202 ELECTROLYSIS. 



with lead. They cost 350 francs (14Z.) each, exclusive of the 

 frames and conductors. Their length is 3 metres (10 feet), 

 their width 80 centimetres (2 feet 8 inches), and their depth 

 1 metre (3 feet 4 inches). The two poles of the machine are 

 connected with two brass frames made in one piece each. The 

 negative frame is underneath the positive one and well isolated 

 from it. 



The baths are joined in tension. The positive frame of one 

 being connected to the negative frame of the following bath, 

 and so on, by means of a copper conductor so curved as to 

 allow a free passage between the baths. 



A galvanometer indicates the strength and direction of the 

 current, and detects the polarising current. A cut-out auto- 

 matically interrupts the operation when the counter-currents 

 become too intense. 



The bath is composed of a solution of sulphate of copper 

 uniformly maintained at 19 Baume. When the bath becomes 

 too much charged with iron, it is purified by crystallisation. 



All the baths communicate together at the bottom, so that 

 their level is uniform. 



The copper is deposited on copper cathodes suspended to 

 the cross-bar of each negative frame. The cathodes are about 

 1 millimetre thick, and are simply folded at the top for 

 hooking on the cross-bars of the frame. 



The ores are treated as if it were only proposed to obtain 

 ordinary merchantable copper; they are brought to a per- 

 centage of 95 per 100 in copper, and care is taken that this 

 raw copper should not be too much charged with iron, sulphur, 

 arsenic, antimony, &c. The copper, which in the bath is 

 thicker at the top than at the bottom, is then melted and made 

 into plates of about 1 centimetre average thickness. 



In order to prevent certain parts, and notably those which 

 are in contact with the top of the bath, wearing out too rapidly, 

 they are coated with a non-conductive composition made of 

 varnish and plumbic chrornate. 



These melted plates are suspended, by means of two copper 

 hooks passing through two small holes made in them, to the 

 cross-bars of the top frame, and serve as soluble anodes. 



