•11'2 Memoir on various Comhinaticyns of Gold. 



washed, aiid dried by the gentlest heat, is nothing more than a 

 liiixture of oxide and metallic gold. 



Tliom5,on, quoting Bergman, says that potash forms in the 

 solution of gold a precipitate of a yellowish-brown colour, ap- 

 proaching sometimes to black, which is insipid, and insoluble in 

 water. 



Vauquelin announces that neither alkalies nor carbonate of 

 potash form precipitates in a solution of gold, cold, but that by 

 the aid of heat they precipitate reddish flakes, which he consi- 

 ders as jHire oxide of gold, and to which he attributes the pro- 

 perty of being soluble in water, and of having a very sensible 

 metaUic styptic taste. 



. I have also obtained, by alkalies, precipitates of very varialjle 

 colours, according to the diiferent circumstances which I shall 

 descnibc. 



1. Having poure-i muriate of gold into a solution of potash, 

 leaving the latter in excess, an inconsiderable precipitate, of a 

 blacliisli-gray colour, was produced. The litjuid exposed to a 

 moderate heat deposited a similar precipitate, but still retained 

 a (juaiitity of gold in solution. 



2. With less excess of potash a yellow precipitate was formed, 

 v.hich I separated from the licinid, which was turbid and blackish. 

 The li([uid, when left to itself, deposited a blackish powder si- 

 milar to that of No. 1. 



3. Another experiment prod\iced an orange-yellow precipi- 

 tate. Tlic liquid, jierfoctlv clear, was of a fine yellow colour, 

 bordering on red : it was alkaUne, but less so than the two pre- 

 ceding. Ex])osed to a moderate heat, it gave a yellow precipi- 

 tate of a tihade a little more red than the other. 



4. I poured a concentrated solution of jjotash into muriate 

 of gold, taking care to stop at the point of saturation, and even 

 ttt leave a slight excess of the nnniate. A yellow precipitate 

 was formed, which I separated. By adding to the liquid a great 

 excess of alkali, I procured a brown-black precipitate. 



Lastly: I have, at will, produced either yellow or black pre- 

 cipitates with the same solution. When excess of alkali is 

 avoided, or a very slight excess is used, the precipitate is yellow, 

 inciiuing more or less to orange : when the potash iii. in great 

 excess, it is black. In both cases the clear liquid when sub- 

 mitted to heat forms yellov/ or black precipitates according to 

 circumstances. 



The variable colour of these precipitates shows that^they are 

 not i<}entieal : let us inquire into the cause of these differences. 



Presuming from analogy that the differences may be owing to 

 ^'id retained in combination, as in most other metallic pre^ 



parations. 



