252 GENERAL SCIENCE 



following expressions by which any one of the three 

 units can be found if the other two are given. 



Electromotive Force E 



(1) Current = - - - or C = - 



Resistance R 



Volts 



(2) Amperes = 



Ohms 



175. The Simple Electric Cell. Place some water 

 in a small glass beaker or tumbler and then add a few 

 drops of sulphuric acid or hydrochloric acid. Place in 

 it on opposite sides a clean strip of zinc and one 

 of copper, as shown in the figure. This is the simple 

 Voltaic cell and is capable of supplying a continuous 

 flow of electricity through a wire which joins the strips 

 of copper and zinc. It will be observed that the zinc 

 strip wastes away when the current flows. The eat- 

 ing away of the zinc by the acid fur- 

 nishes the energy necessary to drive the 

 electric current through the liquid of the 

 cell and the external wire connection. 

 This cell may be thought of as a 



rr o/-\ IB l':_^ ; fir// 



kind of chemical furnace in which 

 fuel is consumed to drive the current. 

 A SIMPLE CELL Since zinc will burn in a stove, it can 

 Made of copper be thought of as the fuel, the acid is 

 the oxidizer, and the copper is a me- 

 tallic hand in the cell, which gathers 

 the current but takes no part in the chemical action. 

 Before the zinc and copper are connected by a wire, 

 the zinc is trying to dissolve in the acid and throw a 

 current across to the copper, while the copper is also 

 trying to dissolve, but with less force, and- to throw a 

 current across to the zinc. 



