of air, it would quickly set fire to the whole. Now, this is a metal--a
beautiful and bright metal--which rapidly changes in the air, and, as you
know, rapidly changes in water. I will put a piece on the water, and you
see it burns beautifully, making a floating lamp, using the water in the
place of air. Again, if we take a few iron filings or turnings, and put
them in water, we find that they likewise undergo an alteration. They do
not change so much as this potassium does, but they change somewhat in the
same way; they become rusty, and shew an action upon the water, though in
a different degree of intensity to what this beautiful metal does: but
they act upon the water in the same manner generally as this potassium. I
want you to put these different facts together in your minds. I have
another metal here [zinc], and when we examined it with regard to the
solid substance produced by its combustion, we had an opportunity of
seeing that it burned; and I suppose, if I take a little strip of this
zinc and put it over the candle, you will see something half-way, as it
were, between the combustion of potassium on the water and the action of
iron,--you see there is a sort of combustion. It has burned, leaving a
white ash or residuum, and here also we find that the metal has a certain
amount of action upon water.

By degrees we have learned how to modify the action of these different
substances, and to make them tell us what we want to know. And now, first
of all, I take iron. It is a common thing in all chemical reactions, where
we get any result of this kind, to find that it is increased by the action
of heat; and if we want to examine minutely and carefully the action of
bodies one upon another, we often have to refer to the action of heat. You
are aware, I believe, that iron-filings burn beautifully in the air; but I
am about to shew you an experiment of this kind, because it will impress
upon you what I am going to say about iron in its action on water. If I
take a flame and make it hollow;--you know why, because I want to get air