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It has been supposed by many, that the yellowness,resulting from mixtures of zinc and copper, was no otherthan a dilution of the coppery red by the whiteness of thezinc : if this was the cafe, silver would have a like effect,but silver is not found to give any yellowness to copper.The yellow colour produced from the combination ofcopper and zinc, is apparently a new quality ; as much asthe brittlenefs produced from the combination of twomalleable metals, gold and tin. It has not been observedthat any metal, besides zinc, yields any considerable yel-lowness with copper, though tin, in certain proportions,yields a flight one ; or that any metal besides copper formsa yellow compound with zinc.

Silver is tarnished superficially, by certain vapours, asthat of putrefied urine, to a colour so like that of gold,that abuses are said to have been often practised on thisfoundation, particularly in regard to wire and laces :Savary gives an account of several edicts iflued in Francefor preventing these frauds. It is observable also that finesilver, on being melted with nitre, acquires frequently ayellow spot on the surface where the salt lay in con-tact with it i and Stahl affirms that silver, by beingtreated in a certain manner, with certain substances, ofwhich nitre is the principal, may be tinged throughoutof a golden colour : he conceals the process, for fearof giving occasion to imposition; though of this theredoes not appear to be much danger, for he observesthat the silver acquires none of the other distinguishingcharacters of gold, and that the adventitious colour is veryreadily destroyed.

II. Gold coloured pigments.

In the gilding of wood, some pigments, approaching asneat as may be to the colour of gold itself, are both laid

under