Chemistry / [Michael Donovan].

  • Donovan, Michael, -1876
Date:
1834
Catalogue details

Licence: Public Domain Mark

Credit: Chemistry / [Michael Donovan]. Source: Wellcome Collection.

    399/438 (page 377)
    culation by Avogadro * ; and he has constructed a table, in which the relative affinity of various substances for caloric is expressed numerically,—the affinity of common air for heat being taken as unity. These numbers he deduced from the specific heat of gases, as given by Berard and. Delaroche. We discover caloric entering into a state that seems to possess the characteristics of chemical combination ; for a decided change of properties is manifested. Ca- loric, when presented to ice, is absorbed ; the ice loses most of its properties as such, and becomes water, while the caloric loses its chief remarkable property of raising the temperature. The same observations apply to all other cases in which heat becomes latent; and other illustrations of the position derived from specific heats might be adduced, did space permit. If there exist a reciprocal attraction between caloric and all other kinds of matter, why may not such an attraction be subject to the general laws of affinity? Why may we not suppose that the exertion of such affinity:causes bodies to combine with caloric, atom to atom, and thus produces combinations bearing a deter- minate ratio to each other? We are not in the habit of considering determinate ratios of heat, or atoms of it ; yet such may exist: and if experience prove that such an admission harmonises with, and leads to, the explanation of phenomena, which otherwise must stand in the situation of ultimate facts, then we are bound to admit the notion as probable.’ It is no more than an hypothesis ; but hypotheses are often the beacons of discovery: the atomic constitution of matter was an hypothesis in the hands of Higgins ; yet what depart- ment of the science has not since experienced its bene- ficial influence ? There are some combinations of carbon with hydro- gen which may be here referred to, as illustrative of this part of the subject: they are gases ; and have been described at page 170. of this volume. The first con-