678 LECTURE LIV. 



which the subject of galvanism afforded before Mr. Davy's late ingenious and 

 interesting researches, which have thrown much light, not only on the foun- 

 dation of the whole of this class of phenomena, but also on the nature of 

 chemical actions and affinities in general. Mr. Davy is inclined to infer from 

 his experiments, that all the attractions, which are the causes of chemical com- 

 binations, depend on the opposite natural electricities of the bodies concerned; 

 since such bodies are always found, by delicate tests, to exhibit, when in con- 

 tact, marks of different species of electricity; and their mutual actions may 

 be either augmented or destroyed, by increasing their natural charges of elec- 

 tricity, or by electrifying them in a contrary Avay. Thus, an acid and a metal 

 are found to be negatively and positively electrical with respect to each other; 

 and by further electrifying the acid negatively, and the metal positively, their 

 combination is accelerated; but when the acid is positively electrified, or the 

 metal negatively, they have no effect whatever on each other. The acid is 

 also attracted, as a negative body; by another positively electrified, and the 

 metal by a body negatively electrified, so that a metallic salt may be decom- 

 posed in the circuit of Volta, the positive point attracting the acid, and the 

 negative point the metal: and these attractions are so strong, as to carry the 

 particles of the respective bodies through any intervening medium, which is in 

 a fluid state, or even through a moist solid; nor are they intercepted in their 

 passage, by substances which, in other cases, have the strongest elective attrac- 

 tions for them. Alkali, sulfur, and alkaline sulfurcts, are positive with respect 

 to the metals, and much more with respect to the acids: hence they have a 

 very strong natural tendency to combine with the acids and with oxygen: 

 and hydrogen must also be considered as belonging to the same class with the 

 alkalis. 



Supposing now a plate of zinc to decompose a portion of water: the oxy- 

 gen, which has a negative property, unites with the zinc, and probably tends 

 to neutralise it, and to weaken its attractive force; the hydrogen is repelled 

 by the zinc, and carries to the opposite plate of silver its natural positive elec- 

 tricity; and if the two plates be made to touch, the energy of the plate of 

 zinc is restored, by the electricity which it receives from the silver: audit re- 

 ceives it the more readily, as the two metals, in any case of their contact, 

 have a tendency to become electrical, the zinc positively, and the silver ne- 

 gatively. Mr. Davy therefore considers this chemical action as destroying, or 



