d.

The manufacture of barley-sugar is a familiar example of
crystallization. The syrup is evaporated over a slow heat, till it has
acquired the proper consistence, when it is poured on metal to cool, and
when nearly so, cut into lengths with shears, then twisted, and again
left to harden.

Heat.

Why does hay, if stacked when damp, take fire?

Because the moisture elevates the temperature sufficiently to produce
putrefaction, and the ensuing chemical action causes sufficient heat to
continue the process; the quantity of matter being also great, the heat
is proportional.

Why is the air warm in misty or rainy weather?

Because of the liberation of the latent heat from the precipitated
vapour.

Why is heated air thinner or lighter than cold air?

Because it is a property of heat to expand all bodies; or rather we
should say, that we call air hot or cold, according as it naturally is
more or less expanded.

Why is a tremulous motion observable over chimney-pots, and slated roofs
which have been heated by the sun?

Because the warm air rises, and its refracting power being less than
that of the colder air, the currents are rendered visible by the
distortion of objects viewed through them.

Within doors, a similar example occurs above the foot-lights of the
stage of a theatre; the flame of a candle, or the smoke of a lamp.

Why are the gas chandeliers in our theatres placed under a large funnel?

Because the funnel, by passing through the roof into the outer air,
operates as a very powerful ventilator, the heat and smoke passing off
with a large proportion of the air of the house.

The ventilation of rooms and buildings can only be perfectly effected,
by suffering the heated and foul air to pass off through apertures in
the ceiling, while fresh air, of any desired temperature, is admitted
from below.--Brande.

Why do heated sea-sand and soda form glass?

Because, by heating the mixture, the cohesion of the particles of each
substance to those of its own kind is so diminished, that the mutual
attractions of the two substances come into play, melt together, and
unite chemically into the beautiful compound called glass.

Why is sand used in glass?

Because it serves for stone; it being said, that all white transparent
stones which will not burn to lime are fit to make glass.

Electricity.

Why is an arrangement of several Leyden jars called an electrical
battery?

Because by a communication exist