THE CONQUEST OF NATURE 



except perhaps a type of pump known as the sinking 

 pump. This is a movable pump that can be easily 

 lowered from one place to another, and has proved to 

 be a great time- saver over steam or air pumps used 

 for similar purposes. 



For some time the question of the durability of elec- 

 tric pumps was in dispute, but developments in quite 

 recent years seem to prove that, in some instances at 

 least, such pumps are practically indestructible. 



"The question of what would happen to an electric 

 motor in a mine if pumps and motors get flooded has 

 often come up. From tests made recently at the Uni- 

 versity of Liege, Belgium, it appears that a suitably 

 designed polyphase alternating-current motor of a type 

 largely used on the continent of Europe was completely 

 submerged in water. It was run for a quarter of an 

 hour; it was then stopped and allowed to remain sub- 

 merged, under official seal, for twenty-four hours, at 

 the end of which time it was again run for a few min- 

 utes. 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 

 imagine a test more severe than this. 



"As bearing upon this question it is interesting to 

 note that among the pumps in use around Johannes- 

 burg, 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 5o-horse- 

 power induction motor of American construction with 

 three i5-kilowatt transformers. When the mines were 



[264] 



