Properties of the Platinum Metals
Platinum.—The colour is white with a greyish tinge. When pure it is very malleable and ductile. Its coefficient of expansion is less than that of all other metals. Platinum fuses at about 1750° C., but the presence of impurities lowers the melting-point. Its specific gravity is 21·5, and its hardness is from 4 to 5. Its electric conductivity is low, being 13·4 at 0° C.[[3]] p. 398.
| Composition of Native Platinum and Osmiridium | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Locality. | Pt. | Fe. | Pd. | Rh. | Ir. | Os. | Cu. | Os-Ir. | Remarks. |
| Platinum | Per cent. | Per cent. | Per cent. | Per cent. | Per cent. | Per cent. | Per cent. | Per cent. | |
| Urals 1[[B]] | 76·22 | 17·13 | 1·87 | 2·50 | tr. | 0·36 | 0·50 | Magnetic grs. | |
| Urals 2 | 73·58 | 12·98 | 0·30 | 1·15 | 2·35 | tr. | 5·20 | 2·30 | Magnetic grs. |
| Urals 3 | 81·34 | 11·48 | 0·32 | 2·14 | 2·42 | tr. | 1·13 | 0·57 | Non-magnetic. |
| Urals 4 | 78·94 | 11·04 | 0·28 | 0·86 | 4·97 | 0·70 | 1·96 | Non-magnetic. | |
| Urals 5 | 86·50 | 8·32 | 1·10 | 1·15 | tr. | 0·45 | 1·40 | Non-magnetic. | |
| Borneo | 82·60 | 10·67 | 0·30 | 0·66 | 0·13 | 3·80 | Gold, 0·20 per cent. | ||
| Brazil | 72·62 | tr. | 21·82 | 0·88 | Sand, 0·42 per cent. | ||||
| Granite Cr., B.C. | 68·19 | 7·87 | 8·26 | 3·10 | 1·21 | 3·09 | 14·62 | Gangue, 1·69; non-magnetic. | |
| Granite Cr., B.C. | 78·43 | 9·78 | 0·09 | 1·70 | 1·04 | 3·89 | 3·77 | Gangue, 1·27; magnetic. | |
| Chocó, Col. | 86·20 | 7·80 | 0·50 | 1·40 | 0·85 | 0·60 | 0·85 | Sand, 0·95. | |
| Chocó, Col. | 84·30 | 5·31 | 1·06 | 3·45 | 1·46 | 1·03 | 0·74 | Gold, 1·0; sand, 0·61. | |
| California | 85·50 | 6·75 | 0·60 | 1·00 | 1·05 | 1·40 | 1·10 | Gold, 0·8; sand, 2·95. | |
| California | 79·85 | 4·45 | 1·95 | 0·65 | 4·20 | 0·75 | 4·95 | Gold, 0·55; sand, 2·69. | |
| Oregon | 51·45 | 4·30 | 0·15 | 0·65 | 0·40 | 2·15 | 37·30 | Sand, 3; gold, 0·85. | |
| Fifield, N.S.W. | 75·80 | 10·15 | tr. | 1·30 | 1·30 | 0·41 | 9·30 | Gold, nil; sand, 1·12. | |
| “Australia” | 61·40 | 4·55 | 1·80 | 1·85 | 1·10 | 1·10 | 26·00 | Gold, 1·2; sand, 1·4. | |
| Currumbin, Q. | 26·12 | 27·17 | 2·51 | 40·02 | Sand, 1·33. | ||||
| Osmiridium | |||||||||
| Urals | 10·08 | tr. | tr. | 1·51 | 55·24 | 27·23 | tr. | Ru, 5·85 (Nevyanskite). | |
| Urals | 0·14 | 0·63 | 1·65 | 43·94 | 48·85 | 0·11 | Ru, 4·58 (Nevyanskite). | ||
| California | 2·60 | 53·50 | 43·40 | Ru, 0·50 (Nevyanskite). | |||||
| “Australia” | 3·04 | 58·13 | 33·46 | 0·15 | Ru, 5·22 (Nevyanskite). | ||||
| Currumbin, Q. | 3·00 | 62·00 | 33·00 | Sand, 2·00 (Nevyanskite). | |||||
| /\ | |||||||||
| Tasmania | 0·37 | 0·30 | 0·21 | 33·80 | 57·09 | tr. | Ru, 8·19; Au, ·04 (Siserskite). | ||
| Platiniridium | |||||||||
| Condado, Brazil | 55·44 | 4·14 | 1·49 | 6·86 | 27·79 | tr. | 3·30 | ||
| Native Iridium | |||||||||
| Urals | 19·64 | 0·89 | 76·80 | 1·78 | |||||
| Reference—Pt., platinum; Fe., iron; Pd., palladium; Rh., rhodium; Ir., iridium; Os., osmium; Cu., copper; Os-Ir., osmiridium; Ru., ruthenium. | |||||||||
[B]. Average percentage of Urals platinum is a little under 80.[[4]] p. 558.
