MANUFACTURING LEAD-COVERED TELEPHONE CABLE 329 



large gauge loaded toll cables are treated with a special drying process 

 to diminish the leakance. 



Under-water Cables 



Either quadded or non-quadded cable may be used on occasion for 

 crossing rivers, bays, etc., and in these cases the lead-covered cable is 

 protected by being first served with two or three layers of jute roving 

 impregnated with tar, then wound with galvanized steel armor wire, 

 and again served with jute yarn, impregnated with an asphalt com- 

 pound, although in many cases at present this outer serving of yarn is 

 omitted. In case of injury causing an opening in the sheath of such a 

 cable, water may enter the interior and interrupt the service. It is 

 also liable to penetrate for a considerable distance and thus ruin a 

 substantial length of cable which it then becomes necessary to replace. 

 To diminish the amount of cable damaged in this way, this type of 

 cable is sometimes made with a very large amount of paper insulation 

 crowded into a small space to make the cable within the lead pipe very 

 dense. The swelling of this paper as it becomes wet tends to retard 

 the penetration of water and to diminish the amount of cable damaged. 



This dense core construction has, however, the objection that it 

 tends to produce circuits of lower transmission efficiency on account of 

 the higher capacitance and leakance obtained. For this reason cables 

 for this purpose in many cases are made with less dense core con- 

 struction similar to that used in land cables but with the core treated 

 so as to provide water barriers at frequent intervals to prevent or 

 greatly diminish the passage of water through the barrier, commonly 

 known as a "plug," so that the damage resulting from an injury to the 

 sheath is substantially confined to the portion between two consecutive 

 plugs. 



The Cable Sheath 



One of the outstanding developments in cable manufacture which 

 occurred about 1911 was the substitution of 1 per cent antimony in 

 lead cable sheath for 3 per cent tin. The use of tin alloyed with lead 

 for cable sheath had been instituted many years before, as it had been 

 found that such sheath was more durable than sheath composed of 

 lead alone and had better mechanical characteristics. 



Exhaustive tests showed that lead-antimony alloy sheath is equal in 

 quality to lead-tin alloy and, although its use required the development 

 of improved methods of mixing and extrusion, it has resulted in large 

 cost savings. 



Another decided improvement introduced later was the substitution 

 of vacuum drying ovens for the old gas or steam-heated air ovens. 



