34 ELECTROLYSIS. 



The resistance of the metallic conductors can be estimated 

 at 0014 ohm ; it is that of a bar of copper 10 metres long 

 and 1 square centimetre in section. To illustrate a case, we 

 will suppose that the internal resistance of the dynamo is equal 

 to the tenth part of the total external resistance, and that its 

 mechanical efficiency is 90 per 100, a result which is often 

 realised in practice. 



The resistance B,' created by the counter electromotive 

 force is 



' 



The internal resistance of the dynamo, as well as that due 

 to friction, may be estimated at 0*0006 ohm. Then it can 

 be admitted that a resistance of 0'002 ohm is due to the 

 polarisation of the electrodes, and to other causes of a varied 

 nature which necessitate an expenditure of energy, and which 

 have not been calculated ; the total resistance of the circuit is 

 thus shown : 



E = 0-003 + 0-000512 + 0-0014 + 0-0006 + 0-002 

 = 0-007512 ohm. 



The number of amperes 833 remaining constant, the electro- 

 motive force required to overcome this total resistance will be : 



E = 5 = 833 x 0-007512 = 6 -25 volts. 



XV 



The proportion between the work actually required for 

 liberating the zinc and that absorbed in the electrolysis of the 

 chloride of zinc is therefore 



The primitive work being 2 7 horse-power, the total work 



2 7 

 is in reality TrriT) = 6-75 horse-power. 



In order to extract one kilogramme of zinc per hour from a 

 bath of chloride of zinc, it will thus be necessary to have : 



(1) An engine of about 7 horse-power ; 



(2) A dynamo electric machine giving a current of 833 



