"I. Having put a drachm of platina, in a cupel, into a furnace, I
kept up the fire two hours, when the covers sunk down, the supporters
having run, nevertheless the platina was only agglutinated; it stuck to
the cupel, and had left spots of a rusty colour. The platina was then
tarnished, even a little black, and had only augmented a quarter of a
grain in weight; a quantity very small in comparison with that which
other chemists have observed. What surprised me still more was, that
this drachm of platina, as well as that I used for other experiments,
had been successively carried away by the loadstone, and made a
portion of 6/7 of eight ounces, of which the Comte de Buffon has before
spoken.
"II. Half a drachm of the same platina, exposed to the same fire in a
cupel, was also agglutinated; I adhered to the cupel, on which it had
left spots of a rusty colour; the augmentation of weight was found to
be nearly in the same proportion, and the surface as black.
"III. I put this half drachm into a new cupel, but instead of a cover I
placed over it a leaden crucible. This I kept in the most extreme heat
for four hours; when it was cooled I found the crucible soldered to the
support, and having broken it I perceived that nothing had penetrated
into the internal part of the crucible, which appeared to be only more
glossy than before. The cupel had preserved its form and position; it
was a little cracked, but not enough to admit of any penetration; the
platina was also not adherent to it, though agglutinated, but in a much
more intimate manner than in the first experiments; the grains were
less angular, the colour more clear, and the brilliancy more metallic.
But what was the most remarkable during the operation, there issued
from its surface, probably in the first moments of its refrigeration,
three drops of water, one of which, that arose perfectly spherical,
was carried up on a small pedicle of the vitreous and transparent
matter. It was of an uniform colour, with a slight tint of red, which
did not deprive it of any transparency; the smallest of the other two
drops had likewise a pedicle, and the other none, but was only attached
to the platina by its external surface.
"IV. I endeavoured to assay the platina, and for that intent put a
drachm of the grains taken up by the loadstone into a cupel, with two
drachms of lead. After having kept up a very strong fire for two hours,
I found an adherent button, covered with a yellowish and spungeous
crust of two drachms twelve grains weight, which announces that the
platina had retained one drachm twelve grains of lead. I put this
button into another cupel in the same furnace, observing to turn it, by
which it only lost twelve grains in two hours; its colour and form were
very little changed. The same piece of platina was put into Macquer's
furnace, and a fire kept up for three hours, when I was obliged to take
it out, because the bricks began to run. The platina was become more
metallic, but it, nevertheless, adhered to the cupel, and this time
it lost 34 grains. I threw it into the fuming nitrous acid to assay
it, and there arising a little effervescence, I added distilled water
thereon. The platina lost two grains, and I remarked some small holes,
like those which its flying off might occasion.
"There then remained only 22 grains of lead in the platina. I began to
form a hope of vitrifying this remaining portion of lead, for which
purpose I put the same piece of platina into a new cupel, and by the
care I took for the admission of air, and other precautions, the
activity of the fire was so greatly augmented that it required a supply
every eleven minutes; to this degree of heat we kept for four hours,
and then permitted it to cool.
"I perceived the next morning that the leaden crucible had resisted,
and that the supporters were only glazed by the cinders. I found a
piece in the cupel, not adhering, of a uniform colour, approaching more
the colour of tin than any other metal, but only a little ragged. It
weighed exactly one drachm. All, therefore, announced that this platina
had endured an absolute fusion, and that it was perfectly pure, for if
we suppose it still contained lead, we must then admit that it had lost
exactly as much of its substance as it had gained of foreign matter;
and such a precision cannot be the effect of pure chance.
"I passed several days with M. Buffon, whose company has the same
charms as his style, and whose conversation is as complete as his
books: I took a pleasure in presenting him with the production of our
essays; we examined them together, and observed, First, that the drachm
of platina, agglutinated by these experiments, was not attractable by
the loadstone; that, nevertheless, the magnetical bar had an action on
the grains that were loosened from it.
"2. The half drachm of the third experiment was not only attractable in
the mass, but the grains of gold separated therefrom did not themselves
give any signs of magnetism.
"3. The platina of the fourth experiment was absolutely insensible to
the loadstone.
