REFINING OF COPPER AND LEAD. 215 



elements of a battery joined in tension ; their number varied 

 from one to forty -eight, but they all had electrodes of the same 

 surface (16 square decimetres). The speed of the machine was 

 increased as the number of baths grew larger, and the electro- 

 motive force varied from 1 to 8 volts. 



The figures of these tables establish that the deposition of 

 the copper increased with the number of baths, and this not 

 only as an absolute quantity, but also in a ratio to the work 

 expended in the operation. The weight of copper per kilogram- 

 metre varied from 1'58 gramme up to 23 '18 grammes, and 

 even up to 140 grammes if the loss of motive power which was 

 found to occur, as we shall see further on, is taken into account ; 

 whereas in the first series of experiments the weight of the 

 deposited copper did not exceed 1 '96 gramme. 



The practical conclusion of these experiments is self-evident ; 

 a great economy is afforded by joining the baths in series when 

 dynamo-electric machines are used. 



Third Series of Experiments. M. Gramme purposed main- 

 taining constant the intensity of the current in a series of 

 comparative trials ; this led him to increase the surface of the 

 electrodes as well as the number of baths joined in series, so as 

 to maintain constant the total resistance of the circuit. 



Table No. 2 indicates that the quantity of copper deposited 

 in a bath is much the same in all the experiments. The 

 speed of the machine and the electromotive force of the cur- 

 rent did not vary, and the work expended remained practically 

 invariable. 



These experiments are in perfect accordance with all the 

 known theoretical notions except on one point ; it will at once 

 be observed that M. Gramme was driven to increase the 

 sections of the liquid in a greater ratio than the number of 

 baths joined in tension. 



However this may be, various circuits are seen here, with 

 uniform resistances and invariable electromotive force and in- 

 tensity of current ; it is therefore not surprising to see that in 

 each part of these various circuits the quantity of deposited 

 copper practically remains constant. But it will be observed 

 that the total quantity of copper deposited in the complete 



