THE 



LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE.. 



SUPPLEMENT to VOL. XIL FOURTH SERIES. 



LXV. Memoir on the Specific Heat of some Simple Bodies, and 

 on the Isomeric Modifications of Selenium. By M. V. Reg- 



NAULT*. 



DULONG- and Petit were the first to announce the remark- 

 able physical law, that " the specific heats of simple bodies 

 are reciprocally proportional to their atomic weights." The 

 experiments on which they had established this law were not 

 numerous, and many of them have been found to be contradictory, 

 in consequence of the considerable changes which more exact 

 analyses, and a more complete knowledge of chemical compounds, 

 have produced in the adopted atomic weights of some simple 

 bodies. Nevertheless the numerous experiments which I made 

 fifteen years ago, on all the simple bodies which I could procure 

 in sufficient quantity, proved that the law of Dulong and Petit 

 ought to be admitted ; not, indeed, in the rigorous acceptation 

 which those celebrated physicists had claimed for it, but as an 

 approximative law, which may be usefully appealed to in many 

 scientific considerations. In fact, according to the precise enun- 

 ciation of this law, the product of the specific heat of a simple 

 body by its atomic weight ought to be a constant number; 

 whereas in my experiments on solid bodies, this product varied 

 from 36 to 41. This variation arises from the fact, that the 

 calorific capacity of bodies, as determined in our experiments, 

 comprehends not only the specific atomic heat, that is to say, the 

 quantity of heat necessary to elevate the temperature of the atom 

 one degree, but also the heat which disappears in causing the 

 expansion of the body, or in the molecular changes which pro- 

 duce its successive softening, or determine the variations of its 

 crystalline groups. These secondary effects absorb quantities of 

 caloric which are by no means reciprocal to the atomic weights 

 of the bodies, and each of which varies according to the limits 

 of the temperature within which it is observed, 



* From the Annates de Chimie et de Physique for March 1856. 

 Phil. Mag. S, 4. No. 82. Suppl Vol, 12. 2 K 



