212 SATURATION [APR D. 



It is noteworthy that while ^/(/c/x) is of the same 

 dimensions as 1/v, ^/(K~/) corresponds to 1/e, where e is 

 an electrochemical equivalent. 



APPENDIX E. 

 Electric Saturation, etc. 



In my Report on Electrolysis to the British Association 

 for 1885 (see the Aberdeen volume, pp. 762, 763), I call 

 attention to the possibility that an atomic theory of 

 electricity would give rise to a maximum charge possible 

 on a given area. The maximum surface-density would 

 be attained when every atom was polarised so that its 

 atomic charge faced outwards; and for a solid or liquid 

 it would be very great. For the charge on each being 

 10 ~ 10 , and the number of atoms per square centimetre 

 being 10 16 , it follows that the maximum surface density 

 possible is (r=10 6 electrostatic units per square centimetre. 

 The corresponding gradient of potential would be 4?ro-= 10 7 , 

 or 3,000 megavolts per centimetre; and the corresponding 

 tension would be 27r<7 2 = 6 x 1() 12 c.g.s. = 40,000 tons to the 

 square inch. Of course no dielectric would stand this 

 pressure, but absolute vacuum might. 



In practice, therefore, it follows that when a surface is 

 charged highly, only an exceedingly small percentage of 

 the molecules are polarised with their charges facing 

 outwards. For instance, common air breaks down when 

 the tension rises to a value 2-7n7 2 = J gramme per square 

 centimetre = 400 c.g.s. ; wherefore the maximum or in 

 ordinary air is 8 electrostatic units per square centimetre ; 

 and this quantity would be afforded by the facing outwards 

 of 10 11 molecules, or one in every hundred thousand of a 

 solid surface, or about a tenth per cent, of those in air. 



