Chemical Affinity in terms of Electromotive Force. 271 



taining-vessel in contact with the liquid will exhibit a greater 

 or less difference of potential, and a current will flow between 

 them through the liquid, the points on the glass surface acting as 

 electrodes ; after a half revolution the potentials of the two 

 points are reversed, the current flowing in the opposite direc- 

 tion relatively to the points (but in the same direction rela- 

 tively to the magnets) ; so that so far as these two points are 

 concerned a series of alternating currents (or rather of 

 currents going through a regular cycle increasing from to 

 a + maximum, decreasing to and then to a — maximum, 

 and then increasing again to 0, and so on) are set up, the 

 effect of which is to eliminate the effects of " polarization " 

 as completely as in Kohlrausch's method of determining con- 

 ductivity by means of alternating currents, the products of elec- 

 trolysis being reunited, so to speak, by the action of the reverse 

 currentbefore they have time to escape. Since the nett chemical 

 action is nil, the work done by the currents appears solely as 

 heat ; but it does not therefore follow that electricity passes 

 through the liquid without causing electrolysis, any more 

 than in Kohlrausch's experiments. 



Relationships between the Counter Electromotive Force set up 

 during Electrolysis and the Rate of Flow of the Current 

 passing. 



83. It has often been noticed by previous observers that 

 the so-called " polarization," or, more strictly, counter E.M.F. 

 (§ 57) set up during electrolysis, especially of acidulated water, 

 by a given current, gradually rises until it becomes approxi- 

 mately constant. The cause of this is doubtless that so long 

 as the fluid surrounding the hydrogen-electrode contains 

 dissolved air, and so long as the electrodes and the fluids 

 surrounding them are capable of further attracting, occluding, 

 or dissolving the gases evolved in their proximity, the aura 

 surrounding each electrode does not possess its normal 

 average density ; that is, the values of %(nli) and 2(H), in 

 the expression for the counter E.M.F. set up (Part III. § 61), 



6 = E 1 +p{(l-n)H-2(n/0-S(H)] % J,' 



are greater at first than the values to which they finally 

 subside. 



For the same reason, if an electromotor of E.M.F not 

 greater than 1 to 1*5 volt or so be connected with a voltameter 

 containing diluted sulphuric acid (unboiled, or even if boiled), 

 and provided with electrodes of non-oxidizable material, as is 

 well known, a current flows at first, the strength of which 

 gradually diminishes to a minute amount, whilst the so-called 



