Experimental Examination of a White Metallic Substance Said to be Found in the Gold Mines of the...

Experimental Examination of a White Metallic Substance Said to be Found in the Gold Minesof the Spanish West-Indies, and There Known by the Appellations of Platina, Platina di Pinto,Juan Blanca. By William Lewis, M. B. F. R. S.Author(s): William LewisSource: Philosophical Transactions (1683-1775), Vol. 48 (1753 - 1754), pp. 638-689Published by: The Royal SocietyStable URL: http://www.jstor.org/stable/105200 .

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r 638 3 ther, I Ilial1 endeavour toSprocure them<ItbErlSts to their work, -and {hew them ¢very-civilt in my power.

.

LXXX9VI. ffX<mental t3caEntnation ,of

a white metallic Subfice kd-XoXbe fbvxd in tbe GolV Snws of ̂ e +mb XJf;JefF

- Indies, aad tXere 4rorN X the peAlNw

tions of Platina} Plaiina di Pinto, Zan Blanca ty Willia lkwis M. B B. Re S.

P A P 35: R 1^ Read-May30 I 5-4*

EXpEfZf.lt I.

-JPTS H E fubPrance brought into England under the - | name of platina appears a mixtufe Qf diismilar

particles - The moIt -conEpicllousX and by fkr the largeR part

of the mixt, arev whitet lhining grains, of ISmingly Emooth furfaces, Irregular figuresl, generally planes with the edges rounded off. upQn examining there

with a microScope, the furfa-ce appear'd in fome parts irregular s the prominencies fmooth, bright, and lhining , the cavities dark-colo-ur'd and roughi&. A fgw of them svere attrsired, tho) weakly) -by a magnetic bar .

The grains above defcrib'd are the true platz'nao The heterogeneous matters intermi.ngled among them, -n the fieveral parcels} were,

r 638 3 ther, I Ilial1 endeavour toSprocure them<ItbErlSts to their work, -and {hew them ¢very-civilt in my power.

.

LXXX9VI. ffX<mental t3caEntnation ,of

a white metallic Subfice kd-XoXbe fbvxd in tbe GolV Snws of ̂ e +mb XJf;JefF

- Indies, aad tXere 4rorN X the peAlNw

tions of Platina} Plaiina di Pinto, Zan Blanca ty Willia lkwis M. B B. Re S.

P A P 35: R 1^ Read-May30 I 5-4*

EXpEfZf.lt I.

-JPTS H E fubPrance brought into England under the - | name of platina appears a mixtufe Qf diismilar

particles - The moIt -conEpicllousX and by fkr the largeR part

of the mixt, arev whitet lhining grains, of ISmingly Emooth furfaces, Irregular figuresl, generally planes with the edges rounded off. upQn examining there

with a microScope, the furfa-ce appear'd in fome parts irregular s the prominencies fmooth, bright, and lhining , the cavities dark-colo-ur'd and roughi&. A fgw of them svere attrsired, tho) weakly) -by a magnetic bar .

The grains above defcrib'd are the true platz'nao The heterogeneous matters intermi.ngled among them, -n the fieveral parcels} were,



r 639 ]

xf A blackslE dul1, feparable by a fine fieve. This was farths divided by a magnetic bar, into two different fubRmces: the part attradted, was of a fine fparkling black colour, much reSembling the black fand from Yirginia the part not attradred was of a dalrk browIlifh hueX w-ith feveral bright modecal> which appear'd to be fragments of the grains of platina.- -

z. Among. the. larger grains, feparated by a coarfe fievet were obI5erv'd I;mdry irregular darkcolour'd particles, fome blacki0}, others with a cafl:0 of browniffi red, in appearance refembling fragments of emery^ or loadkene Several were attradced, weakly, by the magnetw

g. There were a few rough yellow particles, refem bling goldfi wrhich -upon farther examination they were found to bey tiho' probably not cntirely free from platina.

4* A few globules of qu-ickfilver, contai;ning- gold,. with fome particles of platina intermix'd and pretry flcrongly adkering.

5. Some fine tranfparent -particles, probably fpar* t. A lrery few irregiar particles, of a jet-black co

lour. TheSe broke eaIily, and look'd like the finer kindsof pitcoal Laid on :a red-hot iron, they emitted a yellowiSh fmoke, and fnelt like burntng coal.

Remarks. T. It appears fiwom the foregoing obfer_ vations, that this mineral has not come to us in its native form; besng, probably, taken out of the -mines in large maXes, which have been broke, and treated

- wit;h 2



[ 640 ] with me1^cury, in order to extradc the gold, of which pofl*sbly it at firft corltain'd a confiderable quantity. rhe *Juantity left by the workmen is extremely fmall; fiome pounds of the mixt having yielded only a few grains. A moderate fire renders more of thefe golden particles dScoverable, than can be feen . at firIt; the mercury evaporating, by which feveral of them were concealed.

. Some part of the browniSh powder is probably adsrentitious, as well as the mercury; being worn off <fiotn the Rasnpers and mllls employ'd for comnni nutmg the mineral, and triturating it wii the mercury,

3. The roughnds snd dark colour of the cavities of the grains of platina feem to procced from a fub- Rance fimilar to the black dalfc, adhering tin them, It- is probably owmg likewife to this heterogerleous magnetic nlattewr, that fome of -dlem are ttradrd by the loadRone.

. Ent 2

Some of ihe purs grain$ of platint, by gentle flcrokes of a flat hammer, upon a lmooth anvil, bore to beconfidablyflattenbdswithoutbreakingor crackw ing about t}}e eQges: fome quickly crack'd, and dif- :over'd illt:ets -ially 9 clofe granulated texture. All are reducibleZ by rude fcrokes sn an iron mortar, tho' with diEculty, into powder They feem'd to be rather more brittle when ignited, than when cold.

Experiment 3* -The fpevifi¢ gravitOr of platina, with its hetero neous admifresX as brought to usX was found to

b



[ 64r ] be to atof water as x6*g9f-to I§030. The qum- tity weighd for this purpofe was no leEs than 2000 Troy grains

The larger grasns of platina, leparated as much as pofl lble from the other matters by the fieve, and cleans'd by heatingX boiling ln aqua fbrtis, mixing them with fal ammoniacs and forcing off the falt by fire, and afterwards wa{hing them; weigh'd in air 642, in water606.7y: whenw:their gravity tilrns out x 8.2 X 3. The microficope llill diScoverXd a conrsder- able portion of blacklfh matter in their cavities.

TheSe trials were Several times repeated on different parcels of platina: the refult was nearly the ine n all.

Remark. The gravity of this minerala great as it appears to be fbm the foregoing experiments, wauld probably turn out llill greater upon a farther purifi- cation of the platinas fince itis manifeRly mu d erith fome of the lighttr heterogmeou s mat t erg

Eeerwnt 4. s. A quantity- zof plafing, tltaining iS ufual ad-

mixture of magnetic duR, was kept for fome time of a moderate red heat irs aa iron ladle. lthe bright particles became fomewhat duller-colouffld a the mag- netsc ones were no longer attradEed. In other refipedr; there was no fenfible alteration.

s. An oullce of platina was urg'd with a Ilrong fea-coal fire, in a blaIlfurnace, ibr above an hour: the heat was fo vehement?* that the black-lead crucible vithfy'd, and the {lip of WindSor brick, which courffl'd it melted) and ran down. The grains of platina were fcound iperficially coheringJntoalump,--

4M of



[ 642 ] of ie figure of the bottom of the cruc1ble, of a brighter colour than at^firIt. On a Ilight blow, they readily fell afunder again, and feem'd not to hasre alter'd tIleir nlape.

3* In feveral repetitions of the experiment, the platina began to cohere in a moderate white heat^ the grains were at thIs time very eafily feparableX and feemd to cohere the more ltrongly in proportion as the heat was rais'd. In the moR intenfe lSres, which the co£nmon veXels could not long fupport, the pla tina did not melt, or foftenX or alter its figure, -or loSe>: fenfibly, of its weight. The colour was conPrantly brightend by a firong heat, and genera-lly render'd duSky by a fmall one: on quetlching it, when vxo- lently heatedS iEn cold water, the hgralns, which compos'd the internal part of the lllmp? acquirtd a vielet or purple colour.

EsMeritnent S 1. As tlle power of fire upon metallic} as well as

earthy fubItances, is ren:larkably promoted l3y the imw mediate contadc of fuel, and the impulSe of air upont the fubjedc; platina was expo5'd to its adioxi in tlaofe circumItances. A crucible, havingRa- id of charcoal in it, was laid on its fide, in a good bla{i furnace, svitll it moiJth towards the nofe of thc bellows; andr four ounces of platina fpread upon the charcoalF The fire was lrehetnently urg'd for above an laourJ during which an intenSe white flame pafs'd thro' the cruciblea and iffiu'd at an aperture made for that- purpoSe. The craxible was vitrify'd: the grains of platina ohly filperficially coher?d, atnd became brighter>. as in the preceding experimetlt, wlthout feeming to l.zave foften'd Q.1 alte;Xrd tlleir apeb

2. The



t 643 3

2. The experiment was feveral times repeated, and varied: once, common falt was 4thrown on the fuel before the crucible, and its fumes llrongly impell'd oll the platina: fome platina was likewife placed before the nofe of the bellows in violently excited fea-coal xSres, fo flcrong as to almoR inItalltly melt of a piece of the end of a forg'd iron rod, without eXeEt; except that once there were a very fegr globular drops, -about the fize of very fmall {hot :- thefe-broke eafily on the anvil, and look'd, both internally and externally, like platina.

Remark. It is probable, that the filfion here was owing to fome accidental admixture, pofl^1bly iron: for the unmelted grains, expos'd after-wards to a fire rather more intenfe, fuffer'd no fenffble alteration.

