PROFESSOR KOPP ON THE SPECIFIC HEAT OF SOLID BODIES. 
73 
and most trustworthy experimental determinations, without alteration of the bases for 
the adoption of these numbers. The numerical relations presented in the above Table 
require, from the chemical point of view, no further explanation. The relations of these 
numbers to the specific heat form the subject of the investigations which are presented 
in the sequel. 
3. The experiments by which Dulong and Petit * * * § showed, in the case of mercury 
various solid metals, and glass, that the specific heat increases with increasing tem- 
perature, were made by the method of mixtures. They determined at ordinary tem- 
peratures the specific heats of a greater number of elements by the method of cooling f. 
They found that when the numbers in the first column in § 2 corresponding to the 
elements Bi, Pb, Au, Pt, Sn, Zn, Cu, Ni, Fe, and S (the Berzelian atomic weights) 
are multiplied by the respective specific heats of these bodies, approximately the same 
number is obtained ; and that approximately the same number is also obtained when 
Ag, \ Te, and f Co are multiplied by their corresponding specific heats. They were 
of opinion that the atomic weights of the elements could and should be so selected that, 
when multiplied by the specific heats, they should give approximately the same number 
as product. This observation and this view, which Dulong and Petit stated in 1819 in 
the following manner, “The atoms of all simple bodies have all exactly the same 
capacity for heat,” have since that time been known as Dulong and Petit’s Law. 
I shall not here dwell upon Potter’s investigations on the specific heat of metals 
and on the validity of Dulong and Petit’s lawj, but proceed directly to discuss 
Neumann’s investigations, which rank worthily by the side of those of Dulong and 
Petit. 
4. In his “Investigation on the specific heat of Minerals,” Neumann (in 1831) first 
published § more accurate determinations of the specific heats of solid compounds. He 
investigated a large numbfer of such compounds, especially those occurring in nature, 
partly by the method of mixture, and partly by the method of cooling ; and he deter- 
mined the sources of error in both these methods, and the corrections necessary to be 
introduced. In a postscript to this paper, he mentioned that he continued the investi- 
gations with an apparatus which, compared with that he had previously used, promised 
far greater accuracy in the individual results, without needing tedious and troublesome 
reductions. This apparatus, by means of which the specific heats of solid bodies, which 
may be heated in a closed space surrounded by steam, can be determined with great 
accuracy, he has not described ||. 
Of the general results of Neumann’s investigations, one must be particularly men- 
* Annales de Chimie et de Physique, [2] vol. vii. p. 142. + Ibid. vol. x. p. 395. 
+ Edinburgh Journal of Science, New Series, vol. v. p. 75, and vol. vi. p. 166. J. F. W. Johnston’s remarks, 
vol. v. p. 278. I only know these papers from Berzelius’s e Jahresbericht,’ vol. xii. p. 17, and Gehxer’s 
‘ Physicalisches Worterbuch,’ new edition, vol. x. part 1, p. 805 et seq. 
§ Poggendorff’s ‘Annalen,’ vol. xxiii. p. 1. 
|| Pape (Poggendorff’s ‘ Annalen,’ vol. cxx. p. 337) has recently described this apparatus. I have had no 
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