y
first to maintain a vessel containing water, by means of a heated closed
steam coil, at 212 deg. F. (100 deg. C.), and at a certain stage to raise the
temperature to about 327 deg. F. (164 deg. C.). The pressure on the boiler
connected with the steam coil is raised to nearly seven atmospheres, and
thus the heat of the high-pressure steam rises to 327 deg. F. (164 deg. C.), and
then a considerable quantity of nitrate of ammonium, a crystallised
salt, is thrown into the water, in which it dissolves. Strange to say,
although the water alone would boil at 212 deg. F., a strong solution in
water of the ammonium nitrate only boils at 327 deg. F., so that the effect
of dissolving that salt in the water is the same as if the pressure were
raised to seven atmospheres. Now let us, as hat manufacturers, learn a
practical lesson from this fact. We have observed that wool and fur
fibres are injured by boiling in pure water, and the heat has much to do
with this damage; but if the boiling take place in bichrome liquors or
similar solutions, that boiling will, according to the strength of the
solution in dissolved matters, take place at a temperature more or less
elevated above the boiling-point of water, and so the damage done will
be the more serious the more concentrated the liquors are, quite
independently of the nature of the substances dissolved in those
liquors.

_Solution._--We have already seen that when a salt of any kind dissolves
in water, heat is absorbed, and becomes latent; in other words, cold is
produced. I will describe a remarkable example or experiment, well
illustrating this fact. If you take some Glauber's salt, crystallised
sulphate of soda, and mix it with some hydrochloric acid (or spirits of
salt), then so rapidly will the solution proceed, and consequently so
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