186 ANNUAL OF SCIENTIFIC DISCO VEKY. 



To make chemical combination take place without generating its equivalent 

 of heat, all that is necessary is to resist the chemical force operating in the 

 combination, and take up its effect in some other form of energy than heat. 

 In a series of admirable researches on the agency of electricity in, transforma- 

 tions of energy,* Joule showed that the chemical combination taking place in 

 a galvanic battery may be directed to produce a large, probably in some 

 forms of battery an unlimited, proportion of their heat, not in the locality of 

 combination, but In a metallic wire at any distance from that locality ; or that 

 they may be directed not to generate that part of their heat at all, but, 

 instead, to raise weights, by means of a rotating engine driven. by the current. 

 Thus, if we allow zinc to combine with oxygen by the beautiful process 

 which Grove has given in his battery, we find developed in a wire connecting 

 the two poles the heat which would have appeared directly if the zinc had 

 been burned in oxygen gas ; or, if we make the current drive a galvanic 

 engine, we have, in weights raised, an equivalent of potential energy for the 

 potential energy between zinc and oxygen spent in the combination. 



The economic relations between the electric and the thermodynamic 

 method of transformation from chemical affinity to available motive power 

 were indicated, in accordance with the limited capability of heat to be trans- 

 formed into potential energy, which the modification of Carnot's principle, 

 previously alluded to, shows, and the unlimited performance of a galvanic 

 engine in raising weights to the full equivalent of chemical force used, which 

 Joule has established. 



The transformation of motive power into light, which takes place when 

 work is spent in an extremely concentrated generation of heat, was referred 

 to. It was illustrated by the ignition of platinum wire, by means of an 

 electric current driven through it by the chemical force between zinc and 

 oxygen in the galvanic battery ; and by the ignition and volatilization of a 

 silver wire by an electric current driven through it by the potential energy 

 laid up in a Leyden battery, when charged by an electrical machine. The 

 luminous heat generated in the last mentioned case was the complement to a 



* On the Production of Heat 'by Voltaic Electricity, communicated to the Royal Society, 

 December 17th, 1840 (see Proceedings of that date), and published Phil. Mag., October, 

 1841. 



" On the Heat evolved by Metallic Conductors of Electricity, and in the cells of a 

 battery during Electrolysis." Phil. Mag., October, 1841. 



"On the Electrical Origin of the Heat of Combustion "-PMI. Mag., March, 1843. 



" On the Heat evolved during the Electrolysis of Water," Proceedings of the Literary 

 and Philosophical Society of Manchester, 1843, vol. vii. part 3. Second Series. 



"On the Caloriiic Effects of Magneto-Electricity, and on the Mechanical Value of 

 Heat," communicated to the British Association (Cork)j August, 1843, and published 

 Phil. Mag., October, 1843. 



"On the Intermittent Character of the Voltaic Current in certain cases of Electrolysis, 

 and on the Intensity of various Voltaic Arrangements." Phti. Mag., February, 1844. 



" On the Mechanical Powers of Electro-Magnetism, Steam, and Horses " By Joule and 

 Scoresby. Phil. Mag., June, 1846. 



"On tho Heat disengaged in Chemical Combination." 7Vw7. Mag., June, 1852. 



" On the Economical Production of Mechanical Effect for Chemical Forces." Phil. 

 Mag., Jamiary, 1S53. 