Encterivatnt 6. Platina was lilewife expos'd to the fire in con

jun£tion with feveral fabRances, which are found to promote the fuf1ctl of other bodies, or to occalion confiderable alterations in them.

x. Platina mingled with powder'd charcoal, with compofitions -of charcoal, foot, common falt, and wood afEesX fiubItances employ'd fior changlng iron into Ileel; fuffer'd no change in weight or appearance, whether urg'd with an intenfe fire, or cemented for nlany hours ih-a weaker one.

:. Platina was injedced into meled borax, and urg'd with an intenSe fire for feveral hours, without undergoing any -alteration Nor had black fluxX tomm-on falt, -pure fix'd alcaline falts, or cauIlic al calies, any fenfible effe&.

3. vi- +.M 2



r6+4] 3. titreous matters were no more powerful thaw

the faline. Platina was kept in firong fires, for Severat hours, with common green glafsX with glaEs of anti- mosly, and with sglaEs of lead, without feeming to be in the Ieak afted upon by either.

+. Platina was likewife Itratified with plaI}er of Paris} a powerful flux for the moI} difficultly-fufi1ble metallic body hitherto known, fiorg'd iron; -as alfo with quicklime and with calcin'd flirt; urith as little efEed: as in the former trials.

hperzgent 7. Stitre, sYhichs reduces all the known metallic bo-

diesX except p1& and filver, into a calx, was mix'd with an equal weight of platinaX the mixture injeiced into a Ilrongly-ignited crucible, and the fire kept up for a confiderable iime no deflagration happenbd; and the platinas freed fiom the falt by repeated ab- lutions withX water., prov'd of the fame. weight and appearance as at frR

Experxnwent W. 1* An} ourlce of platina was fpread upon twice its

weight of fulphur, with which fo-me powder'd chart coawl had been previoRy mix'd to prearent its becom ing fluid in the fire fo as to fuffer the platina to fub_ fi&e. The crucible, having another wsth a hole ia ie bottom; inverted into its mouth, was kept in a ce- menting furnace for feveral hoursX when the fulphurt was found to have «tirely exhal'd, leaving the pla_ tina IEparablc from the charcoal by wa}ing, without aIttertation orL diminution. -

20. wes



[ 645*] 2. We likewife varied the experiment, injedring

repeatedly pieces of fulphur upon platina ltrongly heated, and conllantly found} thatpure fulphur had m more effed upon this mineral than on gold iSelf.

3. As fix?d alcaline falts enable fillphur to diSlolve gold ; platina was expos'd to the fire with a mixture d fulphur and aleali call'd bepar /ulpbgrit Aftera confiderable- heat had been contina'd for fome time, and the matter occafionally I;tirr'd, very little of thea platina was found remaining in its proper form; the greatek part being talmen by the fulphureo faline mixturea fo as to diiStlve ale>ng wit} it in water

Gcnerai Remarks. It appears, from the foregoing experiments and

obServations,

;. Thae ply this mineral is originally found in large, hard mafl"es, compos'd of true platina, a fubX ilance fimilar to the black Virginia fandj and another irruginous matt-er of- the emery kind; fome fpar, and prticles of gold

2. That tileSe malEes are, rst without great labour, reduced into fmall grains, which are afterwards ground with -mercury, in order to extra&- the goldt

3* That the pure platina is a white metallic fub- flcance in fome Snali degree malleable. that it is nearly as pollderous as gold, equally fixd and per_ marnent in the firt equally inde{crudtible by nitre unaflided by ftllphur, diXolable by bepar Jlphvris. That it is not to be brought into fufiors by the great-* eflc degree of fire procurable in the ordinary furna¢es, whether expos'd r i^ts adion in clie ve}ilss or in contaft with the fuel, by itfielf} or with the addition s£ inflammable, faline, vitreous or earthyfluxes



[- 646

P APER II.

Read 3llne w-°,T H E 1nore obvious properties of tllis 1754t t extraordinary luineral, and its ka

&*tas to fire, flngly, and in conjunEtion with the va liOUS fulvI}ances call'd by the chetniRs ./t4ses, made the: objedc of tlle firA paper. In this3 it is proposXd tc -eJfamine the effedc of acid fpirits, fimple and compound, applied after various manner; in order to detelmine not only its relation or habitus to them) but likewife its leEs obvious agreemert or difagreement with the metallic bodies, whoft hiRory is more linown.

The platina employ'd in the following experiments was prelrIouily freed fiom its fine duil by a fieve; from the mercury, by ignition; and from the golden and fome Sof the other heteroge1leous particles) by the eye aiVed with glaffies.

Encterzzent tx Platina with the Vitiolic Acid

1. Several parcels of platina were digeIled for fonze hoursX in a gentle heat, with Epirit of vitrio], both concentrated) and -dilated with-different proportions c)f water. No Iblution happend, nor any fenfible alterationw, eithex in the liquors or the platina.

2v lhree ounces of well-dephlegmated fpirit of vitriol were boiltd with one ounce of-platina, in a tall, narrow-neck'd glaEsX for fome hours. The liquor {vtmainXd nearly off the fime quantity as at firti; and

- -no



t 647 ] no change could be perceisrfid eithet in it, or in the platina.

3. The glafs being cut ofX a little above the li quid, the heat was gradually increas'd, till the liquor} which now began to evaporate, had, in fisre or flx hours, totally exhal'd, and the platina become drys and red-hot. When grown cold, waSh'd ssith waterX and exilrcatedX it was found exadly of the lLame weight as at firIl, a,nd its grains not divided, or apparently alter'd.

llemark, Platina appears therefore to entirely re- fiIt ie lritriolic acid ; which7 by one or other of the above proceSes, diXolves or corrodes every other knowa metallic body except gold.

Experitnent 2¢

Platlna wtb the Marine Acid.

1. Weak and firong fpirits of falt being lgeRedw feparately, with one-third their weight of platina, in a; gentle heat, fbr feveral hours, the liquors remaind uncolourvd, the platina unalter'd, and undimininlvd The heat was afterwards increas'd, and the-liquors: kept firongly boiling till they had totally exhal'd,< without occafioning any Senfible change in the pla tina.

z. Three ounces of a mixture of two parts decre pitated fea-falt and three parts of vitriol higllly cal-- cin'd, were prefs'd fmooth into a crucible; an ounce of plttina fpread evenly upon the furfice) and cover?& with fome more of the mixture; the crucible cloSely luted, and kept in a moderate red heat for Senteral hours. 0n examining it svhen grown cold, the falinc

2 mstvlre



E 64g 3 mixture was found to have melteda and fiormd a fmoothX uniforrn lump. The platina, which had funk to the bottomt being feparated from the mixture by wathing, prov d of the fame appearance as at firR, tho' a little Aeficient in weight.

<3. The experiment was repeated with wllatis call'd the regal cement, a lefs fiulible mixture compos'd of common falt and colcothar each one part, and four parts of powder'd red bricks. An ounce of platinas furrounded, as- above, with fix ounces of this com_ poIition, and cemented in a clofe-luted crusible with a red heat, for twenty hours, was Itill foundqunalterXd in appearance) tho' there was fom.e deficiencya as before, in the weight.

Remark The marine acid, when -thus detain'd m the fire by the combination of other bodies, till flrongly heated, and then fet at liberty in the form of fume, diflioles or corrodes all the known metallic fubPcances, gold alone cscepted. As the platinaX in thefe experiments, retain'*d its original polilh'd fer- face, without any mark of corroElon -; it was prefum'd, that this mineral likesvife had reSiRed the marine fiRnes; and that the deficiency was owing to fome of the fmaller grains having been waSh'd ofl; along with the ponderous colcothar or metallic matter d the vitriol; an accident not eafily avoided.

+. Platina 57uas therefore treated with mercur3r-fub limate, a combination af the highly-concentrated marine acid with a volatile;fpubllance, wthich in a proper degree -of heat it read;ily f8rfakes to unite-with other metallic bod-ies. An ollnce af platina was fpread upOll three ounces ef powder'.d fllblimate; the glars wver'd, and fet in fansl.: After a lnoderate fire for

fome



[ 649 ] fome hours, the fublimate was found to laave etatirely arifen, leaving the platina of its oribinal weiglle, as well as appearan-ce.

S Fifiy grains of a mixture of one part of platina and two of gold, well ne-al'd) and cautiouRy hana_ mer'd into a thin plate} were furrowlded with regal cement, tbe velEl coverd} clofely luted, and kep£ for a couliderable tsme in a red heat. Upon e3ca mining thx rnetal, it was found to retain the wlaite nefs and brittlenefs, which gold conIlantly receives from fo large a proportson of platina; and to have loflc in w¢ght about half a grain, or onebhundredth

Remark. The lofh here appears to have proceeded} not from the platina but fron alloy in the wld employ'd, which was above Randasd, but noteperfedsly fixle: FQR the metal cemwted a fecoM tHnev with frelh misture9 fufferM no farther diminution. I-f thc marineacid were capable of diSolvin;g platna, in- ilead of one-hundredth nearly one-third would Mve been exeded. This experiment therefore determines, with certainty, the r¢fiRance of platina to the marine fumes; and that the regal cement, fo calld from its being fuppos'd to purify gold from all heterogeneous mgtal}ic malJ;ers, is incapable of feparatq platins from it

E$peri2ent a.

- Platina with tbe nitrous acid.

I. Spirit of nitre diluti with wkrs proof aqua fortis, and the Rrong nitrous rpffit were digeRed We- parately, with one-hird their wewight of platina, in a gentle heatX fQr feveral hours. During the dlg§ionX

4 N fome



r 6So 3 fotne babbles ssere obGelXv'd, as if a iSolution was be g;inning: but tlle liquors acquir'd no colour; and the platina, sva0a'cl atld drst'd, was found to have neither alter'd its appearance, or loIt of its weight. Tlle fite beislg afterwards increasXd, and the acid fpirits- kept ilrongly boiling till they had entirely evaporated, no change could be obferv'd in the platina.

