TREATMENT OF ORES. 247 



of zinc ; in the experiment previously described, 5 horse-power- 

 hours were expended for obtaining the same result. 



2 * 6 

 The efficiency was therefore -^- = 0'52. The yield is 



4 8 kilogrammes per 24 hours per horse-power. 



By perfecting his process, M. Letrange will no doubt obtain 

 a better result, but he will certainly not exceed 6 to 7 kilo- 

 grammes per horse-power per 24 hours ; still it will be neces- 

 sary, in order to reach that result, to considerably reduce 

 the resistance of his actual bath. From an electrical point of 

 view everything turns on that : join the baths in series, give 

 them immense surfaces of anodes and cathodes so as to reduce 

 their resistance, and a great production with a minimum of 

 dynamos and a small expenditure of motive power is obtained. 

 Can this result be industrially obtained ? We do not know ; 

 but what we are certain about is, that the success will never be 

 impeded by the use of machines. Dynamos of considerable 

 power, of simple working, and indefinite duration, may be 

 economically established, but a superior efficiency to that indi- 

 cated by the theory should not be expected from them; that 

 is to say, the production of a great electrical energy without 

 borrowing from any given source a still greater mechanical 

 energy. 



Messrs. Bias and Miest* when calculating the required 

 power for decomposing sulphate of zinc by the current, found 

 that theoretically 2J horse-power were required for the pro- 

 duction of 24 kilogrammes of zinc per day, which amount 

 corresponds to 9j kilogrammes per day for 1 horse-power. 

 This calculation is correct, but Messrs. Bias and Miest are 

 mistaken when they only value at 30 per cent, the practical 

 efficiency of the electrical energy utilised in the precipitation 

 of the metal, compared to the original expenditure of work. 

 This efficiency can certainly reach as high a figure as 70 and 

 even 80 per cent. M. Letrange therefore might, as we said 

 above, hope to obtain 6 to 7 kilogrammes of zinc per horse- 

 power, but never more ; his own calculations, based, not on the 



* Note sur 1'application de 1'electrolyse a la metallurgie,' by C. Bias and E. 

 Miest. 



