PLATINUM. 271 



gold is produced upon articles of jewelry, made of im- 

 pure metal, by first heating them, and then dissolving 

 out the copper by means of nitric acid. 



PLATLNTJM. 

 680. DESCRIPTION. Platinum is the 



Platinum 



Description, last of the noble metals. It resembles 



^sofoentsT' Stee ^ m c l r > anc ^ possesses a high degree 

 of malleability. It is the heaviest and the 

 most infusible of all metals. At a white heat it may 

 be welded, like iron. Like gold, it resists the action 

 of any single acid, but may be dissolved in aqua-regia. 

 It is commonly found, like gold, in small flattened 

 grains, in the sand of certain rivers. Its pecuniary 

 value is about half that of the more precious metal. 



681. PLATINUM CONDENSES GASES. The 



Mention a re- 

 markable ef- metal platinum has the remarkable pro- 



P eri Y of condensing gases upon its surface, 

 and thereby increasing their affinities. 

 This effect is in proportion to the surface 

 exposed. It may be prepared for this experi- 

 ment by burning paper, previously moistened 

 with a solution of this metal. Such an ash, 

 by simple exposure to the air, condenses and 

 retains a large quantity of oxygen within its 

 pores. On holding it in a jet of hydrogen, 

 the condensed oxygen immediately unites with the 

 latter gas so energetically as to inflame it. 



682. Platinum is employed for similar 



Give another 



illustration of purposes, in the form of a sponge, and as a 

 this effect. powder, called p latinum black. A mixture 



