Chap. 36,] Union of Platim with other 'Metals. 241 



it receives a very fine polifli. A mixture of three 

 or four parts of copper to one of platina poffefied 

 all the above properties in great perfection, and was 

 not tarniihed in the air in the fpace cf ten years. 

 With iron it alfo produces a compound of great den- 

 fity, which is hard, ftrong, and tough, and admits of 

 a good polifh. Moil metals increafe the fufibility 

 of platina fo much, that the mixture may be melted in 

 ordinary furnaces. 



Gold is greatly injured in appearance by a mixture of 

 platina, and becomes of the colour of bell metal by the 

 addition of no more than one twenty- fourth part, 

 though half that quantity produces little change. 



Platina with bifmuth and tin forms alloys, which 

 are brittle, but eafily fufed. Platina and lead unite 

 very well by fufion, but the ductility of the lead is 

 deftroyed, and the compound quickly tarnifhes on 

 expofure to air. Platina partly deftroys the ductility 

 of filver, augments its hardnefs, and impairs its co- 

 lour. 



Platina completely refifls the action of mercury, 

 with which it mews no difpofition to unite. On this 

 account it does not mix itfelf with the gold,, which is 

 extracted from the fubftances with which it is mixed by 

 amalgamation. 



From the extreme infufibility of platina, it is ex- 

 cellently fitted to contain other matters, which it is 

 intended to fubmit to a violent heat. M. Achard 

 fucceeded in making crucibles of platina, by fufing 

 equal parts of platina, white arfenic, and vegetable 

 alkali. This matter, when cooled, was reduced to 

 a powder, and rammed into a- mould. A ftrong heat, 

 quickly raifed, and continued for fome time, fufed the 

 mafs, and after diflipating the arfenic and alkali, left 

 the platina in the defired form. 



VOL. II. R Platina, 



