ELECTRICITY IN MINING 43 



tons per year. Numerous data received from various mining 

 sections bearing upon ilie cost of operating such apparatus 

 per ton of coal give figures ranging from one tenth of 1 cent 

 up to 2 cents, according to the hardness of the coal and the 

 degree of care and skill observed in operating. 



Discussing the subject in an admirable article on coal- 

 cutting machinery, Mr. E. W. Parker expressed the opinion 

 that the evolution of the chain machine was one of the most 

 notable steps — and practically the final step — in the develop- 

 ment of a successful mining machine. The speed with which 

 the chain machine can do its work seems incredible. After 

 the machine has been placed in position an average period 

 of only five minutes is required to make a cut 44 inches 

 wide, 4J or 5 inches high, and G feet deep, and then withdraw 

 the cutting frame. In fact, for one of these machines there 

 is claimed a record of cutting 1,700 square feet in nine and 

 one half hours. 



As to the advantages of the modern chain machine over 

 the earlier forms of pick machine, the former bases its claims 

 upon the rapidity with which the work is done, the very small 

 amount of slack coal that is made in the cutting process, and 

 the fact that the runner is not subjected to the wearisome 

 racking of the pick machine. The advantages of the pick 

 machine, which is driven bj?" compressed air, and strikes about 

 190 to 210 blows per minute, are, first, that it can be used in 

 mines where the narrow conditions of room and floor do not 

 permit the introduction of chain breast machines ; and, second, 

 that in mines where the quantity of gas is so great that safety 

 lamps have to be employed it obviates the dangers which 

 might arise from sparking if a motor driven machine were 

 employed. 



Several long Avail machines — driven sometimes by com- 

 pressed air, but frequently by electric motore — are in use. 

 As the name indicates, in long wall mining the coal is ex- 

 tracted from a long face, which is gradually moved forward in 

 widening, irregular circles. The nature of long wall work is 

 such that the face must be jagged or circular instead of 

 straight and regular, as in room and pillar mining. One of 

 the leading t\^es of long wall machines, involving to a cer- 



