Forces betiveen Atoms and Chemical Affinity. 765^ 



The values of M found in this way show that, to separate- 

 two molecules in class II., placed so that the axes of their 

 doublets are in the same straight line, will require an amount 

 of work larger than that required to separate the atoms in 

 many chemical compounds. The work required to separate 

 two doublets of the strength of those in the molecule of 

 ammonia, when the distance between their centres is 10~ 8 cm., 

 calculated from the formula 2M 2 /r 3 , is equal to 4*5 xlO" 12 

 erg. The work required to dissociate a molecule of iodine, 

 as deduced from experiments on the dissociation of iodine 

 vapour, is 2'3 X 10~ 12 erg. The work required to separate a 

 corpuscle at a distance of 10~ 8 cm. from the centre of the 

 doublet is 6*7 x 10~ 12 erg, equal to that gained by a fall of the 

 atomic charge through 4*5 volts. This large value explains 

 why gases which show abnormally large values for the specific 

 inductive capacity may be expected to attract to themselves 

 and keep bound any corpuscles in their neighbourhood, and 

 thus, by diminishing the chance of a corpuscle existing in 

 the free state, to diminish the mobility of the negative ions 

 in gases. This effect has long been known to be produced 

 by the vapours of water and alcohol, two gases which 

 Badeker has shown to possess abnormal specific inductive 

 capacities; it would be an interesting subject for investi- 

 gation to see whether this property is possessed by all 

 vapours with exceptional specific inductive capacities. 



It may be asked why, if the work required to separate 

 two molecules of ammonia is greater than that required 

 to separate two atoms of iodine, is the proportion of free 

 iodine atoms so much smaller than that of free ammonia 

 molecules ? The answer to this is found in the con- 

 sideration of the relative mobility of the systems which 

 exert the attractions in the two cases. If we take two 

 ammonia molecules A and B at random, the force between 

 their doublets is just as likely to be a repulsion as an 

 attraction. In order to develop the maximum attraction 

 the two molecules A and B must wheel round until the 

 axes of their doublets are in the same straight line and 

 point in the same direction : this involves the rotation of 

 two massive molecules. Whereas if we take two iodine 

 atoms C and D and place them at random, all that is 

 necessary to develop their maximum attraction is for the 

 corpuscles inside the atoms to move into new positions; 

 as the inertia of these corpuscles is much less than that 

 of the molecules, the maximum attraction is much more 

 likely to be developed in the case of the iodine atoms than 

 in that of the ammonia molecules, and thus the number 



