112 On the Electric Origin of the Heat of Comhustion. 



by the union of zinc and gaseous oxygen must be sufficiently 

 intense to propel a current of 0°-874. Q x 3-7 = S^'SSi Q 

 against an unit of resistance. Now I°"S8 Q, when urged against 

 an unit of resistance, was able in one hour of time to increase 

 the temperature of a pound of water by 15°"12; therefore 



(3"234\- 

 , ' ) 

 1*88 / 



X 15°'12 = 44'°"74 of heat. But in (70.) of my former paper, 

 I proved that the same quantity of heat should always (ac- 

 cording to the theory which refers the whole of the heating 

 power of the voltaic apparatus to resistance to the electric cur- 

 rent) be produced by a given quantity and intensity of electro- 

 lysis, whether the resistance opposed to the current be small 

 or great. Wherefore, the heat, which on these principles 

 ought to be generated by the combustion of 3*234 equivalents 

 of zinc, is 44°"74 ; or, in other words, one equivalent, or 32'3 

 grains of zinc, should generate heat sufficient to increase the 

 temperature of a pound of water by 13°"83. 



61. Now, as 1 have before stated, the quantities of heat 

 evolved bv the combustion of the equivalents of bodies, ought, 

 according to the theory of resistance to electric conduction, 

 to be proportional to the intensities of their affinities for gaseous 

 oxygen. These, in the cases of zinc, iron, potassium, and hy- 

 drogen, are 1-32, M8, 2-05 and 1. Hence 13°-83, 12°-36, 

 21°'47, and 10°*47, are the quantities of heat which ought, ac- 

 cording to our theory, to be produced by the combustion of 

 32-3 grains of zinc, 28 grains of iron, 40 grains of potassium, 

 and 1 grain of hydrogen. 



62. Bv comparing these results of theory with the quantities 

 of heat, lo°-8, 9°-48, 17°'6, and 8''-36*, which were (53—56.) 

 obtained from experiment, it will be seen that the former ex- 

 ceed the latter by about one quarter. Considering the difficulty 

 of preventing some loss of heat, in consequence of the escape 

 of air from the mouth of the inner jar (51.) during the first mo- 

 ments of combustion, &c., it will, I think, be admitted that 

 experiment agrees with the theory as well as could have been 

 expected. 



63. I conceive, therefore, that I have proved in a satisfac- 

 tory manner that the heat of combustion (at least when it ter- 

 minates in the formation of an electrolyte) is occasioned by re- 

 sistance to the electricity which passes between oxygen and 

 the combustible at the moment of their 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 resist- 



• Crawford, whose method was well adapted lo prevent loss of heat, ob- 

 tained 9'-6. More recently, Dalton observed about 8°'5. 



