76 



ELECTROLYSIS. 



FIG. 13. 



The whole arrangement of the ring, the induced wires, the 



collector, the intermediary mandril, and of the washers used 



for the mounting on the spindle is generally called the bobbin. 



This bobbin, the essential part of all Gramme machines, is 



illustrated in Fig. 10. 



The induced wire is divided into a certain number of equal 

 parts constituting as many elementary bobbins. Each elemen- 

 tary bobbin is connected at one end to one of 

 the blades or segments of the collector, and at 

 its other end to the following segment of the 

 same collector. The wire is insulated by means 

 of one or more strands of cotton passed through 

 a bath of bitumen or of gum lac. The seg- 

 ments of the collector are also isolated from 

 each other so that the ring is wound with an 

 endless wire of great length. 



In order to produce machines of great 

 capacity and low electromotive force, M. 

 Gramme has altered the construction of his 

 bobbin in the following manner (Fig. 11) : 

 a series of long copper bars, isolated from 

 each other and constituting a complete cylinder, 

 are placed on two copper washers keyed on 

 the spindle and having a certain number of notches. The two 

 ends of this cylinder act as collectors. The iron wire con- 

 stituting the ring is wound on this cylinder, and a second series 

 of copper bars placed externally to the ring complete the 

 bobbin. The internal and external bars are connected by 

 means of radiating pieces so as to form an endless conductor as 

 in the case of bobbins made with wire wound round the ring. 

 The Gramme machines for electroplating are of extremely 

 varied forms. The No. 1 type illustrated in Fig. 12 is most 

 generally used. All these machines, without a single exception, 

 have their electro-magnets in circuit, as they can be driven at 

 variable speeds, and when excited in shunt or by double wire 

 destructive sparks accompany the variations of speed. 



In order to avoid the reversals of current resulting from 

 the polarisation of the electrodes dipping in the electrolyte, 



