196 THE ELECTRIC TELEGRAPH. 



security that the coating will not spring off or crack in 

 bending the wire. When the wire is badly covered it rusts 

 at those points most exposed to wear and tear, as at the 

 points of suspension, just as soon as a naked wire. In the 

 neighbourhood of manufacturing towns also, the best " gal- 

 vanising " is of no use, as the sulphurous acid gas in the air 

 quickly attacks the zinc, with which it combines, and the 

 salt, washed off by the rain, leaves the iron exposed to the 

 weather and the further action of the acid. In addition to 

 this, the process of galvanising is said to alter the molecular 

 structure of the iron and to render it brittle. 



Instead of zinc, an alloy may be used, as proposed by 

 Callan, which not only protects the wire against the attacks 

 of acids and weather, but the coating is ductile and bends 

 with the wire, a condition essential to its success. The 

 alloys which Callan tried and recommends are composed of 

 one part of tin with from one to eight parts of lead. 



A proposal has also been made by Mr. Bucklin, of New 

 York, to dip the galvanised wires into molten copper or 

 brass, by which means a protection, that may be increased 

 to any required thickness by repeating the operation, can be 

 obtained. This would be a cheaper way than that suggested 

 by Professor Brix, the editor of the German Telegraph 

 Journal to cover a bar of iron in this way with brass or 

 copper, and then to draw it down to the required guage. 



Joints in land line wire are made by bringing the ends 

 together and wrapping them with a binding wire, or by 

 twisting them round each other. 



Fig. 108. 



Figure 108 represents a joint made by the former method, 

 called the Britannia joint. The wires to be joined are bent 

 at right angles, about half an inch from the ends, as at a a. 



