l from 25 deg. to 20 deg. C., the heat
given out by the water is equivalent to 5 x 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 deg. than is required
to raise the temperature of an equal quantity of water 1 deg.. 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 deg. as to
heat the same quantity of water 1 deg..

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 deg. 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 deg. 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