480 REPOKT — 1888. 



had in fact been able to deduce the atomic weights of elements whicli 

 were not at the time capable of examination as to their specific heats 

 directly, as in the cases of Rb, Cs; of Li; of Sr, and Ba; by means of the 

 rule that the molecular heats of bodies of similar atomic composition and 

 chemical constitution are equal ; no rule had been found by which the 

 molecular heats of compounds were connected with the atomic heats of 

 the component atoms ; with the exception of Woestyn's law (1848) that 

 the molecular heat is the sum of the atomic heats for all the atoms in the 

 molecule. But this exception was indeed important (1) for the frank 

 recognition of the fact that the atomic heats of elements cannot be 

 reckoned as equals — at the best as varying within narrow limits; in fact, 

 as putting forward as of fundamental importance that Duloug and Petit's 

 law is only approximate and not a very near approximation ; (2) for the 

 extension to compounds generally of the rule which Regnaulb had found to 

 apply to alloys. But Wo3styn's law led to no important results, as it was 

 not followed up by a determined attempt to confront the questions, what 

 are the atomic heats which must be assigned to elements such as chlorine, 

 oxygen, hydrogen, nitrogen, fluorine, and others, the specific heats of 

 which in the solid state cannot be determined directly ; and of carbon, the 

 specific heat of which in the free state at ordinary temperatures varies so 

 much with its state of aggregation and in allotropic modifications of it. 

 The number of compounds which contain one of these elements or more is 

 so very large a proportion of the compounds to which the rule should be 

 applied, and by means of which it should be verified, that it is not to be 

 wondered at that no important generalisation resulted from it. To 

 "Wcestyn, however, must be given the credit of giving definite expression 

 to an idea which Hermann Kopp independently took as the basis of his 

 great work on the subject. 



Gamier in 1852' proposed, as did Cannizzaro in 1858,^ the following 

 relation : if C be the specific heat of a compound, n the number of atoms, 



AC . 



and A the molecular weight, then is constant, 



11 



Kopp's Investigations on Specific Heats. 



Hermann Kopp was among the first to draw the attention of chemists 

 to the relation of physical properties of compounds to chemical composi- 

 tion ; as early as 1841 he first stated his law of boiling points of homo- 

 logous series of carbon compounds. The very existence of such a law-like 

 relation struck many chemists as paradoxical ; so axiomatic had seemed to 

 them the assumption that the properties of elements are extinguished 

 when these enter into combination that the regularity of the effect on the 

 boiling-point of the addition of one atom of carbon and two of hydrogen to 

 the molecule of a compound was combated at first, but has long been 

 accepted in principle universally ; other investigations with a similar 

 object by H. Kopp need not be mentioned here. His work on specific 

 heats of bodies in the solid state was part of this general plan, and his 

 object in it was to find if possible a relation between the specific heats of 

 compounds and of their component elements. With this object he made a 

 large number of determinations of specific heats of elements, and of corn- 

 rounds prepared in the laboratory, as also of a number of minerals ; ^ and 



> a R. 37, p. 130. = II Nuovo Cimento, 7, p. 321. 



3 L. Ann. Siq>2>li-ment, b. 3, 1864, p. 1 ; and loo. cit. p. 289. 



