Effect of Dissolved Salts on the Boiling of Water.—­Let us inquire what this effect is?  Suppose we dissolve a quantity of a salt in water, and then blow steam at 100 deg.  C. (212 deg.  F.) into that water, the latter will boil not at 212 deg.  F., but at a higher temperature.  There is a certain industrial process I know of, in course of which it is necessary 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 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.