we saw just now throwing off abundance of fumes. We can, of course, burn
away this iron by giving plenty of air to it; but with the bodies which
Deville wants to expose to this intense heat he has not that means: the
gas itself must have power enough to drive off the slag which forms on the
surface of the metal, and power to impinge upon the platinum so as to get
the full contact that he wants for the fusion to take place. We see here,
then, the means to which he resorts--oxygen, and either coal-gas or
water-gas[19], or pure hydrogen, for producing heat, and the blowpipe for
the purpose of impelling the heated current upon the metals.

I have two or three rough drawings here, representing the kind of furnaces
which he employs. They are larger, however, than the actual furnaces he
uses. Even the furnace in which he carries on that most serious operation
of fusing fifty pounds of platinum at once is not much more than half the
size of the drawing. It is made of a piece of lime below and a piece of
lime above. You see how beautifully lime sustains heat without altering in
shape; and you may have thought how beautifully it prevents the
dissipation of the heat by its very bad conducting powers.

[Illustration: Fig. 38]

While the front part of the lime which you saw here was so highly ignited,
I could at any moment touch the back of it without feeling any annoyance
from the heat So, by having a chamber of lime of this sort, he is able to
get a vessel to contain these metals with scarcely any loss of heat. He
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,