274 STJBMARINE CABLE LAYING AND EEPAIEING. 



pressure amounts to one ton and a quarter per square inch for 

 every 1,000 fathoms depth ; and -when the cable is sunk ard 

 subject to this pressure any places where a:r is imprisoned are 

 liable to burst open and cause serious faults. 



The soldering fluid is first cleaned off the joint by rubbing 

 •with a clean bit of rag soaked in wood naphtha, and after drying 

 it the first coat of Chatterton's compound is laid on. The end 

 of a stick of this compound is heated in the spirit lamp flame, 

 care being taken not to keep it in the flame long enough to 

 burn, or there will be trouble from air-holes. The bare part of 

 the joint is also heated very slightly to receive the coat. The 

 stick of compound is then worked along over the joint as well as 

 possible to cover every part, and is followed up by a smoothing 

 iron. This is a smooth iron tool, curved at the erd (Fig. 157) 

 which, when heated and worked over the coating of compound, 

 spreads it out in any desired way ; thus where the compound 

 is too heavily laid on in places it can be worked down into 

 cavities so as to make it everywhere of the same depth. Any 

 imprisoned air is worked out by this tool, and the coating 

 finally smoothed round evenly by the finger and thumb, 

 first wetted, so as not to adhere to the material. The 

 gutta-percha covering of the core on each side of the joint 

 is now dealt with, the spirit flame being held underneath 

 while the core is turned round backwards and forwards. The 

 ends of the insulation, after warming, are then drawn to- 

 gether till they are about Jin. apart, and one end is drawn 

 down to a point, while the other is drawn over it (Fig. 160) 

 thus completely enveloping the joint in the same maberial as 

 covers the conductors on each side. The end so left is further 

 heated and smoothed down. A second layer of compound is now 

 spread over the percha, precisely as before. Some sheet gutta- 

 percha is now taken, and a square piece about Sin. wide cut ofl'. 

 This is heated over the flame, and a strip cut off, about l|in. 

 wide, which is then taken, and one end laid against the core 

 underneath at A (Fig. 160) the other end hanging down. 

 From this point the strip is pressed upwards against the core 

 by the fingers working along from A to B, and is then heated 

 again and pressed all round the core till the ends meet at the 

 top, as in the figure. The reason for this careful treatment is 

 to make sure there are no air bubbles imprisoned by commenC' 



