs reddidi. The folution of tin, which I 

 employed for thefe experiments, was compofed of four parts 

 of nitric acid, one of muriatic acid, and one and a quarter 

 of granulated tin, (lowly diifolved, to prevent, as much as 

 poffible, the nitrous gas from being dikngaged in loo great 

 quantity. Thefe oxyds of tin, coloured by the oxyd of gold 

 more or lefs de-oxygenated, do not require much metal, and 

 confequently are not dear. They all prefent, when dry, dif-, 

 ferent (hades of grey and lilac more or lefs intenfe, and in 

 all probability might be employed for painting porcelain. 



Stuff 



