ON PREPARATIONS OF GOLD. g5| 



sumes its natural colour only fi cm the union of a certain 

 number of its particles. 



This would explain, 1st, why a very thin leaf of ?^oId, 

 perforated with minute holes, when held between the eye 

 and the light appears green ; because the blue colour of the 

 most nrjinutely divided particles mixes with the yellow of 

 those that are less so : 2dly, why, when to a somewhat concen- 

 trated solution of gold sulphate of iron is added ia suffici- 

 ent qnantity to reduce the whole of the gold, the hiuid ig 

 of a fine green; because the yellow colour of the parti- 

 cles of gold united in little masses combines in some mea- 

 sure with the blue of those that are not yet united: and 

 Sdly, why, in proportion as the former fall down, the liquid 

 gradually changes to a pure blue, which it continues till 

 the whole is precipitated. Hence it is probable, that the Purple powder 

 preclpitiit.e of Cassiu"* does not consist wholly of metallic °^*^^*^''^** 

 gold, but is rather a mixture of oxide of gold, oxide of tin, 

 »ad a little uietallic gold. 



Carbonate of potash also added to a solution of gold does Action of ear- 

 not eifect its precipitation, but only produces an efferves- u^^,'^.*u ''°^' 

 cence. At the expiration of thirty hours the solution be- lution. 

 comes turbid, without any thing separating; and it assumes 

 a very rich red colour, in proportion as the carbonic acid it 

 had absorbed flies off. 



On boiling this'raixture a very thick magma is formed of Precipitate oi^ 

 the colour of pale kermes u»ineral ; but this colour is not °' '"^' 

 altered by ebullition with excess of carbonate, as is the 

 case with caustic potash, which indicates, that the latter has 

 some action on the precipitate. 



When the liquid, from which the red matter was sepa- Gold stillinj 

 rated, fvppeared to have lost its colour, I Bltered it, to ob- '^"' * 

 tain the precipitate by itself. The liquid then exhibited 

 only a very slight tint of yellow, whence, and from its taste, 

 which was by no means metallic but simply saline, it might 

 have been presumed no longer to contain any gold ; but 

 this would have been a mistake. In fact a part of the li- 

 quid, into which I let fall a few drops of muriatic acid, im- 

 mediately assumed a very decidedly yellow colour ; and on 

 the addition of sulphate of iron it threw down a pretty con- 

 giderable quantity of metallic gold. 



Th 



