7iJ Oil the Oxides of Gold, Tin, ^c. 



the oxide of tin, which, giving up to it its oxygen during 

 its application to porcelain, hinders, in my opinion, the gold 

 from reducing itself and regaining its metallic lustre. I 

 cannot subscribe to the opinion of Dr. Richter, of Berlin, 

 who asserts, in a memoir which I have not read, to have 

 mathematically demonstrated that the gold of a crimson co- 

 lour on porcelain is in the metallic state. 



The purple tincture of gold might, perhaps, be made use 

 of to advantage in the dyeing of silks, although tlie price 

 might be high : the colour obtained from it surpasses every 

 other in solidit}', because there is no combustion which can 

 destroy it. It will be prudent, however, to agitate the .stulFs 

 a long time in the tincture ; and, to obtain shades more or 

 less deep, it will be necessary to repeat the immersion of the 

 stuffs more or less often, taking care to squeeze them well, 

 and drying and shaking them between every immersion. 



The gradation of shades through which a mixture of the 

 nitro-muriatic and muriatic solutions of tin passes, weakened 

 by pouring into it, drop by drop, a solution of gold with a 

 great excess of acid, and very much diluted with water, in- 

 dicates, as I think, a gradual oxidation. An acetic solu- 

 tion of iron, even, appears to ascertain the same; because, 

 from a watery tureen, it acquires more and more a reddish 

 yellow cast when exposed to the atmospheric air, or in con- 

 tact with oxygen gas. 



I have made it appear, in a memoir upon the tincture of 

 the alkaline mars of Stahl, that the sulphate of iron may 

 also hyper-oxygenate itself, and lose the excess of oxvgeti by 

 the action of light. In making a mixture of the concen- 

 trated sulphuric acid and the nitric solution of iron, I ob- 

 tained, after the evaporation of the nitric acid, and upon 

 makii5g the residue attract the humidity of the air, by al- 

 lowing it to rest a few months, crystals of hyper-oxygenated 

 sulphate of iron, which I could scarcely distinguish, owing 

 to their whiteness, from sulphate of alumine ; but the action 

 of light gradually yellowed the surface : their whiteness 

 could be restored, however, by a slight washing. We may 

 in the same manner procure a sulphate of iron hvper-oxy- 

 g^enated, a little similar in whiteness, by precipitating the ni- 

 I trate 



