On crystallising, the solution gives
off heat, as is shown by the expansion of the air in the corked tube,
and the consequent forcing of the coloured liquid up the narrow tube.
Consequently in your works you never dissolve a salt or crystal in water
or other liquid without rendering heat latent, or consuming heat; you
never allow steam to condense in the steam pipes about the premises
without losing vastly more heat than possibly many are aware of. Let us
inquire as to the latent heat of water and of steam.
_Latent Heats of Water and Steam._--If we mix 1 kilogram (about 2 lb.)
of ice (of course at zero or 0 deg. C.) with 1 kilogram of water at 79 deg. C.,
and stir well till the ice is melted, _i.e._ has changed its state from
solid to liquid, we find, on putting a thermometer in, the temperature
is only 0 deg. C. This simply means that 79 deg. of heat (centigrade degrees)
have become latent, and represent the heat of liquefaction of 1 kilogram
of ice. Had we mixed 1 kilogram of water at 0 deg. C. with 1 kilogram of
water at 79 deg.
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