tell us the story so beautifully, so gradually and regularly, that I think
it will please you very much.
I have here a furnace with a pipe going through it like an iron
gun barrel, and I have stuffed that barrel full of bright iron-turnings,
and placed it across the fire, to be made red-hot. We can either send air
through the barrel to come in contact with the iron, or we can send steam
from this little boiler at the end of the barrel. Here is a stop-cock
which shuts off the steam from the barrel until we wish to admit it. There
is some water in these glass jars, which I have coloured blue, so that you
may see what happens. Now, you know very well that any steam I might send
through that barrel, if it went through into the water, would be
condensed; for you have seen that steam cannot retain its gaseous form if
it be cooled down.
[Illustration: Fig. 14.]
You saw it here [pointing to the tin flask] crushing itself into a small
bulk, and causing the flask holding it to collapse; so that if I were to
send steam through that barrel, it would be condensed supposing the
barrel were cold: it is, therefore, heated to perform the experiment I am
now about to shew you. I am going to send the steam through the barrel in
small quantities; and you shall judge for yourselves, when you see it
issue from the other end, whether it still remains steam. Steam is
condensable into water, and when you lower the temperature of steam, you
convert it back into fluid water; but I have lowered the temperature of
the gas which I have collected in this jar, by passing it through water
after it has traversed the iron barrel, and still it does not change back
into water. I will take another test and apply to this gas. (I hold the
jar in an inverted position, or my substance would escape.) If I now apply
a light to the mouth of the jar, it ignites with a slight noise. That
tells you that it is not steam. Steam puts out a fire it does not burn;
but you saw that what I had in that jar burnt. We may obtain this
substance equally from water produced from the candle-flame as from any
other source. When it is obtained by the action of the iron upon the
aqueous vapour, it leaves the iron in a state very similar to that in
which these filings were after they were burnt. It makes the iron heavier
than it was before. 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,
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