31B C H E M I 
brittle, and difficult to file; its colour is bluiffi. When 
the platina is molt abundant, thefe two metallic fub¬ 
ftances are feparated by the aftion of fire, which vblati- 
lizes the zink, though the platina always retains a fmall 
portion. 
Platina docs not unite with mercury, though triturated 
for''federal hours with that metallic fluid. It is likewi'fe 
known, that platina refifts the mercury ufed in America 
td feparate the gold. Mdny intermediums, fuch as wa¬ 
ter, ufed by Lewis and Beau me, and nitro-muriatic acid 
by Scheffer, have not been found to facilitate the union 
Of thefe two metals. In this refpeft platina appears to 
refemble iron, to wbofe colour and hardnefs it likewife 
in fome refpefts approaches. 
Platina mixes very ealily with tin, and forms a very 
fufible and fluid alloy. It is brittle, fo as even to break 
by a fall, when the two metals are united in equal por¬ 
tions. When the tin is in the proportion of twelve or 
more to one of platina, the mixture is confiderably duc¬ 
tile, but its grain is coarfe, and it becomes yellow in the 
air. Platina remarkably diminifhes the duftiiity of tin, 
and the alloy does not promile to be of any ufe ; yet, 
when it is well polilhed, it may remain long expofed to 
the air without alteration. It feems that Lewis, to whom 
we are indebted for moft of the knowledge we poffefs re- 
fpefting the alloys of platina, fucceeded in oxydating this 
metal, and dilTolving it in the muriatic acid by means 
of tin. 
Lead and platina unite very well by fufion; but they 
require a llronger heat than the laft-mentioned alloy. 
Platina deprives lead of its duftiiity; the combination 
of thefe two metals ds of a purplifh colour, and brittle, 
according to the proportion of platina, ftriated and gra¬ 
nulated in its fracture, and quickly changes by expofure 
to air. Cupellation with lead was one of the firft and 
raoft important experiments attempted to be made with 
platina, becaufe this operation was expefted to deprive 
it of the foreign metallic fubftances it might contain. 
Lewis, and feveral other chemifts, have in vain attempt¬ 
ed to cupel platina in the ordinary cupelling furnaces, 
though they applied a moft violent heat. The. vitrifica¬ 
tion and abforption of the lead takes place as ufual at the 
commencement of the procefs, on account of the. excels 
of that metal; but the platina foon becomes fixed, and 
the operation is at an end. The metal remains united 
with a portion of the lead, and is not at all duftile. 
Macquer and. Baume fucceeded in the perfect cupellation 
of platina, by expofing an ounce of the metal, and two 
ouncesof lead, in the hottest part of the porcelain furnace 
at Seves. The wood-fire lefts for fifty hours fucceffively ; 
at the end of this time the platina was found flattened on 
the cupel; its upper furface was dull and rough, and 
eafily l'eparated ; its under furface was brilliant, and, 
what is the moft valuable, it was eafily extended under 
the hammer. Thefe chemifts were convinced, by every 
p'oflible method, that the platina did not contain lead, 
but was very pure. Morveau likewife fucceeded in cu¬ 
pelling a mixture of one drachm of platina, and two 
drachms of lead, in the wind-furnace of Macquer: this' 
operation, made at four fuccefiive times, lafted eleven or 
twelve hours. Morveau obtained a button of platina, 
not adhering to the cupel, uniform, of a colour refetn- 
bling tin, but rather rough, which weighed exaftly one 
drachm, and was found to be not at all afted on by the 
magnet. This procefs appears to be excellently adapted 
for obtaining platina in plates or laminae, which may be 
forged, and confe’quently may be employed in making 
various utenfils of great value, with refpeft to hardnefs 
and unchangeablenels. Baume has likewife obferved an¬ 
other very ufefu-1 property, viz. that of wielding and 
forging together, like iron, without the afliftance of any 
other metal. After having.'heated two pieces of platina 
to whitenefs, which had been cupelled in the furnace of 
Seves, he placed them one on the other, and linking 
them biilkly with the hammer, they welded together as 
a 
S T R Y. 
quickly and firmly as two pieces of iron would have done.. 
