582 



I'LATINA. 



burnished particles of platina will not weld) ; and in- 

 deed every degreeof burnishing would prevent the par- 

 ticles from cohering in the further stages of the pro- 

 cess. And since platina cannot be fused by the utmost 

 heat of our furnaces, and consequently cannot be 

 freed, like other metals, from its impurities during 

 igneous fusion by fluxes, nor be rendered homoge 

 neous by liquefaction, the mechanical diffusion 

 through water should here be made to answer, as 

 far as may be, the purposes of melting, in allowing 

 earthy matters to come to the surface by their light- 

 ne?.s, and in making the solvent powers of water ef- 

 fect, as far as possible, the purifying powers of 

 borax and other fluxes, in removing soluble oxides. 

 By repeated washing, shaking and decanting, the 

 finer parts of the gray powder of platina may be 

 obtained as pure as other metals are rendered by 

 the various processes of metallurgy ; and if now 

 poured over, and allowed to subside in a clean basin, 

 a uniform mud, or pulp, will be obtained, ready for 

 the further process of casting. The mould to be 

 used for casting the metallic powder, is a brass bar- 

 rel, 6$ inches long, turned rather taper within, with 

 a view to facilitate the extraction of the ingot to be 

 formed, being 1.12 inches in diameter at top, and 

 1.23 inches at a quarter of an inch from the bottom, 

 and plugged at its larger extremity with a stopper 

 of steel, that enters the barrel to the depth of a 

 quarter of an inch. The inside of the mould being 

 now well greased with a little lard, and the stopper 

 being fitted tight into the barrel by surrounding it 

 with blotting paper (for the paper facilitates the 

 extraction of the stopper, and allows the escape of 

 water during compression), the barrel is to be set 

 upright in a jug of water, and is itself to be filled 

 with that fluid. It is next to be filled quite full 

 with the mud of platina, which, subsiding to the 

 bottom of the water, is sure to fill the barrelwithout 

 cavities, and with uniformity a uniformity to be 

 rendered perfect by subsequent pressure. In order, 

 however, to guard effectually against cavities, the 

 barrel may be weighed after filling it ; and the ac- 

 tual weight of its contents, being thus ascertained, 

 may be compared with that weight of platina and 

 water which it is known, by estimate, that the barrel 

 ought to contain. A circular piece of soft paper 

 first, and then of woollen cloth, being laid upon the 

 surface of the barrel, allow the water to pass during 

 partial compression by the force of the hand with a 

 wooden plug. A circular plate of copper is then 

 placed upon the top, and thus sufficient consistency 

 is given to the contents to allow of the barrel being 

 laid horizontally in a forcing press. After compres- 

 sion, which is to be carried to the utmost limits, the 

 stopper at the extremity being taken out, the cake 

 of platina will easily be removed, owing to the coni- 

 cal form of the barrel ; and, being now so hard and 

 firm that it may be handled without danger of break- 

 ing, it is to be placed upon a charcoal fire, and there 

 heated to redness, in order to drive off moisture, 

 burn off grease, and give to it a firmer degree of 

 cohesion. The cake is next to be heated in a wind- 

 furnace ; and, for this purpose, it is to be raised upon 

 an earthen stand, about two and a half inches above 

 the grate of the furnace, the stand being strewn 

 over with a layer of clean quartzose sand, on which 

 the cake is to be placed, standing upright on one of 

 its ends. It is then to be covered with an inverted 

 cylindrical pot of the most refractory crucible ware, 

 resting at its open end on the layer of sand ; and 

 care is to be taken that the sides of the pot do not 

 touch the cake. To prevent the blistering of the 

 p'atina by heat, which is the usual defect of this 

 metal in its unmanufactured state, it is essential to 

 expose the cake to the most intense heat that a wind- 



furnace can be made to receive, more intense than 

 the platinu can well be required to bear under any 

 subsequent treatment, so that all impurities may he 

 totally driven off. The furnace is fed with coke, 

 and the aciion of the fire maintained for about twenty 

 minutes from the time of lighting it. The cake is 

 now to be removed from the furnace, and, being 

 placed upright upon an anvil, is to be struck, while 

 hot, upon the top, with a heavy hammer, so as at one 

 beating effectually to close the metal. If in this 

 process the cylinder should become bent, it must on 

 no account be hammered on the side, by which 

 treatment it would be cracked immediately, but 

 must be straightened by blows given upon the extre- 

 mities, dexterously directed, so as to reduce to a 

 straight line the parts that project. The ingot of 

 platina, when cold, may be reduced by the processes 

 of heating and forging, like any other metal, to any 

 form that may be required. After forging, the ingot 

 is to be cleaned from the ferruginous scales which 

 its surface is apt to contract in the fire, by smearing 

 over its surface with a moistened mixture of equal 

 parts, by measure, of crystallized borax and common 

 salt of tartar, which, when in fusion, is a ready sol- 

 vent of such impurities, while it does not act, like 

 caustic alkali, upon the platina itself. It is then to 

 be exposed upon a platina tray, under an inverted 

 pot, to the heat of a wind-furnace. The ingot may 

 then be flattened into leaf, drawn into wire, or sub- 

 mitted to any of the processes of which the most 

 ductile metals are capable. The mean specific gra- 

 vity of the metallic cake of platina powder, when 

 taken from the press, is 10; that of the cake fully 

 contracted by heat, before forging, is from 17 to 

 17.7 ; that after forging is about 21.25, and that of 

 wire, 21.5, being the maximum density of this 

 metal. 



Pure platina has a white colour, very much like 

 that of silver, but is inferior in lustre to that metal. 

 Its malleability is far less than that of gold or silver, 

 but superior to that of tin. It may be drawn into 

 wires that do not exceed the 2000th part of an inch. 

 It is a soft metal, and, like iron, admits of being 

 welded at a high temperature. A wire one tenth 

 of an inch supports 590 pounds without breaking. 

 As a conductor of heat, it ranks between gold and 

 silver. It undergoes no change from the combined 

 agency of air and moisture, and it may be exposed 

 to the strongest heat of a smith's forge without suf- 

 fering either oxidation or fusion. On heating a 

 small wire of it, by means of galvanism, or the com- 

 pound blow-pipe, it is fused, and afterwards burns 

 with the emission of sparks. Platina is not attacked 

 by any of the pure acids. Its only solvents are 

 chlorine and nitro-muriatic acid, which act upon it 

 with greater difficulty than on gold. The resulting 

 orange-red coloured liquid, from which the excess 

 of acid should be expelled by cautious evaporation, 

 may be regarded as containing either chloride of 

 platinum, or the muriate of its oxide. According to 

 Berzelius, there are two oxides of this metal, the 

 oxygen of which is in the ratio of 1 to 2. The 

 protoxide prepared by the action of potash on pro- 

 tochloride of platina is of a black colour, and is re- 

 duced by a red heat. The peroxide is obtained with 

 difficulty ; for, on attempting to precipitate it from 

 the muriate, by means of an alkali, it either falls as 

 a sub-salt, or is held altogether in solution. It is of 

 a yellowish-brown colour, resembling rust of iron 

 when dry, and is nearly black when anhydrous. 

 Like peroxide of gold, -it is a very feeble base, and 

 is much disposed to unite with alkalies. 



Chlorides of platina. The perchloride is procured 

 by evaporating muriate of platina to dryness, by 

 means of a gentle heat. It is deliquescent, and is 



