SKCT. xxrx.J THE VOLTAIC BATTEKY. 333 



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 to- 

 gether by metallic wires, the zinc rod of one with the copper 

 cylinder of that next to it. The zinc rods are amalgamated, 

 so that local action, which, in ordinary cases, is so destructive 

 of the zinc, does not take place, and no chemical action is 

 manifested unless the circuit be completed. The rods are 

 easily detached, and others substituted for them when worn 

 out. This battery, which possesses considerable power, and 

 is constant in its effects for a very long period of time, is 

 greatly superior to all former arrangements, either as an 

 instrument of research, or for exhibiting the ordinary phe- 

 nomena of Voltaic electricity. 



A battery charged with water alone, instead of acid, is 

 very constant in its action, but the quantity of electricity it 

 developes is comparatively very small. Mr. Cross, of Broom- 

 field in Somersetshire, has kept a battery of this kind in full 

 force during twelve months. M. Becquerel had invented an 

 instrument for comparing the intensities of the different 

 kinds of electricity by means of weights ; but, as it is impos- 

 sible to make the comparison with Voltaic electricity pro- 

 duced by the ordinary batteries, on account of the perpetual 

 variation to which the intensity of the current is liable, he 

 has constructed a battery which affords a continued stream 



