possession of the
bottles and their contents, hear a pop on the occasion of the bursting of
the one bottle or the other; and, when we come to examine the bottles, we
shall find their contents masses of ice, partly enclosed by the covering
of iron which is too small for them, because the ice is larger in bulk
than the water. You know very well that ice floats upon water: if a boy
falls through a hole into the water, he tries to get on the ice again to
float him up. Why does the ice float?--think of that, and philosophise.
Because the ice is larger than the quantity of water which can produce it;
and therefore the ice weighs the lighter, and the water is the heavier.

To return now to the action of heat on water. See what a stream of vapour
is issuing from this tin vessel! You observe, we must have made it quite
full of steam to have it sent out in that great quantity. And now, as we
can convert the water into steam by heat, we convert it back into liquid
water by the application of cold. And if we take a glass, or any other
cold thing, and hold it over this steam, see how soon it gets damp with
water; it will condense it until the glass is warm--it condenses the water
which is now running down the sides of it. I have here another experiment
to shew the condensation of water from a vaporous state back into a liquid
state, in the same way as the vapour, one of the products of the candle,
was condensed against the bottom of the dish, and obtained in the form of
water; and to shew you how truly and thoroughly these changes take place,
I will take this tin flask, which is now full of steam, and close the top.
We shall see what takes place when we cause this water or steam to return
back to the fluid state by pouring some cold water on the outside. [The
Lecturer poured the cold water over the vessel, when it immediately
collapsed.] You see what has happened. If I had closed the stopper, and
still kept the heat applied to it, it would have burst the vessel; yet,
when the steam returns to the state of water, the vessel collapses, there
being a vacuum produced inside by the condensation of the steam. I shew
you these experiments for the purpose of pointing out that in all these
occurrences there is nothing that changes the water into any other
thing--it still remains water; and so the vessel is obliged to give way,
and is crushed inwards, as in the other case, by the further application
of heat, it would have been blown outwards