it; but there it is burning, and the
more air I give it, by this or any other action, the better it is. So,
then, we have here not merely a mighty source of heat, but a means of
driving the heat forcibly against substances.

Let me shew you another experiment with a piece of iron. It will serve two
purposes--shewing you what the blowpipe does as a source of heat, and what
it does by sending that heat where it is wanted. I have taken iron in
contrast with silver or other metals, that you may see the difference of
action, and so be more interested in the experiment. Here is our fuel, the
coal-gas; and here our oxygen. Having thus my power of heat, I apply it to
the iron, which, as you see, soon gets red-hot. It is now flowing about
like a globule of melted mercury. But observe, I cannot raise any vapour:
it is now covered with a coat of melted oxide, and unless I have a great
power in my blowpipe, it is hardly possible to break through it. Now,
then, you see these beautiful sparks: you have not only a beautiful kind
of combustion, but you see the iron is being driven off, not producing
smoke, but burning in a fixed condition. How different this is from the
action of some other metals--that piece of antimony, for instance, which
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.

[Illus