CHEMISTRY. 
feveral pieces; the latter, examined more narrowly, ap¬ 
pear to be hollow, and particles of iron and a white pow¬ 
der has been found within them. The property of being 
attracted by the magnet, which thefe grains pofiefs, though 
accurately leparated from the ferruginous fand they con¬ 
tain, mull doubtlefs be attributed to a portion of iron con¬ 
tained within them. The liardnefs of this metal nearly ap¬ 
proaches to that of iron ; the fpecific gravity of platina, 
mixed with all the foreign matters we have fpoken. of, 
nearly approaches to that, of gold; it lofes in water be¬ 
tween one-fixteenth and one-eighth of its weight. Buf- 
fon and Tillet compared together an equal volume of 
platina, and of gold reduced into particles fitnilar to thofe 
of the platina, and found that the fpecific gravity of the 
former was about one-twelfth lefs than the gold. Late 
experiments have (hewn, that platina exceeds gold in 
weight, when it has been purified by a long fufion. 
It is not probable that platina exifts in its ores in the 
fame form as is comes to us, but that its granular or 
plated figure is produced by the motion of the waters by 
which it is carried from the mountains to the plains : 
that found in the largeft grains, or lumps, is molt valu¬ 
able. It has been fometimes found in mafles of confider- 
able magnitude; the fociety of Bil’cay pofiefs one of the 
fize of a pigeon’s egg. As it is found in the neighbour¬ 
hood of gold mines, it is always mixed with a quantity 
of this metal. The mercury it contains is part of that 
ufed in extracting the gold. The firft perfon who paid 
any particular attention to platina, was a Spanifh mathe¬ 
matician, Don Antonio Ulloa, who accompanied the 
French academicians in the celebrated expedition to Pe¬ 
ru, for determining the figure of the earth. This phi - 
lofopher gives a curfory account of it in the relation of 
his voyage, publifhed at Madrid in 174-8. Charles Wood, 
an Erigllfh metallurgifl, brought a quantity of this me¬ 
tal from Jamaica in 1741, which he afterwards examin¬ 
ed, and gave an account of his experiments in the Phi- 
lolbphic.il Tranladtions for 1749 and 1750: at this era, 
the greateft chemifts in Europe appeared emulous in their 
inquiries refpeiting this new metal, which promifed, by 
its lingular properties, fuch confiderable advantages. 
Scheffer, a Swedilh cheniilt, publifhed his experiments 
on platina in the Memoirs of the Academy of Stock¬ 
holm, in 1752. Dr. Lewis made a connected and almolt 
complete feries of experiments on this metal, which may 
be found’ in the Philofophical TranfaCtions for 1754. 
Margraaf has inferted in the Memoirs of the Academy 
of Berlin for 1757, an account of his experiments on this 
new metal. Moll of thefe memoirs were collected by 
Morin, in a work entitled La Platina, I'or blanc, ou le hui- 
tictne Metal, Paris, 1758. At the fame time Macquer and 
Beanme made, in conjunction, a great number of impor¬ 
tant experiments on platina, which were publilhed in the 
Memoirs of the Academy for 1758. The fcarcity of pla¬ 
tina, and the difficulties attending the experiments made 
on it, Hopped for a time the progrefs of inquiries, but 
within the lalt few years they have been relumed with 
new fpirit. Bergman,bAchard, and Morveau, have ex¬ 
erted thcmfelves in the examination of the properties of 
this metal., Guyton has lately publilhed remarks on the 
gangue of this metal 5 he found fome grains adhering to 
feld-fpar, which makes it to be prefumed, that the pla¬ 
tina had been loofened by a flood, and warned down as 
an auriferous land. 
