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 same locality, though brought by way of Jamaica; and it was he who first described it in 1750 as a new metal.

Native platinum was discovered in 1819 in the gold washings of Verkhniy-Isetsk, in the Urals, but it was not until 1822 that its true nature was recognized. The chief Russian localities are in the districts of Nizhne Tagilsk and Goroblagodatsk, where it is found in shallow drift deposits, containing pebbles of serpentine, which represent the original matrix. The Iset district has acquired importance in recent years. Although the platinum-bearing gravels usually contain a very small proportion of the metal, the average in 1895 being only dwt. to the ton, rich discoveries have occasionally been made in the history of the workings, and nuggets of exceptional size have been unearthed. The largest recorded specimens are one of 310 oz. from Nizhne Tagilsk, and another of oz. from the Goroblagodatsk district.

In 1831 platinum ore was recognized in the gold-bearing deposits of Borneo, where it had previously been regarded as worthless, being known to the natives as mas kodok (frog gold). Although recorded from various parts of the island, its occurrence seems to be definitely known only in Tanah-Laut, in the south-east of Borneo. In Australia platinum ore has been found near Fifield (near Condobolin), New South Wales; whilst in New Zealand it occurs in sands and gravels in the Thames gold-field, the Takaka River and the Gorge River flowing into Awarua Bay. Many localities in North America have yielded platinum, generally in beach sands or in auriferous alluvia, and in some cases the deposits are of commercial importance. The metal is found in Alaska, British Columbia, Oregon (Douglas county) and California (Butte county, Trinity county, Del Norte county). It has been recorded also from the states of New York and North Carolina. In a nickeliferous sulphide ore worked at Sudbury, in Ontario, platinum has been discovered in the form of an arsenide (PtAs2), which has been called sperrylite by H. L. Wells, who analysed it in 1889, and named it after F. L. Sperry, of Sudbury It belongs to the pyrites group, and is interesting as being the only known mineral in which platinum occurs in combination except as alloy.

Native platinum seems to be a mineral of rather wide distribution, but in very sparse quantity. The sands of the Rhine, derived from Alpine rocks, have been found to contain platinum in the proportion of 0·0004%. It has also been found in the sands of the Ivalo River in Lapland; it is recorded from Roros in Norway; and it was detected by W. Mallet in some of the gold-sands of the streams in Co. Wicklow, Ireland.

The table shows the official amount (in ounces Troy) of platinum produced in Russia for certain years, the actual amounts are much larger.—

Platinum is largely used for the manufacture of chemical apparatus, incandescent lamps, thermo-couples; in the manufacture of sulphuric acid by the contact process, in photography, and in jewelry. The price of the metal has risen considerably, not so much on account of the restricted supply, but chiefly because the sources of supply have passed into the hands of a few individuals The following data show the fluctuations in the average price of platinum ingot per ounce Troy:—

Platinum may be extracted from its ore by both wet and dry processes. In the latter method, due to H. Sainte-Claire-Deville and H. J. Debray, the ore is smelted in a furnace constructed of two blocks of lime, and the metallic button so obtained is re-melted in a reverberatory furnace with galena or litharge, the lead platinum alloy being then cupeled, and the platinum fused into an ingot by re-smelting in a lime furnace (see Dingler's Polytech. Journ. 1859, 153, p. 38; 1859, 154, p. 383, 1862, 165, p, 205). The platinum so obtained is not pure. In Wollaston's wet method the ore is dissolved in aqua regia., the osmiridium, ruthenium and rhodium being left unattached, and the platinum precipitated as ammonium platinochloride by adding ammonium chloride in the presence of an excess of acid. The double chloride is then washed, dried and ignited, leaving a residue of metal. G. Matthey (Chem. News, 1879, 39, p. 175) obtains pure platinum from the commercial metal by fusing the latter with a large excess of lead. The lead alloy is then treated with a dilute nitric acid and the insoluble portion taken up in dilute aqua regia, From the solution so obtained lead is precipitated as sulphate, and platinum and rhodium as double ammonium chlorides. The rhodium ammonium chloride is converted by fusing with potassium and ammonium bisulphates into rhodium sulphate, which is then removed by extraction with water, when a residue of finely divided platinum remains. The German firm of Heraus (in Hanover) heat the raw ore with aqua regia and water under pressure, evaporate the solution to dryness, and heat the residue to 125° C. A clear aqueous extract of the residue is then acidified with hydrochloric acid and precipitated with ammonium chloride. The double chloride is ignited and the finely divided platinum so obtained is fused in the oxyhydrogen blowpipe.