2* Platina was likewife treated with nitrous mixS tures, Sby proceINes flmilar t-o thoSes in which it had been expos'd to the marine fumes. After cementa tion for many hours, in a red heat, with a mixtureo of three parts calcin'd vitriol, and two of melted nitreX the grains were recover?d not only unalter9d, but likewife witlaout any d-eficienczr in weight.

Refnark. From thefe experiments it is plainS t-hat platilla, equally with gold} ref109s the force of the 57itriolic, marine, and nitrous acids, tho' apply'd ill fuch a manacr, as to be capable of perfedcly diffiolvin-g all other known metallic bodies.

* zxpergmeat 4. Platina with aqua regia.

1-. Aqua; regia, which perfedly diflôlvnd goldX pour'd upon platina, began to adc on it: in the cold, and, by thz affi1flance of a moderate heat, llowly dif folv'd it; acquiring at firk a yellow colour, wihich fleepen'd lty degreesf as the menltruum became more faturated, into a dark browlliSh red. - A fesw drops of the faturated folution tinged av large quantity of water of a- fine golden colour.

^ The- experiment was Several times repeated wit-lS diffierent aqua regia, made by dilIolving fea-Ealt and

fal 2



[ 651 ] fal ammoniac, Separately, in four tlmes tlleir weig}lt of aqua fortis; alld by abIErading t he nitrous fpiri from the fame proportion of eacll of tlae falts With all theSe menItrua the folution feetn d to fllC- ceed eqllally.

3. In order to determine tlle quantity of men Ilruum necelIary for the folution; three ounces of an extremely itrong aqua regia, diluted with water) were pour'd upon one ounce of platina, in a retort, to whic-h was adapted a recipient A gelltle heat being applied, the menIlruum afted violently, and red fumes aroSe in abundance. When about twothirds of the liquor had come over, the adtion was Scarce, if at all, fenfible, though the fire was co1lfiderably rais'd The diItill'd liquor, which appearXd of a light rediSh colourX being pour'd back agaill into the retort, the folution began afreth; the vapour, which now came over, appear'd pale) compar>d with the xErit. The cohobation was repeated four times, the diRillsd liquor proving paler and paler every time: At length, both the fiJmes and aftion ceas'd, though the fire was rais'd, and a confiderable part of the platina remainsd undifl:olv'd. The folution was therefore pour'd oh; fome more of the menilruum added, the diItillation and cohobation renewXd, and this oc- caI1onally repeated, till the whole was taken up, excepting a lietle blackifh matter} of which hereafter. The quantity of firong aqua regia, employd for dif folving the ounce of platina, was five ounces; but the laIt parcels appear'd from tlleir ye}low colour nor to be fully faturated, and, upon tlial? vere found to take up near fifty grains of freXh plati2la.

N4 2 1<47§t0



[ 652 3

Rervark. It appear'd, that by this methed of managing the procefs, one- part of platin-a was diS foluble in about four and a half of aqut rega: But that when the digeRion was perform'd in open velIcls in the common manner, and the fumes, which arsfe copiouIly during a11 metallic difl4ollltionss foffer'd to exhale, Inore than half a-s much again af t-he men- Airuum was requifite. Thxs p;roceX mlght therefore poffi1bly be applicable to advantage, in makng folu_ tions of metals in t-he way of bufxnefs.

Examan;fitioa of Solattorl af Platim.

Est¢rizen! .

As the vitriolic acid carries down metall;c bodiesf gold not excepted, firom their folutions in other menitrua; this acid was x'd with folution of platin-a

I. When the folution of platina was previouily diluted with water; the addition of dephl-egmated Epirit of vitriol occaElon'd no precipitation, or change of colour, tho' a large quantlty of t:he acid wasF at diffierent times, dropp'd in, and the mixture fuicr'd to fl:and for feveral days.

2. Dephle$mated fpirit of vitriol, added to an un- dlluted folxisn of plaina, immediately render'd it turbi(l, and threw down a duSky colour'd precipitate. The precipitate was not re-diISolv'd on the affufion of water; nor was the precipitation prevented by adding water immediately agter the acid had been dropp'd in.

Expe



Etter#Serit 2*

Solutions dplatina, cvaporated by a gentIe warmth, to a proper pitch, and then fet to Dloot, yselded cry- Ilals, of -a dark, aImo* opake, red ¢olour, in brm of leaves, like flders of bentin, but thicker. Tlle - cryftals, waffi'd with proof fpirit, became fomewhae paler, but Ril1 remam'd of a hibh cololxr, rOmbling lfhe deeper c}lives of faffiron Expostd to the firea {hq feem'd to melt, emitted white fumes, a-nd at iength i1I into a dufky a**col-our'd calx.

ExptriXe*t 3. Solutions of platina, dropp'd upon hot marble,

itsnedittdy corroded it, bUt did not, like folutions o£ told md ite odler mrtaIs, communicatPe- any col-our. Nor did they gite any flcain to the {kin, to feathers irory, or otir lrke mimal filbRancesX mrhich liquQxs ¢ontaining goid tinge purple.

E$p 4 As a m1nute proportion of gbld contaiis'd in li-

quors is diScoverable by thQr flrikxng a prple-colour with tin.

x. Some bright plates of pure tin were put into a fotuton of fatina dlluti with water. The plates, in a little tlme, look'd of a dark olive colour, and foon after were courer'd with a redifh brown matter- The liquor became at firR darker coJourM) and after wards by degreess as the precipitate fell, nearly co lourlefs;- without axhibiXDgtheleait apEvranz of A purpliffi hue,

. PlaZ

[ 653 J



* r " * t54"

:* Platina was diid in a qua£ltity Qf aqua reglt infuffiicient to diXive tyhe wshole > and the refidaum AddlUlvid in a finffi pwzl of the menflruum* he two fblutims, treated as abov&, yielded^ fomeXat different phanomena but no tendency to a purplifh caR>souldf be peivtd in ewher The latter} which lo(iked yellow Som aot being fillly liunted, was, when diluted wah water, almoR 11^. Never thele} m the addltion d the tin} it bwame yellow agai thm md} and at length of a dsk browrliffi red mui;derably deezr than tliother tnore fit=ated

oletionX *0n inding br bme time, it grew per; feiy bleaB depofiting a palerX ycllowilh prexpstat«

3* To determine ether platina- was capable of preventxng a iall prqponim of gold im difcowrs sng itSelf m this Fal>* one dmp of a blution of gold was let i11 into fieveral ounces of aS bllltion of plb tina d;luted tth water On adding fome plates of fin the mrhole became imtnediately g a fine purplc

Rffl4rk*- It may be proper to obirves that in theSe kini d expersmotS plates of tin am fW nzxe eligible than -the blutions of tin ufiually employ'd FQr the lblutions iil of fl:riking a purple zlour- wii lWolution of pum pld} unlefs certain arcumRances ârs oblErvsda which aw not eaIily hit upon; but tia in filbRan¢e micandy izeeds>-: and requires no p tnlar prectution

- I:xperzzent 5* As gold ss reviv;>d from its folutions by inflammable

4;wits the metal gradually atiflng to the irface} il- fxm d a brlght ycllow cutlcle >



t 655 ] lv A folution of platina was mix'd with a large

proportion of highly-reftified Epirit of wine, ahd ex pos'd for many days to the fun, in a wide-mouthd glafs, flightly cover'd with papers fo as to keep out dull.. There was no appearance of any yellow- Skin ; nor any other alteration, than that-the platlna hadfbe gun to cryRallize from the evaporation of the fluid.

2. k drop or two of a folution of gold being added to- a large guantity of a -mixture of folution of platina and fpirit of wine, and the 5rholezexpos'd as above to the fun; a golden film was in a>-few days obferv'd upon the furface.

Remark. It fUllows frs3tn- this experiment, aRnd -the foregoing one with tin, that platina contains no gold; and that it cannte, any more than the cothmon metallic or other foluble fabflcances,- prevent a fmall proportion of gold niix'db with: it from being diS coverab}e.

ExperiVent 6. :

I. Ne fpir-its of fat ammoniacs prepar'd both by quicklime and by fix'd: alealine fales, added t(3 r Intions of plauna-diluted: wsth diftill'd water, preciX pitated a fine red rparkling powder ;- which, exfi> cated, and expofd to the fire in an ironladle>^ became blackinl; without at all fulminating, which calcesw of goW, preparid in the- fame manner, do violentlyv On waiing fome of thi6 precipitate upon -a filterX by 3mepeatedxafftsfions of watert the greateff part of it diC i*ols'd; only a fmalls quantityl:d a blackiSh matterE rtmaining, and the- liquor paffing throu-0i of a;deepX brightX golden colour, :A-very :large quanfitXof the

fluid;



[ 656 3 fluid was tinged of this-colour by a fmall one of the nowder.

2. Salt of worsmwood -fis'd nitre, -the lx'wszurn fapovriun of the London tbirwsppat precipitated a-powder :-fiXmllar tQ theeforegosng, eXcept that its colour svas lefs brilliant.

3. Sal ammoniac likewilk, one of *e -ingredients, to which the -menEuum ow'd.its power of difslolving the platina at firi3:, pr<pitatedvgrxat-part of it m form of a fimilar powder.

+. The liquors remaitlmg after all thefe precipi- tations with- faline (llbflcanges, appear'd of a yellow solouB almok as deep A ifore the precipitation, Fixbd and-vol:*le alvli¢Xi-beiig added alternately the liquor ItiXll csatinu'd yellow: But titber of themt added tair 1- ammoniac had perform'd its oice; threw down a fHi precipitate^> w}*h l¢E ffie liquor colourl¢fs.

