1892.] on Electro- Metallurgy. 631 



shows that, in point of electrical conductivity, one ton of the copper 

 of to-day will go as far as two-and-a-half tons of such copper as 

 was used for the cable of '58. 



This change is largely due to electrolytic copper refining. 



The process of electrolytic copper refining is the same in principle 

 as that which produced the thickening of one of the wires and the 

 thinning of the other in my first experiment. To prepare the crude 

 copper for the refining process it is cast into slabs ; these form the 

 anodes, and correspond to the wire which in my experiment became 

 thin. The cathodes, corresponding to the wire which became thick, 

 are formed of thin plates of pure copper. Here are plates such as 

 are used in electrolytic copper refining works. They are portions 

 of actual cathodes and anodes, and represent the state of things at 

 the commencement, and at the end, of the depositing operation — an 

 operation that takes several weeks to complete, and efi'ect the great 

 change these plates show. In copper refining works, an immense 

 number of these plates, each having 6 to 10 square feet of superficial 

 area, are operated upon together, in a great number of large wooden 

 vats, containing sulphate of copper solution and a small proportion of 

 sulphuric acid. Electric current from a dynamo, driven by a steam- 

 engine or water-power, is conveyed by massive copper conductors to 

 the vats, arranged in long lines of 50 or 100 or more in series. 

 Thick copper bars connect adjoining vats, and provide a positive and 

 negative support for the plates, which hang in the solution, opposite 

 each other, two or three inches apart. During the process, the 

 impure slabs dissolve, and at the same time pure copper is deposited 

 from the solution upon the thin plates. The deposition and dis- 

 solving go on slowly, in some cases very slowly, for a slow action 

 takes less power, and gives purer copper than a more rapid one. The 

 usual rate is one to ten amperes per square foot of cathode surface. 

 You will better realise what these rates of deposit mean, when I say 

 that one ampere per square foot rate of deposition gives for each foot 

 of cathode surface, nearly one ounce of copper in twenty-four hours 

 and a thickness of one-eight hundredth of an inch ; and therefore 

 the production of one ton of copper, at that rate, in twenty-four 

 hours, would require a cathode surface in the vats, in round numbers, 

 of 36,000 square feet. At the higher -rate of ten amperes per square 

 foot, which is used where coal is cheap, one-tenth of this area 

 would be required. 



The importance of the electrolytic copper refining industry, 

 and the extent of the plant connected with it, may be inferred from 

 the fact that, reckoning the united production of all the electrolytic 

 copper works in the world, nearly one ton of copper is deposited 

 every quarter of an hour. 



Very little power is required for copper deposition if the extent 

 of the dissolving and depositing surfaces is large, relatively to the 

 quantity of copper deposited in a given time. 



Some of the impurities ordinarily found in crude copper are 



