ELECTRO-METALLURGY 



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set in motion in front of the poles of a permanent magnet, in such a manner that the 

 soft iron core of the electro-magnet becomes alternately a magnet and not a magnet : 



in the act of becoming a magnet, it raises up a current in one direction in the wire 

 with which it is wound ; in the act of ceasing to be a magnet, it raises up a current 

 in the reverse direction. The ends of the wire are led away and insulated. The in- 

 strument is fitted with a commutator, so adjusted that it collects the currents from the 

 ends of the wire, and guides them in a uniform direction into the vessel that contains 

 the solution and articles to be gilded or plated. In practice, a single machine consists 

 of many electro-magnets grouped together, and many powerful magnets for exciting 

 them ; by which means a continuous flow of a large amount of electricity is ob- 

 tained. Fig, 802 is an illustration of such an arrangement as adapted by Mr. Wool- 



rich : aaaa are four clusters of permanent steel magnets, seen from above ; 

 is the frame-work of the machine ; c c c c are four bars of soft iron, wound with largo 

 size insulated copper-wire ; d is a circular disc, on which they are nuranted, and which 

 rotates on a vertical axis, of which / shows the upper end ; e is the commutator, 

 from which two wires are led off to the solution to be operated upon. The permanent 

 magnets are U-shaped; one pole only of each bur. die is visible; the other is beneath 

 the disc d, and its freight of electro-magnets c c, c. The axis is set in rotation by 

 a strap passing over the drum of a shaft of the steam-engine, that does the ordinary 

 work in a factory ; and the disc carries the electro-magnets between the poles of the 



