Transactions of the American Society of Civil Engineers

(A) Previous to June 25th, 1907

		Cubic feet of free air per minute.
40	Drills (22 by 174)	3,828
2	Shovels	1,600
	Pumps and machine-shop, say	1,000
2	Derricks	1,000
	Total	7,428

(B) After November, 1907 (After Completion of Enlargement of Central Shaft Headings)

		Cubic feet of free air per minute.
32	Drills (17 by 174)	2,958
2	Shovels	1,600
	Pumps, etc	1,000
3	Hoisting engines on concrete, each working one-third time	500
2	Derricks	1,000
	Total	7,058

The average number of drillers per shift was about 25 at the two main working faces. There were also from 5 to 10 drills trimming and cleaning up for concrete, say an average of 7, making 32 in all.

After November 1st, it actually required three boilers under steam all the time, and not less than seven compressors running at full capacity, to keep the air at proper pressure, the theoretical capacity of the compressors being 8,750 cu. ft. of free air per min., as against 7,000 to 7,400 cu. ft., the theoretical maximum requirement.

Some of this deficiency was due to losses in transmission, part also was due to the fact that the actual was probably considerably below the theoretical capacity of the compressors.