REFINING OF COPPER AND LEAD. 207 



There are five similar installations at Selly Oak Works. The 

 weekly number of working hours is 156, which allows of a 

 twelve-hours' rest on Sunday. 



The production for forty-eight baths is: 13*5 kilogrammes 

 per hour ; 324 kilogrammes per twenty-four hours ; 2268 kilo- 

 grammes per week. 



Each bath therefore produces Jf = 275 kilogramme per 

 hour, which corresponds to a current intensity of 233 amperes. 



The temperature in the bath-room is maintained uniform at 

 20 C. The degree of concentration of the baths is 16 Baume. 

 The anodes, having a thickness of 0*0125 metre, are replaced 

 every five weeks. 



The first Wilde machines, in use at Messrs. Elkington's and 

 in a few large English factories, were, as we have explained 

 in Chapter VI., composed of two superposed machines; one 

 magnetic and of small dimensions, the other electro-magnetic 

 and of large dimensions. The only duty of the small one was 

 to excite the electro-magnets of the large one, the latter 

 supplying the current to the refining bath. These apparatuses 

 became, after a few hours' working, so much heated, that it 

 was necessary to cool them by means of a circulation of water 

 in the electro-magnets and the armatures. They entailed a 

 considerable expenditure of work for a given quantity of elec- 

 tricity, and deteriorated somewhat rapidly. Notwithstanding 

 these multiple inconveniences, it must be acknowledged that 

 they rendered valuable service, and were superior to all the other 

 known systems before the invention of the Gramme machines. 



The Wilde machines used at Selly Oak are of an improved 

 type (Fig. 33); but as in the previous types, they produce 

 alternating currents, which have to be rectified with a com- 

 mutator before sending them through the refining bath. 



This new type consists of an armature provided with a 

 series of bobbins revolving between the free extremities of a 

 certain number of cylindrical electro-magnets arranged in 

 a circle on each side of the said armature, and secured to the 

 frame at their other extremities. 



The armature bobbins are provided with iron cores, thus 

 differing from the Siemens' alternating-current machines, in 



