M. F. M. Raoult on the Thermal Phenomena of Voltameters, 551 



This property may in any case be diminished by using special 

 cartridges, consisting of paper cylinders covered with woven 

 gun-cotton ; but in experiments made in Austria with twelve- 

 pounders, a less initial velocity was reached than was desired 

 in France. 



Moreover an opinion opposed to the use of gun-cotton pre- 

 vails now in Austria ; for the special form of artillery which had 

 been created for its employment has been there given up. 



LXV. Researches into the Thermal Phenomena of Voltameters, 

 and Measurement of the quantities of Heat absorbed in Electro- 

 chemical Decomjjositions. By F. M. Raoult*. 



THE method employed in these researches is founded upon 

 theorems relative to electromotive forces which have been 

 recently published in the Annates de Chimie et de Physique (4th 

 series, vol. ii. p. 317, July 1864). 



The voltameter is placed inside a mercurial calorimeter, and is 

 traversed by the current i of a DanielPs battery, P. In the 

 course of this current there is a sine-compass A, which has two 

 turns of a thick wire. Another sine-compass, B, with a very 

 long and very thin wire (length 3600 metres, diameter 01 mil- 

 limetre), is connected with the electrodes of the voltameter, and 

 is traversed by an exceedingly feeble derived current e, negligible 

 in comparison with the principal current i. 



Let 23,900 be the heat evolved by the current of a DanielPs 

 cell, of unit strength, during the reduction of 1 equivalent 

 of copper t; 



31*6 grammes the equivalent of copper (H = 1 gramme) ; 

 T, the heat evolved in the voltameter; 

 p, the weight of copper reduced, in one element of the bat- 

 tery P, during the electrolysis ; 

 e, the intensity of the derived current in the sine-compass 



with long wire B ; 

 d, the intensity of the current which a unit DanielPs ele- 

 ment produces in the same compass B ; 

 /, the intensity of the current produced in the same com- 

 pass B, by an element whose electromotive force is equal 

 to that of the voltameter. 

 e, d, and /measure respectively the electromotive forces of the 

 compound battery, of a DanielPs element, and of the voltameter. 

 e varies usually by nearly T ~ in the course of an experiment : 

 as the variation takes place uniformly, the value of e introduced 



* Comptes Rendus,vo\. lix. p. 521 (September 19, 1864). 



t Comptes Rendus, Sept. 14, 1863. [Phil. Mag. S. 4. vol. xxvi. p. 522.] 



