Laws of Molecular Force. 39 



shows a close approach to constancy, except in the case of 

 the second family, whose place seems to be taken by the dyad 

 zinc subfamily, in which the ratio (M/p)/M 2 / is 1*3, and 

 therefore the product n(M/p)/M.H is 2'6. As the subfamilies 

 have a ratio (M/p)/M% which is a simple multiple or sub- 

 multiple of the value in the main family, we can say that in 

 the metals n(M/p)/M 2 Z is close to 2*8, or a simple multiple or 

 submultiple of 2*8, except in the second family, where it is 

 2*0. Thus the attracting-power of a metallic atom is pro- 

 portional to the square root of its volume or of a simple 

 multiple of its volume, and also to the square root of its 

 valency. This relation for the metals can also be stated in 

 another interesting form, for as lp represents the potential 

 energy due to the attractions of the molecules in unit mass, 

 M 2 //(M//o) is the potential energy of mass M, which may be 

 taken as forming the greater part of the heat of vaporization 

 of the gramme-molecule ; thus, then, the potential energy of 

 the molecules in a gramme-equivalent (and probably the 

 latent heat of vaporization of a gramme-equivalent) of the 

 metals in the main families has nearly the same value for all, 

 and in the other metals a value which is a simple multiple or 

 submultiple of this. The methods devised in this paper for 

 calculating M.H for inorganic compounds also lead to approxi- 

 mate values of their latent heats of vaporization, which are of 

 some importance in Thermochemistry. 



With this knowledge of the relation between M 2 Z and 

 volume in the uncombined metals, we can return to the study 

 of the relationship of the parts carried by the metallic atoms 

 into (M 2 /) 5 and M/5. We have already seen that the metallic 

 atoms in combination do not have their parts of (M 2 Z) 2 and 

 M/3 proportional to one another; and in the light of what we 

 have just found for the free metals, we ought to compare the 

 square of the part F carried by a metal atom into (M 2 /) 8 in 

 compounds with the part B carried into M/p. Here are the 

 values for the Li family : — 



Table XXXI. 

 (Li family in compounds.) 



Li. 



B or volume of atom ... 2'0 



F 2 58 



•9B+4-4 62 



The first two rows of numbers show that F 2 and the volumes 

 of the atoms in compounds run a parallel course, but are not 



Na. 

 7-4 



18-6 



Eh. 

 34-4 



Cs. 



560 



12-2 



21-2 



36-0 



53-2 



11-1 



21-1 



354 



54-8 



