380 Prof. Oliver Lodge on the Seat of the 



will at least hold a layer of oppositely charged atoms facing 

 toward it across molecular distance ; so that near each plate 

 we have an excessively thin condenser of enormous capacity ; 

 but in the mass of the liquid is no such strain, the slightest 

 E.M.F. being sufficient to redistribute the atoms here and to 

 produce perfect equilibrium. If the atoms are torn asunder 

 by the electrode and liberated, fresh ones are continually sup- 

 plied by the rest of the liquid, the state of strain being con- 

 stantly re-formed and instantly broken down. 



Thus are the phenomena of polarization and electrolysis 

 explained. 



Now insert into the liquid a pair of plates of zinc and copper 

 in contact. By the contact the zinc has become positive and 

 the copper negative, and accordingly the zinc attracts the 

 oxygen (or S0 4 radical) and combines with it : the copper 

 attracts the hydrogen, and does the best it can with it. 



This crudely is Helmholtz's view of a voltaic cell. 



There is, however, one important detail not yet mentioned. 

 I have spoken as if the work done by an electrode were to tear 

 the atom from its combinations. This is not exactly Helm- 

 holtz's view. He adduces arguments to show that the work 

 required to effect decomposition has for its object, not the 

 separation of the atom from the liquid, but the separation of the 

 &tom from its electric charge. It is to this that it clings, and 

 this that has to be taken from it. If it be made to give this up 



kind of electricity per gramme ; so if n 3 be the number of molecules in a 

 gramme of water, the charge of each dyad atom is 

 1*6 X 10 13 



q = — n* — > - 1#6 x 10 ~ l l P robabl y • 



Hence 1*6 xlO 13 



*'" zmw > - 3x 10 " 12 P robabl y ; 



and, the difference of potential between either plate and liquid being given 

 by 47r.ro-, the whole difference of potential between the electrodes is 



10 13 



V = 8w.ro- = 6-4 X -g— • £. .Q064 electrostatic units probably, 



or 1-92 volt. 



In reckoning the approximate numerical values above, I have assumed 

 that n=10 8 and that nx = l. The resulting decomposition force comes 

 out, quite accidentally as far as I am concerned, very near that needed to 

 decompose acid-water. But I need hardly point out that order of mag- 

 nitude is all that is really calculated in these figures ; and that not only 

 decimals but even numerals, prefixed to the power of 10, have very little 

 meaning. The value of x may perhaps vary somewhat for different sub- 

 stances ; and as to the value of n, though that is definite enough, it is very 

 probable that it ought to be something more like 2 X 10 8 than what I have 

 above assumed it. 



It is at any rate satisfactory that the electrostatic hypothesis should 

 give, as a polarization E.M.F. , a number so entirely comparable with 

 actual results. 



