f 
ON THE HEAT OF COMBINATION. 69 
to all similar cases of combination. Indeed his own experiments with lime 
and ammonia do not accurately agree with it; I refer particularly to his ex- 
periments with ammonia, which, when properly interpreted, appear to me to 
prove clearly that that base in combining with acids developes less heat than 
potash or soda, although I am aware that Hess himself has drawn from them 
a different conclusion. 
About the time of the publication of the first part of Hess’s memoir, I had 
completed an investigation of the same subject, but instead of employing strong 
solutions of the acids and bases, I diluted all the liquids largely with water 
previous to examining their thermal reactions. In this way I hoped to avoid 
the complex effects that arise when successive combinations and decomposi- 
tions of different kinds occur in the same chemical action, and the result 
fully realized my anticipations. The general conclusion deduced from this 
investigation may be briefly expressed, by stating that the heat deyeloped during 
the union of acids and bases is determined by the base and not by the acid. 
The following special laws will be found to comprehend the greater number 
of cases of chemical action to which the foregoing principle can be made to 
apply. 
1. An equivalent of the same base, combined with different acids, produces 
nearly the same quantity of heat. ' 
2, An equivalent of the same acid, combined with different bases, produces 
different quantities of heat. 
3. When a neutral salt is converted into an acid salt by combining with 
one or more equivalents of acid, no disengagement of heat occurs. 
4. When a double salt is formed by the union of two neutral salts, no dis- 
engagement of heat occurs. 
5. When a neutral salt is converted into a basic salt, the combination is 
accompanied by the disengagement of heat. 
6. When one and the same base displaces another from any of its neutral 
combinations, the heat evolved or absorbed is always the same whatever the 
acid element may be. 
_ As some of the bases (potash, soda, barytes and strontia) form what we 
‘may perhaps designate an isothermal group, such bases will develope the 
same, or nearly the same heat in combining with an acid, and no heat will be 
developed during their mutual displacements. 
_ These laws are not intended to embrace the thermal changes which occur 
during the conversion of an anhydrous acid and base into a crystalline com- 
pound. The steps by which such a conversion is effected are generally very 
complicated, and involve successive combinations and decompositions. We 
cannot combine, at ordinary temperatures, a dry acid and a dry base; and 
when combination takes place in presence of water, hydrates of the acid and 
base are first formed, which are afterwards decomposed, and the crystalline 
salt finally obtained is sometimes anhydrous, sometimes combined with water. 
To expect simple results where so many different actions must produce each 
its proper thermal effect, would be altogether vain, and to introduce the con- 
"sideration of some of these actions without the whole would only render the 
_ numbers empirical. In the experiments from which the foregoing laws were 
_ deduced, the acids and bases before combination, and the compounds after 
_ combination, were as nearly as possible in the same physical state. The only 
_ ehange which occurred was the combination of the acid and base, and the 
heat evolved must therefore have arisen from the act of combination. Such 
_ changes of temperature as are produced by solution are not in any way con- 
cerned in producing these thermal effects, as none of the reacting bodies 
~ assumed at any time the solid state. The insoluble bases form, it is true, an 

