1864.] Dr. Kopp on the Specific Heat of Solid Bodies. 235 



The opinion that the elements enter into compounds with the atomic heats 

 they have in the free state has been already expressed ; but the view has 

 also been defended that the atomic heat of an element may diifer in a com- 

 pound from what it is in the free state, and may be different in different 

 compounds. The author discusses the latter view, and criticises the reasons 

 which may be adduced for it ; he comes to the result that it is not proved 

 and is inadmissible. 



As the result of all these comparisons and observations, the author arrives 

 at the conclusion. Each element, in the solid state and at an adequate dis- 

 tance from its melting-point, has one specific or atomic heat, which may 

 indeed somewhat vary with physical conditions (different temperature, or 

 different density for example), but not so much as to necessitate such 

 variations being taken into account in considering the relation in which the 

 specific or the atomic heat stands to the atomic weight or composition. 

 For each element it is to be assumed that it has essentially the same 

 specific heat or atomic heat in the free state and in compounds. He then 

 passes on to determine what atomic heats are to be assigned to the indivi- 

 dual elements. As data for determining this he takes (1) the atomic heats 

 which follow from determinations of the specific heat of the elements in 

 the free, solid state ; (2) the atomic heats obtained for an element if, from 

 the atomic heat of one of its compounds, which contains beside it only 

 elements of known atomic heat, the atomic heats corresponding to the 

 latter elements are subtracted ; (3) the diiference found between the atomic 

 heats of analogous compounds of an element of unknown and of an ele- 

 ment of known atomic heat, in which case the difference is taken as beino- 

 the difference between the atomic heats of these two elements. The au- 

 thor dwells upon the fact that in the indirect deduction of an element by 

 (2) and (3) the result may be uncertain, — first, because the atomic heats 

 of compounds are frequently not known with certainty, as is seen by the 

 circumstance that analogous compounds, for which there is every reason to 

 expect equal atomic heat, are found experimentally to exhibit considerable 

 differences ; but secondly, because in such deductions the entire relative 

 uncertainty, in the atomic heats for a compound and for that to be sub- 

 tracted from its composition, is thrown upon a small number, viz. the 

 residue remaining in the deduction. 



The details of the considerations by which the author deduces the 

 atomic heat of the individual elements cannot be gone into ; the results 

 simply, which are not all attained with equal certainty, may be adduced. 

 The author adopts the atomic heat 1-8 for €, 2-3 for H, 27 for B, 37 for 

 rSi, 4 for O, 5 for Fl, 5 "4 for P and S, 6*4 for the other elements for which 

 or for whose compounds the atomic heat is known in somewhat more 

 trustworthy manner, it being left undecided in the case of the latter ele- 

 ments, whether (in accordance with Dulong and Petit's law) they have the 

 same atomic heats, or whether the differences in the atomic heats cannot 

 at present be shown with certainty. 



