248 ELECTROLYSIS. 



theory, but on a comparison with Bunsen cells actuating 

 electric motors, are inexact from the starting-point, and cannot 

 therefore offer any guarantee as to certitude. 



The only cause opposed to M. Letrange being able to reach 

 to such a high degree of efficiency is the necessity which obliges 

 him to use a current having an electromotive force exceeding 

 1*5 volt; this entails the decomposition of water and conse- 

 quently an appreciable loss of the motive power. 



The electromotive force required by the decomposition of 

 sulphate of zinc effectively is 53 5 x 0438 = 2 34 volts. In 

 his experiment, M. Cadiat had 13 '05 volts for 5 baths, or 

 2 6 volts per bath. We do not know of any practical means 

 for suppressing or even of lessening the effect of this abnormal 

 decomposition. 



TKEATMENT OF THE SULPHIDES. Deligny' s Method. We 

 extract from a letter addressed by M. Deligny to the journal 

 'La Lumiere Electrique,' in 1881, the following information 

 respecting a mode of treating ores, which it appears to us has 

 served as a basis to the processes of Messrs. Bias and Miest, 

 and of M. Marchese, as we will explain further. M. Deligny 

 writes: "I started from this fact, that the various natural 

 cupric sulphides and their compounds or mixtures with iron 

 pyrites are tolerably good conductors of electricity, and are 

 more or less rapidly attacked by an acid in the presence of 

 nascent oxygen. It was therefore to be expected that one of 

 these compounds taken as a positive electrode in any electro- 

 lytic action should throw off, at least slowly, a certain portion of 

 its metal to the solution, from which the electrical action would 

 afterwards easily withdraw it. In order to realise these con- 

 ditions, I have placed in a rectangular vessel either a weak 

 solution of sulphate of copper, or some ordinary acidulated 

 water, such as is used in voltameters. I have then placed in 

 the liquid a copper plate as a negative electrode, and for a 

 positive electrode a carbon surrounded with pulverised copper 

 ore, and contained either in a linen bag or in a porous cell, or 

 even at the bottom of the electrolytic cell and without any 

 diaphragm. With the electromotive force of one or two 

 Bunseu cells, the reaction takes place rapidly enough, and 



