Chemical Affinity in terms of Electromotive Force, 259 



1*00396; so that this observed heat-evolution corresponds to 

 34103*5 x 1-00101 = 34138, or to 34103-5x1-00396 = 34239 



gramme-degrees per 8*98 grammes of water, according as the 

 specific heat of water is calculated from the one or the other 

 formula. If, however, the combination of the oxygen and 

 hydrogen took place at 0° (producing water at 0°) instead of 

 at 18° throughout, the amount of heat-evolution would be 

 increased by a— b; where a is the heat given out by 8*98 

 grammes of water in cooling from 18° to 0°, and b the amount 

 of heat required to raise 1 gramme of hydrogen together with 

 7*98 grammes of oxygen from 0° to 18°. Since the specific 

 heats for equal weights under constant pressure of oxygen and 

 hydrogen are respectively 0*218 and 3*405, the value of a — b 

 is sensibly 69 gramme-degrees ; so that Thomsen's value be- 

 comes 34,207 if Kegnault's formula is used, and 34,308 if 

 Bosscha's be employed. 



28. Favre and Silbermann found (Annales de CJdmie [3], 

 xxxiv. p. 357) that when 9 grammes of water were formed 

 from oxygen and hydrogen, the gases being at a mean tempe- 

 rature of 9° (at 6° to commence with and 12° to end with), 

 and the water produced being at 6° (the heat required to raise 

 the temperature of the water produced being taken into ac- 

 count in determining the water-equivalent of the calorimeter), 

 the average heat-evolution sufficed to raise 34,462 grammes 

 of water 1°, the water being at the average temperature of 9°. 

 According to Regnault's formula the specific heat of water at 

 9° is 1*00043, and according to Bosscha's 1*00198 ; whence 

 the heat-evolution per 8*98 grammes becomes 



O.QO 



^P x 34462 x 1-00043 = 34400, 

 or 



^- x 33462 x 1-00198=34453, 



according as the one or the other formula is used. To this 

 must be added a quantity c— d to reduce the value to that 

 which would have been produced had the gases and water 

 produced been all at 0°: c is the heat given out by 8*98 

 grammes of water in cooling from 6° to 0°, whilst d is the 

 heat required to raise the hydrogen and oxygen from 0° to 9°; 

 whence c — d is sensibly 8 gramme-degrees. So that the heat- 

 evolution becomes 34,408 by Regnault's formula, and 34,461 

 by Bosscha's formula. 



29. Andrews found (Phil. Mag. 1848, vol. xxxii. p. 321) 

 that a litre of dry hydrogen gas at 0° and 760 millims., in 

 combining with oxygen, the gases being at the average tern- 



