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tion, and by the time the fixth is added theamalgam is compleated. If the amount ofmercury is even nine times as great as that ofthe fait the amalgam will ftill be very {tiff andtenacious, and as brilliant as the beft amalgamof tin. It is a remarkable property however ofthis mixture, that if it is triturated for a fewminutes with water, or rubbed in the palm ofthe hand, it is rapidly converted into a greypowder which is oxyd of mercury, with feveralbrilliant particles of platina difperfed throughit, and a little running mercury ufually alfomakes its appearance. This grey powder byfublimation in a retort, furnilhes metallic mer-cury, and a little calomel. k

Platina is not capable of combining with ful-phur, but unites readily with phofphorus, fromwhich it cannot be feparated by mere heat.

4- Ofmium, Iridium, Rhodium and Palladium .

Of the above four new metals which haverecently been difcovered in crude platina fofew particulars have as yet been obferved thatwe have thought it moll advifable to treat ofthem in an appendix to the article platina.

It has been already mentioned that in dif-folving crude platina in nitro-muriatic acid, ablack powder is feparated which has been fup-pofed by fome chemifts to be oxyd of iron, byothers has been confidered as plumbago, buthas been lately difcovered by Mr. Tennant tocontain two new metals. If in treating thecrude platina a large proportion of ftrong acidat a boiling temperature is made ufe of, nearlythe whole of the black powder is diffolved, andthe platina thrown down from the folution bymuriated ammonia inftead of being yellow is ofa brick-red. But if a weaker acid at a muchlower temperature is employed, the folution ismuch lefs coloured and nearly 3 per cent, ofthis black powder remains, which may be rea-dily feparated by filtration and wafhing.

‘This black matter is partly in fcales andpartly pulverulent; it leaves black traces onpaper as plumbago does, but differs remarkablyfrom this latter in its sp. gr. which is = 10.7.It unites readily with lead, but the compoundeven if containing no more than T ' T of thisblack matter, poffeffes very little fluidity whenmelted. Nitrous acid diffolves out the lead,leaving the other ingredient nearly in the fameftate as at firft. With bifmuth, zinc, and tin,t he effefhs are nearly fimilar; but with copperjjt a very high heat it contracts a more intimatek An. Ch. xxiv, p. 109. 1

union, for by digefting the compound in nitro-muriatic acid fome of the powder was taken uptogether with the copper forming a very dark-coloured folution.

With filver and gold it unites eafily and inti-mately, and is incapable of being feparatedfrom either by cupellation, or from gold evenby quartation: the alloys retain confiderableduftility, and the colour of that with gold isnot materially different from pure gold.

If this black powder be mixed with a largeproportion of cauftic foda, and kept for fometime at a red heat, in a filver crucible, the mafsacquires a brownifh-yellow colour. On theaddition of water a peculiarly pungent odour isextricated and the alkali with part of the yel-low powder is diffolved. This alkaline folutioncontains the oxyds of osmium and iridium,the former of which may be obtained pure byflightly fuperfaturating the folution with ful-phuric acid and proceeding to diftillation, themetallic oxyd being very volatile, riling withthe water and remaining in folution with thisfluid in the receiver; as however a little ful-phuric acid is liable alfo to come over, a fecondvery gentle diftillation is required to procurethe oxyd quite pure. The folution thus ob-tained is as colourlefs as water; it has a fweetifhtafte and a ftrong peculiar odour; it does notchange vegetable blues to red. Oxyd of of-mium may be obtained in a much more con-centrated ftate by diftilling the original blackpowder with nitre. When the materials ap-proach to a red heat there fublimes into theneck of the retort a fluid apparently oily, butwhich on cooling concretes into a folid colour-lefs femi-tranfparent mafs. In this concentratedftate it ftains the Ikin of a permanent dark co-lour. It is foluble iirwater, and then exhibitsthe properties of the above-mentioned folution.The falts of platina or gold when dropped intoit produce no apparent chemical change, butwith nitrat of lead it gives a yellowifh brownprecipitate, with nitrat of mercury a white one,and with muriat of tin a brown one. An infu-fion of galls produces a purple colour whichfoon changes into a deep vivid blue. Withpure ammonia or carbonat of foda it acquires alight yellow colour, and with lime a fimilarcolour but of a brighter tinge; this latter folu-tion affords with infufion of galls a deep redprecipitate which becomes blue by acids. Puremagnefia or carbonat of lime produce no effecton this oxyd. On the addition of alcohol, the'ennant in Phil. Tranf 1804, p. 413.