78 
PROFESSOR KOPP ON THE SPECIFIC HEAT OF SOLID BODIES. 
state, applying Dulong and Petit’s law, or indirectly by ascertaining the specific heat 
of solid compounds, assuming Neumann’s law ; or finally (and only in a few cases), he 
has determined them by means of their probable analogies. These are the atomic 
weights given in the second column of the Table in § 2. 
With regard to the relations of the specific heats of solid compounds to those of their 
constituents, Regnault has shown * that with metallic alloys, at a considerable distance 
from their melting-points, the specific heats may be calculated from those of their con- 
stituents in tolerable accordance with the experimental results, assuming that the 
specific heats of the metals are the same in the alloys as in the free state. The investi- 
gation, whether for true chemical compounds there is a simple relation between their 
specific heats and those of their constituent elements, Regnault has reserved *f* till the 
conclusion of his experiments on the specific heats of gaseous bodies $. To my know- 
ledge he has published nothing for solid bodies. But in 1862, with reference to the 
relations which had been recognized between the specific heats and atomic weights of 
solid, simple or compound bodies, he spoke as follows §. “ It is true that these laws, in 
the case of solid bodies, only apply approximately to simple bodies and those compounds 
of least complex constitution ; for all others it is impossible to pronounce anything in 
this respect.” From some remarks of Regnault in reference to carbon || and silicium ^f 
he considers it possible, or probable with certain elements, that they have a different 
specific heat in their compounds to that which they have in the free state. 
9. In 1840 De la Rive and Marcet published ** investigations on the specific heat of 
solid bodies. They made their determinations by the method of cooling. They found 
that, assuming Berzelius’s atomic weights, selenium, molybdenum, and wolfram fall 
under Dulong and Petit’s law, which they consider as universally valid; but that 
carbon forms an exception, and they consider it as probable that its true atomic weight 
has not yet been ascertained. For several sulphides they found a greater specific heat 
than was calculated for them, assuming that their constituents have in them the same 
specific heat as in the free condition. They think that for solid as well as for liquid 
and gaseous compounds the law governing the specific heat is still unknown. A sub- 
sequent memoir by these physicists treated of the specific heat of carbon in its various 
conditions. 
10. In 1840 H. Schroder made an investigation as to what volumes are to be 
assigned to the constituents of solid and liquid compounds when contained in those 
compounds. In his memoirs on the subject, he expressed the view that the specific 
heat of compounds depends on the specific heats of the constituents in that particular 
* Ann. de Chim. et de Phys. [3] vol. i. p. 183. t Ibid. p. 132. 
i Regnault has made known the results of these experiments in 1853 by a preliminary account in the Comptes 
Rendus, vol. xxxvi. p. 676, and more completely in 1862 in his ‘ Relation des experiences pour determiner les 
lois et les donnees physiques necessaires au calcul des machines a feu/ vol. ii. p. 3. 
§ Relation, &c. vol. ii. p. 289. || Ann. de Chim. et de Phys. [3] vol. i. p. 205. Ibid. [3] vol. Ixiii. p. 31. 
** Ibid. [2] vol. lxxv. p. 113. ft Ibid. [3] vol. ii. p. 121. Poggendoeee’s * Annalen/ vol. 1. p. 553. 
