REFINING OF COPPER AND LEAD. 223 



Its density at 16 is 1 1247. 

 The equivalent of CuS0 4 , 5HO = 124 '1. 

 The equivalent of CuS0 4 , = 79 '7. 



The relation between the equivalent of the solution and of 

 the sulphate of copper is 



CuS0 4 -{-5HO "124-7 



from which, for a density of 1 1247, we have 



18-267 x 0-68 = 12 -42 of CuS0 4 . 



The density of the bath being known, the distance, according 

 to the temperature, can easily be determined by means of the 

 tables which we have published in the first portion of the work. 

 At 20 C. a solution of 12 '42 per 100 of CuS0 4 has a specific 

 resistance of about 32 ohms. 



So that 1 cubic centimetre of the bath, considered between 

 its two opposite faces, has a resistance of 32 ohms. 



This resistance is 10,000 times smaller per square metre or 

 0032 ohm for a thickness of 1 centimetre. With 2, 3, 4, 5, 

 . . . centimetres, the resistance is naturally 2, 3, 4, 5 times 

 greater. 



We have ascertained from direct experiments that the baths 

 of sulphate of copper used in refining were much less resistant 

 than shown in the previous calculations. This result is due to 

 the facts that the heat developed in the electrolyte owing to 

 the passage of the current, increases its conductivity, and that 

 the degree of acidity which increases after a few hours working 

 diminishes the resistance of the bath in a comparatively large 

 proportion. 



In estimating the resistance, the layer of liquid situate 

 between the anodes and the cathodes should not be exclusively 

 considered, for the total conductivity depends not only on that 

 layer, but also on the underneath and lateral expansions of the 

 said layer, which expansions are often considerable compared to 

 the surface of the electrodes. 



The following are a few of the results which we have 

 obtained in operating on sulphates of copper of the trade : 



