626 
PLATINUM. 
improved and Amplified, it ftill requires from the opera¬ 
tor a certain degree of dexterity and experience. 
Before we defcribe the improved procefsin queftion, it 
may be proper to notice the earlier and lefs fuccefsful at¬ 
tempts, which were made for the confolidation of plati¬ 
num. It had been difcovered that arfenic readily uni¬ 
ted with platinum, and formed with it an alloy of great 
fufibility. An alloy, therefore, was made of crude plati¬ 
num and arfenic ; and the latter metal, being eafily vola¬ 
tilized, was driven olf by heat; whilft the iron, being 
oxydated during the procefs, was alfo feparated from the 
mafs ; fo that the platinum was left in an impure, but 
malleable, ftate. This mode of confolidation of the crude 
ore by means of arfenic, firft propofed by Achard and 
others, was brought to a great degree of improvement 
by Jeannetty, a working filverfmith of Paris ; (Ann. de 
China, vol. xiv.) and utenfils of platinum were procured 
by his method at a reafonable price. But the platinum 
fo prepared was far from being pure; for it had a lower 
fpecific gravity, and ftill contained fmall portions of arfe¬ 
nic, iron, lead, copper, befides the four new metals above 
mentioned; and it did not, therefore, pofiefs in a fuffi- 
cient degree thofe qualities which render platinum fo ufe- 
ful for its various purpofes. 
The late improvements in the procefs confift principally 
in obtaining the platinum, not immediately from the 
crude ore, but from the ammoniaco-muriate, the acid by 
means of which it had been feparated from the other me¬ 
tals. By applying heat to this fait, the muriated ammo¬ 
nia is gradually expelled, and the metal paffes to the ftate 
of a fpongy mafs, which, by patient and repeated heating 
and hammering in a ftrong mould, is at laft brought to 
a malleable ftate. Count Mouftin Poufchkin was, we 
believe, the firft perfon who propofed to prepare platinum 
from the ammoniaco-muriate (Nicholfon’s Journal, vol. 
ix.) but he ufed mercury in the procefs. An amalgam 
was formed with the fpongy mafs above defcribed; and 
by fucceflively heating and hammering this amalgam, the 
mercury was driven off, and the metal was confiolidated 
into a malleable mafs. This method was afterwards far¬ 
ther Amplified by other chemifts, the intervention of mer¬ 
cury being altogether difpenfed with. One of the ear- 
lieft accounts of this laft improvement was publifhed by 
Mr. Knight; (Phil. Mag. vol. vi. 1800.) but the moft 
perfeff defcription of this mode of working platinum, is 
that given by Mr. Cock, in Aikin’s Dictionary of Che- 
rniftry and Mineralogy, vol. ii. as follows. “ The plati¬ 
num being difl'olved in nitro-muriatic acid, the liquor is 
to be filtered through clean white fand, in order to f'epa- 
rate the black powder which floats among it. . The clear 
folution being then decompofed by fal-ammoniac, the 
yellow precipitate is to be collefled, waftied in warm wa¬ 
ter and dried. It is then to be diftributed into faucers, 
which are placed in a fmall oven conftru&ed lor the pur- 
pofe, where they are expofed for a fhort time to a low red 
heat, in order to bring the platinum to the metallic ftate, 
and drive off by fublimation the greater part of the mu¬ 
riated ammonia. When withdrawn, it is a fpongy rpafs 
of a grey colour. About half an ounce of the platinum 
in this ftate is to be put into a ftrong iron mould, about 
inches long by wide, and is to be compreffed as 
forcibly as poffible, by ftriking with a mallet upon a 
wooden peftle, cut lo as accurately to fit the mould : ano¬ 
ther half-ounce is then added, and treated in the fame 
manner ; and fo on, till fix ounces have been forced into 
the mould. A loofe iron cover, juft capable of Aiding 
down the mould, is then laid upon the platinum ; and, by 
means of a ftrong fcrew-prefs, almoft every particle of 
air is forced out from the platinum. This is a part of 
the procefs that requires elpecial care; for if any mate¬ 
rial quantity of air is left in the mafs, the bar into which 
it is formed is very apt, in the fubfequent operation, to 
fcale and to be full of flaws. The preffure being duly 
made, the mould is to be taken to pieces, and the plati¬ 
num will be found in the form of a denfe compaft paral- 
