Electrical Devices and How They Work 



Primary Battery Cells — I. 



This article is the first of a series on electricity, each one of 

 which is complete in itself. Some interesting experimen- 

 tal problems are illustrated and very explicitly described 



By Peter J. M. Clute, B. E. 



THE agency which comes into action 

 when a circuit containing an electro- 

 motive force is closed is called 

 electric current. This current flow is 

 analogous to the flow of water in pipes, 

 or over the surface of the earth. Such a 

 flow of water takes place only when 

 from any cause, a difference in pressure 

 exists between two points, or when the 

 water is at different levels. When either 

 of these conditions exists, the flow takes 

 place in a certain direction; namely, 

 from the higher to the lower level, the 

 amount of flow being dependent upon the 

 obstacles in its path. Electric currents, 

 likewise, flow only in obedience to elec- 

 trical pressure, and the quantity of cur- 

 rent flowing is dependent upon the re- 

 sistance to the flow offered by the circuit. 



A simple primary cell is shown in 

 Fig. 1. It consists of a glass jar nearly 

 filled with a dilute sulphuric acid solu- 

 tion, into which are placed a plate of 

 zinc and one of copper. While the ends 

 of the. wires connected with the plates 

 remain separated, no current flows; but 

 an electrical pressure exists, as can be 

 readily shown. As soon as the ends of 

 the two wires are brought into contact, 

 a flow of current commences. It is the 

 high resistance of the air between the 

 two terminals which prevents the flow 

 of current in this case, just as the presence 

 of a closed valve in a waterpipe prevents 

 water flow. 



The current itself cannot be seen as it 

 flows through the wire, but its effects 

 are evidences of its presence. A current 

 flowing through a thin wire will heat it; 

 flowing through water and other liquids 

 it decomposes them; flowing near a mag- 

 netic needle it will cause it to deflect. 

 All these phenomena cease at once 

 when the current is interrupted, either 

 by breaking the circuit or by separating 

 the acid around one plate from that 



around the other by a non-conducting 

 partition. 



The direction of current is said to be 

 from the zinc to the copper inside the 

 cell and from copper back to zinc in the 

 external circuit. In all cells the plate, 

 or terminal, from which the current 

 flows, is called the positive pole, and the 

 terminal toward which the current flows 

 in the circuit is the negative pole. 



From the cell shown, Fig. 1, which is 

 the simplest of all forms, a very insignifi- 

 cant current is given. If several cells 



ZINC CROWFOOT. 



ZINC 



-= — ^ COPPER STRi; 

 FIQ.l 



FIG. 2 



^\M\^'r^ 



^ — Wh — ' 



T T.T T 



L-vww 



FIG. 3 Fie.4 FIG. 5 



The simplest form of battery, the primary cell, 

 and the gravity cell with wiring diagrams 



are coupled together, as conventionally 

 indicated in Fig. 3, 4 and 5, a consider- 

 able current is obtainable. In this repre- 

 sentation, the long thin lines indicate 

 the positive plates and the short thick 

 lines the negative plates. 



The term "battery" is applied to a 

 number of cells grouped together either 

 in a series or in parallel and should never 

 be applied to a single cell. Representa- 



151 



