Chap. V.] 



THE ELECTRO-MAGNET. 



53 



the liquid. As a result, however, hydrogen is left, 

 having no oxygen with which to recombine, and as it is 

 electro-positive, it attaches itself to the negative pole. 

 Thus only at the two poles are the effects of the 

 decomposition visible. The quantity of an electrolyte 

 decomposed is proportional to the action in the battery ; 

 and the quantities of the different substances pro- 

 duced at the different poles are in proportion to their 

 chemical equivalent. 



Production of magnets by currents. Let 

 AB (Fig. 28) be a portion of a large link of soft iron, 

 and let a thick copper wire 

 be wound round each end, 

 each turn being insulated 

 from the other. The wire 

 must be wound in such a 

 way that, if the link were 

 straightened out, the wire 

 would be all in the same 

 direction. Connect the ends 

 of the wire with a battery 

 of two or three Grove's 

 cells, and an electro-magnet 

 is formed. Let T be a bar 

 of soft iron with a hook at- 

 tached. While the current flows round the wire, the 

 soft iron will become converted into a horse-shoe mag- 

 net, of such strength as to attract the bar T, and keep 

 it in contact though a weight of many pounds be 

 suspended from it. Interrupt the current, then in u 

 moment the link will lose its magnetism, and the 

 weights will drop. The soft iron is thus only tem- 

 porarily magnetised by the passage round it of a 

 current. All the magnetism is not, however, lost ; 

 some generally remains, and is called residual 

 magnetism. The less thorough the annealing of the 

 iron, the greater is the tendency for some degree of 



Fig. 28. Electro-magnet. 



