930 Transactions of the American Institute. 



a conchoidal fracture. Decomposed by light, or at an incipient red 

 heat, into metallic gold and oxygen gas; it gives up its oxygen to 

 vegetable acids, and many other substances. When boiled with 

 potash lye, it is resolved into protoxide of gold and aurate of 

 potaasa. 



Hydrated aunc acid, Au 0^-{-H0: This is obtained by mixing a» 

 solution of terchloride of gold, not containing free acid, with a 

 quantity of potash, only just sufficient to neutralize the hydro- 

 chloric acid, and repeatedly washing the reddish yellow precipitate, 

 which does not appear till after the lapse of several hours. The 

 hydrate, after drying in the air, which takes place but slowly, 

 exhibits a chestnut brown color. When heated to one hundred 

 degrees C, or when treated with potash solution, it gives up its 

 water, and is converted, with diminution of volume, into the black 

 oxide, part of which, however, is reduced to the metallic state. 

 This hydrate is perfectly soluble in hydrochloric acid. 



Identical with this appears the precipitate which Vanquelin 

 obtained, by heating the acid gold solution with pure potash or 

 carbonate of potassa. This precipitate, when recently formed, was 

 of loose texture, and of reddish yellow color, resembling, when 

 deprived of its moisture, dried blood. With acids it forms the salts 

 of aUric oxide, or auric salts, and with the alkalies and some of the 

 earth's compounds, called aurates. 



Gmelin describes another very interesting combination with 

 ox}'gen. Perauric acid: Au 0^; but this seems to be a mixture of 

 oxides. 



Gold and sulphur: Protosuljphide of gold Au S. A black-brown 

 powder, exhibiting a deep yellow streak, is produced by passing 

 eulphuretted hydrogen through a boiling solution of chloride of gold. 



T efi^sulpliide of gold Au S^. By precipitating a solution of ter- 

 chloride of gold with sulphuretted hydrogen, or an alkaline 

 hydrosulphate at ordinary temperature, a black precipitate results. 

 According to Levol {N. Ann. Chim. Phys., 30, 355), the precipitate 

 thus formed consists of Au S^ which contains water, and does not 

 give it up till heated to one hundred and forty degrees C. It is 

 also prepared by fusing gold in excess with peutasulphide of 

 potassium, and' dissolving the fused mass in water, and precipitating 

 by an acid. The sulphide of gold then falls down in deep yellow 

 flakes, which turn brown on drying. (Berzelim.) 



I will only quote a few more of the artificial gold combinations, 

 whicli of late have grown to a formidable number. 