lelopiped. It is now' to be placed in acharcoal forge fire, and 
heated to the moft intenfe w’hite heat, in order completely 
to drive off the remaining ammoniacal muriate. This be¬ 
ing done, it is to be quickly placed on a clear bright an¬ 
vil, and gently hammered in every direction with a clean 
hammer. This is to be repeated feveral times, at the end 
of which the mafs will be perfectly compaft, and fit to 
be laminated or wrought in any other manner that the 
artift choofes. It is to be obferved, that while the plati¬ 
num is heating, it muft lie loofe in the fire; for if it were 
held by the tongs, they would infallibly become welded 
to the platinum, and thus greatly damage it. By the 
time that the platinum is thus drawn down to a compadf 
bar, it will be covered by a fomewhat reddilh femi-vitre- 
ous cruft, proceeding chiefly from particles of the afhes 
melted down upon it, and extended over its furface by 
the hammer. To remove this, the bar, being made red- 
hot, is to be fprinkled over with pulverized glafs of borax, 
and then kept for a few minutes at a white heat. When 
moderately cool it is to be plunged into dilute muriatic 
acid, by which the borax and other vitreous matter will 
be diffolved, leaving the platinum with a perfectly clean 
white furface.” 
A new method of purifying platinum was difcovered 
in 1816 by the Marquis of Ridolfi, calculated to diminifh 
the price of that moft ufeful metal. He firft feparates 
from the crude platinum fome of the extraneous fub- 
ftances ufualiy mixed with it, and wafhes the remainder 
with nitro-muriatic acid diluted with four times its 
weight of water. He then melts it with half its weight 
of pure lead, throws it into cold water, and thus obtains 
an alloy which he pulverizes, mixes with an equal portion 
of fulphur, and throws into a white hot Heflian crucible; 
covers the crucible inftantly, and keeps it in an intenfe 
heat for ten minutes. When cold, a brittle metallic but¬ 
ton, compofed of platinum, lead, and fulphur, is found 
beneath the fcoria. This button he fufes with a fmall 
addition of lead: the fulphur feparates itfelf with frefti 
fcoria, and there remains only an alloy of platinum and 
lead. This alloy he heats to whitenefs, and in that ftate 
beats it with a hot hammer on a hot anvil, which forces 
out the lead in fufion. If the alloy be not a white heat 
when beat, it will break. The platinum thus obtained 
is duflile, malleable, and as tenacious as that obtained 
from the ammoniacal muriate. 
Some fhort time after this, adifcovery was made by Dr. 
Sir H. Davy, (now prefident of the Royal Society,) by 
means of which he produced a lamp to burn without flame. 
It was found by this gentleman, that a fine platinum- 
wire, heated red-hot, and held in the vapour of ether, 
would continue ignited for fome time; and it was after¬ 
wards afcertained, that, if a cylindrical coil of thin pla¬ 
tinum-wire were placed, part of it round the cotton wick 
of a fpirit-lamp, and part of it above the wick, and the 
lamp be lighted fo as to heat the wire to rednefs ; on the 
flame being blown out, the vapour of the alcohol would 
keep the upper part of the wire red hot for any length of 
time, according to the fupply of alcohol, and with little 
expenditure thereof, fo as to be in conftant readinefs to 
kindle German fungus, or paper prepared with nitre; 
and by this means to light a fulphur match, &c. at plea- 
fure. This lamp, whilft it affords a fufffeient light to 
fhow the hour of the night by a watch, or even to read, 
and to perform many other ufeful fervices, does not hin¬ 
der the repofe of perfons unaccuftomed to keep a light 
burning in their bed-room ; and from its preferving an 
uniform heat, and not requiring to be fnuffed, as other 
lamps do, may proven valuable acquifition to the chemift 
in performing experiments on a minute fcale, where a 
long continuance of a gentle heat is defirable. 
The proper fize of the platinum-wire is the i-iooth 
part of an inch ; a larger fize will only yield a dull red 
light ; and a fmalier one is difficult to ufe. About 
twelve turns of the wire will be iufficient, coiled round 
any cylindrical body, fuited to the fize of the wick of the 
2 lamp 5 
