338 HISTORY OF GOLD. 



Ammonia takes some of the colouring principle from it, but 

 cloes not dissolve it. 



The muriatic acid at 10° has not the slightest action on 

 this lake, even when it is fresh prepared. The gold in it, 

 therefore, is not oxidated. 



Nitric acid attacks it, and is decomposed into nitrous gas, 

 &.C. ; and the lake is reduced to pure gold by the destruction 

 of the colouring principle, 

 lake with The juice of pine-bark, which is used in Spain for tanning 



puie-baik. leather, affords likewise a lake similar to the preceding, and 

 Laving all its properties; but it contains only 23 hundredth 

 parts of gold. 



Gold, in the metallic state, therefore, is capable of forming 

 combinations with the colouring parts of vegetables. 



On the State oj Gold in the Purple applied to Enamels. 

 Is it metallic We have seen, that gold is in the metallic state in the purple 



lours "las-i and P<^wder of Cassius; but does it still continue so in the tints it 

 enamels ? gives to glass and to enamel ? This is a question, which, in 



the present day, it is time to examine, that we may begin at 

 least to throw some light on it, if not to resolve it. Let us 

 take things up a little higher. 

 I.oug used for The practice of using gold, either oxided or simply divided, 

 us purpose. ^^ ^ purple pigment, is of long standing in Europe. The 

 iiitists of the seventeenth century employed, indiscriminately, 

 fulminating gold, the oxide precipitated by liquor of flints, 

 gold disoxidated by tin or mercury, gold grated to powder by 

 pumice stone, &:c. Ilomberg and Macquer, afterward, observ- 

 ed, that this metal gave a purple tinge to the vitrified parts of 

 what supported it when it was exposed to the focus of a 

 burning-glass. Ronelle and Darcct, that gold, struck by the 

 electric spark, likewise gave this colour to enamel. 

 Din'erenceof From the time of Stahl to the discovery of oxidation, 



opinion respec- chemists were divided in opinion on the nature of the purple. 

 iV'-Z it. . . 



Some thought it too repugnant to the doctrines of chemistry, 



to admit, that gold, furnished with the whole of its pl.logiston, 

 could fiissolve in glass, and furnish a solitary instance of a 

 combination, of which there was no example among all the 

 other metulii. They concluded, therefore, that it was not 

 capable of colouring glass, but in proportion as it parted with 



its 



