One of the metals, and the heaviest body hitherto discovered in nature; its specific gravity being 21.54 when pure. It is obtained from an ore or metallic sand brought from South America, which contains, besides platina, four new metals, namely, palladium, iridium, osmium, and rhodium; also iron and chrome. Platina, combined with palladium and rhodium, is as hard as iron. It is not altered by exposure to the air, neither is it acted upon by the most concentrated simple acids, even when boiling or distilled from it. It is very malleable, though considerably harder than gold or silver, and it hardens much under the hammer. Its colour on the touch-stone is not distinguishable from that of silver. Pure platina requires a very strong heat to melt it; but when urged at a white heat, its parts will adhere together by hammering. This property, which is distinguished by the name of welding, is peculiar to platina and iron, which resemble each other, likewise, in their infusibility. Platina is obtained by dissolving the crude metallic particles in nitro-muriatic acid, precipitated by ammonia, and exposed to a very violent heat, by which the acid and alkali are expelled, and the metal is reduced in an agglutinated state, when it may be pressed together by a button-headed iron, be taken out of the furnace, forged, reheated, and forged again into a bar.
Willis found that platina might sometimes be melted upon a bed of charcoal in a crucible; and M. Bousingault recently found that it might always be melted in a blast furnace, if the crucible be lined inside with a mixture of clay and charcoal; the silicon, in his opinion, assisting in the reduction. Platina may be melted in quantities not exceeding two ounces at a time, by the oxy-hydrogen blow-pipe, and be kept in fusion for some time. Platina is much used for crucibles, evaporating dishes, and even alembics. Though it resists most of the acids, it is acted upon by caustic potash, and several of the neutral salts. The proper solder for it is gold. The concentration of sulphuric acid is now usually performed by platina stills, with leaden heads. Mr. Parkes has one of this kind, which holds only thirty-five gallons, yet cost 300 guineas.