Platinum is not acted upon by either nitric, sulphuric or hydrochloric acid, but is soluble in aqua regia (1 part of nitric to 2 parts of hydrochloric acid), or in other mixtures liberating chlorine, with the formation of platinum tetrachloride (PtCl4). It is not acted upon by air or moisture, even at high temperatures. It is corroded by caustic alkalis, sulphides, sulphates, phosphates and arsenides, if heated in contact with them. It will not amalgamate with mercury unless sodium is present, in this respect differing from gold and silver.
Platinum, in a finely-divided condition, absorbs large quantities of hydrogen or other gases, which on occlusion become more active: hence its value as a catalytic agent.
Palladium.—This metal resembles platinum, but is sometimes fibrous, the colour being between that of platinum and of silver. It possesses a lower melting-point than platinum—about 1550° C. It is malleable, has a hardness of from 4·5 to 5, and a specific gravity of 11·5. As already stated, palladium, when found in copper ores, is probably present in combination with arsenic. Porpezite, a rare mineral, containing gold and up to 10 per cent. palladium, has been identified in gold-bearing veins in Brazil [see p. [54]].
Palladium is produced from the refining of copper matte and of base gold bullion from Australia and elsewhere.
Iridium is a brilliant white brittle metal, with a specific gravity of 22·4, and hardness of 6 to 7. Its fusion point is very high—about 2200° C.—and under ordinary conditions it is not attacked by any acid. At 1100° C. it begins to oxidize to a purple oxide. Iridium usually occurs either in crude platinum, or alloyed with osmium, as iridosmine, or as native metal. The bulk of iridium is derived from the platinum placer deposits of the Urals, but the Californian metal is more valuable, on account of its better quality. It is also obtained in small amounts from copper bullion.
Osmium is a hard and brittle metal, bluish-grey in colour. Its specific gravity is 22·5, and it has a very high melting-point, in this respect being the most refractory of the group.
Iridosmine, or Osmiridium, an alloy of iridium and osmium, occurs as hexagonal crystals, or flattened grains of lighter colour than platinum. It may contain from 40 to 77 per cent. of iridium, and from 20 to 50 per cent. of osmium. If the iridium predominates, the alloy is called Nevyanskite, and Siserskite if the osmium content is high. It is distinguishable from platinum by the brittleness of the flakes. Siserskite gives off a pungent odour, if strongly heated, caused by the volatilization of osmium. Iridosmine has a hardness of 6 to 7, and a specific gravity of 19 to 21.
Ruthenium is a white metal, with a specific gravity of 12·1. It is scarcely acted upon by aqua regia. Ruthenium occurs mainly in small amounts in iridosmine. It is also found in the copper ores of Sudbury and other places. Laurite is a very rare sulphide of ruthenium (RuS2), containing a small amount of osmium, which has only been recognized in the Borneo deposits.
Rhodium is a white metal resembling aluminium, with a specific gravity of 12·1, and a melting-point of about 2000° C. It is ductile and malleable at red heat. In addition to its occurrence in crude platinum, the metal is also contained in small quantities in the sperrylite found in the copper ores of Sudbury, Canada[[5]] p. 779.
Colloidal Platinum.—This has only recently been detected in ores, and therefore its occurrence might not be detected qualitatively. By destroying its colloidal condition, however, its presence can be discovered in the ordinary ways[[4]].