[ 74 ] 

 IX. Intelligence and Miscellaneous Articles. 



THE ABSORPTION OP HEAT BY DECOMPOSITION. 



To the Editors of the Philosophical Magazine and Journal. 

 Gbntlemkn, Parsonstown, June 1866. 



TN an abstract of a paper sent by me to the Royal Society, pub- 

 -■■ lished in the ' Proceedings' for January last, I claim the discovery 

 of the law that " decomposition absorbs as much heat as the com- 

 bination of the elements originally produced." In the ' Proceedings' 

 of the Society for March following, Mr. Joule disputes my claim, 

 and refers to papers of his published in the Philosophical Magazine, 

 October 1841. He also says he sent a memoir to the French Aca- 

 demy in 1846, which however was not published until 1852, in the 

 Philosophical Magazine. 



As to the paper published in the Philosophical Magazine for 

 October 1841, after carefully reading it, I cannot find anything 

 in it which proves the law I have mentioned. Mr. Joule proves 

 in it that the heat produced in a conductor by a galvanic cur- 

 rent is in proportion to the resistance and the square of the inten- 

 sity of the current, meaning by "intensity" the quantity passed 

 through a certain resistance in a given time. When he caused 

 the current to pass through an electrolyte, he found that this law 

 did not hold good, that the same amount of heat was not pro- 

 duced as when it passed through a solid body. He therefore con- 

 cluded, — and he says he found by an experiment, which he does not 

 describe — that part of the intensity of the current is used up in pro- 

 ducing electrolysation, and therefore cannot be employed in evolving 

 heat. Now, so far from any proof being here offered that " decom- 

 position absorbs as much heat as combination produces," an exactly 

 opposite doctrine is taught ; for the conclusion to be arrived at is, 

 that if the intensity of the current was not lessened by electrolysa- 

 tion, the same amount of heat would be produced in the electrolyte 

 as in the solid conductor offering the same resistance, or in other 

 words, that if the same quantity of galvanic current from the same 

 source passed through an electrolyte and through a wire (an expe- 

 riment easily made by accommodating the length of the wire to the 

 resistance of the electrolyte), the same quantity of sensible heat 

 would be generated. But this is quite opposed to the truth. In my 

 experiments published in the Philosophical Magazine for October 



1851, and in Mr. Joule's, published in the same Magazine for July 



1852, it is shown that the current under these circumstances developes 

 different amounts of heat, and that the difference is the quantity 

 absorbed by decomposition. 



With respect to the memoir sent by Mr. Joule to the French 

 Academy in 1846, although it proves the law referred to exactly in 

 the same manner in which my paper does, it cannot interfere with 

 my claim to the discovery, as it was not published for nine months 

 after mine. In sdl cases I believe the first publication of a discovery 

 decides the priority. The publication of his paper nine months 



