88 



In that case, secure a ready-made commercial cell (Fig. 65) 

 from your instructor. These cells are manufactured and 

 sold by all electric companies, and are stronger and more 

 convenient than the simple cell. Although such a cell 

 may look very different from your own arrangement, the 

 principle is the same ; within the cell chemical action takes 



place between an acid solution 

 and metal strips, and produces 

 a current of electricity. 



We have seen that when any 

 separation or break occurs in 

 the connecting wires, the elec- 

 trical properties of the wire 

 vanish. This is because current 

 must have an unbroken path. 

 It can pass along wire, but it 

 does not pass easily through air, 

 and as soon as a gap occurs in 

 the connecting wires, the circuit 

 path is broken, the electric circuit is not complete, and 

 current ceases. In future experiments be sure that your 

 electric circuit is complete. If your experiments do not 

 work as they should, it may be because of a broken circuit. 



FIG. 65. A ready-made com- 

 mercial cell. 



EXPERIMENT 85. ELECTRICITY AS A SOURCE OF HEAT 



Put a pint and a half of water of known temperature 

 into a glass vessel large enough to be about half filled with 

 this quantity. Then place in the beaker a 16 candle 

 power electric-light-bulb. Connect the bulb with the elec- 

 tric light circuit in your laboratory, and allow the glowing 

 bulb to heat the water for five or six minutes. 