5. The addition of tin likewife, after either of the falts feparately had thrown ;down all they were capalRle: of doing? a¢ca A freffi and cQmp}ete prxipiation; prourided :a little more of ti en- fcruum was dropt in, to eznable thew liquQr to a4; upon the metal.

Eompertgent 7* As gold ssS totall3r precipstati hy algalina it- bqt -

platina only in psrt; and as a mmute portion of plak tina, remaining diSolVda iinges a lfingty largt quaniy of the fluiXd Of a yelloNv colour; it was prefum'd,< that a rmall admixture of platina witii gGld might by t:his meens b; readuly dilble.

Afew



[ 657 ] A few drops-af a foluttwe of platma w there-

bre xed with above an hundred times the quantity of a folution d gold, the whole diluted with water and a pure alcalinefaltgraduallyadded as Iong as it siid any effervefeen-or -preaplta tion The remaining llquor was of fo deep a yelks nolour, that it was judged the platina would hasre Qovered ifilf though its pmportion llad been lefs than one thou* part of tit of X ^*

.

E 8* - - t Zxnc} which totally precipitates a}l the othe

known metallic bodies, put into a diluted folation of- platina was rery quickly afted ons and threw down a blackiffi calx. The liquer in good meaire preO firved its yellow colour; a markX that part of the

. *. ^ ^ . ^

P at:lna remalne£ ; tuipended. 2. Iron which precipitates all the metals from

their folutons, except XitlCX threw down a fimilr calx. It could not be judged by the eye, whether the prpitatl-on wa$ complete, the foludons of iron and platu}a nearly agreeing wldl one another mn cou l.oun .

3* Copper, the precipltant of mercuz and goIdfi readily threw down platina Sorn- its folution in form of a greyiih calx, which was bund- upon triAlv to re

tain a notabJe quantity of the copper. The liquor remaining after ihe platina had fallen was of a more dullQy green tin blutions of pure copper, prXbly fiQm ltS relw fome of & Satlnav

+ Mucllrya which precipitateS gold -alone *om soiua regia, pat into a diluted foluixon of platina} feemed in a little tsme to be divided} and did ne

4 0 run



[ 658 ]

run freely, Soon after, it appeared covered witb a greyilll mavter, which at firfl: was apprehended to be a precipitate} but was found afterwards to be a part ofthe mercury corroded. Upon applying a moderate heat, the whole of the quickfilver, the quantity of which was very confiderable, was difl olved, without any precipitation.

The experiment was repeated with a larger quantity of mercury than the folation was capable of taking up. The platina now gradually fell dowIl xmong the undifl"olved quickrllver, in form of a durk brownilh powder; leaving the liquar nearly colourlefs.

5. A folution of gold mingled aniformly with a folution of platina, without occafioning any turbid- nefs or precipitation. The mixture, diluted-with water, and fuffered to lland for fome time, threuw up a bright golden pellicle to the fur£icev

Encterxvment g. t. A follltion of p1at;na, fuper-iml?regnated witli

av much mencury as it was capable of taking up, a being evaporated a little, fo as to difpofe it to Ihoot, yielded cryRals not at all like thaIe dplatim, hat ir} ffiorm Qf f-picula, externally of a yellowiSh hue. ThefeX flightly waffied wah proof fpirite became colourlefs: Expofed to the fire, they emitted copious whit fumes, with a hifl:*mg Qr crackling noife; alld left a v&ry fmall quantity of a reddiSh powder.

2. A mixture of folutions of goid and platina, be_ ing treated in the fame manner, ruby coloured cry- flals were obtaineda which appeared to be chiefly gold, with very little Qf the platinaX

Rema?rkE



[ 659 ] Remark. It feems therefore, that mercury and gold

cryIlallize from their folutions before platina, leaving greatelE- part of that mineral difl*olved. This affair, particularly with regard to gold, deServes farther in quxry.

- - En¢perianent lo. As the calces of metalsX obtained by precipita

tion from acids or by other means) ritrify along with fritt or glaEsj and tinge them of various colours; and as this procefs is recommended bytfome for in- veRigating the nature of unknown metallic bodies; the following trials were made with precipitates of platina.

T. Half an ounce of a precipitate thrown down fromfolution of platina byplates of pure tin, was tritu- rated in an ir-Qn mortar with elght times its quantity of common white glaSs, the mixture put into a crucible, which was clofely luted, and placed in a wind furnace. The fire was gradually raifed, and kept up extremely Itrong for about ten hours; when, the crucible being taken out and broken, thematter appeared of a dark blackifh colour, untranfparent, eafily frigbte; interEperSed with a fbright whitifh matter, apparently metallic.

Remark. It is probable, that this metallic matter was the platina; and that the glaSs owed its opacity and dark colour, not to this mineral, but to the tin in the precipitate, fome particles of iron abraded from the mortar, or other accidental callfes.

2. A quarter of an ounce of a precipitate of plUa- tinaX made by alcaline falt, was ground in a giaSs mortar with twelve times its weight of white fafis; and committed to the fame fire as the foregoing. The

+ 0 2 refult



r 66o ] rit was s Ompaet, cloudy glafs, ett3r *mtparent ,! thial pieces, covered sn pa;rt wlth a thl--tx thielE cat Towards the upper part, and all round thes fidesfiwere obServed feareral p=iscles of metala thich appeted to the eye like bright platina} and praved hard to t:he point of a knife.

Remark hr does tlt gla -Ss here -feem to have teveived any thing from the platina- ; ie cAwnge be-- xng sxo der i than what white glafi is iend to m ^ d:ergo fr s -ight impregnatson w#h inflmable: m-ater. ;

G¢ntral PEevrs.^ It apwars from the experiments related in EhisF

paper,< that platma, ltke gold7 is not on by

the fmple acidsX which diSolve earery kn^n metal- Iic body lieEldes: That aqua regig, the folvents o£ gold, prove lkewife mRrua for platina. And ffia-t. confeqllmtly the common methods; of aSiyixig or purieing-gold by aq.uafortis,:... afua. rNzt, or the re_ gal cementr can no long$t be depended an: That lt diffiers fromA gold, in giving no Rain to the folid parts of animals, not Ilriking a purple colotlr with tm,, not being revivedo from its folutons by inflammable fpirsts, not being totally precipitable by alca;line falts ,, that in certain circumkances it throws out: gold *oma its folutions, that thefe properties afford means- of diIllnguiIBing a fmall proportion of gold mised w-tth a large one o f platina, or a-fmall proportion of plaw tina with a large one of gold; andt that platina con tains no gold, excepting the few particles diRingui^ ed by the eye: That platina is precipitated from its folutions by the vitriolic acidX and by the metallic fulRances, which precipitated gold, though fcarce

totally



[ 66I ]

totxtlly by sny And that its precipitates retiR vitri ication, and this perhaps in a more perfedc mantler tlsan precipitates of p ld it Self.

P A P E 1t III..

Read Junt THE -two fiormer papers have gi:ven - 27t 754- * ^ m account of the babitas Qr relation of phtinax tb the prsttipal fabftances, which ad up_ en metallic bodiesX and Ilaewn, that it ts- a fimple mehly of a par-ticulg ltind, eflintially din£t frotn all thofe hitherto knowxl thotagh poifl ed of fome ?roperies nerally fipofed peculiar to gold. bIany ef its ddtirShi &arder-s - have been already lpl-nted out: Qthers wili refult from combining it with the feveral metals; with each of which, not- withflc-anding its re6Rance to the moR intenfe fires by i;tSelf, or with unmetal-lic additions, it tnelts perfedly; 0ccaS0ning- remarkabie alterations in their cobur, texture, a,tl hardnefsW

A x r I c L E r PlatinaX e?ath Tin.

I. Equat pvres of platina and pure tin were in- EtBd into a mixture of black iax and common

ilt in Ilrong- fiifion; and urged with -a quick fire, tn a- good bla furrnacej - After a few minutes the thole appeared perfedy melted; and on being in- Mcantly-poured out, run fixly along a narrow mould,

forming a fmooth inpta nearly 0f the fame weight with the pl-atina and tin employedW The compound proved extremely- brlttle, breakmg eafxly Som a fall:

-- InterK



[662 ] Internally it appeared of a clofe and fmooth, though uneYen furface; and of a dark-grey colour. By the fle,, or a knife, it was readily fcraped into a blackSh duRv

2. 0XE part of platina and fwo of tin, covered with black flux, borax and common falt, were melted in a wind furnace : The platina appeared-perfeEtly taken up by the tin, foon afier the fire had been raifed eO a light white heat. The ingot was found deficient in weight about oneninetieth. It greatly refembled the foregoing, being only a little lefi brittle} and of a fornewhat lighter colour.

3. One ourlce of platina andfsue of tin,, covered with black flux and common falt, and urged with a quick fireX melted together without lofs. This com- pollnd yielded a little to gentle ltrokes of a flat hammer, but vras by no means toughb It broke in pieces from a rude blow, and was Rill readily fcraped into duR by a knife. The furface of the frafEure was rough and granulated

4. One part of platina and eight of tinX injeded xnto a fluid mixture of black flux and common falt, unitedg without lofsa into a pretty tough compound; which bore to be confiderably flattened under the hammer without breaking, cut fmooth with a tlwin chiIIel} and Ihaved wlth a knife. BrokenX it appeared of a rparkling, dark-coloured, coarSe-grained texture.

. One part of platina and twelve of tinw treated in the famc Dlaiiner fortned a mixture tolerably duc- tile ; but {till of a dull, dark hue, and a rough coarfe glair) thougll fonwewlwat leSs fo than the preceding.

