276 SUBMAEINE CABLE LAYING AND KEPAIEING. 



Before anything more can be done the joint must be 

 thoroughly cooled, and for this purpose it is held down in a 

 gutta-percha tray (Fig. 161) containing either a diluted mix- 

 ture of muriate of ammonia and saltpetre, or a few lumps of 

 ice in water. The proportions of this cooling mixture are given 

 in Munro and Jamieson's " Pocket Book of Electrical Rules and 

 Tables " as five parts of muriate of ammonia to five parts of 

 saltpetre and 16 parts of water. The joint is held down in 

 the cooling mixture by two hooks at the bottom of the tray, 

 and remains in for 15 or 20 minutes. The tray is entirely of 

 gutta-percha and provided with four lugs for suspending, thus 

 thoroughly insulating it when required for use during tests of 

 joints in short lengths spliced up on board. 



Meanwhile the further end of the new piece of cable in tank 

 (on the near end of which the joint has just been made) is 



Fig. 161 . — Joint Cooling Tray, 



connected to the testing-room, and remains so connected, in 

 order to test the cable as it is payed out, and communicate 

 occasionally with the shore. From this end, when the joint is 

 cool, a test is taken through the united cables, the end on 

 shore being free. The insulation of the seaward end, and 

 that of the new piece spliced on being known, it is easily 

 calculated what the two jointed together ought to give ; and 

 if the joint is not perfect the resultant insulation will be 

 lower than this. But jointers very rarely fail to make a perfect 

 joint, having served their time in the factory, where joints 

 occur on every two miles of core manufactured, and the men 

 being chosen as reliable for sea work. 



Cable Splice.— Before the splice in the sheathing wires 

 is made, the core Is served with a layer of tape or loose spun 

 threads, over which is laid a serving of brass tape, followed 

 by jute or Russian hemp, bound at intervals with seizings of 



