frosty day, he perceives, that in
time the water grows colder; that a thin, brittle skin spreads over
it; which grows thicker by degrees, till at length all the water
becomes ice; and if the cup be again put before the fire, the ice
returns to water. Thus he discovers, that by diminishing the heat of
water, it becomes ice; by adding heat to ice, it becomes water.

A child watches the drops of melted sealing-wax as they fall upon
paper. When he sees you stir the wax about, and perceives, that what
was formerly hard, now becomes soft and very hot, he will apply his
former knowledge of the effects of heat upon ice and snow, and he will
tell you that the heat of the candle melts the wax. By these means,
the principle of the solution of bodies by heat, will be imprinted
upon his memory; and you may now enlarge his ideas of solution.

When a lump of sugar is put into a dish of hot tea, a child sees that
it becomes less and less, till at last it disappears. What has become
of the sugar? Your pupil will say that it is melted by the heat of the
tea: but if it be put into cold tea, or cold water, he will find that
it dissolves, though more slowly. You should then show him some fine
sand, some clay, and chalk, thrown into water; and he will perceive
the difference between mechanical mixture and diffusion, or chemical
mixture. Chemical mixture, as that of sugar in water, depends upon the
attraction that subsists between the parts of the solid and fluid
which are combined. Mechanical mixture is only the suspension of the
parts of a solid in a fluid. When fine sand, chalk, or clay, are put
into water, the water continues for some time turbid or muddy; but by
degrees the sand, &c. falls to the bottom, and the water becomes
clear. In the chemical mixture of sugar and water, there is no
muddiness, the fluid is clear and transparent, even whilst it is
stirred, and when it is at rest, there is no sediment, the sugar is
joined with the water; a new, fluid substance, is formed out of the
two simple bodies sugar and water, and though the parts which compose
the mixture are not discernible to the eye, yet they are perceptible
by the taste.

After he has observed the mixture, the child should be asked, whether
he knows any method by which he can separate the sugar from the water.
In the boiling of a kettle of water, he has seen the steam which
issues from the mouth of the vessel; he knows that the steam is formed
by the heat from the fire,