1892.] , on Electro-Metallurgy. 629 



raony to the wonderful power of electrotype to transmit an exceedingly 

 faithful copy of such a surface. 



Nickel, has, of late years, come into extensive use for what is 

 termed nickel-plating, as applied to coating polished steel and brass 

 with nickel. Nickel, not only has the advantage over silver of cheap- 

 ness, but also, in some circumstances, of greater resistance to the 

 action of the air. 



Another metal, usually deposit^ in the form of a coating, is iron. 

 The electrolytic deposit of iron is peculiarly hard — so much so, that 

 it is commonly, but erroneously spoken of as s/eeZ-facing. The 

 deposition of a film of iron upon engraved copper-plates, as a means 

 of preventing the wear incidental to their use in being printed from, 

 has become almost universal. Valuable etchings, mezzo-tints, and 

 photogravure plates are thus made to bear a thousand or more impres- 

 sions without injury. By dissolving off the iron veil with weak acid, 

 when the first signs of wear appear on the surface of the plate, and 

 re-coating it with iron, an engraved copper-plate is, for all practical 

 purposes, everlasting. 



In this case, of course, the film of iron is extremely thin — one or 

 two hundred thousandths of an inch. But it is possible to produce 

 most of the metals commonly used as coatings, in a more massive 

 form. Here, for example, is an iron rod half-an-inch in diameter, 

 entirely formed by electrolytic deposition. I am indebted to Mr. 

 Koberts- Austen for being able to show this, and also for this other 

 example of a solid deposit of iron, and for this beautiful specimen of 

 electrolytic coating with iron. Here also are solid deposits of silver. 

 This drinking cup is a solid silver electro-deposit. 



These are all departments of electro-metallurgy which would have 

 maintained a perfectly healthy industrial existence and growth without 

 the dynamo ; but now I come to speak of a branch of the subject — 

 electrolytic copper refining — which, without that source of cheap 

 electricity, could not have existed. This is the most extensive of 

 all the applications of electro-chemistry, and is rendering valuable 

 assistance to electrical engineering by the improvement it has led to 

 in the conductivity of copper wire. 



One of the results of this is seen in the raising of the commercial 

 standard of electrical conductivity. 



Ten years ago, contracts for copper wire for telegraphy, stipulated 

 for a minimum conductivity of 95 per cent, of Matthiessen's standard 

 of pure copper. Now, chiefly owing to electrolytic refining, a con- 

 ductivity of 100 per cent, is demanded by the buyer and conceded by 

 the manufacturer. 



To show the difference between the past and present state of 

 things in relation to the commercial conductivity of copper, I am 

 going to exhibit on the screen measurements of the resistance of six 

 pieces of wire of equal length and equal cross section — they have 

 been drawn through the same drawplate. Three of the pieces are 

 new, and three are old. The three new pieces are made from elec- 



