CHAMBERS'S INFORMATION FOR THE PEOPLE. 



Platinum. 



A Spanish traveller, named Anton Ullsa, appears 

 to have been the discoverer of platinum. He 

 found it in Peru in 1735 or 1736. It was first 

 found in Russia in 1822, but it was years after 

 this even before any exact knowledge of it was 

 obtained. Platinum is always found in the metal- 

 lic state, although never pure, being invariably 

 alloyed with one or more of the rare metals rho- 

 dium, iridium, osmium, palladium, and ruthenium. 

 Copper and iron are likewise usually present. It 

 occurs in the form of flattened grains in alluvial 

 soil ; more rarely it is found in lumps, the 

 largest yet met with being the nugget from the 

 Ural chain, in the Demidoff collection, which 

 weighs 2 1 Ibs. The chief supply of platinum is 

 derived from these mountains. Brazil, Peru, New 

 Granada, California, and Borneo also furnish 

 supplies. 



Until recently, platinum could only be prepared 

 in a state for use by Wollaston's process, in which 

 it is first obtained in the spongy state, and after- 

 wards consolidated by welding. The melting- 

 point of platinum is so high that, a few years ago, 

 the fusion of a globule was looked upon as a feat. 

 Great astonishment was therefore occasioned by 

 the appearance, in the International Exhibition of 

 1862, of an ingot weighing two and a third hundred- 

 weight, and bearing unmistakable evidence of its 

 having been melted. Its value was ^3840. The 

 merit of providing a means for fusing such large 

 masses of platinum is due to the French chemist 

 Deville, and the process is carried on in a furnace 

 in which the heat is produced by jets of coal-gas 

 and oxygen. Previous to smelting, the ore is 

 mixed with a small quantity of lime, which is also 

 used as a lining to the furnace. During the oper- 

 ation, the impurities are partly imbibed by the 

 lime, partly volatilised, and the platinum is ex- 

 tracted from the remainder by aqua-regia. 



Platinum is the heaviest substance known, it is 

 one of the most difficult to fuse, and no single acid 

 has any action upon it. It is white in colour, and 

 has a high lustre when polished, although inferior 

 to silver in brilliancy. It does not oxidise in air 

 at any temperature. In ductility and tenacity 

 platinum resembles iron, and is of about the same 

 hardness as copper. The great use of platinum is 

 in the construction of crucibles, evaporating dishes, 

 and other apparatus for chemical research ; and 

 for stills and other vessels used in the manufacture 

 of sulphuric acid, and the refining of gold and 

 silver. It is doubtful, indeed, if the great progress 

 made in scientific chemistry during the present 

 century could have been accomplished without 

 platinum. Formerly, a piece of spongy platinum, 

 which has the singular property of becoming red- 

 hot in hydrogen, was used, together with a jet of 

 that gas, to produce a light Platinum coins were 

 for some time current in Russia, but are now 

 abandoned. The value of the metal is about five 

 times that of silver. 



Manganese. 



Like a few other metals, manganese is as yet 

 of no service alone in the arts, but plays an hn- 



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portant part in some alloys, and especially when 

 mixed to a small extent with some kinds of steel. 

 Pure manganese is white, with a faint reddish 

 tinge, and is very hard and brittle. It takes on 

 a fine polish, and does not tarnish in air. Its 

 chief ore is the black oxide or pyrolusite, which 

 is a tolerably abundant substance. Large quanti- 

 ties of this oxide are imported into England for 

 he manufacture of bleaching-powder, the total 

 annual consumpt being estimated a few years ago 

 at 11,450 tons. It is also used in the manufacture 

 of both clear and coloured glass. 



Chromium. 



It is not long since metallic chromium was 

 obtained in a state of purity. It is remarkably 

 lard, difficult to fuse, and costly to prepare. Only 

 the compounds of chromium are turned to any 

 useful purpose, and these are chiefly prepared 

 Vom chromite or chromate of iron, which is found 

 n the Shetland Islands, Norway, Spain, and 

 several other countries. Chromate and the bi- 

 chromate of potassium, and the chromate of lead, 

 are used in dyeing, calico-printing, and for other 

 purposes. The green oxide of chromium is a 

 valuable material in enamel-painting, as it is not 

 decomposed by heat. 



Magnesium. 



Of late years this metal has been made on a 

 considerable scale from magnesium carbonate. It 

 is a beautiful silver-white metal, becoming coated 

 with a crust of magnesia when exposed for a short 

 time in moist air. It burns at a red-heat with a 

 dazzling white flame, and on this account it has 

 been a good deal used for taking photographs 

 where sunlight cannot penetrate. 



Cadmium. 



Both cadmium and magnesium closely resemble 

 zinc in their properties, and the former is also 

 commonly associated with it in the ore. Cadmium 

 could be produced at a comparatively low price if 

 it were much in demand, which as yet is not the 

 case. Its use in dentistry has already been re- 

 ferred to under Mercury, but it is chiefly consumed 

 in the state of sulphide of cadmium, which fur- 

 nishes the painter with a beautiful and permanent 

 yellow pigment. 



Palladium Iridium Osmium. 



Palladium is a rare metal, resembling platinum 

 in appearance, but not nearly so heavy. It forms 

 a fine white alloy with silver, which, as well as an 

 amalgam of the metal, has received some useful 

 applications. Iridium is a hard, brittle metal, 

 fusible with great difficulty, the oxide of which 

 gives an intense black colour to porcelain. Osmium 

 is another rare, highly infusible metal, the most 

 refractory, indeed, of all. A native alloy of osmium 

 and iridium occurs, which is the hardest metallic 

 substance known, and used to tip the ends of the 

 so-called gold pens, 



