COATING OF IRON WITH COPPER. 97 



this, as will be apparent, can only be done within certain limits ; 

 for by increasing the intensity of the battery it may be rendered 

 too strong for the solution near the battery, and thus a sandy 

 deposit will be given at the one end and none at the other. The 

 electro-metallurgist, when coating long rods of iron wire with any 

 metal, has to make connections with the battery every few feet. 

 The wire is generally coiled up in the form of a cork-screw, and 

 suspended by copper wires. We have found it very convenient to 

 coil it upon a reel, having its armatures tipped with copper, and 

 connected with the battery. This plan insures a regular coating, but 

 the position of the wire requires to be changed during the operation, 

 otherwise the parts which press upon the arms of the reel will be 

 left without deposit. 



illustration of Conduction. As an illustration of the property of 

 conduction, we mention the following circumstance. Having a large 

 iron shaft, or rod, about 12 feet long and 3 inches average diameter, 

 to cover with copper, we had it properly cleaned, placed in a hot 

 solution of cyanide of copper and potassium, and surrounded by 

 sheets of copper as a positive electrode. Two batteries of 7 pair 

 intensity were attached, one at each end of the shaft ; but by 

 an oversight one of the batteries was not properly connected, the 

 copper terminal of the battery having been attached to the shaft. 

 Had the shaft been of copper, the one battery would have neutra- 

 lized the other, so that there would not have been any deposit ; or, 

 had the one battery been stronger than the other, there would have 

 been a current and deposit equal to the excess of power of the one 

 over the other. But, under the stated circumstances a different 

 result was obtained. After the batteries had been in action two 

 hours, we found that a beautiful copper coating was imparted to 

 that half of the shaft which extended from the point properly con- 

 nected, while the other half was quite bare no deposit having 

 taken place upon it ; but a deposit had been made upon the copper 

 electrode opposite this non-affected half. The batteries did not (as 

 we could perceive) affect one another, except that the one impro- 

 perly connected prevented the deposit effected by the other pro- 

 ceeding further than the half length of the shaft ; but it made the 

 deposit obtained more perfect than would have been the case had 

 there been only one battery at one end. 



In this instance, the distance of the shaft from the electrode 

 was 6 inches, so that the resistance of 6 feet of the iron was 

 more than 6 inches of the solution; hence the influence of the 

 contra-acting battery could not reach further : or if any power 

 passed further it was neutralized by the other battery, which 

 we are inclined to think did not take place, as the amount or 

 thickness of deposit upon the one half was fully more than we 



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