CH. XVL] MOLECULAR FORCES 153 



On Chemical and Molecular Forces. 



The force of chemical affinity has long been known 

 to be electrical. This opinion was propounded by 

 Berzelius, and was also held previously by Davy 

 and afterwards by Faraday. Ordinary electrical 

 attraction between charged bodies may be called 

 molar chemical action ; only there is no combination 

 in ordinary cases, because the opposing charges 

 spark into one another, and so the attraction ceases 

 when a certain proximity is reached. This dis- 

 charge and cessation of attraction does not seem to 

 occur among atoms ; the difference of potential 

 between them is too low to permit of mutual 

 exchange or neutralisation of charge, so the combi- 

 nation is permanent.* 



Keal chemical attraction occurs between two atoms 

 each of which contains an unbalanced electron one 

 extra, or it may be more than one extra, electron of 

 given sign. Such an atom thus has a centre of force 

 whereby it can attach itself to other atoms and enter 

 into pairing or chemical combination with them. It 

 is probable that a negative charge is an excess, and a 

 positive charge a defect ; and that when pairing 

 occurs the excess charge of one fills up the deficiency 

 of the other, and composes a complete and neutral 

 molecule. 



Union of this kind, however, never seems quite as 

 strong and permanent as the union of the electrons in 

 the atom itself: the molecule easily separates at the 

 same place again, under the influence of decomposing 

 influences, and does not seem able to split up in 

 other ways into new substances ; except in organic 

 chemistry, where various modes of splitting up a 



*See Lodge, Brit. Assoc. Report, 1885, pp. 744, 5. 



