Platinum

Platina. In mineralogy, a genus of the cla metals, deriving its name from the Spanish word plat a or silver, in consequence of its external resemblance to it, or from the’ river ‘Plata, in Spanish America, near which it is found. It is characterized by a silvery colour not tarnished by ‘the air, very hard and tenacious, sonorous, exceed- ingly malleable and ductile, specific gravity 23,000 3 not fusible in any degree of heat, but detonating ‘with nitre; soluble only by boiling it in sixteen times its weicht of nitro-muriatic acid, and giving the solution first a yellow and then a red-brown colour; its oxyd is precipitated from this solution by the addition of muriat of ammonia, in the form of an orange powder. Found near Quito in Peru, near Santa Fe in New Granada, and near the village Choco, in mines, or mixed with sand on the banks of rivers, always in the form of small, smooth, compre ed grains of the colour of polished tin, it is always combined with iron or some other metallic substance, sometimes amounting to an eighth part, which may be readily separated from it by di olving it in muriatic acid: the heaviest and most refractory of all metals, and requires a very vehement degree of heat to render it liquid. Its tenacity is such that a wire of it 0,078 of an inch in diameter is capable of supporting a weight of 27,434 pounds averdupoise without breaking. It is easily melicd by a flux of powdered gla , borax, and charcoal; and is frequently magnetic, from the quantity of iron it contains. In consequence of its great malleability, ductility, tenacity, durability, and insolubility, it is a very precious metal. The precipitate of this metal obtained by its so-_ lution in nitro-muriatic acid, and which was at first conceived to be entirely oxyd of iron, and afterwards to be plumbago, has since been found to consist of ores of four new metals which have never been found otherwise than in this precipitate, or ore of platina. ‘fhese metals are 1. Osmium. 3. Rhodium. g, Iridium. 4. Palladium. Platinum was first brought into Europe in 1749, by Mr. Charles Wood, a paymaster of Jamaica; and in the succeeding year specimens were pre-= sented by Dr. Brown rigg to the Royal Society. These came from Carthagena; from which place also were dispersed, through the Spanish West Indies, various toys and trinkets consisting of this metal alloyed with some other, probably silver, as the price of the alloy was nearly equal to that of this latter metal. Mr, Wood and Lewes began the investigation of the properties of this new substance in the very year in which it was imported: it has since employed the abilities of all the most eminent chemists of all countries; but many difficulties still remain to be overcome before the chemical history of thid substance can be completed. Crude platinum comes from America in small flat grains of a silvery lustre. In this state it is exceedingly impure, containing, either chemically mixed, or chemically united, no le than nine other metals: but it may be reduced nearly to a state of purity by the following proce .—Decant the solution from the black matter which resists the ace tion of the acid; drop into it a solution of sal-ammoniac, an orangé ye!low-coloured precipitate falls to the bottom; wash this precipitate, and when dry expose it to a heat slowly raised to redne in a porcelain crucible. The powder which remains is platinum neagly pure. By re-di olving it in nitro muriatic acid,and repeating the whole proce ,it may be made still purer. When these grains are wrapped yp ina thin plate of platinum heated to redne , and cautiously hammered, they unite, and the whole may be formed into an ingot. Piatinum thus obtained is of a white colour like silver, but not so bright. It has no taste nor smell. Its hardne is 8.; its specific gravity, after being hammered, 23,000, so that it is by far the heaviest body known. Its ductility and tenacity we have already noticed, It is one of the most infusible of all the metals, and cannot be melted, inany quantity at least, by the strongest artificial heat which can be produced. Macquer and Beaumé melted small particles of it by means of a blowpipe, and Lavoisier by exposing them on red-hot charcoal to a stream of oxygen ga . It may indeed be melted without difficulty when combined or mized with other bodies, but then it is not in a state of purity. Pieces of platinum, when heated to whitene , may be welded together by hammering in the same manner as hot iron. This metal is not in the smallest degree altere by the action of air or water. It cannot be combined with oxygen and convert- ed into an oxyd by the strongest astificial heat of our furnaces. Platinum, indeed, in the state in which it is brought from America may be partially oxydized by exposure to a violent heat, as numerous experiments have proved; but in that state it 1s not pure, but combined with a quantity of iron. It cannot be doubted, however, that if we could subject it to a sufficient heat, platinum would burn and be oxydized like other metals; for when exposed to a very violent action of electricity, or voltaism, it has been reduced in small quantities to an oxyd form. To obtain therefore the oxyds of this metal to any €xtent, it is nece ary to have recourse to the action of an acid. When the deep-brown solution of platinum in\nitro-muriatic acid is treated with lime-water, a yellowish brown powder falls. Di olve this powder in nitric acid; evaporate to dryne , and apply a heat sufficient to drive off the acid. The brown powder which remains is the peroxyd. of platinum. Itis tastele , and insoluble in water. When heated to redne , the oxygen is driven off, and the oxyd reduced to the metallic state. One hundred and fifteén parts of oxyd by this treatment Jeave 100 parts of metal. Hence the oxyd is composed of 87 platinum 13 oxygen If the heat in this experiment be very cautiously raised, the oxyd, before it is reduced, a umes a green colour, This change is occasioned by the separation of a portion of the oxygen. The green coloured powder is, according to Chevenix, a protoxyd of platinum. From his experiments we learn that it is composed of 93 platinum 7 oxygen The action of the simple combustibles on this metal is not more remarkable than their action on gold. - Neither hydrogen nor carbon have been hitherto combined with it. Phosphorus unites without difficulty, and forms a phosphuret. By mixing together an ounce of platinum, an ounce of phosphoric gla , and a: drachm of powdered charcoal, and applying a heat about 320 Wedge wood, Mr. Pelletier formed phosphuret weighing more than an ounce. It was partly in the form of a button, and partly in cubic crystals. It was-covered above by a blackish gla , of a silver-white colour, very brittle, and hard enough to strike fire with steel. When exposed to a fire strong enough to melt it, the phosphorus was disengaged and burnt on the surface. He found also that when phosphorus was projected on red- “hot platinum, the metal instantly fused and formed a sulphuret. As heat expels the phosphorus, Pelletier has proposed this as an easy method of purifying platinum. Platinum cannot be made to unite to sulphur by heating them together. In this respect it resembles gold, yet there seems to be an affinity between the two substances; for when the metal is heated with a mixture of potash and sulphur it is corréded and rendered partly soluble in water, as was proved by the experiments of Lewis and Marckgraaf- And when sulphuretted hydrogen ga is pa ed into a solution of platinum in an acid, the metal is thrown down in dark-brown flakes, apparently in combination with sulphur, 492