6. A mixture of otle part of platina and twenty- r pf tin, proved not much Iqciffer than tin. The

colour



-

Speciiic Gravity. By Experiment. By Calculationi Diffetence,

I 7. ooo TO 827 12. 090 I. z63 8 975 X0 S3 I 48IF

i 7 794t 9. xx I 350 7* 7°S 8* 27 T 0 566

7* 6l3 7. 93so*322 7 487I 7 373 o Io2

[ 663 3

colour was svhiter, and the grain finer and earenera than thofe of the preceding corrrnIRtions; though in both reEpedcs it fell confide-ably ffiort of pure tirl.

7. Several of thefe compofitions, covered with black fluxt which had been previouIly melted, were expoSed, in crucibles cloSel)t Iuted, to a firolzg fire in a wirld furnace, which svas Readily kept up for eight hours. When taken out, they were all found to have fuflSered fome diminution, amounting to about one- fortieth of the tin. In appearance and qualityX there was no fenfible alteration, except that the misture feemed more uniform, and the grain a little ISner,

8. The remarkable gravity of platina induced us; to examine the Selreral mixtures hydroPratically. Here it was found, that the Epecific weight of the compound conItantly turned QUt lefs than the medium of the gravities of the two stlgredients; and generally the more fo, as the proportion of the platina was the greater.

Platitla Platina x, rln I Platina x, Tin 2 Platina Ix Tin + Platina x, Tin 8 Platina I, Tin IZ

Platina Tin 24

Tin s -

Remarks. It appears from the foregoing esperiZ ments, that platina melts with at leafl: equal its weight Qf iin: That it deRroys the malleability of

near



[ 664 near four times its welght: That wlth larger proportions it forms compounds tolerably dudtile, but renders the texture of the tin coarfer, and debafes its colour. The difference in colour of thefe compo- filti0ns was much lefs confpicuous on the touchtionea than when the fraftures of the Ingo-ts were examined; though) on clofe mEpedcion) they appeared all fenlibly duller md darler than pure tin and the- more i:o, in proportion as the platina prevailed. They all tartiiShed- in the air; thofe- leaR, whlch had a lrery ^zall or a very large proportion of platIna.

It is remarkable, that though tin is a metal very readily deItrlldible by fire, yet in moft of the preceding fifions, there was fcarce any fenfible lofs of weighe This is to be ateributed not folely to the admixture of the platina, but likewife to the flux made uSe of, and more particularly to the celeritJr and {hort continuance of the heat. In No 2 and 7, the only ones, in which the loSswas at all confiderable, the fire was {lowly raifeds and lFong contisued

A R T I C L E 2.

Platina owith Lvd

x. Equozlparts of platina andleadwereinjefted into a mixture of black flux and common falt, pre-

vioufly melted together and the fire ha{lily raiS-ed

by bellows. A much Itronger heat was requifite than for the fufion of platina with an equal quantity -of tirl o and the lofs svas confiderably greater, amounting to about one-fixty-fourth. The metal yielded difiicllltly to the file; broke, from a moderate blow, of a cloSe textures uneven furface, and xough jagged

edges:



[ 665 ] edges * The colour was rery dark, with a Sint pur pliffi caft.

2. One part of platina and two of lead, covered with borax and black flux, and expofed to a gradual fire, in a wind furnace, did not come into fiRfio.n till the fire had been raifed to a Itrong white heat From the continuaxlce of heat in this experimerst the lofs was greatX being ntarly one-twenty-fourth of the mlxture. lRhe ingot proved hard and brittles lile the pFeceding, but broke o£ a kriated furface.

3* One ounce of platlna and three of leadX treated in the fame mannerX required fiill a very Ilrong fire for thesr perfeft fuSon, and lok about one-twentyJ fixth The metal broke lefs eafily than either of the preceding, and in fome meafure yiclded b the hans mer: The colour was fomewhat darker, and inclined more to purplilla

4" OnQe part of platina and four of leada being courered with black flux and common lilt) and committed to a wind furnace, the platina was not per- feflcly taken up, till the fire had beers raifed to a con fiderably firong white heat: The 19{s was one-fior- tiethX The fame proportions of the metals, iweded into a fluid mjxture Qf the flux and falt} previouny brought to the above degree of heat} almoR inItantly melted, and loR only one-hundred-and-f1xtieth The ingot was much tougher than of the foregoing,, filed well} and cut tolerably fmooth with a knife. Upon breakingz the upper part appeared compoid of brlght plates, the lower of dark purplifh graias.

S One part of platina and exght of lead united eafily in a quick fire, and loR little or nothing. The snetal worked and looked like very bad lead- On

+ P breaking,



[ 666 ] breaking? the texture appeared partly compofed of tranfverfe fibres, and partly of grains; the colour dull and purplilh.

6. One part of platina and Zwet52e of lead unitedX without lofs, into a compound rery little different from the foregoing. Ori breaking3 its texture was fomeuvhat finer, and compofed chiciRy of fibres, with very few grains.

7. A mixture of one part of platina and fwenty- four of lead proved not very much barder than lead of a middling qualily. The colour was 1}s11 fomewhat purpliSh, and the texture fibrous; but the fibres were remarkably finer than where the platina was in larger proportion.

8. The foregoing compofitions, when newly po- liIMed, appeared in t,eneral of a dark iron coloul; which, upon expofure to the air, quickly tarnifhed to a browniSh yellow, a deep purpliffi, and at length a blackith. They all filed freely, without Ricki$g in the teeth of the file, as lead does by i£feif.

9. Upen returning thefe compounds to the fire a fecond time, it was conflcantly obServed, that after they had come into perfcEt fufion, if rlle hca-t was i[lackened a little, great part of the platina fubfi(Ied * Enat neverthe]efs, the lead decanted off, even in a }eat beiow igrlition, retained fo much of the platilla, as rendered it of a fiIle fi13r0us textureX and purpliih color.

The feveral mixturs, covered vvith black flllx} and kept in ltrong fufion, in crllcibles clo-Sely luted, for eight hours, fuffered a diminution in weight, amounting to about one-tSnirtieth of the lead. 0n breaksg, thefe with a large proportion of platina ap-

pearec}



[0 667-3 .

peared of a leafy, and thofe with a £mall=, of a fine fibrous textu-re,- which igmed in general to be cha- raESerillics af dic perEft union-of ffie platma al lead. Thezy all looked whiter and brighter- ian at at firflc, but tarnilhed fooner in the air. O{le mixture in particulara of bur ounces of platina and twelve of lead, broke into large, whlte bright,, {hiningX talv like flakes; which, on expofure to the air, changed in a little - time to a mddiha a purple, and a deep b1X; and at Egth turned ilowly to a dark blcliiSh colour. - Io. On examining theSe compounds-hydroRati_ cally, thelr gravities turned --out leSs than they ougM to have been according to their calculation, but not fo much lefi as thofe of the, compofitions of platina and tin,

j, . Sp¢ci'fic Gavity.

IBy I3xpriment. By Calcahi QDifirente. Platina -I7. Q00

Platina x Lead I I+. 029 I+. I93io. -X6+

Platina I, Lead 2 I 2* 92 S I3* - ^ S7 33 2

Platina I) Lead 4 I2* +O4 12. S09 O 105 Plai;ns I} lLead 8 II. g47 XZ oov -o o62 l:'latina I Lead : 1]:. 774r;I1*- 8I8-O 044 Platina IX Leadz4 tI 575 It. 61O 0* 035

Lead- 1X 386

* _ . ,

Ranark. It appe$rs, that a ftnall proportioqn of platina is taken up and kept fafpended by lead, in a very gentle heat, but that a larm yroportion is not taken up near fo eafily as by tin,- and if alnited by a Rrong fire, fubSides in part uporl its abatement A little quantit:y Rifins and hardens lead more than it

+ P 2 does



t 668 ] dQes tin g but a large etle does not near ro much diminifh its malleability. A leafiy or fibrous texturey a purplilb xlour or dirpofxtton to acquire this colour -in c w; are peculia; to ie tnitr wt*s lead

A R T t-C L E 3* Piadna with Silverv

e.- EgS pzS of platink and d pure- filver rs vied fiôm }kna n a, covered Wl b, and wrged with a firong fi* m Z blaffi ful-tlace, melted perfeftly together, and without loli;, be dsd not run *eely along the mould. ;The ingot was hard to the file, and broke from a ruder blow; though by gende -fl*kes it bore to -be conftderably llattened. Xnter_

nally it appeared of a mubh duller and iour

than flveo alld of a coarSer textureb

One part of plati-na and tw of Iilver, coarerect

with tiu and common faltX did not flovw thIn till the fire wts raiSed to a very Rrong white heat. The compound ptolred lefs brlttle than: ie foregoinga and not fo hard to ehe iRle: The texture was comw poSed of fmaller grains, and the colour whiter

3. One part of platina shd tbree of filver llill re quired a very firong fire for their perfeEt fufion . The metal was hard and brittle? though lefs fo ttin the precedsng Whens well and reatedly nwaled, it bore to be hamtacred, or flattened betwixt Ree} roll_ ers, into ehin plates.

4 One part of platina and J2uen of filver melte;d- together with eafie Thls compound hammered to-- lerably we!l, proved much harder dwan filver, and not fo whtte} or of fo-fine a grain

f. There



[ 669 ] 5. Thefe compofitions, wesghed hydroiTatrcily,

turned out like the others, a little lighter than by cal_ culation: But the diffierence, which betre 4Ccmcd to increaSe with the plattna, was here gcatell when the platiIla was in leafl: proportion.

