great will be the demand for heat, that if a vessel containing water be
put in amongst the dissolving salt, the heat residing in that vessel and
its water will be rapidly extracted, and the water will freeze. As
regards solubility, some salts and substances are much more quickly and
easily dissolved than others. We are generally accustomed to think that
to dissolve a substance quickly we cannot do better than build a fire
under the containing vessel, and heat the liquid. This is often the
correct method of proceeding, but not always. Thus it would mean simply
loss of fuel, and so waste of heat, to do this in dissolving ordinary
table salt or rock salt in water, for salt is as soluble in cold water
as in hot. Some salts are, incredible though it may appear, less soluble
in boiling water than in cold. Water just above the freezing-point
dissolves nearly twice as much lime as it does when boiling. You see,
then, that a knowledge of certain important facts like these may be so
used as to considerably mitigate your coal bills, under given
circumstances and conditions.




LECTURE IV

WATER: ITS CHEMISTRY AND PROPERTIES; IMPURITIES AND THEIR ACTION; TESTS
OF PURITY--_Continued_


In the last lecture, under the head of "Solution," I mentioned that some
salts, some chemical substances, are more soluble in water than others,
and that their solubilities under different circumstances of temperature
vary in different ways. However, some salts and compounds are