So long as the iron remains in the tube and is heated,
and is cooled again without the access of air or water, it does not change
in its weight; but after having had this current of steam passed over it,
it then comes out heavier that it was before, having taken something out
of the steam, and having allowed something else to pass forth, which we
see here. And now, as we have another jar full, I will shew you something
most interesting. It is a combustible gas; and I might at once take this
jar and set fire to the contents, and shew you that it is combustible; but
I intend to shew you more if I can. It is also a very light substance.
Steam will condense: this body will rise in the air, and not condense.

[Illustration: Fig. 15]

Suppose I take another glass jar, empty of all but air: if I examine it
with a taper, I shall find that it contains nothing but air. I will now
take this jar full of the gas that I am speaking of, and deal with it as
though it were a light body. I will hold both upside-down, and turn the
one up under the other; and that which did contain the gas procured from
the steam, what does it contain now? You will find it now only contains
air. But look! Here is the combustible substance [taking the other jar]
which I have poured out of the one jar into the other. It still preserves
its quality, and condition, and independence, and therefore is the more
worthy of our consideration, as belonging to the products of a candle.

Now, this substance which we have just prepared by the action of iron on
the steam or water, we can also get by means of those other things which
you have already seen act so well upon the water. If I take a piece of
potassium, and make the necessary arrangements, it will produce this gas;
and if, instead, a piece of zinc, I find, when I come to examine it very
carefully, that the main reason why this zinc cannot act upon the water
continuously as the other metal does, is because the result of the action
of the water envelopes the zinc in a kind of protecting coat. We have
learned in consequence, that if we put into our vessel only the zinc and
water, they by themselves do not give rise to much action, and we get no
result. But suppose I proceed to dissolve off this varnish--this
encumbering substance--which I can do by a little acid; the moment I do
this, I find the zinc acting upon the water exactly as the iron did, but
at the common temperature. The acid in no way is altered, excep