THE 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOUKTH SERIES.] 



DECEMBER 1851. 



LXVI. On the Mechanical Theory of Electrolysis. 

 J5y Prof. William Thomson*. 



1. I^ERTAIN principles discovered by Mr. Joule^ and pub- 

 ^^ lished for the first time in his various papers in this 

 Magazine, must ultimately become an important part of the 

 foundation of a mechanical theory of chemistry. The object of 

 the present communication is to investigate, according to those 

 principles, the relation in any case of electrolysis between the 

 electro-motive intensity, the electro -chemical equivalents of the 

 substances operated on, and the mechanical equivalent of the 

 chemical effect produced in the consumption of a given amount 

 of the materials ; and by means of it to determine in absolute 

 measure the electro-motive intensity of a single cell of DanielFs 

 battery, and the electro-motive intensity required for the electro- 

 lysis of water, from experimental data which Mr. Joule has 

 kindly communicated to me. 



2. If a galvanic current, produced by means of a magneto- 

 electric machine, be employed in electrolysis, it will generate, in 

 any time, less heat throughout its entire circuit than the equiva- 

 lent of the work spent, by an amount which may be called the 

 thermal equivalent of the chemical action which has been effected, 

 being the quantity of heat which would be obtained by recom- 

 bining the elements of the decomposed substance, and reducing 

 the compound to its primitive condition in every respect; or 

 generally, by undoing all the action which has been done in the 

 electro-chemical apparatus. Now the quantity of heat which is 

 equivalent to the work done is obtained by dividing the number 

 which measures the work by the number which measures by the 

 * Communicated by the Author. 

 Phil Mag, S. 4. Vol. 2. No. 13. Dec. 1851. 2 G 



