MOLECULAR VOLUME 689 



the action of these forces, so that there results a certain com- 

 pression. This in the first instance affects the Simple Felspathic 

 constituents, but ultimately the constituent atoms also. 



It follows that the individual atoms have different volumes in 

 the two modifications, owing to the difference in the constraint 

 imposed by the attracting forces. 



We can speak of a crystalline atom and a glassy atom, for 

 they are different. Crystalline and glassy modifications of sub- 

 stances have their origin in the peculiarities of intermolecular 

 forces. These are in reality residual affinities due to the atomic 

 constituents of the molecules and their special arrangements. 

 We are, consequently, led to look for the ultimate cause of physical 

 modifications in the nature and arrangement of the atoms. 



In conclusion we see that a study of the Molecular Volumes 

 of Substances gives us, as it were, an external view of the 

 structures. From the peculiarities noticed, by a process of 

 analysis of the data for known substances, we proceed induc- 

 tively to arrive at conclusions concerning the internal conditions 

 and the modes of arrangement of the atoms in the molecules. 

 By the opposite— or deductive — method R. Kleeman {Phil. Mag. 

 vi. 19, 840-46) has recently studied the question. This author 

 concludes that the range of action of the molecular forces is 

 equal to the distance between the molecular centres. The 

 molecules are thus strongly attracted. In opposition to these, 

 the kinetic heat-forces act. By supposing that the intervening 

 space is occupied by matter, then owing to the extensive motion 

 of the vibrating atoms the resistances to compression which 

 Richards has studied would be represented by the mechanical 

 resistance occasioned by this motion. The molecular kinetic 

 forces are so far reduced as compared with vapours that only 

 slow diffusion is possible. 



