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The next method which we fliall mention ofpurifying this metal was difcovered by CountMouflin Poufchkin. c It is effected in thefollowing manner. Diffolve the crude platinain nitro-muriatic acid, and throw down theplatina by muriat of ammonia, and wafh theprecipitate in a little cold water. Then heatthe yellow powder in a crucible till it is decom-pofed, and the platina becomes fpungy andreturns to the metallic ftate: now wafh themafs with hot water, and boil it in very dilutemuriatic acid, to diffolve out any iron that maybe cafually mixed with it; then edulcorate anddry the refidue. Of this refidue take a fewdrams with twice its weight of pure mercury,and triturate the mixture in a ftone mortar tillan amalgam is produced, which may be effect-ed without difficulty, after which by the alter-nate addition of mercury and platina feveralpounds weight of ingredients may be amalga-mated in the courfe of a few hours. Thisamalgam when firft made is foft, but in an houror a little more acquires a confiderablehardnefs;while yet foft therefore it fhould be clofelyrammed into a tube of wood of convenient fize,and after it has become hard, the tube with itscontents may be placed in a muffle, and by thetime that the wooden covering is confumed, agreat part of the mercury will be volatilized,fo as to prevent all rifk of the bar of platinabreaking when deprived of the fupport of itswooden cafe. The metal is now to be cau-tioufly heated till all the mercury is driven off,after which it is to be forged in the ufual wayat the higheft poffible heat.

A ftill more Ample and equally effeflualmanner of working this metal has been publifhedby Mr. Knight. d The platina being diffolvedin nitro-muriatic acid and precipitated by muriatof ammonia, the yellow powder hence refultingafter being edulcorated by wafhing in coldwater is to be thus managed. “ A ftrong hol-“ low inverted cone of crucible earth beingprocured, with a correfponding ftopper to fit“ it, made of the fame materials, the point of“ the latter is cut off about three fourths of the“ diftance from the point to the bafe. The“ platina in the ftate of a light yellow powder18 preffed tight into the cone, and a cover“ being fixed flightly on, it is placed in an aira “ lrnace and the fire railed gradually to afC tron g white heat. In the mean time thea f niC uf ^°PP er fixed in a pair of iron tongsuitable for the purpofe, is brought to a red* or a. bright red heat. The cover being then

“ removed from the cone, the tongs with the“ heated ftopper is introduced through a hole“ in the cover of the furnace, and preffed at<c firft gently on the platina, at this time in a“ ftate nearly as foft as dough, till it at lengthcc acquires a more folid confidence. It is then“ repeatedly ftruck with the ftopper as forcibly“ as the nature of the materials will admit, till it“ appears to receive no further impreffion. The“ cone is then removed from the furnace, and“ being ftruck lightly with a hammer the platina“ falls out in a metallic button, from which“ ftate it may be drawn by repeatedly heating“ and gently hammering, into a bar.”

The laft method that we fhall notice and onethat has been attended with compleat fuccefs,was invented by Mr. T. Cock, through whofeliberality we are enabled to communicate it toour readers. 6

The platina being diffolved in nitro-muriaticacid, the liquor is to be filtered through cleanwhite fand, in order to feparate the blackpowder which floats among it. The clearfolution being then decompofed by fal-ammoniacthe yellow precipitate is to be collected, mode-rately well wafhed in warm water and dried.It is then to be diftributed into faucers whichare placed in a fmall oven conftrufled for thepurpofe, where they are expofed for a fhorttime to a low red heat in order to bring theplatina to the metallic ftate, and to drive off bylublimation the greater part of the muriatedammonia. Wh^n withdrawn it is a fpungymafs of a grey colour. About half an ounceof the platina in this ftate is to be put intoa ftrong iron mould about 2f inches long by ifwide, and is to be compreffed as forcibly aspoffible by ftriking with a mallet upon a woodenpeftle cut fo as accurately to fit the mould;another half ounce is then added and treated inthe fame manner, and fo on till fix ounceshave been forced into the mould: a loofe ironcover juft capable of Hiding down the mould isthen laid upon the platina, and by means of aftrong fcrew prefs, almoft every particle of air isforced out from among the platina. This is apart of the procefs that requires efpecial care,for if any material quantity of air is left in themafs, the bar into which it is formed is veryapt in the fubfequent operations to fcale and befull of flaws. The preflure being duly made,the mould is to be taken to pieces, and theplatina will be found in the form of a denfecompaft parallelopiped. It is now to be placedin a charcoal forge fire and heated to the raoft

‘ Nich. Journ, ix,VOL. II.

* Tilloch Phil. Mag. vi. p. 3 .

' Original communication -2 G

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