[Illustration: Fig. 37.]

By uniting these we obtain a flame of such a heat as to melt platinum. You
will, perhaps, hardly imagine what the heat is, unless you have some proof
of it; but you will soon see that I have actually the power of melting
platinum. Here is a piece of platinum-foil running like wax under the
flame which I am bringing to bear against it. The question, however, is
whether we shall get heat enough to melt, not this small quantity, but
large masses--many pounds of the metal. Having obtained heat like this,
the next consideration is what vessel is he to employ which could retain
the platinum when so heated, or bear the effects of the flame? Such
vessels are happily well supplied at Paris, and are formed of a substance
which surrounds Paris; it is a kind of chalk (called, I believe, by
geologists, _calcaire grossière_), and it has the property of enduring an
extreme degree of heat. I am now going to get the highest heat that we can
obtain. First, I shew you the combustion of hydrogen by itself. I have not
a large supply, because the coal-gas is sufficient for most of our
purposes. If I put a piece of lime obtained from this chalk into the gas,
you see we get a pretty hot flame, which would burn one's fingers a good
deal But now let me subject a piece of it to the joint action of oxygen
and hydrogen. I do this for the purpose of shewing you the value of lime
as a material for the furnaces and chambers that are to contain the
substances to be operated on, and that are consequently to sustain the
action of this extreme heat. Here we have the hydrogen and the oxygen,
which will give the most intense heat that can be obtained by chemical
action; and if I put a piece of lime into the flame, we get what is called
the lime-light. Now, with all the beauty and intensity of action which you
perceive, there is no sensible deterioration of the lime except by the
mechanical force of the current of gases rushing from the jet against the
lime, sweeping away such particles as are not strongly aggregated. "Vapour