P L A

PL A

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a bright orange colour, from which by repeatedflow evaporation and cryftallization may be ob-tained fmall o&ohedral cryftals of a high topazcolour. The yellow amnioniacal muriat whendecompofed by heat leaves behind about 42.5per cent, of platina which is rapidly fotuble innitro-muriatic acid; the red fait on the otherhand affords about 44 per cent, of metal, whichis with difficulty added on by aqua regia, and afmall portion in the form of a black powderabfolutely refufes to difl'olve. That this red faitcontains fome other metal befides platina isfurther obvious from this circumftance, that ifthe refidue after its decompofition by heat beplaced in a tube heated red hot, and expofed toa ftream of oxygen gas, a blue metallic oxydwill be volatilized, which appears to be thefame with the iridium of Mr. Tennant. Ammo-niaco-muriat of platina is alfo decompofable byoxymuiiatic or nitro muriatic acids which deftroythe ammonia and reduce the folution to Amplemuriat. It is alfo in part at leaft decompofableby the cauftic fixed alkalies and lime-water.

Potafh is alfo capable of uniting with muriatof platina forming with it a triple fait, thegeneral properties of which are analogous tothofe of the preceeding. Soda combines inlike manner with muriat of platina into a triplefait. The moll convenient way of preparing itis to mix with the muriat of platina a folutionof common fait, from which by evaporation andcooling may be obtained long prifms or trian-gular tables of the fait in queftion. The colourof this fait if the platina was pure is a brightyellow. It is very foluble not only in waterbut in alcohol, in which it differs from the twopreceding falts ; it is decompofable by muriatof ammonia, which throws down the ammoni-aco-muriat of platina; it is alfo decompofableby the fixed alkalies either pure or cauftic, butif they are added to excefs the oxyd of platinais again diffolved by them. When heated be-fore the blow-pipe on charcoal this fait boils,and is decompofed, the platina being reducedto the metallic ftate. b

The fulphuric, nitric, and oxalic acids, thoughthey have no effetSI on the pure metal, diffolveits oxyd and form with it falts that have hithertobeen very little examined.

rhe falts of platina are not decompofedeither by gallic acid, infufion of galls, or pruf-, of potafh. Sulphuretted hydrogen throwsnown a brown precipitate confifting for themolt part of metallic platina

The a£lion of the cauftic fixed alkalies at ahigh heat on platina is coniiderable, the metalbeing corroded and partly diffolved, a circum-ftance which confide’ably diminilhes the ufe ofcrucibles formed of this jubilance in the ana-lyfis of the more refractory ftony minerals.Nitre produces a fimilar effe£t. Mr. Tennantfound' that by heating nitre with fome thinpieces of platina in a cup of the fame metal,the cup was much corroded and the thin pieceswere entirely deftroyed. By diffolving the fa-fine mafs in water the greater part of the pla-tina was precipitated in the form of a brownpowder. This powder was entirely foluble inmuriatic acid, and confifted of oxyd of platinacombined with potafh. Part of the platii a wasretained by the alkaline foiiuion to which itcommunicated a yellowilh brown colour. Onthe addition of an acid an infoluble triple faitwas produced confifting of oxyd of platina, pot-afh, and the acid employed.

Platina combines by fufiou with many of themetals. With gold it forms an alloy that hasbeen already deicribed. With filver it com-potes a moderately eafily fufible alloy, of a fil-very white colour, confiderably malleable, andcapable of a high polifii ■, but when heated redit becomes of an iron-black colour, blitters andthrows off fcales fo as to render it incapable ofbeing wrought. A remarkable property of thisalloy is that it is very apt on confolidating fromfufion to become entirely covered with a fortof imperfedt cryftallization, thus becoming asrough as the coarfeit file. Lead combineswithout difficulty with platina at a full red beat,forming a fomewhat malleable, alloy of eafyfufibility; by cupellation a confiderable portionof the lead is worked off, but the remainingalloy is too fufible and too eafily a tied on bymenftrua to enable it to fupply the place ofpure platina as a material for crucibles, &c.

The fpungy metallic mafs remaiuing afterthe decompofition by heat of the ammoniaco-muriat of platina enters readily into combina-tion with mercury, as we have already menti-oned, forming an amalgam. If inftead of theplatina, the triple fait itfelf is triturated in anearthen ware mortar with an equal weight ofmercury, the fait in a ftiort time, according toMouffin Poufchkin, lofes its orange yellow co-lour, and pafles firft to brown and then togreenifti brown; a'fecond portion of mercurybrings the whole to the ftate of a grey powder,a third caufes a commencement of amaigama-

k Befcotils in An. Ch. xlviii. p. i6j. ; Kill. Tranf 1797. P- *21-

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