Atom and the Charge of Electricity carried by it, 523 



and a positively electrified chlorine one should be connected 

 by a conducting circuit. From the mechanical illustrations 

 previously given, it seems unlikely that the atoms would inter- 

 change their charges by coming into contact, the positive 

 charge passing from the chlorine to the hydrogen atom 

 and vice versa. From these illus- 

 trations we should rather expect that if Fig. 

 a negative hydrogen atom came very 

 near to a positive chlorine one, the two, 

 if alone in the field, would tend to 

 repel rather than to attract each other, 



the Faraday tube connecting the atoms ceasing to be straight, 

 and bulging out into the surrounding medium somewhat in 

 the manner shown in fig. 3. 



If in addition to the two atoms there were other charged 

 bodies producing a very intense field tending to push the 

 hydrogen and chlorine atoms together, then the interchange 

 of their charges might take place by the ends of the Faraday 

 tube gliding from one atom to the other after these atoms had 

 been forced into contact by the external field. There are 

 indications that the external field would have to be such as to 

 produce a potential difference of a large number of volts 

 between the two atoms before this method of exchanging their 

 charges took place. In the absence of this potential differ- 

 ence, the atoms would not exchange their charges unless the 

 medium into which the Faraday tube spread contained some 

 conductor along which the ends of the Faraday tube could glide 

 from one atom to the other. The necessity for this conduct- 

 ing circuit is perhaps one of the reasons why the presence of 

 a third substance seems necessary for the continuance of 

 many chemical reactions. How much a third substance able 

 to act as a conductor could facilitate chemical combination 

 may be seen from the following example. Suppose we have 

 a mixture of hydrogen and chlorine molecules, and that by 

 some external cause we split up these molecules into atoms ; 

 half of the hydrogen atoms produced by the dissociation of the 

 hydrogen molecules will be positively electrified, while the 

 other half will be negatively electrified ; the same will also be 

 true of the chlorine atoms. This condition will be permanent 

 if the negative hydrogen atoms have no opportunities of inter- 

 changing their charges with the positive chlorine atoms, 

 and a positive hydrogen atom would thus not be limited to 

 combining with a negative chlorine one to form a molecule of 

 hydrochloric acid, but might instead combine with a negative 

 hydrogen atom to form a hydrogen molecule. If, however, 



