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tals with these agents, to change of temperature, to evaporation, &c., 

 and never to the mere union of the elements; and supports his opinion 

 by several experiments. 



When platinum is brought in contact with an acid, the pole touch- 

 ing the acid is negative, the opposite pole positive ; and vice versd 

 when it touches an alkali ; and the same is the case with rhodium, 

 iridium, and gold : and the same holds good in all cases, the effect 

 being greater as the action of the acid on the metal is greater. From 

 this it follows, that when a metal is in contact with an acid or an 

 alkali in one cup, and water or a neutro-saline solution in another, 

 on completing the circuit, the contact of the metal with the acid or 

 alkali will determine the character of the pole in contact with it ; 

 and that in contact with the other fluid will, of course, be of the op- 

 posite name, and this result is confirmed by experiment. In such 

 combinations the chemical changes are such as might be expected, 

 oxygen and acids tending to circulate towards the negative surface, 

 and hydrogen and the alkalies towards the positive. 



In combinations consisting of two perfect conductors and one fluid, 

 the order in which the metals exhibit their electricities is connected 

 with their oxidability, the more oxidable metal being positive with 

 respect to all below it. It is not, however, any inherent quality in 

 the metals which determines this effect, but their fitness for chemical 

 action ; for if the state of aggregation be altered, and the cohesive 

 force, which always acts as antagonist force to chemical changes, be 

 weakened, the positive energy is exalted in proportion : thus the 

 amalgams of the positive metals are positive with respect to the pure 

 metals of which they are amalgams. 



In general the electricities developed by metallic contact are too 

 strong to be subverted by an opposite action of the fluids, with which 

 both are in contact. Such, however, is sometimes the case ; and in 

 all cases the influence of the fluid is perceptible. An instance is 

 given in the case of zinc and platinum, in contact with each other, 

 and the one immersed in alkali, the other in acid : the energy of 

 electrical action will here be found very much greater when the pla- 

 tinum is plunged into the acid, than in the contrary arrangement. 

 And in this and similar cases, the general law, that the chemical 

 changes produced are such as tend to restore the equilibrium, holds 

 good. 



The author next considers the accumulation of electricity, and the 

 chemical changes it produces in voltaic arrangement. According to 

 Volta's view of the action of the pile, the metals were regarded as 

 the only agents, and the chemical changes arising in the fluids as 

 mere results not essential to the development of the electricity. This 

 view, however, is sufficiently opposed by the inactivity of combina- 

 tions in which no chemical changes occur, but may be regarded as 

 altogether disproved by an experiment here described, in which, 

 when two glasses filled with solution of nitrate of potash, in which 

 were plunged respectively zinc and platina, connected by the multi- 

 plier, were connected by substances capable of conducting electricity, 



