Laws of Molecular Force. 45 



are at a distance r apart, and if the force between the atom or 

 radical B in one molecule and C in the other is k/3yf(r) , and 

 between C in one and D in another is IcySf(r), and so on, 

 then the attraction between the two molecules is 



k(b 2 /3* + c y + . . . + 2cdy$ + 2db$p + 2hcf3y + . . .) 

 = k{h/3 + cy + d8 + ...) 2 , 



so that a, the parameter for the whole molecule, is given by 



a = k i (b/3 + cy + d8 + . . .), 



which is the symbolical statement of our result for the carbon 

 series of compounds that the parameter a for a molecule is the 

 sum of parts due to the separate atoms and radicals in it, and 

 shows that in these compounds the atoms and radicals attract 

 one another with a force proportional to the product of 

 parameters characteristic of each. This does not imply that 

 the parameter belonging to an atom is invariable, for the 

 atoms in a free element have different parameters from those 

 they possess in a compound : by chemical combination both 

 the volumes and force-parameters of many atoms are altered, 

 and the amount of alteration depends on the chemical function 

 of the atom in the molecule ; while the chemical function of 

 an atom or radical in an organic compound is constant, its 

 force-parameter is constant. This influence of chemical 

 function on the parameter of molecular force becomes mani- 

 fest in the typical inorganic compounds, especially of the 

 metals. If the compound is of the type RS % , where R is an 

 atom of valency n combined with n monad atoms S, then the 

 expression for a takes the form 



(p and <t being parameters belonging to R and S) ; or perhaps 

 a more suggestive form in which to put it is 



a 2 /n = {p/n-\-a)% 



which means that the mutual energy of two molecules of this 

 type divided by the number of equivalents in each can be 

 obtained by regarding each equivalent as a separate attracting 

 entity. The equations just given hold true not only when R 

 is a metal and S a non-metal, but also when R is an acid 

 radical of any basicity and S a monad metal. The law for 

 the more general case of a compound R m S n has not been 

 investigated in this paper because of the want of suitable 