"4. The specific weight of this piece was determined by a good
hydrostatical balance, and being, for the greater certainty, compared
to coined and to other very pure gold, used by M. Buffon in his
experiments, their density was found, with water, in which they were
plunged,
Pure gold - 19-87/1
Coin gold - 17-1/2
Platina - 14-2/5
"5. This piece of platina was put upon steel to try its ductability;
it supported the hammer very well for a few strokes; its surface
became flat and even, a little smooth in the parts which were struck,
but it split soon after, and nearly a sixth part separated. The
fracture presented many cavities, some of which had the whiteness and
brilliancy of silver, and in others we remarked several points like
chrystalization; the tops of these points examined with the lens, was
a globule absolutely similar to that of the third experiment. All the
other parts of this piece of platina were compact, the grain finer and
closer than the best brass, which it resembled in colour. We offered
several of these pieces to the loadstone, but not one was attracted
thereby. We powdered them again in an agate mortar, and then remarked
that the magnetical bar raised up some of the smallest every time they
are placed under it.
"This new appearance of magnetism was so much the more surprising,
as the grains were detached from the agglutinated mass of the second
experiment, which seemed to have lost all sensibility at the approach
and contact of the loadstone. In consequence we again took some of
these grains, which were alike powdered, and soon perceived the
smallest parts sensibly attach themselves to the magnetic bar. It is
impossible to attribute this effect to the smoothness of the bar,
or to any other cause foreign to magnetism. A piece of smooth iron,
applied in the same manner on the parts of this platina did not raise
up a single grain.
"By these experiments, and the observations which have arisen
therefrom, we may judge of the difficulty of determining the nature
of platina. It is very certain that it contains some parts which are
verifiable even without the addition of a fierce fire; it is also
certain that all platina contains iron and attractable parts; but if
the Prussian alkali never affords blue but with the grains which the
loadstone attracts, we should conclude, that those which resist it are
pure platina, which of itself has no magnetical virtue, and of which
iron does not make an essential part. We must suppose that a sufficient
fusion, or perfect cupellation, might decide the question; at least,
these operations appear to have, in fact, deprived it of every magnetic
virtue, by separating it from all foreign bodies; but the last
observation proves, in an incontrovertible manner, that this magnetic
property was, in reality, only weakened, and perhaps masked or buried,
since it reappeared when it was ground."
From these experiments of M. de Morveau there results, 1. That we may
expect to meet platina without addition, by applying the fire of it
several times successively, because the best crucibles might not resist
the action of so fierce a fire during the whole time that the complete
operation would require.
2. That by melting it with lead, and assaying them several times, we
should in the end vitrify all the lead and the platina; and that this
experiment would be able to purge it from a part of the foreign matters
it contains.
3. That by melting without any addition, it seems to purge itself
partly into the vitrescible matters it includes, since it emits to its
surface small drops of glass, which form pretty considerable masses,
and which we can easily separate after refrigeration.
4. That by making experiments on Prussian blue with the grains of
platina, which appeared to be most insensible to the loadstone, we were
not always certain of obtaining it; a circumstance which never fails
with grains that have more or less sensibility to magnetism.
5. It appears that neither fusion nor cupellation can destroy all the
iron with which platina is intimately penetrated; the pieces melted or
assayed, appeared, in reality, equally insensible to the action of the
loadstone; but having pounded them in a mortar, we found magnetical
parts; so much the more abundant as the platina was reduced to a fine
powder. The first piece, whose grains were only agglutinated, being
ground, rendered many more magnetical parts than the second and third,
the grains of which had undergone a stronger fusion; but, nevertheless,
being both ground, they furnished magnetical parts; insomuch that it
cannot be doubted that there is iron in platina, after it has undergone
the fiercest efforts of fire, and the devouring actions of the heat in
the cupel. This demonstrates, that this mineral is really an intimate
mixture of gold and iron, which hitherto has not been able to separate.
6. I made another observation with M. Morveau on melted, and afterwards
on ground platina; namely, that it takes in grinding precisely the same
form as it had before it had been melted; all the grains of this melted
and ground platina are similar to those of the natural, as well in form
as variety of size; and they appear to differ only because the smallest
alone suffer themselves to be raised by the loadstone, and in so much
the less quantity as the platina has endured the fire. This seems also
to prove, that, although the fire has been strong enough not only to
burn and vitrify, but even to drive off a part of the iron with other
vitrescible matter which it contains; the fusion, nevertheless, is not
so complete as that of other perfect metals, since, in grinding, it
retakes the same figure as it had before fusion.