166 Intelligence and Miscellaneous Articles. 



the battery. Then the entire amount of heat evolved will be ex- 

 pressed by 100X20= '2000. Suppose, secondly, we employ the same 

 battery to decompose water ; the virtual intensity of the entire bat- 

 tery circuit will then be 20— 3^=16f (seep. 272 of the above- 

 named memoir) ; and when 100 atoms of zinc in each cell of the bat- 

 tery have been dissolved, or what comes to the same thing, when 

 100 atoms of hydrogen have been liberated in the decomposing 

 cell, the heat evolved by the entire circuit will be expressed by 

 100 X 16f = 1666. The difference between 2000 and 1666, or 334, 

 represents of course the heat taken up in effecting the separation of 

 100 atoms of hydrogen from 100 atoms of oxygen, and liberating 

 them in the gaseous state. 



In p. 276 it will be seen that I deduced the heat of combustion 

 of hydrogen from the quantity of heat due to the intensity of battery 

 required to electrolyze water. In other words, I found the heat of 

 combustion of hydrogen by observing the heat lost in the voltaic cir- 

 cuit when water was decomposed. 



My subsequent papers confirm and extend the facts arrived at in 

 1841, and indicate the effects of secondary actions in the battery, 

 the laws which regulate the evolution of heat when positive metals, 

 such as zinc, are employed as electrbdes evolving hydrogen, the 

 mechanical value of chemical changes, &c. It is in giving a more 

 defined expression to the law of the evolution of heat by combustion 

 that Dr. Woods erroneously supposes I have contradicted myself. 

 The passage he refers to (Phil. Mag. Dec. 1843, pp. 442, 443) sim- 

 ply states " more explicitly, that it is not precisely the attraction of 

 affinity, but rather the mechanical force expended by the atoms in 

 falling towards one another, which determines the intensity of the 

 current, and consequently the quantity of heat evolved." This mo- 

 dification appeared to me necessary, inasmuch as, according to the 

 mechanical theory of heat, the product of the attraction of particles 

 into the distance they have to traverse in order to combine, rather 

 than the attraction itself, is to be considered as the source of heat. 



If, therefore, my paper on the heat disengaged in chemical com- 

 binations, sent to the French Academy in 1846, and published in the 

 Philosophical Magazine, June 1852, were to go for nothing, my 

 claim to priority would be completely established ; but I maintain, 

 along with the most eminent scientific authorities, that a paper dates 

 from the time that its receipt has been certified by a scientific body. 

 My opinion is confirmed by the practice of the Royal Society and 

 other learned bodies, who cause the date on which a paper comes to 

 hand, as well as that on which it is read, to be duly certified. I 

 may add, that Faraday has dated his * Experimental Researches ' 

 from the time they were received by the Secretary of the Royal 

 Society. My own paper was not only duly acknowledged in the 

 Comptes Rendus for February 9, 1846, but was referred to a Commis- 

 sion. It still remains in the possession of the Academy. 

 I have the honour to remain. Gentlemen, 



Yours very respectfully, 



James P. Joule. 



