On the thermal changes accompanying basic substitutions

The author gives an account of a series of experiments which he made on the heat evolved during the mutual reaction of acids and bases upon one another, from which he draws the general conclusion that when the influence of all extraneous circumstances is eliminated from the result, the change of temperature is determined by the nature of the base, and not by the acid element of the combination. Hence he deduces the general law that, when one base displaces another from any of its neutral combinations with an acid, the heat evolved or abstracted is always the same, whatever the acid element may be, provided the bases are the same. The base employed in the first set of experiments for displacing others was the hydrate of potash in a state of dilute solution of known strength; this was rapidly mixed, in a suitable apparatus, with an equivalent solution of the salt to be decomposed; the change of temperature which resulted was accurately determined, and the due corrections for the influence of the vessels and the specific heats of the solutions and of the precipitates produced, were applied. The experimental results are stated in various tables, from which it appears that the changes of temperature, referred to 1000 parts of water, were, with salts of The differences in the results of experiments with different acids, the author observes, are not greater than usually occur in chemical reactions, in consequence of the uncertainty that exists with regard to the accurate proportions of chemical equivalents. He points out various circumstances in experiments of this nature, which tend to affect the results and lead to inaccurate conclusions, if care be not taken to guard against these sources of error. One of the principal of these is the heat which is generally evolved by the separation of a base, or new compound, in a solid form: and the author discusses the influence of this change on the results deduced from his experiments. He considers that these experiments sufficiently establish the general principle announced in the beginning of his paper.