-;

By Experimentt By Calculation. Difference. |

Platina I7. 000

- Platina TX Silver I I3 53S I3 99° °@ 55

Platina IX Silver 2 IZ- ............. 452 I}. 987 °e S35

Platina I, Ssllver 3.II. 79O I2. 485 o. 695 Platina I, Silver 7 lo. 867 II. 732 o. 86S

Silver -IO 980

Remark Platina appears to unite more difficultly with filver than with either of the for5going metals. WEven when tlie proportion of the platina is fmall, the greate{t part of it fubfides upon -an abatement of the heatX by which- the union had been eieEted. This was preverlted by pollring out the metal, when per- feEtly fluid, at one jet, into a broad; tuould; in which the compoundnbegun to congeal before the platina could feparate.

Platina diminifhes the malleability cif filver far lefs than that of tin or lead; and- does not, in Zwhatever proportion employed, fo mllch debafe its colour, or difpofe it to tarni& in the air.

A R r I C L E 4.

Platina with Gold.

I. Equal parts of platina and gold, expofed tc3 an intenfe fire, melted perfeEtly together, and rarx

thtn



[ 670 ] di-n snto a long mould, without lofs. The metal was of a white colour, hard to the file, broke from a rade blow, but when well nealed, yielded confiderably to the hammer

:. One part of platina and fosr of gold came in- to fuSlm in armo&erate ISte, but Ilill required a very firong one for thelr perEfl: union. This compound appeared but a little paler than Randard gold with filver alloy; arld proved fo tough, as to be beat, with proper care, into thin platess wthout breaking or cra;cking about thc edges. Oll melting it a fecond time with nitre and borax, ie became Yery pate, and was not without great difficulty made to recover its colou:r.

A R r I C L E .

Platina wtth Copper. . .

t. Etzl parts of platint and copper, expoted, witheat addkion, to a firong fire haltily excited by bellowS foon bemme fluid} but not thin; and loIl abollt on>xty-fiourth. The meal proved extremely hard o the file, broke Xfflcoltly on the anvfl > flew afunder on endeavouring to cut it with a chlfliel ; and appeared internally of a coarfe-grained te-xture and whitew colour.

2. One ounce of platina and twn of copperj urged with a quick fire in a blaI} filrna-w, wxthout addition} flowed fufiiciently thin, and- fcarce fuffered any fen flble loSs. The metal was llill very hard, and yielded but little to the hammerb It ltked darker coloured than the fbregoing, with a night reddiffi caIt.

3. One ounce of platina andJogr of copper, treated in the £ame manncrs arlited, wAhaut lofs, suto a;

- pretty



fw 67I 3

pretty bugh compound; which bore to be confiderably flattened, cut with a chiffiel, and bent almoR double before it cracked. Internally, it looked of a fine texture} andsa very pale copper colour.

4. A misture of owe ounce of platina and fi1ze of copper? flretched fomewhat more eafily under the hammer than the preceding; and appeared of a redder colour.

5. Upon illcreafing the copper to tight times the quantity of the platina, the compound proved fllffi- ciently tough, broke difflcultly, and harunzered well. lt was much harder than copper, and of a paler colour.

6. A mixture of one part of platina and twelve of copper was fomewhat more eaflly extended under the hammer than the foregoing and proved fofter to the file. 1t Iluck a little in the teeth of the file, ̂ rEsich the compofitions with a larger proportion of platint dld not.

7. A mixfure of one part of platina- and twentv- ve of copper was Rill a little paler coloured than pere copper, and confiderably harder and lliffer) thougll very malleable. Upon increaflng the coppPr a little farther, the mixture retained a degree of hardnefs, and appeared of a fine rofe tolour.

8. Upon weighing the foregoing compofltions hy dxollatically, the diminution of gravity was found more regular tl:wan in the mixtures with other metalsX being con{laxltly greater in proportion as the quantity of platina was larger.

Platina



4-- Br Experiment. 0 By Calculatiox Differenee. t 7@ 000 1 I. 400 I* 9I5 I. :lf I0. 410 I X Ss3 1. I43 9. 908 I 0. +64 ° SS6 99 6g3to 19l o-498 9. 30cs 9. 738 o. 438 9. 25I 9 4s8 0. 207 8 970 9 1+4 9. I 74

8. 830 l _

Platina = - Platina T, Copper- X Platina I, Copper 2 Platina I, Copper 4 Platina 1, Copper 5 Platina I, Copper 8 PIatinaI, Copper I2 Platins 1 > Copper 2s

Copper ^

Remar*. In the foregoing fufions, though in general no flux was made uSe off there was fcarce any fenfible lofs of weight, unlefs in N° I, where the large proportion of pla.ina required the fire to be raifed to a violent degree.. This feems.owing, in good meafure, to the platina preventing the korifi- cation of the copper: For .upon melting pure cot per a great number of times, both with and with out fluxes, there was coniCantly a little .lofs.

A fmall proportion of platina appears to improve the hardnefs of copper} without injuring its colour, or, fo far as could be judged, its malleability. The mixtures with a large proportion of platina are dif ficultly extended under tlle hammer when cold; and whilI red kot, fly in pieces. They all bear a good poliIhX and do not tarniAh in the air fo much, or fo loon, as pure copper.

A R T I C L E 6.

Platina uXith.Iron. Iron, -the 1aR of the metals in. point of fufibility,

was several times attempted to be-urOited with platina * ta

f 672 ]



- - [£73 ]- n i-ts fpi* mvalleable Rate. Bdt:as 1he es nb setlary X--t-rendering forgtd iron fiXf-ble-;oorroded the crucibles before Whe metal flowed tthanF cnough t diSolvcthe platina, pure caflc iron was fubftituted

I-. Caflc iron and platina, of each three ounces, pefed without ^ addltion; tb a flcrong fire, united into a thi£k- fldid, frhich, on adding an ounce more o£: iron, flowed thin. The compound filfEered X cooL in the -criscible (whiEh had le tooli;eR froln the heat t-admit of its- being pur*lf-Jiou4-

found, on breXking the stfl el? in -one lutnp- not con- vex, the--form; Wlch- ieZ iron- dually Jumes, bu-e of: a veryecon^cave /irfce.: The weight about one fixtieth lefs an iat of the meuls employed. It proved exly hard, Ib; as tiot to be -muched by the: file ; . and Ib tough, - as not to tbe brokse by repeat- ad blows i0-a fedehamtner, from-wdiidi itreceived fome- fliqnt EXeated red, it broke-effily and looked ially of an- uniform- textut, compoSed

not of plaths wlike Xe - firon at firflc, but of

very * dark+£o}our grains. '2.: One ounce of fiatina beit -i*d uptn four

£)f £aR lron beginning to melt,- and the -fire kept up llrow, the whovle came quickly into fufion,, and on cooling, formed an equable compound} which lik}- tlic fiormer proved -extremely- hard? and feemed to Aretch-aflittJe under ffie-great hammer without breaking The colour was Rill rery dai, though lefi fo than when the piaelna was win larger proportion

3. Oxe part of platina and ve of iron mUlted without difficult)rX and with little or no lofs.< This compound was ilill muchtharder than the Xn sat

firIl, and had a very confi1derable degree of towh 4 (t nefs.



- w t

.- 5pedfic Graviq. By Exgiment.l*By Calculation, Difference..

t7 oOQ 9- 9I7It. 3;43 . 426 8. Zoo 9. o80 o 38o 8. 2o2 8. 663 o. 46x 7. 800 7. 862 o o62 7* xoo

_

General

- [ 67*] nefs LAe the o*ers, k wuld -tat & ik-e whilft zold, withcu -eureme vfilenoc , it prwed very irlt- fle when-hezil-red.

+* lFie foregoing xmporions, e-fpecially thofie in which the prworti d pliatina wss large, -receisred a fine plida.; and did not ruk or tsrji*^ od bing uHad to she ;air in a dry room for flewral monis.

g. A unspoin of xe part d plaiixa and foar of >rea tras td tth - fu9m>t, iiich iprndux

notabl¢- aitions in irotl.- Strnded ve

murssieelmaZxg mmure (cip*d of d}wO bal_powds, =os, d tss d znmon 1 Rsl Ctd it e dtSe ied cruchE tfor tw1w hourss it gmed Rvinexat¢ df tît nisth oits

weigbt,, vlid .to ie-fIe-rwXre e§* at fir*>

iemi " +e no *&i&XPl Ehardnefi } bee if ted md>-5ut&ed it t, ai1 diicweri none of * quali- of 1}i A pxeco broke <oif Soxn e ixne i ttetted : the :Arte - manner, wit-h e poX* for f-iteniig caitiiron (tx2;* ine-a with a fmall proportion of charcoal)) was-found crwaid in weight aS7-ut me-thwt?tl, prved lefs ;hard to the file tha-n at firit, it ma^ harder aa the purt rwed wsth the cel*mak

* * xg stwe

P. . . . . . . latlaa -, .. Pla;tina-3, Iton -4 Platina 3> Iton 12 Plana 3, Iron x6

. . ,

rW atlna 3 lr 3t - Iro-t



[ 67S ] Gene-ral RenwrS.

Platina melts wlth equa itsS wri«t of each of the -metals; withone more readily than withanotherw With fome i£bemmes fluX, if the prworfon of the platins is not largeX in a xnoderate fire; but a lArong one i6 conflcantly requlfiite for its perfeEt folution. Compo&isons of lilver, wpper, leat, wii *out cxne- third their weight i platina, which had flowed thin enough to r freely idt thE mould, and appeard to the eye periedly mweds or^ bomg digeid in aqua fortis ttll tS menflcru seared to ad, Eft feveral grains <sf platina in their uigznd brm. Up0ti ViCW-

ag tlsefe wlth a rnlcrokope, fo e appeared to have fuflRered no alteration; others exhlbited an infinitc nun}ber of minute brig glilar pretuberases} as if tly-hail ju; began to mc}t.

Planna hadens and Riis all the-metaIs; one more than another, lead the mo*. b a mMerate quantity lt diminilhes, and in a large oae deSroysX the to+s of alt thE mall:able metals; but com manicates I8nae degree of this qualW to cd trom Tln bears much the leaR, and; gald and filver «G

great-eft quantity, without the lofs of thelr malleability..