Platinum is a greyish-white metal which is exceedingly malleable and ductile; the addition of a small quantity of iridium hardens it and diminishes its ductility very considerably. Its specific gravity is 20·85 to 21·71, and its mean specific heat from 0 to 100° C. is 0·0323 (J. Violle, Comptes rendus, 1877, 85, p 543); W. P. White (Amer. Journ. Sci., 1909, iv. 28, p. 334) gives the general formula St=0·03198+3·4×10−6t. St being the specific heat at t°C. Its temperature of fusion is in the neighbourhood of 1700 to 1800°C., various intermediate values having been obtained by different investigators (see J. A. Harker. Chem. News, 1005, 91, p. 262; C. Féry and C. Chéneveau, Comptes rendus, 1909, 148, p. 401; also C. W. Waidner and G. H. Burgess, ibid., 1909, 148, p. 1177). Its latent heat of fusion is 27·18 calories (Violle, loc. cit). The metal has been obtained in the crystalline condition by distillation in the electric furnace, or by decomposing its fluoride at a red heat (H. Moissan), Platinum, like palladium, absorbs large quantities of hydrogen and other gases, the occluded gas then becoming more “active”, for this reason platinum is used largely as a catalytic agent. Several forms of platinum, other than the massive form, may be obtained. Spongy platinum is produced when ammonium platinochloride is ignited; platinum black on the reduction of acid solutions of platinum salts; and colloidal platinum by passing an electric arc between two platinum wires under the surface of pure water (G. Bredig, Zeit. phys. Chem., 1901, 37, pp. 1, 323). Platinum is practically unoxidizable; it combines directly with phosphorus, arsenic, antimony, silicon, boron, and fluorine, and with almost all other metals. It is practically unattached by all acids, dissolving only in aqua regia or in mixtures which generate chlorine. When fused with alkaline hydroxides in the presence of air it forms palatinates. It is readily attacked by fused nitrates, and by potassium cyanide and ferrocyanide. All the platinum compounds when heated strongly decompose, and leave a residue of the metal. Of platinum salts, in the true sense of the word, none exist; there is no carbonate, nitrate, sulphate, &c; halide salts, however, are known, but are obtained in an indirect manner.

Platinum monoxide, PtO, obtained by heating the corresponding hydrate, is a dark-coloured powder which is easily reduced to the metal (L. Wohler, Ber., 1903, 36, p. 3475). The hydrated form, PtO·22H2O, is obtained impure by precipitating the chloride with caustic soda, or by adding caustic soda to a boiling solution of potassium platinous chloride, K2PtCl4, the precipitate being rapidly washed and dried in vacuo (L. Wohler, Zeit. anorg. Chem., 1904, 40, p. 423). It is a black powder; when freshly prepared it is soluble in concentrated acids, but when dried it is insoluble. It is an acidic oxide, the dioxide being both acidic and basic. It behaves as a strong oxidizing and reducing agent. C. Engler and L. Wohler (Zeit. anorg. Chem., 1901, 29, p. 1) have shown that platinum black, containing occluded oxygen, is soluble in dilute hydrochloric acid and also liberates iodine from potassium iodide. and that the ratio between the amount of platinum dissolved and the amount of oxygen occluded agrees with the formation of a compound corresponding to the formula PtO. Platinum dioxide (platinic