678 GOLD. 



out gold from the powder when properly prepared, appear to 

 me to be conclusive against that opinion. The proportions of 

 its constituents vary so much, that there must be more than one 

 compound, or more likely the colouring compound combines 

 with more than one proportion of peroxide of tin. Berzelius 

 proposes the theory that the powder of Cassius may contain 

 the true protoxide of gold combined with the deutoxide of tin, 

 AuO + Sn 2 O 3 , a kind of combination containing an association 

 of three atoms of metal, which is exemplified in black oxide of 

 iron, spinell, gahnite, franklinite and other minerals, and which 

 we have repeatedly observed to be usually attended with great sta- 

 bility. A glance at its formula shews how readily the powder of 

 Cassius, as thus represented, may pass into gold and peroxide of 

 tin; AuO -hSn 2 O 3 Au and 2SnO 2 . The existence of a purple 

 oxide of gold AuO is not established, but it is probably the sub- 

 stance formed when a solution of gold is applied to the skin or 

 nails, and which dyes them purple. Paper coloured purple by 

 a solution of gold becomes gilt when placed humid in phosphu- 

 retted hydrogen gas, which reduces the gold to the metallic 

 state. 



Sssqui-sulphuret of gold, Au 2 S 3 , or the auric sulphuret, is 

 formed when a dilute solution of gold is precipitated cold by 

 sulphuretted hydrogen. It is a flocculent matter of a strong yel- 

 low colour, which becomes deeper by drying ; it loses its sul- 

 phur at a moderate heat. 



Sesqui-chloride of gold, Perchloride of gold, Auric chloride, 

 Au 2 Cl 3 , 3814 or 305.62. Tt is formed when gold is dissolved in 

 aqua regia. The solution is yellow, and becomes paler with an 

 excess of acid, but is of a deep red when neutral in composition. 

 It is obtained in the last condition by evaporating the solution 

 of gold, till the liquid is of a dark ruby red colour, and begins to 

 emit chlorine. It forms on cooling a dark red crystalline mass, 

 which deliquesces quickly in air. But to procure the auric 

 chloride perfectly free from acid salt, the only mode is to de- 

 compose the aurous chloride with water. A compound of chlo- 

 ride of gold and hydrochloric acid crystallizes easily from an 

 acid solution, in long needles of a pale yellow, which are perma- 

 nent in dry air, but run into a liquid in damp air. The solu- 

 tion of this salt deposits gold on its surface, and on the side of 

 the vessel turned to the light. The gold is also precipitated in 

 the metallic state by phosphorus, by most metals, the ferrous 



