224 ELECTROLYSIS. 



1st. Temperature 20 C. ; concentration 10 Ban me; specific 

 resistance 25 ohms. 



2nd. Temperature 20 C. ; concentration 18 Baume ; specific 

 resistance 20 ohms. 



3rd. Temperature 25 C. ; concentration 18 Baume; 

 additional acid 1 per 100 ; specific resistance 15 ohms. 



The foregoing show that it is easy to establish some refining 

 baths having a specific resistance of 20 ohms, and we believe 

 that the solutions in use at Hamburg and Birmingham have a 

 specific resistance lower than 20 ohms ; we will, however, take 

 this figure as the basis of our calculations, because we prefer the 

 use of resisting baths to that of acid ones, as regards the purity 

 of the copper obtained. 



The distance between the anodes and the cathodes varies 

 from 2 to 10 centimetres. In refining work the minimum 

 distance is scarcely less than 5 centimetres, in order to facilitate 

 the manipulations and prevent any contact between the positive 

 and negative plates. We have, however, seen installations in 

 good working order with a distance of only 4 centimetres, but 

 this necessitated an extra quantity of labour for fixing the 

 anodes and the cathodes on the cross bars of the baths. The 

 resistance of refining baths varies between 01 and 03 ohm 

 per square metre of surface of anode. 



It will thus be seen that the greater the surfaces of anodes 

 for a given hourly deposition, the smaller is the resistance 

 which the current has to overcome in order to effect the pre- 

 cipitation of copper ; consequently the power required for driving 

 the dynamo is smaller, or, what amounts to the same, the 

 smaller the thickness of deposition per hour, the smaller the 

 motive power required. If the operations took place on in- 

 finitely large surfaces, large quantities of copper would be 

 deposited with an infinitely small power. This is an important 

 fact which M. Gramme had the honour of being the first ta 

 put in evidence and upon which we could not too much insist. 



Let us now examine what is the total resistance of the baths 

 in a few of the applications which we have described. 



At Marseilles, the surface of anodes is 22 square metres 

 per bath; the electrodes are 5 centimetres apart, and there 

 are forty baths. The resistance for each bath is 



