Chemical Affinity in terms of Electromotive Force. 261 



hence an additional reason is derived for viewing Bosscha's 

 alleged corrections of Regnault's numbers as being more open 

 to objection than these numbers themselves. 



If the combination of the oxygen and hydrogen be supposed 

 to take place at 20° instead of 0° (i. e. if the gases used and 

 water produced be all at 20°), the heat-evolution will be less 

 than that calculated above by g—h gramme-degrees, where g 

 is the heat required to raise 8*98 grammes of water from 0° to 

 20°, and h that requisite to raise the constituent gases through 

 the same range, i. e. where g— h = sensibly 77 gramme-degrees. 

 Whence, if water be decomposed at 20° and 760millims. into 

 oxygen and hydrogen at the same temperature and pressure, 

 the heat-absorption is 34,097, using Regnault's formula, and 

 34,191 using Bosscha's formula. Similarly at 15°, the cor- 

 rection g — h would be 58 gramme-degrees, giving the values 

 34,116 (Regnault's formula), and 34,210 (Bosscha's formula). 



31. On the other hand, experiments have been cited above 

 (§§ 2 & 5), made by Joule, Kiechl, Raoult, and Favre, giving 

 the following values for the heat-absorption during the elec- 

 trolysis of water at the ordinary temperature : — 



Joule 33557 



Kiechl . . 

 Raoult • . 

 Favre . . 



Mean 



33653 

 34028 

 34204 



. 33860 



As these values are mostly calculated per 9 grammes of 

 water, this average value should be reduced in about the pro- 

 portion of -g— ; but since the increase of temperature of the 



calorimeter observed represents a slightly higher number of 

 gramme-degrees than that stated, on account of the increase 

 of the specific heat of water with the temperature, the average 

 value requires slightly raising from this cause. After making 

 all probable allowances for these corrections, however, the 

 mean value still remains perceptibly lower than that calcu- 

 lated as above from the results of Schuller and Wartha, von 

 Than, Julius Thomson, Andrews, Favre, and Silbermann. 



On the whole, the data at present extant may be taken to 

 show that when 8*98 grammes of water are formed from gaseous 

 oxygen and Itydrogen at the ordinary temperature (15° to 20°) 

 throughout, the evolution of heat is sensibly that required to 

 raise the temperature of 34,100 grammes of water from, 0° to 

 1° C ; or when 1 gramme is formed, the heat-evolution suffices 

 to raise 3797 (or practically 3800) grammes from 0° to 1° C, 

 this value being taken from the reductions by Regnault's 



