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, except in its
combination with the oxide of zinc, which is produced. I have now poured
the acid into the glass, and the effect is as though I were applying heat
to cause this boiling up. There is something coming off from the zinc very
abundantly, which is not steam. There is a jar full of it; and you will
find that I have exactly the same combustible substance remaining in the
vessel, when I hold it upside-down, that I produced during the experiment
with the iron barrel. This is what we get from water--the same substance
which is contained in the candle.

[Illustration: Fig. 16.]