Ill FINING OF COPPER AND LKAD. 219 



attention to the necessity of preventing the variations of com- 

 position of their baths. With solutions too rich in copper, the 

 resistance, and consequently the motive power, would be reduced, 

 but the deposition of the metal would be less perfect, and its 

 tenacity smaller. 



In another part of his treatise on electro-chemistry, M. 

 Becquerel describes a curious fact, which we have also noticed, 

 and which we think is worth quoting. 



" When sulphate of copper is prepared on a large scale and 

 stored in wooden vessels, a deposition of metallic copper can be 

 observed to take place, after a certain time, at the extremities 

 of some of the staves. The organic matter intervenes to operate 

 the reduction. The deposition of copper gradually increases 

 until large masses of adhesive copper are formed. In this re- 

 duction the dioxide sulphate is changed into protoxide sulphate. 

 But there remains to be explained why the deposition occurs 

 in certain places and why all the parts offer the same cohesion. 

 Let us admit, as everything seems to prove it, that the first 

 particles of copper deposited have been so deposited by the 

 reaction which we have mentioned. These particles, which are 

 in contact with the carbonaceous matters of the decomposed 

 wood, constitute a voltaic couple; the copper is the negative 

 pole, and the carbonaceous matters on which the sulphuric acid 

 reacts is the positive one: consequently the copper must be 

 deposited on the copper already precipitated." 



THICKNESS OF THE DEPOSITION OBTAINED IN A GIVEN TIME. 

 We will attempt to determine the cost of the electric refining 

 of copper in various conditions of installations ; to that effect 

 we must first calculate the possible thickness of deposition per 

 hour, then the expenditure of power required by the electrolysis, 

 and lastly the capital invested in the manufacture. 



In his work on the theory and the applications of electricity, 

 Mr. John T. Sprague describes his personal experiments on the 

 deposition of copper effected in a bath composed of 3 parts of 

 a saturated solution of sulphate of copper and 10 parts of sul- 

 phuric acid diluted in 10 times its volume of water. 



The operation was not stopped before the thickness of the 

 deposition reached 52 centigrammes for 6 '45 square centi- 



