Forces between Atoms and Chemical Affinity. 783 



We may in a diagram represent the tubes of: force pro- 

 ceeding from a corpuscle in an atom by a straight line 

 •drawn from the symbol representing the atom, and we see 

 that the condition that all the atoms in the molecule should 

 be saturated is that we should be able to draw a diagram so 

 that the symbol which represents any atom which contains n 

 free corpuscles should be the origin of n of these lines going 

 to the symbols representing other atoms, and the termination 

 of an equal number coming from other atoms. 



If we take the structural formula of any valency com- 

 pound as represented in the usual way by bonds between 

 the atoms, and double each of the lines representing a bond, 

 then we may regard one of these lines as representing a tube 

 of force going from the atom and the other a tube entering 

 the atom: and inasmuch as in the diagram of a valency 

 compound the symbol representing an atom of valency n is 

 connected with n of these bonds, we see that the condition 

 given above for saturation will be fulfilled. Thus every 

 compound which satisfies the usual conditions for valency 

 will also satisfy the conditions of our theory. It must be 

 noticed, however, that the conditions of the ordinary theory 

 are more stringent than the new one, and that many com- 

 pounds satisfy the new conditions of valency which do not 

 satisfy the old. When we doubled the lines representing 

 the bonds in the usual structural formula and took one of 

 these lines to represent a tube going from the atom and the 

 other one coming to it, we practically only included the case 

 when if an atom A sends a tube to another B, it receives in 

 return one from the same atom ; this on our view is not 

 necessary : all that is necessary is that the number of tubes 

 which leave A should equal the number which enter it. 

 It is not necessary that the atoms from which A receives 

 the tubes should be the same as those to which it sends them. 



An example or two may make this clearer. On the new 

 view H 3 is a possible valency compound, even when hydrogen 

 is monovalent, as the following diagram shows. Each atom 



in Ho is the origin and also the termination of a tube of 



