r shewing its presence to so many at once, is to exhibit a very visible
action of water, and then to apply that test to what is collected as a
drop at the bottom of that vessel. I have here a chemical substance,
discovered by Sir Humphrey Davy, which has a very energetic action upon
water, which I shall use as a test of the presence of water. If I take a
little piece of it--it is called potassium, as coming from potash,--if I
take a little piece of it, and throw it into that basin, you see how it
shews the presence of water by lighting up and floating about, burning
with a violent flame. I am now going to take away the candle which has
been burning beneath the vessel containing ice and salt, and you see a
drop of water--a condensed product of the candle--hanging from under the
surface of the dish.

[Illustration: Fig. 11.]

I will shew you that potassium has the same action upon it as upon the
water in that basin in the experiment we have just tried. See, it takes
fire, and burns in just the same manner. I will take another drop upon
this glass slab, and when I put the potassium on to it, you see at once,
from its taking fire, that there is water present. Now, that water was
produced by the candle. In the same manner, if I put this spirit-lamp
under that jar, you will soon see the latter become damp, from the dew
which is deposited upon it--that dew being the result of combustion; and I
have no doubt you will shortly see by the drops of water which fall upon
the paper below, that there is a good deal of water produced from the
combustion of the lamp. I will let it remain, and you can afterwards see
how much water has been collected. So, if I take a gas-lamp, and put any
cooling arrangement over it, I shall get water--water being likewise
produced from the combustion of gas. Here, in this bottle, is a quantity
of water--perfectly pure, distilled water, produced from the combustion of
a gas-lamp--in no point different from the water that you distil from the
river, or ocean, or spring, but exactly the same thing. Water is one
individual thing--it never changes. We can add to it by careful
adjustment, for a little while, or we can take it apart, and get other
things from it; but water, as water, remains always the same, either in a
solid, liquid, or fluid state. Here, again [holding another bottle], is
some water produced by the combustion of an oil-lamp. A pint of oil, when
burnt fairly and properly, produces rather more t