ELECTRICITY IN MINING 59 



a eapaoity of 5 (•ii])i(' feet. The dredge is o])oratod at a normal 

 speed of 22 l)U(kets per minute, and ordinarily will lumdle 

 from 50,000 to 75,000 eubic yards of raw material per month. 

 The stacker at the stern of the boat is about 90 feet long and 

 2 J feet wid(\ 



The largest dredge yet installed is that of the Ashburton 

 Mining company, near Folsom, Cal., with 7^ foot buckets. 

 Some idea of the electric power equipment may be formed 

 from the fact that the induction motors for this dredge in- 

 clude one of 150 horsepower for the digger or bucket line, 

 one of 20 horsepower for the winch, one of 75 horsepower for 

 the centrifugal pum]:>, one of 20 horsepower for the stacker, 

 and one of 10 horsepower for the deck pump. 



In addition to the more important appHcations of elec- 

 tricity to mining, already described, numerous appHcations 

 of a miscellaneous character might be mentioned. The flex- 

 ibility of electric circuits and the general adaptability of 

 electric power have led to a wide range of applications, some of 

 which are still in the experimental stage, while many others 

 haye already proved successful. 



An instance may be found in the substitution of electric 

 motors for steam power for driving air compressors, where 

 the latter are still used for the operation of small tools, coal 

 cuttei-s, drills, etc. By this means the compressor can be 

 placed conveniently near the point of application of the air, 

 so as to avoid long and complicated systems of piping, with 

 consequent inefficiency and heavy loss, w^hether of steam 

 or of air. Electrically driven compressors sometimes have 

 belt connections, but in many instances the motor and com- 

 pressor are more directly connected. An alternating current 

 induction motor having a capacity of as much as 200 horse- 

 power has been connected to the air compressor by spur gear- 

 ing. In one California mine the installation of an electric 

 motor to take the place of steam power for driving a 100 

 horsepower air compressor is reported to have reduced the 

 average cost of operation per month from $1,800 to $672. 



A novel and interesting application of electricity to 

 mining is furnished in the large sand wheel equipment at 

 the Calumet and Hecla mine, driven by a 700 horsepower 



