January 4, 1907] 



SCIENCE 



17 



extreme in the direction of high-duty en- 

 gines is represented at present in the Nord- 

 berg quadruple expansion, two-stage air 

 compressor operating at the Champion 

 mine. The engine is equipped with Nord- 

 berg's regenerative feed water heating sys- 

 tem. It holds the world's record for mini- 

 mum consumption of heat per foot-pound 

 of work delivered, having shown a duty of 

 195,000,000 foot-pounds, being about 9 per 

 cent, in advance of its nearest competitor.^ 

 But one mine is so situated to be able to 

 make use of water power. The Victoria, 

 located near the Ontonagon Eiver, has a 

 considerable water power available which 

 has been utilized in a novel manner. Dis- 

 tance from soiirce to points of application 

 is not great and the power for both mine 

 and mill is distributed by compressed air. 

 Moreover, the falling water operates di- 

 rectly on the air without the intervention 

 of water-wheel or other machine. 



Eoughly speaking, this 'hydraulic air 

 compressor' consists of a large under- 

 ground chamber cut from the solid rock 

 and having a length of 281.5 feet, a width 

 of 18 feet and a depth of 26 feet. In nor- 

 mal operation the lower portion of the 

 chamber is filled with water to a level of 

 14.5 feet from its roof. The remainder, 

 having a capacity of over 80,000 cubic feet, 

 is filled with air at 114 pounds gauge. 

 The water outlet is through a tunnel 18 

 feet wide and 10 feet high, the bottom of 

 the tunnel being a continuation of the hori- 

 zontal floor of the chamber. This tunnel 

 opens into an inclined shaft about 18 by 

 20 feet in cross-section, the discharge level 

 of which is 271 feet above the water level 

 in the chamber. The outlet for air is a 

 24-inch pipe leaving the chamber through 

 the roof directly above the tunnel outlet. 

 ' See description and report of test in paper on 

 'A High Duty Air Compressor,' by Professor O. 

 P. Hood, Transactions American Society of Me- 

 chanical Engineers, 1906. 



The inlet for both water and air is 

 through three vertical shafts, each 5 feet in 

 interior diameter, opening through the roof 

 of the chamber at the end opposite to the 

 outlets. Bach shaft is tightly lined with 

 concrete, and is continued down into the 

 chamber by means of a somewhat flaring 

 steel casing to a distance of about 15 inches 

 below the water level. Just beneath, and 

 reaching somewhat into the opening of the 

 casing, is a conical boss of concrete. From 

 water level in chamber through the air- 

 and water-tight shaft to the water level at 

 the intake above is 343 feet. This is 72 

 feet greater than the distance between the 

 water levels at the outlet end, and this dif- 

 ference expresses the available head of 

 water. 



At the intake water is admitted through 

 an annular funnel over a hollow ring from 

 the flat inner periphery of which project 

 1,800 three eighth-inch tubes into the an- 

 nular opening of the funnel. The water 

 must flow over the mouths of these tubes, 

 and in doing so it produces the aspirating 

 effect which entrains the air in small bub- 

 bles. The air comes mainly through the 

 tubes from the hollow ring which has suit- 

 able intake pipes extending above the 

 water level. The mixed water and air fall 

 through the vertical shaft, and are dis- 

 charged radially from the annular outlet 

 formed by the concrete boss and steel casing 

 below. The current through the chamber 

 is slow, and the air disengages itself, col- 

 lecting in the top of the chamber, and dis- 

 placing the water. By its pressure on the 

 water surface in the chamber it maintains 

 the 271 feet of difference in level between 

 that surface and the one at the discharge 

 of the outlet shaft. 



While running at less than full capacity 

 the water level in the chamber is prevented 

 from being depressed further than 14.5 

 feet from the roof by means of a blowoff 

 pipe, 12 inches in diameter, which opens 



