THE HEAT OF COMBINATIONS.

Every molecular change in the condition of matter is almost invariably connected with the evolution or absorption of heat, and the quantity of heat thus set free or absorbed bears always a definite relation to the amount of the mechanical or chemical action. To ascertain this relation has been the object of my investigations, and the following are a few of my principal results. 1. The solution of a salt in water is always accompanied by an absorption of heat. 2. If equal weights of the same salt be dissolved in succession in the same liquid, the heat absorbed will be less on each new addition of salt. 3. The heat absorbed by the solution of a salt in water holding other salts dissolved is generally less than that absorbed by its solution in water. 4. The heat absorbed by the solution of a salt in the dilute mineral acids is generally greater than that absorbed by its solution in water. In reference to the combination of acids and bases, the heat developed during the union is determined by the base, and not by the acid. An equivalent of the same base combined with different acids produces nearly the same quantity of heat. When a neutral salt is converted into an acid salt by combining with one or more equivalents of acids, no disengagement of heat occurs. When a double salt is formed by the union of two neutral salts, the same is the case, but when a neutral salt is converted into a basic salt, there is a disengagement of heat. When solutions of two neutral salts are mixed, and a precipitate formed from their mutual decomposition, there is always a disengagement of heat, which, though small, is perfectly definite in amount. The diamond disengages 7,824 units of heat during its combustion in oxygen gas, in the form of graphite, 7,778 units, and in that of wood charcoal, 8,080.—Dr. Andrews before the British Association at Birmingham.

[The following papers have been furnished us by Mr. Pirsson, one of the former editors of the Eureka, they having been previously published in that Journal; for the cuts, which will appear in our next number, we are indebted to Mr. Starr, one of the present editors of the Farmer and Mechanic, and formerly publisher of the Eureka.]