A rery fmall proportion of platina fcarce injures the colour af wpper and gold A larr rmders both pale: A far 1efi qwntit has this cff upon copper than on gpld. 1t debafies and darkens, in AprDporton to its quasiys the blour of the white metals; that of sfilver mvKh the leaIt, and of lead the tnoPr. - St in good mealure preferves sron and copper from tar- niffiing in the air; fcaree alters gold or filver in this re>dl:; malies tin tarnifh foon, and lead vceeding

qutckly. _ _ .

4Q) P A P E R



t 6-76 ]

P A P E R -IV.

Phiina mixel wth Semi metals. I. itb Mercliry,

Read Jilly 4, IF A N ounce of platina and fix ounces

7544 of pure quickfilve-r were rubbed

together? with a little common falt and-water, - and a few drops of Epirit of falt, irl an iron mortar. Af- ter fome hours trituration, the grains of platina be_ came coated with tlie quickfilver, fo as to-cohere in- to an imperfe9cf amalggam. A part of the lquid quickfilver, poured o£,i md evaporated in an iron ladle; leEt a confideratle-quatltsty of a dark-coloured pow der, intermingEd with bright ffiining molecult: A part flcrained through leather, kft a fmkller prep=^- tion of a fimilhar powder.

The platina, which had been thus attenuated by ehe mercury, fo as to paSs with it through the pores of leather, proved as refra-dory in the fire as at firt Expofed to a very vehement heat, by itSelE, with bow ras) with whiee glafs, it neither meltedy or f;ta*ered any fenfible alteration; nor did it communicate any col:our t either of the fiuxes*-

z, One part of platina and abou:t fout Qf lead were melted perfeEtly together ; and after the heat had fomewhat abatt^, poured gently into three times the qua;ntity of quic-kfilver, heated So as to fiime. A blackiiE- powder was }mmediately thrown to the furface: This appeared to be chicfly platina. On grindw ing them togethera a frefl powder gradually feps rated; whlch, being OcaElally wafiied off, in ap-

pearance



[ 6770 ] pearance greatly refemb}ed the bregolng, but wu founds on proper trials, to participate much more largely of the mercury and lead than of plaiinaJ The amalgamX which was of a very dull colour, on ex- pofilre to the fire fwelled and leapt about, lhough the heat w-as foarce fufficient to evaporate ehe quick_ filver. After confiant and ,apid agitation with water, cBccafionally rnewed, in- an Lirron mill, for a week, it looked bright and uniform, and: fuffered the mercury to exhale freely. A dacoloured cals remained, which proved, upon examination to be platina, with a very little lead.

Remark. -Mercury is fuppoSed to have a; greaEr affinity with lead than any other metallic body, gold and lilver excepted. In this experiment, it had a greafter aflinity with platina than with lead, fince it retained moI} of the platina, after the lead, which was in much larger proportion, had been almoil intirely thrown out. The part of the platins, which the mercury reefted at firk arld that which it retained to ie la*, did not appear diffilmilar to one another, or diXerent sn quklity Som the platina employed.

3. A mixture of one part of pl?tina and tto- of gold, which proured very white and bnttle, af2:r being repeatAly nealed, was cautiouIly flattened into thin plates - and thrown red-hoe into boiling quickfilver - 0n trlturation and ablution with water, X powder fieptrated, coplouIly a-ti firR, and by degrees more fparmgly. After the procefs had been continued about tvwensy-iour hours-iere was nofartherfepara_ tion, except of a very little blackiih matter, into wllich a part of the cury is aiways chaaged in thefe

klnd;



[ 678 ] kt of operation; The algam, wbKh loolied very brW, left, upon tvaporation, * fpongy maEs of a high colour, which being melted, and poured hwo- an ingot, proved ttry f0PcX extremely malleable and in. all mEpe£ts reSembled the pure gold made ufe <9f; wxthout thc leaI} appearance of platilm.

Rer** lt is grearly to be ws{lleds that this me- thod of pursfying gold from platina may provefaft ficiexly accurate to exa£tly deter3nine the quantity of each n the mixtw The experiments hitherto 2nade do not fu-ffiir clear up this pOHlt; a geat number are Ilill neceSary before it can be ially aScero

. tatxc C :. EYith Bifimllth.

ual parts of platiba and bifimh, in3eEed into a mtxture of black flalx md common: fit, prevlonIly brouglu into fifim, a;nd urged wsth a qlisck firef Ilrongly exci-ted by bellows, melted perfedrly in a few minutesb and fuffered very little lofs Without thefe precauiionsJ the biEmuth collld fcarce be made to take up above one-ttlird its weight; great part of which, on an abatement of the heats fubElded.

,Nfistures of platina with different proportions of biEmath proved all, ltke the biEmuth itSelf extremely brittle: One was not r¢markably more fo than m- other. To the -filea they wtre fcarce harder thar pure- bifmuth. They broke of an xtregular furface, compofed chicfly of Ilria, with fome pla£es. When newly broken, they looked bright and lhparkling; except the^ compofiltions with a large proportion of platina, which were of a dull greyiffi col-our, without any brightsdsb Thty all tarniffied nowly in the

air,



[ 679 ] sir, -tc} a darI: yellowiffi, ptrpli-Sh or bluiE coIttlr Selreral acquired in part a fine deep blue, which has fuffered no change in above a twelve-month; fome parts of the maffies Rill remaining white as at firIt} md others incli-ning to parple.

3* Gith Zinc Upon an ourlce of platina, covered with borasy

and heated in a blaA furnace to a Arong white heat, was injeded an equal quantity of zinct A violent deflagration arofe, and the platins was almoR in- llantly diSolved: -The matter, immediately ptured out, was found to have loft near hal£ an ncet

Upotl feveral times repeating this experiment with different proportions of the twc) metals, both in a quick fire, and n one me gradu:aIly raifed in a wind furnaceX the sinc was conkantly found a powerful menlRnlum for platina, but fuffered great lofs from the heat requsiite fior rendering the mixture fllfficicntly fluld. When fo much of the sinc had been dsfl:^pted, that the remalnder amou: nted to no more than one-0Ourth of the platillaX the compound Itill contsuued fluid exlou;gh to rutl freely into a long mould.

Compofiltions of platina and ssnc differed little in appearance from sinc stSelf; except that where ehe qu.antity af plati-na was Iargey they were of & clofer texture, and a duller hue, with rather more of a bluiffi cakw They did not tarniffi, or thange their colour, on lbeing expofed for feveral months to the ail, in a dry room. They were harder to the i1c than the zinc at firficX allxl fell in pieces under tht

hammer;



* [68O] ..

hammer, wlthout at all flcretching; which pure sinc does in a conSiderable degree.

- +. ith Regulus of Antimony. Reglllus of antimony,- the moI} diEcultly fufible

of the femi-metals, diXolvedX in a llrong fire, equal its weight of platina. The compound looked of a. much duller colour than the regulus at firIt; and broke of a cloSe and uniform, though uneven, furface. It proved confiderably harder to the files but not remarkably more or lefs brittle.

On increafing the quantity of the regulus) the compound proved brighter, and of a leafy texture, little diffierent from that of the pure regulus.

Platina mized gvith Compound Metals. 1 Mth BraEs.

x. Equal parts of platina and braSs, coarered witk torax, and urged with a quick fire in a blaR furnace, melted perfidly together, and fcarce fuffered any lofs. The mixt was of a greyifll white colour, filed hard like- bell-metal, brolie from a blow of the hamw mer, without llretching or receiving any impreffi1onX

d flew afurlder on endeavouring to cut it with -a chiffiel. Internally, it appeared of an uniform fine grain, a clofE textures and a darker colour than on the outElde. It bore a very fine polilh, and did not tarnilh on beilog expofed to the air in a dry room for many months.

2. One part of platina and two of braSs, melted in a Ilow fire, loIt about one-thirty flxth. The in- wt was of a duller colour than the foregoing, with

a faint





[-68a ] 2. Phtina and copper, of each one ounce, and

four ounces of tin, melted perfeftly together, and without lofs. This compound filed freely and eaIily, bore to rDe cut with a knife, but broke readily on the anvil, of an irregular filice, and dull whitiXh colour. Polilhed3 it looked like poliShed iron. The fiadrure foon tarniShed to a yellow; the poliShed part grew dull, but retained its colour.

3. A mixture of platina and copper, of each one part, and; eight of tin, proved fo*er than the fore_ gping; -and bore to be -flattened a little under the hammer. It bro-ke of- a very irregular furface, compofed of a great number of bright white plates. The fraeture foon tarniffied; the poliihed part retained its colour.

Remark. It is obfervable, that in the firflc of thefe exwriments, -platina was perfeftly taken up by lefs than half its weight of a mixture of copper and tin; though it could ficarce be made to melt with lefs than its- own weight of either of them fepaxately, in a fire equally, or rather more, intenfe.

The- fpecific gravity of thefe mixtures turned out, upon- experiment, a little lefs than by calculation; though the copper and tin, melted together without platlna, formed a compound fpecifically heavier thars earen the copper by itSelf.

The feveral mixtures with zinc, biEmuth, regulus of antimony and- brafs, dwere likewife weighed hy_ droRatically, and found all fomewhat lighter than they ougls to have been by Sculation. As few hydroflat-ical experiments feem to have been made upon zinc Xarld bifmuth, it may be proper to mention,

that



t 683 3 that e gSaviqr of pure zinc turned out 7. °Sta ind that of biMmllth 9. 733*

Hitherto-we:hare confidered the mxfcibility of pla tina ;with metallic bodies, and the alterations, which different s of it produce in their appearance and qnalites: employing the-necefiry pre cautions for; preveniing the fcorification and diffipa- tion, which mol°c of the metals fuffer in the fire,

- and whiO fcyme remarkably pXnwte in thofe, which by them(Elves aremoredifl:}culdy, or not at all, de- lErudtible. We ffiall now examine the relson of platina, in this rcwt, to thofe metilic filblances, which are-the moff deSudtive.

