ELECTRICITY IN MINING 55 



siibmerji^od in water. It was I'un for a (juark^r of an liour; 

 it was then stopped and allowed to remain snl)merp:e(l, under 

 official seal, for twTnty four liours, at the end of which time 

 it was ap;ain run for a few minutes. It was next removed 

 from the water, again put under seal, and left to dry for twenty 

 four hours. The insulation was then tested, and the motor 

 was found to be in perfect order. It would be hard to im- 

 agine a test more severe than this. 



As bearing upon this question it is interesting to note 

 that among the pumps in use around Johannesburg, South 

 Africa, at the beginning of the Anglo Boer war, there were 

 twelve of a well known American make, each of which was 

 operated by a 50 horsepower induction motor of American 

 construction with three 15-kilowatt transformers. When 

 the mines were shut down, upon the breaking out of the war, 

 the water rose so rapidly that it was impossible to remove 

 the pumps, motors, transformers, etc., and consequently 

 the}" remained under 500 to 1,000 feet of water. Two and 

 a half years later, when peace was declared in South Africa, 

 the water in the shaft was pumped out and the electrical 

 apparatus was removed to the surface. Three of the motors 

 were stripped and completely rewound, but to the general 

 surprise of the experts the condition of the insulation indi- 

 cated that the rewinding might not be absolutely necessarj^ 

 Accordingly the other nine motors were thoroughly dried 

 in an oven and then soaked in oil. After this treatment 

 they were rigidly tested, proved to be all right, and were at 

 once restored to regular service in the mine. The transformers 

 were treated in the same manner as the motors, with equally 

 gratifying results. 



From the earliest days of practical electric lighting, 

 the availability of the method for mining was recognized; 

 and electric illumination in some form or other is now used 

 very widely. Of the two forms — the arc and the incandescent 

 — the latter is ver^^ naturally preferred undergroimd, for 

 various reasons. In the first place, the subterranean spaces 

 to be illuminated are restricted in area, so that small lights 

 are sufficient ; in the second place, both the earlier arc lighting 

 circuits and a great many of those in use to-da}^ have involved 



