52 HEATS OF COMBUSTION. 



electromotive force necessary to effect decomposition " the 

 intensities of the affinities which unite gaseous oxygen 

 with zinc, iron, potassium, and gaseous hydrogen." He 

 then, by a method of his own, determines the absolute 

 quantities of heat which are generated by the combustion 

 of these bodies in oxygen, obtaining results which prove 

 clearly " that the quantities of heat which are evolved by the 

 combustion of the equivalents of bodies are proportional to the 

 intensities of their affinities for oxygen." The same law 

 he had previously proved for the heat developed by 

 electrolysis. 



He then compares the actual quantities of heat pro- 

 duced by combustion with the quantities of heat equivalent 

 to the electric actions in the electrolysis, finding that the 

 latter exceed the former by one quarter. This discrepancy 

 he explains as probably due to loss of heat in his experi- 

 ments on combustion, and concludes : " I conceive, there- 

 fore, that I have proved in a satisfactory manner that the 

 heat of combustion (at least when it terminates in the 

 formation of an electrolyte) is occasioned by resistance 

 to the electricity which passes between oxygen and the 

 combustible at the moment of the union. The amount of 

 this resistance, as well as the manner of its opposition, is 

 immaterial both in theory and in experiment, and if the 

 resistance to conduction be great (as it most probably is 

 when potassium is slowly converted into potassa by the 

 action of a mixture of oxygen and common air) or little (as 

 it probably is when a mixture of oxygen and hydrogen is 

 exploded), still the quantity of heat evolved remains pro- 

 portional to the number of equivalents which have been 

 consumed, and the intensity of their affinity for gaseous 

 oxygen*" 



