the
temperature falls.

Chemical Change, an Effect of Heat. This effect of heat has a vital
influence on our lives, because the changes which take place when food
is cooked are due to it. The doughy mass which goes into the oven,
comes out a light spongy loaf; the small indigestible rice grain comes
out the swollen, fluffy, digestible grain. Were it not for the
chemical changes brought about by heat, many of our present foods
would be useless to man. Hundreds of common materials like glass,
rubber, iron, aluminum, etc., are manufactured by processes which
involve chemical action caused by heat.

CHAPTER II

TEMPERATURE AND HEAT

14. Temperature not a Measure of the Amount of Heat Present. If two
similar basins containing unequal quantities of water are placed in
the sunshine on a summer day, the smaller quantity of water will
become quite warm in a short period of time, while the larger quantity
will become only lukewarm. Both vessels receive the same amount of
heat from the sun, but in one case the heat is utilized in heating to
a high temperature a small quantity of water, while in the second case
the heat is utilized in warming to a lower degree a larger quantity of
water. Equal amounts of heat do not necessarily produce equivalent
temperatures, and equal temperatures do not necessarily indicate equal
amounts of heat. It takes more heat to raise a gallon of water to the
boiling point than it does to raise a pint of water to the boiling
point, but a thermometer would register the same temperature in the
two cases. The temperature of boiling water is 100 deg. C. whether there
is a pint of it or a gallon. Temperature is independent of the
quantity of matter present; but the amount of heat contained in a
substance at any temperature is not independent of quantity, being
greater in the larger quantity.

15. The Unit of Heat. It is necessary to have a unit of heat just as
we have a unit of length, or a unit of mass, or a unit of time. One
unit of heat is called a _calorie_, and is the amount of heat which
will change the temperature of 1 gram of water 1 deg. C. It is the amount
of heat given out by 1 gram of water when its temperature falls 1 deg. C.,
or the amount of heat absorbed by 1 gram of water when its temperature
rises 1 deg. C. If 400 grams of water are heated from 0 deg. to 5 deg. C., the
amount of heat which has entered the water is equivalent to 5 x 400 or
2000 calories; if 200 grams of water coo