632 Mr. J. Wilson Swan [May 20, 



valuable. Silver and gold are common impurities, and these, and 

 some other impurities, do not enter into solution, but fall down as 

 black mud, are recovered, and go to diminish the cost of the 

 process, or increase the profit ; and even those impurities which enter 

 into solution, are, under ordinary conditions, almost completely 

 separated. 



Electrolytic copper refining is both an economical and an effective 

 process. The deposited copper is exceptionally pure. At one time 

 it was supposed that it must necessarily be quite pure, but this is 

 not the case ; other metals can be deposited with the copper, but it is 

 not difficult to realise in practice a close approximation to absolute 

 purity in the deposited copper. Here is an example of the deposition 

 of a mixed metal — brass, that is, copper and zinc deposited together, 

 and there are in the Library a number of interesting specimens of 

 mixed metal deposition. These deposits of brass and other alloys 

 show that more than one metal can be deposited at the same time. 

 The great enemy to conductivity in copper is arsenic, and the depo- 

 sition of arsenic as well as copper, is one of the things to be guarded 

 against in electrolytic copper refining. Not only are the chemical 

 characteristics of electrolytically refined coj^per generally good, but its 

 mechanical properties are largely controllable. Usually electrolytic 

 copper is melted down and cast into billets of the form required for 

 rolling and wire-drawing. This treatment not only involves cost, but 

 the copper is apt to imbibe impurity during fusion ; though, if the 

 process is carefully conducted, the deterioration is slight. 



But it is evident that the re-melting of the deposited copper is a 

 thing to be avoided, if possible, and the question naturally arises, 

 why, now that deposition costs so little, may not the beautiful prin- 

 ciple which comes into play in electrotype, and which enables the 

 most complicated forms to be faithfully copied, be taken advantage of 

 to give to plainer and heavier objects their ultimate form ? 



There are several reasons why this idea is not more frequently 

 acted upon. One is, that the process of electrolytic deposition is 

 slow ; another, that knowledge of the conditions necessary for ob- 

 taining a deposit having the required strength, and other qualities, 

 is not very widespread. Moreover, in the electrolytic deposition of 

 copper, and indeed of all metals, there is a strong tendency to rough- 

 ness on the outside of the deposit, and to excrescent growths, the 

 removal of which involves waste of labour and material. These 

 tendencies can, to a very great extent, be counteracted by careful 

 manipulation, and the use of suitable solutions, and they can also be 

 counteracted by mechanical means. This has been done by Mr. 

 Elmore. He remedies the faults I have mentioned by causing a 

 burnisher of agate (arranged after the manner of a tool in a screw- 

 cutting lathe) to press ui)on and traverse a revolving cylindrical 

 surface on which the deposit is taking place, and while it is immersed 

 in the copper solution. The result is that it is kept smooth and 

 bright to the end of the process. 



