ELECTRIC BATTERY 



1981 



ELECTRIC BATTERY 



looked somewhat like a round stick. An 

 electric shock could be obtained from the pile 

 of disks. This battery was called Fora's pile; 

 it was also sometimes called the electric stick. 



SAL AMMONIAC BATTERY 



Volta also made a battery of zinc and copper 

 strips placed in dilute sulphuric acid; a num- 

 ber of pairs of such strips were used, each 

 pair being in a glass tumbler containing a por- 

 tion of the acid solution. This battery was 

 called the crown of cups. 



How a Battery Works. The working of an 

 electric battery can be best understood by a 

 study of a simple cell made like Volta's crown 

 of cups. A strip of zinc and a strip of copper, 

 if placed in contact in air, would each become 

 electrically charged, the zinc having a positive 

 and the copper a negative charge. If the two 

 strips are placed in dilute sulphuric acid, 

 hydrogen from the acid goes to the copper 

 strip. The hydrogen carries a positive charge 

 and gives this charge to the copper; the re- 

 maining part of the acid goes to the zinc, 

 giving the zinc a negative charge. Thus by 

 the action of the acid the copper becomes 

 positively charged ; the zinc, negatively charged. 

 If the two strips are connected by a conductor 

 of electricity, such as a copper wire, the electric 

 charges flow along the wire, the positive charge 

 flowing from copper to zinc, the negative charge 

 from zinc to copper. The action of the acid 

 continually renews the charges on the copper 

 and the zinc, and a current continues to flow 

 along the wire. (See illustration, "A Simple 

 Electric Battery," page 1980.) 



Since the positive charge flows from the cop- 

 per through the wire, the copper is the positive 

 electrode, or the positive pole, of the battery. 

 Since the positive charge is carried from the 

 zinc through the liquid to the copper, and 

 since when zinc and copper are placed together 

 in air the zinc becomes positively charged 



simply by its contact with the copper, the 

 zinc is the positive plate. During the action 

 of the battery the zinc is being continually 

 eaten away by the acid, forming zinc sulphate, 

 which can be obtained as a white powder by 

 evaporating the liquid. It is the action of the 

 acid upon the metal plates which produces the 

 electric current. Chemical energy is therefore 

 changed into electrical energy. 



Polarization. The hydrogen which collects 

 on the copper in the simple voltaic cell is 

 necessary to the working of the cell in order 

 to give the copper a positive charge, but if the 

 hydrogen remains on the copper it hinders the 

 flow of the current. This action of the hydro- 

 gen is called polarization. Polarization i* due 

 to the resistance which the hydrogen offers to 

 the passage of the current and to an electro- 

 motive force which the hydrogen produces, 

 opposing the main electromotive force of the 

 battery. 



A storage battery requires a current from 

 some outside- source, changing the plates and 

 the liquid in the cell by electrolysis before it 

 is ready to deliver any considerable amount of 

 electrical energy (see ELECTROLYSIS). Storage 

 batteries are sometimes called secondary bat- 

 teries. Batteries that do not require the action 

 of an electric current upon them, but are ready 

 as soon as the materials are put together to 

 deliver current, are called primary batteries. 

 Primary batteries cannot be charged by an elec- 

 tric current as can storage batteries, but can 

 be renewed only by renewing the liquid or the 

 positive plate, or both. 



Primary batteries are of two kinds: first, 

 those that do not polarize and therefore will 

 deliver current at constant strength for a long 

 time; second, those that polarize and therefore 

 can deliver current for a short time only, after 

 which the circuit must be open so that the 

 battery can recover. The first kind are called 

 closed-circuit batteries, because the circuit can 

 be kept closed for a long time; the second kind 

 are called open-circuit batteries, because the 

 circuit must be open moct of the time. In 

 most closed-circuit batteries the plates would 

 waste away if the circuit were left open. An 

 open-circuit must be made of such materials 

 that the plates will not wimte away when the 

 circuit is open. The mont important closed- 

 circuit batteries arc the gravity, Danicll and the 

 Edison-Lalande cells. 



The Gravity Cell. Polarization is prevented 

 in the gravity cell by placing the copper in a 

 solution of copper sulphate. The zinc is in a 



