

Laws of Molecular Foree. 295 



of the atoms in both states, we must consider the volumes of 

 free H, ,0, and N to be smaller than when they are combined, 

 the change of volume corresponding to the change of energy 

 on combination. If this is true, then the elasticity and density 

 of the non-metallic atoms (or the equivalents of these proper- 

 ties in the electromagnetic or any other theory of light) are 

 so related that although the density changes (N — 1)U re- 

 mains constant, whereas in the metallic atoms the relation 

 between density and elasticity must be quite different, because, 

 as we have seen, (1ST — 1)U actually changes sign in some cases. 



It would be possible to determine approximate values for 

 the dynic equivalents of the uncombined metals from Quincke's 

 data for the surface-tension of melted metals, and also to get 

 some light on the constitution of salts from his measurements 

 of the surface-tension of melted salts, but these would be 

 most appropriately discussed in connexion with a general 

 study of the elastic properties of solids. I have, however, 

 satisfied myself that the dynic equivalents of the uncombined 

 metals are different from their values in the combined state. 



To show the existence of an intimate relation between dynic 

 equivalents and chemical energy we can enumerate the follow- 

 ing propositions : — That in the great majority of inorganic 

 compounds the evolution of heat accompanying the passage 

 of an atom from the uncombined to the combined state is 

 almost independent of the nature of the atoms it combines 

 with, similarly the change of dynic equivalent of an atom on 

 combination is almost independent of the nature of the atom 

 it combines with ; that in organic compounds with \\iq excep- 

 tion of the simpler typical forms the same proposition as this 

 applies both as regards heat and dynic equivalent. 



These general remarks are intended to indicate the most 

 hopeful direction for the continuation of these researches to 

 open up new fields ; and yet in old fields there is abundance 

 of scope for the application of the law of molecular force 

 towards the acquisition of a knowledge of the structure of 

 molecules, in the elasticity of solids, in the viscosity of gases 

 and of liquids, in the kinetics of solutions, and many kindred 

 subjects. 



Melbourne, February 1890. 



