In all the properties which have been mentioned water in the form of
steam is an elastic fluid or gas like air.
If a little water is placed in the flask mentioned in the preceding
section all the “empty” part of the space will contain air. If the flask
is now made hot the water will at length boil, bubbles of steam forming
in the water and breaking at its surface. By degrees, the air, which at
first lay above the water, will be driven out; and if the whole flask is
kept hot, the “empty” part of it will be full of the gaseous water,
which is transparent and colourless like air. The steam flows out of the
mouth of the flask still a clear and colourless gas; but it soon cools
and becomes condensed as a cloud of small particles of fluid water.
Steam is lighter than air, and hence it rises in the air, just as bodies
which are lighter than water rise in water.