428 POPULAR LECTURES AND ADDRESSES. 



among the different ingredients of gunpowder or 

 gun cotton. There is potential energy of what 

 may be called chemical force, among the particles 

 of soft phosphorus, which is spent in the allotropic 

 transformation into red phosphorus ; and among 

 the particles of prismatically crystallised sulphur, 

 which is spent when the substance assumes the 

 octoheclral crystallisation. 



To make chemical combination take place with- 

 out 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 scries of 

 admirable researches on the agency of electricity 

 in transformations of energy, 1 Joule showed that 



1 " On the 1'roductioii of IIr.it by Vultaic Electricity, 

 iiiunicatcd to the Royal Society December lyth, 1840 (see /';- 

 (ceding of that date), and published /'////. Mag. October, 1841. 



"On the Heat evolved by Metallic Conductors of Klcctricity, 

 and in the cells of a battery during Electrolysis. '' I'/iil. J/^V- 

 October, 1841. 



"On the Electrical Origin of the Heat of Combustion." /'////. 

 Mag. March, 1843. 



()n the lleat evolved during the Electrolysis of Water," /Vv- 

 (ttw'///:,^ c/" tlic, I.ilci'tiry niul Philosophical .SVcvV/i 

 1843, Vol. vii. Part 3, Second Series. 



(n the Calorific I 1 ! Heels of Magnclo Electricity, and on the 

 Mechanical Value of Heat,'' communicated to the liritish Associa- 



