522 M, Raoult on Chemical Heat and'VoJtajc JTeat. 

 or otherwise if the heat of combustion were known. The same 

 remark applies to chloric ether, CH 2 C1^=32, and indeed more 

 or less to all organic compounds. 



I remain, Gentlemen, 



Your most obedient Servant, 

 Edinburgh, November 8, 1863. J. J, Waterston. 



LXXIV. Researches on Chemical Heat and Voltaic Heat. 

 ByM. Raoult*. 



THE determination of the heat produced by an electric cur- 

 rent in the entire circuit, including the pile itself, has 

 hitherto presented great difficulties. I have the honour to sub- 

 mit to the Academy a method by which it can be easily obtained. 



Let it be required to determine the total voltaic heat W of an 

 element. I arrange in a calorimeter a spiral formed of a plati- 

 num wire rolled round a glass tube and joined by two copper 

 rods to the poles M and N of a strong DanielFs battery P. At 

 the same time I connect the poles M and N with a sine- com- 

 pass with a long wire and of a suitable degree of sensibility. 

 (This is a sine-compass of variable sensibility which I have 

 described in an " Etude des Forces Electromotrices," presented 

 as a thesis to the Faculty of Sciences at Paris, May 13, 1863; 

 the wire is J^th of a millim. in diameter and 3600 metres long; 

 the heat which the current produces is quite negligible.) 



I observe 



(1) The intensity/ of the derived current in the sine-compass. 



(2) The quantity of heat c imparted by the spiral to the calo- 

 rimeter. 



(3) The increase in weight p of the plate of copper in one of 

 the elements of the pile. 



(4) The intensity E of the current produced in the compass 

 by the element E, of which it is desired to know the voltaic 

 heat W. 



I accordingly obtain W, that is the heat disengaged by the 

 current of the element E from the solution of an equivalent of 

 metal, by means of the formula . . 



w ex 31-6 E - ■ 



P f 



(31*6 being the equivalent of copper). 



The demonstration of this formula is very simple. The inten- 

 sity/of the derived current in the sine-compass is proportional 

 to the difference of the electrical tensions at the points of deri- 

 vation M and N, and measures this difference ; / is then the 

 electromotive force of an element of no resistance, which would 

 * Translated from the Comptes Rendus for September 14, 1863. 



