Three compressors, about 5,600 lb. per hour each 16,800 One dynamo About 1,000 One 500-gal. pump ” 1,000 One hoisting engine for elevators ” 2,000 ______ Total 20,800 Actually, there was considerable deficiency of steam when an endeavor was made to work the three compressors at their full capacity. A separate boiler was afterward installed to run the hoisting engine for the elevators and the pumps, thus leaving a requirement of only approximately 18,000 lb. of steam per hour, but even this was beyond the capacity of the boilers, especially as one was almost always out of commission. The two Rand compressors were 24 by 24 by 30-in., straight-line, one-stage, steam-driven, with a nominal capacity of 1,250 cu. ft. of free air per min. at 80 rev. per min. The Ingersoll-Sergeant was of similar type and capacity. Therefore, the theoretical quantity available was 3,750 cu. ft. of free air per min. The theoretical air requirements (as taken from manufacturers’ catalogues) were: Cubic feet of free air per minute. 20 Rand slugger drills (12 by 174) 2,088 2 Little Giant shovels (taking air two-thirds of the time) 1,100 ----- Total 3,188 This estimate, based on the assumption (given in the catalogues) that the drills would be working about three-fifths of the time, and the shovels about two-thirds of the time, left apparently an ample margin between the full capacity of the compressors and the requirements for the drills; as a matter of fact, however, it was seldom that more than 80 lb. of air was available, and the pressure often dropped to 60 or 50 lb. at the compressors. During the time this plant was in use the greatest distance to the drills was about 1,500 ft. As this plant proved to be entirely inadequate to the demands, an arrangement was made with the O’Rourke Construction Company on August 17th, 1906, whereby they agreed to supplement the air supply by 1,000 cu. ft. of free air per min. at 100 lb. pressure. This arrangement was not altogether satisfactory, and finally (on December 5th, 1906) an arrangement was made with the same company to supply air up to 4,000 cu. ft. of free air per min. at 100 lb., and the old plant was shut down.