ELECTRICITY IN MINING 53 



with inclined traction haulage, for after all an elevator is 

 virtually a railway with 100 per cent grade. With these 

 equipments great care is taken to regulate and control the 

 apparatus for safety purposes with safety and emergency 

 brakes, etc. 



One of the instances cited by Mr. Blackwell in his paper 

 is that of a flat rope dou])le reel hoist operating in the Free 

 Silver mine, at Aspen, Colo. In this case the hoist works 

 in a vertical single compartment shaft, with guides for extra 

 weight, and is driven Ijy a direct current motor of 120 horse- 

 power at 650 revolutions per minute, with different gears 

 to give 20 and 30 revolutions to the drum. The speed of 

 hoisting ore is from 315 to 630 feet per minute, and that of 

 bailing water from 510 to 1,020 feet per minute. 



In one gold mine where steam power has been superseded 

 by an alternating current induction motor, the hoist moves 

 through the shaft at the rate of 1,250 feet per minute, doul)le 

 deck cages carrying 3,600 pounds of ore, thus elevating 500 

 tons daily from a 2,500 foot level. It is stated that this sys- 

 tem has shown a net efficiency of 75 per cent, taking into 

 account all electrical and frictional losses, and that the aver- 

 age cost per horsepower per month has been reduced from 

 not less than $20 to $7. 



Electric motors have been found extremely useful and 

 successful in a large number of cases for driving the pumps 

 which are employed to remove the accumulations of water 

 in mines. It is said that the efficiency even of small recip- 

 rocating pumps give as high as 90 per cent. 



One of the problems encountered in connection with this 

 application of electricity has been the proper regulation of 

 the speed of the motors for the purpose of varying the amount 

 of water pumped. In direct current motors this is done b}^ 

 varying the field strength; the electric pumps which have 

 been in operation for ten j^ears past in the Calumet and Hecla 

 copper mines, in Michigan, have adjustments of speed of 2 to 1 

 under this system. ^Vhen induction motors are used the 

 windings are thrown into different combinations for various 

 numbers of poles and rates of speed, and several frequencies, 

 also, are provided for. Some alternating current motors 



