IV 



his elaborate memoir, " On the Specific Heat of Compound Sub- 

 stances," in which he sought to develop Neumann's law, was published 

 by the Royal Society. The * Uoyal Society Catalogue of Scientific 

 Papers ' gives the number of his papers as 65. 



Kopp enjoys an almost unique position as an investigator. The 

 one consistent purpose of his work was to establish a connexion 

 between the physical and chemical nature of substances ; to prove, in 

 fact, that all physical constants are to be regarded as functions of the 

 chemical nature of molecules. It is not implied, of course, that the 

 conception of such an interdependence originated with him. As a 

 matter of fact, almost immediately after the publication of Dalton's 

 ' New System of Chemical Philosophy,' in which the doctrine of 

 atoms was revived to account for the fundamental facts of chemical 

 union, the endeavour was made to connect the chemical attributes of 

 a substance with one of its best defined physical constants, viz., its 

 atomic mass. Prout's hypothesis is, in reality, the generalised 

 expression of such an attempt ; it is an adumbration of Mende- 

 leefFs great discovery of the Law of Periodicity. But it may 

 be justly claimed for Kopp that no one before him made any 

 systematic effort to connect such of the physical qualities of sub- 

 stances as admit of quantitative statement with the stoichiomefcrical 

 values of such bodies. The sporadic attempts made prior to 1840 

 were practically fruitless on account of the imperfect nature of the 

 physical data up to that time extant. 



When Kopp began his inquiries, very few boiling points were 

 known, even approximately ; and he had, as a preliminary step, to 

 ascertain the conditions under which such observations must be made 

 in order that accurate and comparable results could be obtained. 

 The thermal expansions of barely half a dozen liquids had been 

 measured, and the very methods of making such measurements with 

 precision had to be worked out. 



At the outset of his investigations, Kopp found the physical con- 

 stants with which he was more immediately concerned very much as 

 Berzelius found Dalfcon's values of^the relative weights of the atoms ; 

 at the close of his work they were hardly less accurately known than 

 were those stoichiometric numbers to the ascertainment of whicfli the 

 great Swedish chemist had dedicated his life. 



Kopp's more important memoirs readily and naturally fall into 

 comparatively few groups, viz., (1) those concerning the relations 

 between the specific gravities of substances and their molecular 

 weights; (2) those treating of the relations between boiling point 

 and chemical composition ; and (3) the papers relating to the specific 

 heats of solids and liquids. As regards the other papers, only the 

 briefest notice is here possible. Much of this work was of a pioneer 

 character, and his conclusions have necessarily been modified by 



