154 CORRELATION OF PHYSICAL FORCES. 



finitely to relate the forces of chemistry and electricity. 

 When two dissimilar metals in contact are immersed in a 

 liquid belonging to a certain class, and capable of acting 

 chemically on one of them, what is termed a voltaic circuit is 

 formed, and, by the chemical action, that peculiar mode of 

 force called an electric current is generated, which circulates 

 from metal to metal, across the liquid, and through the points 

 of contact. 



Let us take, as an instance of the conversion of chemical 

 force into electrical, the following, which I made known some 

 years ago. If gold be immersed in hydrochloric acid, no 

 chemical action takes place. If gold be immersed in nitric 

 acid, no chemical action takes place ; but mix the two acids, 

 and the immersed gold is chemically attacked and dissolved : 

 this an is ordinary chemical action, the result of a double chemi- 

 cal affinity. In hydrochloric acid, which is composed of 

 chlorine and hydrogen, the affinity of chlorine for gold being 

 less than its affinity for hydrogen, no change takes place ; but 

 when the nitric acid is added, this latter containing a great 

 quantity of oxygen in a state of feeble combination, the 

 affinity of oxygen for hydrogen opposes that of hydrogen for 

 chlorine, and then the affinity of the latter for gold is enabled 

 to act, the gold combines with the chlorine, and chloride of 

 gold remains in solution in the liquid. Now, in order to 

 exhibit this chemical force in the form of electrical force, 

 instead of mixing the liquids, place them in separate vessels 

 or compartments, but so that they may be in contact, which 

 may be effected by having a porous material, such as un- 

 glazed porcelain, amianthus, &c., between them. Immerse in 

 each of these liquids a strip or wire of gold : as long as these 

 pieces of gold remain separated, no chemical or electrical 

 effect takes place ; but the instant they are brought into 

 metallic contact, either immediately or by connecting each 

 with the same metallic wire, chemical action takes place 

 the gold in the hydrochloric acid is dissolved, electrical action 



