WORK ABSORBED IN ELECTROLYSIS. 35 



amperes, with a total electromotive force of 6 25 volts (about 

 5 6 volts at the terminals). 



If the conductor had a resistance ten times smaller than the 

 one which we have admitted, and if the dissociation of the bath 

 was not accompanied by any chemical action, the expenditure 

 of the motive power could be reduced by about 20 per cent., or, 

 what amounts to the same, the return could be increased from 

 0*40 to 0'60. It is therefore important to reduce to a 

 minimum the resistance of the conductors, and to avoid, as 

 much as possible, the polarisation of the electrodes. 



As we have already mentioned, the number of amperes is 

 invariable, whatever the passive metallic resistances or the 

 secondary actions of the current may be. This is an absolute 

 consequence of Faraday's law. 



With a given dynamo electric machine, the electromotive 

 force may be increased or reduced by varying the speed of the 

 induced bobbin ; but it is practically impossible to exceed a cer- 

 tain number of amperes without running the risk of burning the 

 insulating substances with which both the induced and inducting 

 wires are covered.* 



ELECTROLYSIS OF TERNARY COMPOUNDS. In order to explain 

 the electrolysis of a ternary compound, we will as an illustration 

 take the sulphate of copper for example, and follow step by 



* It would even be well, when working out the details of a machine, not to 

 exceed a certain number of amperes, otherwise purely fancy results are obtained, 

 which are of no practical value. It is exactly as if it were proposed to try, with 

 steam at a pressure of say 500 Ibs., a steam engine constructed to work with a 

 pressure of 50 Ibs. to the square inch ; the stuffing-boxes and pistons would let 

 the steam escape, the connecting-rods would bend or break, &c., &c. 



In 1872 M. Gramme had combined, for Messrs. Christofle, a machine capable 

 of depositing 600 grammes of silver per hour, and the wire of which was of a 

 sufficiently large section for a current of 200 amperes, whereas the current re- 

 quired for precipitating the metal was only 150 amperes. This machine gave 

 excellent results. It was later on forwarded to Birmingham, where it deposited 

 1200 grammes of silver per hour. This led the late M. "Werdermann, who con- 

 ducted the experiments, to the conclusion that English manufacturers made a 

 better use of the electric current than French ones. Nothing was less correct ; 

 the English baths had merely less resistance owing to the anodes and cathodes 

 being placed in closer proximity, which is far from being a good .plan for ob- 

 taining a good deposition ; and the machine was run so as to give a current of 

 300 amperes, with the result that it heated veryjinuch, and could not be kept 

 running for a long time without stoppages. 



D 2 



