puts the blowpipes through these apertures, and sends down these gases
upon the metals, which are gradually melted. He then puts in more metal
through a hole at the top. The results of the combustion issue out of the
aperture which you see represented. If there be strips of platinum, he
pushes them through the mouth out of which the heated current is coming,
and there they get red-hot and white-hot before they get into the bath of
platinum. So he is able to fuse a large body of platinum in this manner.
When the platinum is melted, he takes off the top and pours out from the
bottom piece, like a crucible, and makes his cast. This is the furnace by
which he fuses his forty pounds or fifty pounds of platinum at once. The
metal is raised to a heat that no eye can bear. There is no light and
shadow, no chiaro-oscuro there; all is the same intensity of glow. You
look in, and you cannot see where the metal or the lime is; it is all as
one. We have, therefore, a platform with a handle, which turns upon an
axis, that coincides with the gutter that is formed for the pouring of the
metal; and when all is known to be ready, by means of dark glasses, the
workmen take off the top piece and lift up the handle, and the mould being
then placed in a proper position, he knows that the issue of the metal
will be exactly in the line of the axis. No injury has ever happened from
the use of this plan. You know with what care it is necessary to carry
such a vessel of mercury as we have here, for fear of turning it over on
one side or the other; but if it be a vessel of melted platinum, the very
greatest care must be used, because the substance is twice as heavy: yet
no injury has been done to any of the workmen in this operation.
I have said that Deville depends upon intense heat for carrying off
vapour; and this brings me to the point of shewing how vapours are carried
off. Here is a basin of mercury, which boils easily, as you know, and
gives us the opportunity of observing the facts and principles which are
to guide us. I have here two poles of the battery, and if I bring them
into contact with the mercury, see what a development of vapour we have.
The mercury is flying off rapidly; and I might, if I pleased, put all the
company around me in a bath of mercury vapour. And so, if we take this
piece of lead and treat it in the same way, it will also give off vapour.
Observe the fumes that rise from it; and even if it was so far enclosed
from the air that you could not form any litharge, you would still have
those abundant fumes flying off. I may also take a piece of gold, and shew
you the same thing. I have here a piece of gold which I put upon a clean
surface of Paris limestone. Applying the heat of the blowpipe to it, you
see how the heat drives off the vapour; and if you notice at the end of
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