180 Dr. C. 11. A. Wright on the Determination of 



the water surrounding the — electrode the hydrogen is wholly 

 reconverted into water, leaving out of sight the formation of 

 liquids of differing densities round the two electrodes, and 

 supposing that the + electrode and fluid surrounding it are 

 saturated with oxygen, it will result that 



S(H) = E 1 + {(l-n,)H 1 -nA}xJ 

 (the n l7 Hj, and h l} referring to hydrogen), whence 



*={(1— w 2 )H 2 — n 2 h 2 }xJ. 



Now when n 2 = this value is + , being H 2 % J ; but if 

 ?i 2 = lit would become negative, = — A 2 %J : for certain values 

 of n 2 therefore (i. e. for certain rates of current-flow, Part IV.), 

 the value of e whilst still + must be less than 1*50 volt ; 

 i. e. when " electrolytic convection " takes place, so that the 

 hydrogen evolved by electrolysis is reoxidized as fast as 

 generated, electrolysis may be produced by means of a less 

 E.M.F. than 1 # 50 volt. Obviously the same result follows if 

 the hydrogen be unoxidized, but the oxygen be reconverted 

 into water by dissolved hydrogen ; and the same may ensue if 

 only a part of the hydrogen or oxygen is thus reconverted 

 into water. 



64. Again, when 2(H) is negligible compared with the 

 other terms, and n x and n 2 are both small, the value of e may be 

 greatly superior to E x ; for when n x and n 2 are both =0 and 

 % (H) is negligible, 



6 =E 1 + (H 1 + H 2 ) % J=E Z . 



Experiment shows that, cceteris paribus y the stronger the current 

 the smaller are the values of ?i Y and n 2 ; that is, e continually 

 increases as the current increases, tending towards a limiting 

 value in any given case (Crova, Ann. Chim. et Phys. lxviii. 

 p. 413, 1868). Although at present the data for calculating 

 accurately the limiting values of E, for various substances are 

 not extant, yet it is known that in the case of water E, must 

 be upwards of 3 volts; for values of e above 3 volts have been 

 observed : that is, the value of H l + H 2 is greater than 

 34,100 gramme-degrees ; or the heat of transformation of the 

 " nascent " products of electrolysis of water into gaseous oxygen 

 and hydrogen jointly exceeds the heat developed by the combina- 

 tion of these gases at ordinary temperature and pressure to 

 form liquid water. 



The theorem therefore accounts for all possible variations 

 in the counter E.M.F. set up during electrolysis, between the 

 minimum values (when the normally gaseous products of 

 electrolysis are evolved not as free gases, but as condensed 



