f a solid or a liquid. I will endeavour to make this clear to
you by an experiment. I have here, as you see, a wooden stool, and I am
about to pour a little water on this stool. I place a glass beaker on
the stool, the liquid water only intervening between the stool and the
bottom of the glass. You see the glass is perfectly loose, and easily
lifted off the stool notwithstanding the layer of water. I will now pour
into the beaker a little of a very volatile liquid--_i. e._ a liquid
that is easily converted into a gas--(bisulphide of carbon). I wish
somewhat rapidly to effect the change of this liquid bisulphide of
carbon into gaseous bisulphide of carbon, and in order to accomplish
this object I must have heat. So I take this tube which, as you see, is
connected with a pair of bellows, and simply blow on my bisulphide of
carbon. This effects the change of the liquid into a gas with great
rapidity. Just as I converted my solid sulphur into a gas by the heat of
the tinder, so here I am converting this liquid bisulphide of carbon
into a gas by the wind from my bellows. But my liquid bisulphide of
carbon must get heat somewhere or another in order that the change of
the liquid into a gas, that I desire should take place, may be effected;
and so, seeing that the water that I have placed between the glass and
the stool is the most convenient place from which the liquid can derive
the necessary heat, it says, "I will take the heat out of the water." It
does so, but in removing the heat from the water it changes the liquid
water into solid ice. And see, already the beaker is frozen to the
stool, so that I can actually lift up the stool by the beaker (Fig. 28).
Understand then why my sulphur match wanted some time and some coaxing
before it caught fire, viz. to change this solid sulphur into gaseous
sulphur.

[Illustration: Fig. 28.]

But let us go a step further: why must the solid sulphur be converted
into a gas? We want a flame, and whenever we have flame it is absolutely
necessary that we should have a gas to burn. You cannot have flame
without you have gas. Let me endeavour to illustrate what I mean. I pour
into this flask a small quantity of ether, a liquid easily converted
into a gas. If I apply a lighted taper to the mouth of the flask, no
gas, or practically none, being evolved at the moment, nothing happens.
But I will heat the ether so as to convert it into a gas. And now that I
have evolved a large quantity of eth