536 HISTORY OF GOL». 



Effect of Acids on the Purple Powder. 

 Action of aqua If to a hundred grains of well dried purple powder, a very 

 pm-pleof Cas- weak aqua regia be added, such as is composed of marine acid 

 »ius. at 4** or 5°, and a few drops of nitric acid, the powder will 



pretty quickly lose its colour, and afford a solution of gold. 

 This solution, precipitated by sulphate of iron, will yield 24 

 grains of metallic gold. Only 70 grains of oxide of tin 

 remain, which shows, that the aqua regia has dissolved 6 grains. 

 The oxide is white, and vitreous, like every oxide at a paxi- 

 One part gold, mura. This result shows us, that the gold, in precipitating, 

 ■de oflL? °^' carries with it three times its weight of oxide of tin : and as 76 

 grains of oxide at a maximum, answer nearly to 72^ of oxide 

 at a mininum, it is probable, that this is the quantity of oxide 

 capable of loading itself with oxigen enough to oxidate 24 

 grains of gold. 

 Further proofs If a portion of muriate of tin at a minimum be put into, 

 •f their chemi- ^^^^ regia, the oxide passes to the maximum state, but is not; 

 precipitated, even by the action of heat. When the gold, 

 therefore, in quitting its solvent to be converted into the pur- 

 ple powder^ carries down with it such a considerable portion of 

 oxide, this must have resulted from the operation of som^ 

 affinity. 

 Muriatic acid Muriatic acid of 10°, kept boiling on recent purple powder,, 

 fr'^^^ the *o^d ^^^composes it gradually, and reduces it to the state of pure 

 gold. The power of aggregation connects its particles, and 

 unites them in little lumps, which appear of the colour of gold 

 precipitated by irG«, sulphureous acid, &c. 



The acid, rendered transparent by subsidence, is a solution 

 of tin at a maximum of a slightly yellow tinge, A slip of tin 

 destroys this colour, but affords no suspicion of purple. 

 Action of nitric Nitric acid of 32° takes some tin from the purple powder, 

 * and brightens its colour; but never reduces it to the stale of 



Lentin's pure gold, whatever length of time it be kept boiling. This is 



brightening. jj^g brightening proposed by Lentin. 



The nitric acid, when poured off, holds in solution tin at a 

 maximum, and a little gold. A few drops of muriate demon- 

 strate this in an instant. 



This purple, the brightened tint of which approaches to that 

 of cinnabar, still contains tin. Aqua regia detects this easily. 



It 



