292 THE VOLTAIC BATTERY. SECT. XXIX. 



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 al- 

 ternation 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 communication 

 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 completed, 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 has been 

 much improved of late years, but the most valuable 

 recent improvement is the constant battery of Professor 

 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 to the precipitation 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, 



