Page:Outlines of Physical Chemistry - 1899.djvu/174

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��166 OUTLINES OF PHYSICAL CHEMISTRY

The heat evolved by the addition of a large quantity of

water to a more or less concentrated solution of some of

these gases has been studied. Berthelot has found that

the heat of dilution of hydrochloric acid of the com- position HCl+ttH 2 is expressed by the formula

Cal.

It is, therefore, inversely proportional to the amount of water primarily united to the acid.

Numbers found (Berthelot) Heat of Dilution

HC1 + 217H.fi (solution saturated at -12°C.). 5-31 Cal.

A quantity of water amounting to about 200 molecules per molecule of HC1 was used in determining this heat.

For ammonia, dilution of a solution NH 3 + nH^O evolves — Cal.

n

By applying the principle of the initial and final states, we can calculate what quantity of heat is evolved by the combining of each successive molecule of water. Thus, for hydrochloric acid :

HC1 evolves on solution 17*43 Cal.

HC1 + 3-2H 2 evolves on dilution. . . 3*77 „ Gal.) corresponds to the difference of the initial states. The solution of HC1 in the first 8*2 molecules of water there- fore evolves 18*66 Cal.

��Certain liquids dissolve in water with evolution of much heat. For nitric acid, Berthelot has found :

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