410 Memoir on various Combinations of Gold. 



exhibits iio metallic particles. Some consider this as a simple 

 mixture of sulphur and gold ; but I think it should be held as 

 a true combination ; for it has a black colour, never produced by a 

 simple mixture of sulphur and gold ; and when agitated in water 

 the deposit is homogeneous, which would not be the case with 

 a mere mixture, from which the gold, being the heaviest, would 

 precipitate first. The combination, liowever, is but slight, and 

 the sulphur is easily separated bv heat. 2*963 grammes of this 

 tulphuret, exposed to a red heat, left 2-386 gr. of gold; whence 

 it follows that 100 parts of gold combine with 24*39 of sulphur; 

 or that 100 parts of the sulphuret contain gold 80"39, and sul- 

 phur 10-61 = 100. It is possible that this sulphuret, though 

 dried witli care, may yet contain a minute portion of water, 

 \vhich will lessen the proportion of sulphur. Bucholz states 

 the proportions in this sulphuret, at gold 82 and suli)hur IS. 



The alkaline hydro-sulphurets produce, in muriate of gold, a 

 hlack precipitate perfectly similar to that from sulphuretted 

 hydrogen ; but when they are more or less sulphuretted, the 

 precipitate contains more or less sulphur in excess, and the co- 

 lour is more or less deep. 



Hydro-sulphuret of potash dissolves sulphuret of gold entirely, 

 and gives it a reddish-yellow colour. By the aid of heat it can 

 dissolve more. Acids poured into this solution cause the sul- 

 phuret to reappear, by saturating the potash and disengaging 

 the sulphuretted hydrogen. 



Sulj)huret of gold treated with potash loses its colour and 

 becomes yellow. A portion is dissolved, yielding a solution less 

 deeply coloured than that of which I have been speaking, and 

 whicii with the acids exhibits the same jihanomenon. The yel- 

 low residue does not dissolve in muriatic acid, but takes a brown 

 colour : with nitro-muriatic acid a solution is effected. 



Gold is the only metal which does not dissolve in the hydro- 

 sul})hurets ; but by the addition of sulphur and the aid of heat 

 its solution is effected, though with more difficulty than that of 

 j^ulphurct of gold. This seems to prove that alkaline sulphurets 

 dissolve gold only in proportion as it is in a state of sulphuret, 

 or as they themselves are very much sulphuretted. 



Precipitation of Gold by pkosphoretled Hydroge?i. 



The action of this gas on muriate of gold is very variable : 

 gold or phosphoret may be obtained at will. When a current 

 of this gas is passed through a dilute solution of gold, the first 

 portions of phosphoretted hydrogen give to the solution a brown 

 colour, which soon changes to a deep purple. If the operation 

 be stoptat this point, a yellow-brown precipitate forms, which is 

 the gold in a metallic state, and the yellow liciuid is a solution 



of 



