P L A

P L A

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rable either by cupellation or quartation : bydigeftion in nitro-muriatie acid the gold is dif-folved, and the iridium remains behind in theform of a black powder.

All that is hitherto known of the newly-dif-covered metal called Rhodium , has been com-municated to the public by Dr. Wollafton. nIt is thus procured. Some crude platinabeing digelted in moderately dilute nitro-muri-atic acid, a brownifh-red folution is obtained :from this the platina is to be feparated for themoll part by muriat of ammonia, and the refi-dual liquor is to be heated with zinc ; by thistreatment a black powder will be obtained, andthe fupernatant fluid will confiil of the muriatsof zinc and iron. This black po-tder by di-geflion in very dilute nitric acid, will be freedfrom the copper and lead which it ufually con-tains, and the refidue is to be digefted in dilutenitro-muriatic acid, till every thing foluble is.,taken up. To this folution a little common faitis to be added, and the whole evaporated todrynefs, after which, by repeatedly walhing withwarm alcohol, the foda-muriats of platina andpalladium will be difiolved, leaving behind apure loda-muriat of rhodium.

This fait is readily foluble in hot water, anddepofits on cooling rhomboidal cryflals of abright rofe colour. Sal ammoniac occafions not.urbidnefs in the folution, but if a few drops ofmuriat of platina are added to the mixture, animmediate yedow precipitate is thrown down.Neither pruffiat of potafh, nor hydrofulphuretof ammonia, nor the carbonated alkalies, pro-duce any precipitate; but the pure alkaliesthrow down a yellow oxyd refoluble either inalkalies or acids.

The muriat of this metal is an uncryftalli-zable fait of a rofe colour, and foluble in alcohol:with nitre or the muriats of ammonia or foda,are formed cryflallizable triple falts infolublein alcohol.

Nitrat of rhodium is alfo uncryftallizable. Itappears not to be decompofable by filver, but isfo by copper, mercury, and moll of the othermetals.

The foda muriat of this metal affords a blackpowder by digeltion, with zinc, which whenheated with borax,. acquires a white metallicluftre, but is infufible by any heat that hashitherto been applied. It is however fufiblecither with arfenic or fulphur, and may beagain feparated from thefe iubitances by heat,hut it does not acquire by this treatment anydegree of malleability. It combines \yit*’i moilmetals, and with filver and gold, forms very

■» Phil. Trans. 1804. p. 419. » Chenevix in Phil. T

malleable alloys, which are unaltered by a highheat, but become encrufted with a black oxydwhen flowly cooled. An alloy of 6 parts ofgold and 1 of rhodium, differs but little incolour from fine gold, but is much more diffi-cultly fufible. The fp. gr. of rhodium appearsto be fomewhat more than 11.

In the preceding account of rhodium, wehave mentioned the method of feparating thefoda-muriat of this metal from the foda-muriatsof platina and palladium, by means of warmalcohol. This being done, the alcoholic folutionis to be mixed with a folution of muriated am-monia, by which the greater part of the platinawill be precipitated: the fupernatant liquorbeing then poured off and diluted, there is to beadded pruffiat of potafh, as long as any precipi-tate is produced. There is thus obtained adeep orange coloured fediment, which changesby degrees to a dirty bottle green. This whendried is to be heated with a little fulphur, andfufed into a button,after which it is to be flronglyheated with glafs of borax, till on cooling itacquires a bright metallic furface; being nowfeparated from the borax and expofed to theflame of the blowpipe, the fulphur is volatilized,and there remains behind a fpungy malleablemetallic mafs, which is pure Palladium. 0

This metal in its colour greatly refemblesplatina; when rolled into a thin lamina it isvery flexible, but not very elaflic. Its fpecificgravity varies from 10.9 to 11.9. Its hardnefsis fomewhat fuperior to that of bar iron; itsfradlure is fibrous, and it is very malleable.When heated below rednefs it acquires a fuper-ficial blue tinge, but neither at this nor at ahigher temperature, is there the leafl appear-ance of oxydation. At a full white heat itenters into fufion. It readily combines withfulphur, and the compound is brittle, of a•whiter colour than the pure metal, and fufibleat nearly the fame degree as zinc.

Palladium unites .with gold; and the alloy,when equal parts of the ingredients are ufed,-is of a grey colour, equal in hardnefs to wroughtiron, flightly malleable, and of a coarfe-grainedfracture. Sp.gr. 11.07.

Equal parts of platina and palladium form analloy rcfembling the former ingredient in colourand hardnefs, but in fufibiiity rcfembling palla-dium. Sp. gr. r 5.1.

Equal parts of palladium and filver producean alloy fomewhat harder than filver, and incolour rcfembling platina, only whiter. Sp.gr. 11.2.

With an equal weight of copper this metal:»ns. 1803. p. 590. Wollafton in ditto, 1804. p. 416.