CHEMICAL AFFINITY. 159 



united with each plate of zinc, eight parts of oxygen would 

 be evolved from one of the platinum terminals : that is, the 

 weights would be precisely in the same relation which Dalton 

 proved to exist in their chemical combining weights. This 

 may be extended to all liquids capable of being decomposed 

 by the voltaic force, thence called Electrolytes : and as no vol- 

 taic effect is produced by liquids incapable of being thus de- 

 composed, it follows that voltaic action is chemical action tak- 

 ing place at a distance, or transferred through a chain of 

 media, and that the chemical equivalent numbers are the ex- 

 ponents of the amount of voltaic action for corresponding 

 chemical substances. 



As heat, light, magnetism, or motion, can be produced by 

 the requisite application of the electric current, and as this is 

 definitely produced by chemical action, we get these forces 

 very definitely, though not immediately, produced by chemi- 

 cal action. Let us, however, here enquire, as we have al- 

 ready done with respect to the other forces, how far other 

 forces may directly emanate from chemical affinity. 



Heat is an immediate product of chemical affinity. I 

 know of no exception to the general proposition that all bod- 

 ies in chemically combining produce heat ; i. e. if solu- 

 tion be not considered as chemical action, and even in that 

 case, when cold results, it is from a change of consistence, as 

 from the solid to the liquid state, and not from chemical 

 action. 



We shall find that the same view of the expenditure of 

 force which we have considered in treating of latent heat 

 holds good as to the expenditure of chemical force when re- 

 garded with reference to the amount of heat or repulsive 

 force which it engenders, the chemical force being here ex- 

 hausted by chemical expansion that is, by heat. Thus, in 

 the chemical action of the ordinary combustion of coal and 

 oxygen, the expenditure of fuel will be in proportion to the 

 expansibility of the substances heated ; water passing freely 



