654 



GALVANIC BATTERY. 



six times as strongly electric as is the case in a single 

 element. The pole of one element being soldered to 

 the opposite pole of the next, only the terminal strips 

 of metal are free in such an arrangement, and they are 

 called the ' poles of the battery/ 



Six very small test-tubes are placed side by side in holes bored 

 with the centre-bit into a pretty stout piece of board. Six strips of 

 copper and six of zinc are cut out of thin sheet metal, each from 

 5 to 8 cm long and 2 or 3 mm wide ; five of the strips of zinc are 

 soldered each of them to one of the strips of copper, allowing 



7-fiit M.4AAAX. 



FIG. 336 



the ends to overlap each other for a few millimetres. The 

 sixth strip of each metal is left free, and forms respectively one of 

 the poles of the battery ; each of them has a thin copper wire, from 

 15 to 25 cm long, soldered to it, and near to the free ends of the 

 copper wires small pieces of sealing-wax, s s in fig. 336, are fixed. 

 The joined strips are bent as shown in the figure, and each test-tube 

 must contain a strip of each metal. The two single strips form the 

 terminals, one being placed in the first and the other in the last 

 test-tube. The two different metals in each test-tube must not be 

 allowed to touch each other ; their contact is prevented in the tubes 

 at the end by fixing small corks between the metals ; in the inter- 

 mediate tubes they cannot touch each other if a little care has been 

 given to bending them accurately and straight. The corks used in 

 the terminal tubes should only fit loosely, or they press the hard and 

 angular strips too strongly against the sides of the test-tube, and 

 these may get broken. The liquid used is salt water, which is intro- 

 duced very carefully by means of a pipette, so as not to moisten the 

 tubes on the outside. 



