SECT. XXIX. VOLTAIC BATTERY. 299 



the first plate of zinc exposed to its action is taken up by the 

 copper plate belonging to the second pair, and transferred to the 

 second zinc plate, with which it is connected. The second plate 

 of zinc, possessing equal powers, and acting in conformity with 

 the first, having thus acquired a larger portion of electricity than 

 its natural share, communicates a larger quantity to the fluid in 

 the second cell. This increased quantity is again transferred to 

 the next pair of plates ; and thus every succeeding alternation is 

 productive of a further increase in the quantity of the electricity 

 developed. This action, however, would stop unless a vent were 

 given to the accumulated electricity, by establishing a communi- 

 cation between the positive and negative poles of the battery by 

 means of wires attached to the extreme plate at each end. When 

 the wires are brought into contact, the Voltaic circuit is com- 

 pleted, the electricities meet and neutralize each other, producing 

 the shock and other electrical phenomena ; and then the electric 

 current continues to flow uninterruptedly in the circuit, as long 

 as the chemical action lasts. The stream of positive electricity 

 flows from the zinc to the copper. The construction and power 

 of the Voltaic battery have been much improved of late years, but 

 the most valuable improvement is the constant battery of Pro- 

 fessor Daniell. In all batteries of the ordinary construction, 

 the power, however energetic at first, rapidly diminishes, and 

 ultimately becomes very feeble. Professor Daniell found that 

 this diminution of power is occasioned by the adhesion of the 

 evolved hydrogen to the surface of the copper, and by the precipi- 

 tation of the sulphate formed by the action of the acid on the 

 zinc. He prevents the latter by interposing between the copper 

 and the zinc, in the cell containing the liquid, a membrane which, 

 without impeding the electric current, prevents the transfer of 

 the salt ; and the former, by placing between the copper and the 

 membrane solution of sulphate of copper, which being reduced 

 by the hydrogen prevents the adhesion of this gas to the metallic 

 surface. Each element of the battery consists of a hollow cylinder 

 of copper, in the axis of which is placed a cylindrical rod of zinc ; 

 between the zinc and the copper a membranous bag is placed, 

 which divides the cell into two portions, the inner of which is 

 filled with dilute acid, and the one nearer the copper is supplied 

 with crystals of the sulphate of that metal. The battery consists 

 of several of these elementary cells connected together by metal- 

 lic wires, the zinc rod of one with the copper cylinder of th^t 