The great importance of this experiment, with refpeft to« 
the arts, need not to be infilled on. 
Macquer could not obtain an alloy wilh forged iron 
and platina : this mixed metal would polfefs the great 
advantage of uniting the hardnefs of fteel wi'h a eoniider-- 
able dudrility, or at leaft it would not be brittle like fteel. 
Dr. Lewis melted a mixture of call iron and platina; the 
alloy was fo hard as not to be touched by the file; it had 
a High t degree of duftiiity, but broke fliort when ignited. 
Platina communicates hardnefs to copper, with which- 
it melts with 1 confiderable facility: this alloy is dudlile, 
when the dofe of copper is three or four times greater 
than that of platina; it is capable of taking the meft 
beautiful polifh, and was not tarniflred in the air during 
the fpace' of ten years. Platina partly deftroys the duc¬ 
tility of (liver, augments its hardnefs, and impairs its co¬ 
lour. This mixture is very difficult to fufe; by fufion 
and reft the two metals are feparated. Lewis obferved, 
that filver melted with platina was thrown up againft the 
fides of a crucible with a kind of exploiion; a property 
which appears to belong to filver alone ; for Darcet has 
obferved that this metal breaks balls of porcelain, in 
which it is enclofed, and is thrown out by the aftion of 
the fire. 
Platina does not readily combine with gold, but 
by the help of a very llrong fire. It greatly alters the 
colour of platina, unlefs its quantity be very fmall; thus, 
for example, a forty-feventli part of platina, and all the 
proportions below that, do not greatly change the colour 
of gold. Platina does not much impair the duftiiity of 
gold, which is lels affefted than any other metal by 
the admixture. The fpecific gravity of platina being fu- 
perior to that of gold, might give rile'tb frauds ; and for 
this reafon the Spanifli miniftry have prohibited its ex¬ 
portation : however, flnce chemifti-y has difeovered me¬ 
thods for diftinguifhing the alloy of gold with- platina, 
and even of platina alloyed with gold,' thefe fears ought 
no longer to be attended to ; and it is much to be defired 
that platina may no longer be prohibited, but that this 
new metal, which promiles fuch confiderable advantages 
to fociety, may become an article of commerce. The 
folution of ammoniacal muriat, as we have obferved, has 
the property of precipitating platina,; if, therefore, gold 
be f'ufpefted to be alloyed with platina, its folution in 
aqua regia may be afi'ayed with a folution of ammoniacal 
muriat. The fmall quantity of platina. it contains will 
occafion an orange or reddifh precipitate ; if no precipi¬ 
tate is thrown down, the gold does not contain platina. 
If it fhouid happen that the valuable properties of platina 
Ihould at Icme future time render it more fcarce and va¬ 
luable than gold, it will not be in the power of avarice 
to deceive us in alloying it with gold, fince a folution of 
fulphat of iron, which has the property of precipitating 
the folution of gold without producing any change in 
that of platina, would immediately expefe the deception. 
A piece of tin, plunged in a folution of plgtina alloyed 
with gold, would likewife fhew the prefence of the latter, 
by becoming covered with a purple precipitate ; whereas 
platina gives only a dirty brown precipitate, of a reddifti 
colour : this laft precipitate likewife does not colour glafs, 
whereas the precipitate of gold gives it a purple colour. 
This metal is not altered by water, earthy matters, the 
faiino-terreftrial fubftances, or by alkalis. The moft con¬ 
centrated fulphuric acid, and the ftrongeft and moft 
fuming nitric and muriatic acids, do not aft on platina, 
even when boiling; neither is diltiliation, which is known 
to be fo efficacious in promoting the aftion of acids on 
metallic fubftances, of any advantage in the prefent cafe. 
The fulphuric acid,(imply tarnifhes the grains of platina, 
according to Lewis and Baume ; the nitric acid, on the 
contrary, renders them brittle. Margraaf affirms, that 
towards the end of the diftillation of tuis acid from pla¬ 
tina, he obtained a fmall quantity of arfenic, a pheno¬ 
menon not obferved by other chemifts. The muriatic 
acid 
