GALVANISM, OR VOLTAIC ELECTRICITY. 



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Fig. 11. 



liquid capable of acting upon them unequally, the electric equili- 

 brium is disturbed, the one acquiring the positive condition, and the 

 other the negative. Thus, a piece of zinc and a piece of copper, 

 placed in a dilute solution of sulphuric acid, will cause such a dis- 

 turbance of the electrical equilibrium ; the zinc being the metal most 

 attacked, becomes negative, while the copper becomes positive ; and 

 on making a communication between the two, an electrical current 

 is set in motion. The intensity of the electricity thus developed is 

 extremely feeble ; but by arranging a number of single pairs of 

 metals with the intervention of a fluid, or moistened cloth, in such a 

 manner that the direction of the current shall be the same in each, 

 the intensity will be very much augmented ; upon this principle the 

 pile of Volta and the Crown of Cups are contrived. 



The Voltaic pile consists of a number of small 

 plates of zinc and copper arranged in a pile, each 

 pair being separated by means of a piece of cloth 

 moistened with sulphuric acid, as seen by the 

 figure. If the two terminal plates be now touched 

 with wet hands, a prolonged electric shock will be 

 experienced, the intensity of which may be in- 

 creased to almost any extent, by simply increasing 

 the number of plates. 



The Crown of Cups is similar in principle, though 

 different in form; it consists of any number of 

 cups or glasses, arranged in a row or circle, each 

 containing a piece of copper and zinc, and some 

 dilute acid. The copper of the first cup is connected with the zinc 

 of the second ; the copper of the second, with the zinc of the third, 

 and so on ; on establishing 



a communication between Fig. 12. 



the first and last plates, a 

 discharge takes place as 

 before. 



Whenever such an ar- 

 rangement consists merely 

 of a single pair of con- 

 ductors, and an interposed 

 liquid, it is called a siiu'ple 

 circuit; when two or more 

 alternations are concerned, it is a compound circuit ; but, however 

 complex the apparatus may be, the princip)le is, in all cases, pre- 

 cisely the same. The disturbance of the equilibrium may be consi- 

 dered as commencing at the surface of the most oxidizable metal, 

 and to be propagated through the liquid to the least oxidizable metal ; 

 hence, when insulated, the zinc end of the series is always negative, 



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