I CYPel/gTiOn and Scoripton if Lead wx'tb - Platina.

I. A mixtlre of platina .ld lead wa% cupelled} -under a muffle, in an. aiayrnace. For ime time the procefs wmt on well; e lead gradual-ly chang- ing into Scoria, xwhich were row2s :of Dto e fides, -and abibrbed by the cupel} = diffilpated in filme In proporton X the lead workedi off, the matter required a kronger fire .to keep it ;fluid; and e lengthy colleEting into a dull flat lump, could no longa be made to flow in the grc degree; of heat, which the fiarnace was capaKe of pving. The :0lump broke very eaEly, appeared of a ddll grey colour both internally md externdlly, and-of a porous texture. - 1t weigbed abovt one-fE more dlaa the quantity of platins employed

2. Thss experiment was many times repe¢d- md raried: the lead ateempted > be worked off on Wneaffi, prefIid into the bcxttoms of crugiblesX r>

- - 4 R 2 fl - Si



[ 684 ] rifi:edsnaSy-crunibles,-by intenfe fixsj in a bbIt furnace, and blown off on teXts before de nofe d a bellovers, with the fame event; t}e platina not only perfe&ly refiRing the power of lead, which by thie operations deroys every other known metallic body, except gold and filver, but likewife retainmg and preventing the fcorification of a part of t}}e lead st- felf.

3. In the hifiory of the fufion of platina with lead, it has been obServed, that this metal depofites in a gentle heat great part owf the platina, which had been united with it by a Rrong one. As the part, which remained fufl?ended, might be prefumed to differ from that, which fubllded; a quantity of lead was decanted off from fireSh parcels of platina, and both tlae decanted metal and the refisduum fubmitted to the preceding operations feparately. The event was flill the fame; the tnatter becong confiRent, when ehe lead had been worked off to a certain point, and refufing faricr fcorification.

4. A mixture of platina and lead, which had been cupelled in an aSay-filrnace as long as it could be kept flllid) was expofed in a cruclble to a fire ve- hemently excited, bytitfelf, -with powdered charcoal, with black flux, borax, nitre, common falt. The matter neither melted, or fuffered any conrlderable alteration, becoming only fomewhat more porous; probably from a little of the lead haaring exfuded without the liquefaftion of ie maEs. The imme- diate contadc of burning fuel, agitated by bellows, - made fome of thefe mixtures flow, aSer they had refuSed to melt in veffiels- afted upon by intenSe fires. Very little of the lead was difl*lpated by this means.

S Upon



- - r 685 ] S Usn extmsng the cuzlled mXtters hydrs

llatically, thofe, which appeared moft fpongy, werc foursd nesrly as ponderous as the crude platina. Among the more compaft, thc gravity af one turned out I9.083,* of another sg.I36,andofa third I9.240

Resark. It appears from thd-e experiments, that platina, -}ike gold and filver, is intirely indeIlrudti_ ble by lead; that probably the pu-rer grainsX or frag_ ments, have fome heterogeneous admixtures, which are feparated in ehefe operations; and thata perfeEtly pure, it is more ponderous than gold, fitnce, when mixal with a confildcrable propcsrtion of a lighter metal, it fell very little 0Xhert of the gravity of pare gold. There is na reSon to fufpedr any increafe d its f-pecific gravit from the misture;: fince in all the eompfitions with plait hitherto examined, there uras conkantly a diminution of the fpecific gravit; wlsether the propoftion of the platina was large or fmall, the matter mclted wiih a quick fire, or kept xn fiXfion for many bours

6. A 0mittum of one ptf of platina and: three of gold was Xcupelled wi-th lad, ux}der a mufile. Thc matter drove well for a eonfiderable time; at length collefted into a bright hemifpherical lump, which by degrees became flatter, dulla and rough. The button oll being ig}wed, was fisund to retain a confiderable portion of lead.

The experint being repeated with a mixture of One part of plaiina and fix of gold, fome part of the lead was Prill retained. The bead proved rounder and brighter than the foregoing, and of a good golden colour on the outfide : It broke earlly under the ham- xner, -md appeared internally greyi: Some of the

frapents



[ 6-86] fragments hang'together by the outward golden coat.

7. Mixtures of platina and filver, fubmited to :cupellation, retained llkewife a confiderable quantity of the lead. Thefe, in becoming confiRent, formed, not an hemifpherical bead, but a flat maSs, very rough, and brittle, and of a dull grey colour both internally and externally.

2. Cupellation and Scorification of BiEmuth with Platina.

Mixtures of platins vfith biEmuth, a metallic fuS ilance, in fome ref&ts more adrive than lead, were cupelled under a muffle, fcorified in aflky-crucibles, teRed before the nofe of a bellows. In numerous repetitions of theSe - experiments, the event was the fame, as when lead was made uSe of The mixtures, which at firll flowed eafilly, became lefs and lefs fufible, in proportie}n as the biEmuth was driven off; and at length could not be kept fluid in atl intenfe white heat, though they appeared, on weighinz,, to retain a confiderable proportion of the biEmuth Nor could this Semi-metal, any more than lead, be iniirely feparated, by cupellation, from mixtures of platna with either gold or filver.

Platina cupel}ed with bifmuth, differed little in appearance from that, which had been treated in- the Iame manner with lead. The button was more fpongy, and fpecifically lighter.

3. Diatiog of Regulus of Antimony with PIatina. A mixture of platina and regulus of antimony was

melted, by a firong fires in a lhallow wide crucible, and



f 687 ] td the nofe of a bellowst direEted obliquely upon the furface. The nuatter continued to flow, and fume v:Opiouny, for- fome hours; at length became con- fiIlent in; an intenfe white heats and fcarce emitted any- more fumes, though flrongly blown on. The maEs, when grown cold, broke earlly, appeared very porous,- blebby, of - a dull grey colour, and weighed confiderably more than the- quantity of platina em- -ployed.

Platiiza was likewife treated with crude antimony; and the regulus, obtained from this mixture, diated as the foregoing, with the fame event; the platina not only rer1Ring the antimonial femi-metal, but likewife defending a part of it- from the aAioIl of dle fire sad sir, and refuIlng to melt, after a certain quantity had been diElpated.

4. Defagration of Zinc with Platina. A mixture of platina and sinc, expofed to a Rrong

iSre,-deflagrated, and appeared in violent agitationw trhEs continued bllt a little time; the matter quickly became Solid, axld could- no longer be made to flow; or the zinc, of which a confiderable proportion remained in it, to flame. The maSs was very brittlet dull-coloured, Epongy, and of no Epecific graviq.

General Rerks. This extraordinary mineral, on which the mol

aAive fluxes, ail{led by the moll intenSe fires, have no effeft, melts perfedsly with all the known metal lic bodies; unlefs arfenic, a fubRance impatient of a degree of heat fuicient to rellder itfelf fluid, isE an

eYcepiion. All t-he metals tale up equal their own weight;



[ 688 3 weig;ht s lbme metrllic compofihons mare m ttice tletr weight.

Platina appears xn general to ham no remarkable adinity with one metal more than with another. tIsead and iron, which do not mingle togetheB and of which tlie former will take up fome bodies from the latter, and the latter Some from the formerb feem both indifferent tQ platina; which, if combined either, is not feparated by the other

Nc-verthelefs fome fubXces haw greatr or lefs degrees of affinity with platlna than with other mv tallic bodies. Thus, from aqua regia, in certasn cz- cumfiances, it throws out gold; and is itSelf precipitated by the other metals, which difl*olve In that menilruum. From quicXlver it throws out lead; and is itSelf thrown out by gold.

The changqs, which platina occafiions Xn the per- fiedt metals, were examined in a former paper: Its effe#?cs on the femi-metals are lefs temarkable. The principal are, that it increafes the hardnefs of sincX and the antimonial femi-metal, but not of biEmuth , and difpoSes this latt to change its colour in the air} but not the others.

Its effieds on the compound metals are fimilar to thofe, which lt produces on the fimple ones. BraIO st rxenders white, hard, brittle, fuSceptible -of a fine poli and not liable to tarm& in the airs as it does the coppes; and in fome degree the sincX of which this 2netal is compofed. Mixtures of it with copper and tin are more apt to tarniffi than with copper onlye and lefis than with tin only.

All metallic fubIlances} except gold, are exeded firom platlna w the fimple acids ̂ Mercu is ehe only

* on



[ 689 ] one feparable by fire. The platina remtining aftcr the feparaiion of the metals, prwes unfufible as at fid

Platina perfeflly refiflcs the deiRruEtive power of lead and biEmu*, and ie rapacsous antimonial femi- metal; which laik has been hitherto eReemed the feverck teflc of gold, fo as to have received the appet- lain of balneum folius J olis, ffie bath which gold alone can fuRain, and in which it is waffied fromall kinds of impuriites.

Since therefore platina mixed wiF gold is not dil*- coverable by any of the operations by which thae metal is ufually affiayed or refined, or by the hydro- Ilaiic balance; we hope that thefe papers, which contain part of the hifcory of thi8 extraordinary and hitherto unknown mineral, and the methods of dif- tinguiShing any fophiRicaiions of gold made by its means, which might otherwife have pafled undif- covered, will be canflidly received by this illuRrious body, as a means of promoting that kind of know- lege, for which the Royal Society has been ever eminent, and peculiarly inIlstuted.

EXXXVII.



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Experimental Examination of a White Metallic Substance Said to be Found in the Gold Mines of the...

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