in Chemical Combinations. 483 



quantity of heat evolved by combustion, together with the results 

 at which I have arrived by its use. Being convinced of the 

 accuracy of the experiments of Dulong, and knowing that distin- 

 guished philosophers were engaged in confirming and extending 

 his results, I thought that by examining the electrical reactions 

 I should best fulfill the wishes of the Academy. 



2. Davy drew from his electro-chemical experiments the con- 

 clusion, that the heat and light evolved in chemical combinations 

 are caused by the reunion of the two electricities. Subsequently 

 Berzelius has taken up Davy's theory, and, giving it new deve- 

 lopments, has made it the foundation of modern chemistry. 

 Ampere has still further modified the theory, in order to explain 

 the permanency of chemical combinations. The views of these 

 and other philosophers have been ably discussed by Becquerel in 

 his Traite de I'Electricite*, and therefore I need not attempt any 

 criticism of them, were it indeed necessary to my design to do 

 so. It will be sufficient for my purpose to admit, — -1st, that when 

 two atoms combine by combustion, a current of electricity passes 

 from the oxygen to the combustible ; 2nd, that the quantity of 

 this current of electricity is fixed and definite ; and 3rd, that it 

 is the means of the evolution of light and heat, precisely as is 

 any other current of electricity whatever. 



The first of these propositions I consider to have been proved 

 by the experiments of Pouillet and Becquerel f, and the second 

 is naturally derived from the discoveries of Faraday. Therefore 

 it is only necessary to obtain one element more, viz. the intensity 

 or electromotive force of the electric currents passing between 

 the atoms, in order to be able to estimate the heat due to che- 

 mical combinations. 



3. But it is important to decide first, by what laws the evolu- 

 tion of heat by electricity is governed. Brooke and Cuthbertson 

 found that the length of wire melted by an electrical battery 

 varied nearly with the square of its charge ; and Children and 

 Harris showed that more or less heat is evolved by frictional 

 electricity in proportion to the goodness or badness of the con- 

 ductors. P. Riess, however, appears to have made the most ex- 

 tensive and accurate experiments on the calorific effects of fric- 

 tional electricity. This philosopher has shown that the heat 

 evolved by an electrical discharge is proportional to the square 

 of the quantity of fluid divided by the extent of coated glass 

 surface upon which it was induced ; in other words, proportional 

 to the quantity and density of the fluid J. 



* Traits de V Electricity, vol. iii. p. 3fiG. 



t Becquerel, lYtiitr' <!<■ r Elect ricitr', vol. ii- p. 85. 



% Annates de Chimie et de Physique, vol. Ixix. p. 113. 



212 



