PROFESSOR KOPP ON THE SPECIFIC HEAT OF SOLID BODIES. 
7T 
he described his mode of executing this method, and published the results obtained for 
a great number of elements. In a second memoir * he gave the specific heats of several 
metallic alloys containing metals in simple atomic ratios, and of a great number of 
solid chemical compounds ; and he published comprehensive experiments on the specific 
heat of carbon in its different conditions. The investigations announced in the first 
memoir f on the specific heat of organic compounds, as well as those promised in the 
second memoir^ on the specific heat of sulphur at different temperatures, have not to 
my knowledge been published. But in a third memoir § Regnault has investigated 
the difference in the specific heats of certain metals according as they are hardened or 
soft, and also with reference to sulphur according as it is in the native crystallized form, 
or has solidified a longer or shorter time after being melted ; and he has more especially 
tried to impart greater certainty to the method of cooling. In his subsequent inves- 
tigations, however, he has only used the method of mixture as being the more certain. 
These investigations || have given the specific heats of a large number of solid elements, 
and also of individual compounds. 
By his investigations Regnault has removed some objections which seemed to affect 
Dulong and Petit’s law, and has given a great number of new cases in which it 
applies. He considers < |[ this law to be universally valid, and discusses the reasons why 
for individual elements the specific heats found do not quite agree with the law, but 
only approximately. In his view the atomic weight of an element is to be so taken 
that it agrees with Dulong and Petit’s law. He took the atomic weight of silver and 
of the alkaline metals half as great, and that of carbon twice as great as Berzelius 
had done. Yet with regard to selecting, by means of the specific heat, from among 
the numbers which the chemical investigations of an element has given as admissible, 
that which is the correct one, Regnault does not always express himself decidedly. 
In the case of carbon ** and of silicium f f he mentions the possibility of their disagree- 
ment with Dulong and Petit’s law. He proved the validity of Neumann’s law for a 
number of cases very considerably greater than that on which it had originally been 
based ; and he expressed it in a much more general form JJ. “ In all compounds of ana- 
logous atomic composition, and similar chemical constitution, the specific heats are 
approximately inversely proportional to the atomic weights. Regnault designates the 
numbers agreeing with this law as thermal atomic weights. He has either determined 
them directly from the numbers found for the specific heats of the elements in the free 
* Ann de Chim. et de Pkys. [3] vol. i. p. 129. + Ibid. [2] vol. lxxiii. p. 71. 
t Ibid. [3] vol. i. p. 205. § Ibid. [3] vol. ix. p. 322. 
|| Ibid. [3] vol. xxvi. pp. 261 & 268 ; vol. xxxviii. p. 129 ; vol. xlvi. p. 257 ; vol. lxiii. p. 5. Comptes 
Rendus, vol. Iv. p. 887. 
i^[ Ann. de Cbim. et de Phys. [2] vol. lxxiii. p. 66 ; further, [3] vol. xxvi. p. 261, and vol. xlvi. p. 257. 
** Ibid. [3] vol. i. p. 205. But botb before and after (Ibid. [2] vol. lxxiii. p. 71, and [3] vol. xxvi. p. 263) 
Regnault inclined to tbe view that carbon, with the equivalent= 12, and the specific heat found for wood-charcoal, 
must be considered as obeying Dulong and Petit’s law. ft Ibid. vol. lxiii. p. 30. Xt Ibid. vol. i. p. 199. 
