useful objects, such as lamp shades, globes, etc. (Fig. 20). If glass
melted at a definite temperature, it could not be molded in this way.
Iron acts in a similar manner, and because of this property the
blacksmith can shape his horseshoes, and the workman can make his
engines and other articles of daily service to man.

[Illustration: FIG. 20.--Molten glass being rolled into a form
suitable for window panes.]

33. Strange Behavior of Water. One has but to remember that bottles
of water burst when they freeze, and that ice floats on water like
wood, to know that water expands on freezing or on solidifying. A
quantity of water which occupies 100 cubic feet of space will, on
becoming ice, need 109 cubic feet of space. On a cold winter night the
water sometimes freezes in the water pipes, and the pipes burst. Water
is very peculiar in expanding on solidification, because most
substances contract on solidifying; gelatin and jelly, for example,
contract so much that they shrink from the sides of the dish which
contains them.

If water contracted in freezing, ice would be heavier than water and
would sink in ponds and lakes as fast as it formed, and our streams
and ponds would become masses of solid ice, killing all animal and
plant life. But the ice is lighter than water and floats on top, and
animals in the water beneath are as free to live and swim as they were
in the warm sunny days of summer. The most severe winter cannot freeze
a deep lake solid, and in the coldest weather a hole made in the ice
will show water beneath the surface. Our ice boats cut and break the
ice of the river, and through the water beneath our boats daily ply
their way to and fro, independent of winter and its blighting blasts.