310 METALS. 



The coins have the value of 11 and 22 rabies each. The 

 amount coined from 1826 to 1844 equals 2£ millions of 

 dollars. . 



For many years after its discovery, platinum was almost a 

 useless metal on account of the difficulty of obtaining it in 

 masses. The grains weld when heated, but because ot their 

 small size, this was interminable labor, and moreover the 

 metal was not pure. Dr. Wollaston introduced the oroces 

 now in use, which consists in dissolving the metal in nitro 

 muriatic acid, and throwing down from the solution an orangs 

 precipitate by means of muriate of ammonia. This precipi 

 tate (a double chlorid of platinum and ammonium) i« then 

 heated and thus reduced to the metallic state ; the platipum i9 

 now in an extremely minute state of division. This black 

 powder (" spongy platinum") is next compressed in steel 

 moulds by the aid of heat and strong pressure ; and when 

 sufficiently compact, is forged under the hammer and then re- 

 duced at last to solid masses. 



This metal fuses readily before the " compound blowpipe :" 

 and Dr. Hare succeeded in 1837 in melting twenty-eight 

 ounces into one mass.* The metal was almost as malle- 

 able and as good for working as that obtained by the other 

 process ; it had a specific gravity of 19*8. He afterwards 

 succeeded in obtaining from the ore masses which were 90 

 per cent, platinum, and as malleable as the metal in ordinary 

 use, though somewhat more liable to tarnish, owing to some 

 of its impurities. 



Platin-iridium. Grains of iridium have been obtained at Nischne 

 Tagilsk, consisting of 76'8 iridium, and 19-64 platinum, with some 

 palladium and copper. A similar platin-iridium has been obtained at 

 Ava in the East Indies. Another from Brazil contained 27'8 iridium, 

 .555 platinum, and 6*9 of rhodium. 



Iridosmine. A compound of iridium and osmium from the platinum 

 mines of Russia, South America, the East Indies and California. The 

 crystals are pale steel-gray hexagonal prisms : occurs usually in flat 

 grains. H=67. Gr=19'5— 2M. Malleable with difficulty. 



The composition varies. One variety contains iridium 468, osmium 

 49'3, rhodium 32, iron 0-7. Another, iridium 25*1, osmium 74'9 ; 

 another, iridium 20,' osmium 80. They are distinguished by their su- 

 perior hardness from the grains of platinum, and also by the peculiar 

 odor of osmium when heated with niter. Iridosmine is common with 

 the gold of California, and injures its quality for jewelry. It is pro- 

 posed to separate it by keeping the gold melted for a short time, to 

 allow the grains of iridosmine to settle. 



What is the value of Russian platinum coins? How is platinum 

 worked into masses 1 



* American Jour. Sci.. ixxiii, 195; xxxvlii, 155, 163 and User, iv, 39. 



