196 ELECTROLYSIS. 



copper is deposited on the cathode ; the sulphuric acid attacks 

 the anode and regenerates the sulphate of copper decomposed 

 by the current, so that the work performed is equal to the work 

 expended. 



If the metals operated upon had no impurities, and if the 

 operation were conducted with care, no gaseous escape would 

 take place, and there would consequently be no polarisation. 



In electro-plating, the work performed in the carriage of 

 particles may be considered as nil, owing to the fact that the 

 resistance of the baths for the weight of deposited metal is in- 

 significant ; but in refining work, when a single machine often 

 precipitates more than 10 kilogrammes of copper per hour, the 

 motive power necessitated by the said carriage is not to be 

 neglected. This part of the expenditure is, however, always 

 very small, and the electrical energy is almost entirely con- 

 sumed in the overcoming of the resistance offered by the baths 

 to the passage of the current. 



It is, therefore, sufficient to know the intensity of the current 

 in amperes and the resistance of the baths in ohms in order to 

 calculate the power required for a given production of copper. 

 A coefficient, varying with the nature of the coppers under 

 treatment and the speed of the machine, is afterwards applied 

 in each particular case. 



Calling this coefficient k, the formula expressive of the 

 motive power will be 



RC 2 



W = k kilogrammetres. 



But it is always possible to reduce the resistance of a bath 

 by increasing the surfaces of the anodes and cathodes, and to 

 reduce the intensity of the current for a given production by 

 joining the baths in series and giving them a total resistance 

 equal to that of the primitive bath. It is, therefore, possible 

 to at will reduce the expenditure of electricity, and consequently 

 that of the motive power, and this in a very large proportion. 

 For example, it is easy to conceive a factory with a plant laid 

 down for the refining of 1 ton of copper per hour, with the 

 expenditure \f only 1 horse-power, if the economy of motive 



