366 Dr. C. R. A. Wright on the Determination of 



that the resistance of the cell was wholly negligible (?) in 

 comparison with it, and consequently the heat developed in 

 accordance with Joule's law was practically nil, Favre ob- 

 tained values in terms of heat corresponding to the difference 

 between the work done in decomposing the electrolyte into 

 the primary and the final products of decomposition. E. g. in 

 one set of experiments with water, the actual mean heat- 

 development was close to 14,000 gramme-degrees per gramme- 

 equivalent of water decomposed ; adding to this 34,100 

 gramme-degrees, the heat corresponding to the formation of 

 gaseous oxygen and hydrogen (Part I. § 31), it results that 

 in this experiment the total work done during the electrolysis 

 was equivalent to 48,100 gramme-degrees, or 2*12 volts ; i. e. 

 the mean value of e in these experiments was 2*12 volts. By 

 comparing together various values obtained in this way with 

 different electrolytes, Favre was led to the conclusion that of 

 this 14,000 gramme-degrees (which he regarded as a constant 

 heat-absorption during water-electrolysis over and above the 

 heat taken up in the formation of gaseous oxygen and hy- 

 drogen = 34,100), about 9500 were due to the transforma- 

 tion of allotropic oxygen formed by the first action of the 

 current into ordinary oxygen gas, and the remainder to the 

 transformation of allotropic hydrogen into ordinary hydrogen 

 gas. The above-described results, however, indicate that 

 these particular numerical values have only reference to the 

 particular apparatus and current-strengths used by Favre : 

 had the size of the electrodes been varied, or their nature, or 

 the current-strength, quite different numbers would have been 

 obtained in each case, not only in these particular experi- 

 ments cited, but also in a number of other analogous ones with 

 other substances ; for each change would have brought about 

 a corresponding change in the value of e, and hence in the 

 heat-evolution. Apart from this, however, as Favre's values 

 were obtained with the mercury-calorimeter, a considerable 

 probable error attends the determinations ; so that finally no 

 reliance at all can be placed on the conclusions arrived at 

 by Favre in this series of experiments, as regards numerical 

 values. 



It is noticeable in this connexion, that experiments by 

 Raoult {Annates de Chimie et de Phys. ii. p. 317, and iv. 

 p. 392, 1864 and 1865) show that the value of the counter 

 electromotive force set up during electrolysis varies with the 

 current cceteris paribus. Raoult observed the "subsequent 

 polarization" of an electrolytic cell very quickly after the 

 rupture of the current, determining it in terms of a Daniell's 

 cell, this being itself valued in terms of the heat producible by 



