General Science | Page 8

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° 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° C. It is the amount of heat given out
by 1 gram of water when its temperature falls 1° C., or the amount of
heat absorbed by 1 gram of water when its temperature rises 1° C. If

400 grams of water are heated from 0° to 5° C., the amount of heat
which has entered the water is equivalent to 5 × 400 or 2000 calories; if
200 grams of water cool from 25° to 20° C., the heat given out by the
water is equivalent to 5 × 200 or 1000 calories.
16. Some Substances Heat more readily than Others. If two equal
quantities of water at the same temperature are exposed to the sun for
the same length of time, their final temperatures will be the same. If,
however, equal quantities of different substances are exposed, the
temperatures resulting from the heating will not necessarily be the same.
If a basin containing 1 lb. of mercury is put on the fire, side by side
with a basin containing an equal quantity of water, the temperatures of
the two substances will vary greatly at the end of a short time. The
mercury will have a far higher temperature than the water, in spite of
the fact that the amount of mercury is as great as the amount of water
and that the heat received from the fire has been the same in each case.
Mercury is not so difficult to heat as water; less heat being required to
raise its temperature 1° than is required to raise the temperature of an
equal quantity of water 1°. In fact, mercury is 30 times as easy to heat
as water, and it requires only one thirtieth as much fire to heat a given
quantity of mercury 1° as to heat the same quantity of water 1°.
17. Specific Heat. We know that different substances are differently
affected by heat. Some substances, like water, change their temperature
slowly when heated; others, like mercury, change their temperature
very rapidly when heated. The number of calories needed by 1 gram of
a substance in order that its temperature may be increased 1° C. is
called the specific heat of a substance; or, specific heat is the number of
calories given out by 1 gram of a substance when its temperature falls
1° C. For experiments on the determination of specific heat, see
Laboratory Manual.
Water has the highest specific heat of any known substance except
hydrogen; that is, it requires more heat to raise the temperature of water
a definite number of degrees than it does to raise the temperature of an
equal amount of any other substance the same number of degrees.
Practically this same thing can be stated in another way: Water in

cooling gives out more heat than any other substance in cooling
through the same number of degrees. For this reason water is used in
foot warmers and in hot-water bags. If a copper lid were used as a foot
warmer, it would give the feet only .095 as much heat as an equal
weight of water; a lead weight only .031 as much heat as water.
Flatirons are made of iron because of the relatively high specific heat of
iron. The flatiron heats slowly and cools slowly, and, because of its
high specific heat, not only supplies the laundress with considerable
heat, but eliminates for her the frequent changing of the flatiron.
18. Water and Weather. About four times as much heat is required to
heat a given quantity of water one degree as to heat an equal quantity of
earth. In summer, when the rocks and the sand along the shore are
burning hot, the ocean and lakes are pleasantly cool, although the
amount of heat present in the water is as