Platina may be obtained in plates and in wire, and 
may be worked like gold and fiiver. There are feveral 
ways of purifying this metal: r. By the magnet, which 
ieparates the iron. 2. By walhing, which carries off the 
land. 3. By acids. 1 he methods molt ufually employed 
to make it pure and malleable, are as follow : i.Take 
equal parts of crude platina, oxyd of arfenic, and acidu¬ 
lated tartrit of potalh, or potalh only. Put the mixture 
into a well-luted crucible, and expoi’e it for an-hour to 
a violent heat; the platina melts; but it. is brittle, fra¬ 
gile, and whiter than ordinary; expofe it to a ftrong 
Vol. IV. No. 199, 
3 *7 
heat under the~mufiie, by which means all the arfenic i s 
driven oil', and the platina remains pure. 2. Take three 
parts of platina, fix of oxyd of arfenic, and two of pure 
potalh : throw the mixture into a crucible in feveral 
parcels, or by degrees, to promote the oxydation of the 
iron. Then melt in crucibles with very flat bottoms, 
that the button may be very thin: thus you have the 
arfenical alloy. Put the button under the cupel, and 
heat for thirty hours, to volatilize the arfenic. The ope¬ 
ration muff be performed with great care and addrefs £ 
if the fire be .too ftrong, it is often neceffary to begin 
afrefli: the degree of heat fliould be juft fufficient to vo¬ 
latilize the arfenic without meiting the metals ; a begin¬ 
ning of fufion makes the arfenic adhere, fo that it can¬ 
not be driven off. The refult of this operation is platina 
in the fpongeous form. To render it malleable, give it 
a red heat, put it on an anvil, and give it one good ftrolce 
with a hammer; one fteady ftroke will be fufficient, as a 
fecond might make it fly. Then give it a white heat, 
after-which about fourfeore ftrokes with a heavy ham¬ 
mer will make it malleable. Veflels are advantageoufiy 
formed of platina, by pouring a mixture of arfenic and 
platina into moulds of clay, and expofing the moulds to 
a heat fufficient to diffipate the arfenic. 
. Guyton f'ubftituted the arfeniat of potafh to the oxyd 
of arfenic. The fame chemift likewife fucceeded in melt¬ 
ing platina in the wind-furnace deferibed by Macquer, 
by means of bis own reducing flux, compol'ed of eight 
parts of pounded glafs, one part of calcined borax, and 
half a part of charcoal in powder. Small portions alone, 
and without addition, are now very eafily melted, by 
heating them on a lighted charcoal, with a ftream of vi¬ 
tal air; but thefe fmall ductile globules cannot be applied 
to any ufe, on account of their inconfiderable fize. The 
platina, when pure, is nearly of the colour of fiiver. lir 
refifts a very ftrong heat, but is oxydified by the electric 
Ipark. 
Phofphorus combines eafily with platina: Mix equal 
parts of platina and phofphoric glafs with one-eighth of 
charcoal; put them into a crucible, and fprinkle over a 
little charcoal-duft; give a heat nearly fufficient to melt 
gold, and continue it for an hour; break the crucible, 
and underneath a blackifh glafs will be found a little 
white filvery button, the lower furface of which prefents 
cubic cryftals. The platina thus alloyed with phofpho¬ 
rus is very brittle, and pretty, ftriking fire with flint, and 
has no magnetic property ; when expofed to a fire ftrong 
enough to hold it in fufion, the phofphorus quits it, and 
burns at the furface. Thefimple acids have no aftion upon 
this phofphuie; but the nitro-muriatic acid decompofes 
it, forming a phofphat of platina. A mixture of phof- 
phorated platina, and fuper-oxygenated muriat of pot¬ 
afh, thrown into a red-hot crucible, produce a ftrong de¬ 
tonation ; the platina remains in the crucible. The fame 
effedl takes place when phofphorated platina is thrown 
upon melted nitre. Another way of obtaining phofphure, 
of platina, is by giving it a ftrong red heat; then throw¬ 
ing in a piece of phofphorus, and ftirring it with an iron 
rod,-the combination takes place. Sulphur combines 
all'o with platina. This metal is foiuble in the alkaline 
fulphures, though only in fmall quantities. 
Platina does not unite with all metallic fiihftances. 
This metal unites very well with bifmuth, which renders 
it fo much the more fufible, as the quantity of the latter 
is greater; the alloy is brittle, and becomes yellow, pur¬ 
ple, and blackifh in the air. This mixed metal cannot 
be cupelled without the greateft difficulty, and never 
forms a mafs of any confiderable duitility. It fufes rea¬ 
dily with twenty parts of antimony, and produces a 
brittle metal of a plated texture, from which the anti¬ 
mony may be leparated by the action of fire, though not 
io completely, but that the platina always retains a fuf¬ 
ficient quantity to render it defective in weight and duc¬ 
tility. Zink renders platina very fufible, and combines 
readily with it, aififted by a little borax; this alloy is 
4 M brittle. 
