1920] on Researches at High Pressures and Temperatures 3 



fact that the rock is becoming more plastic, and that cavities would 

 probably close up at 20 miles below the surface. 



The deepest single stage shaft on the Rand is Hercules E.R. P.M. 

 It is 4500 feet vertically and is rectangular in section. 



The deepest shaft in the world is Morre Yelho. The bottom is 

 6400 feet vertically below the surface, and it has been sunk, and is 

 worked in stages, two of which are about 1200 feet vertical. The 

 deepest shaft designed on the Rand is by the City Deep Company. 

 It is 7000 feet vertically, is circular of 20 feet diameter, and is to be 

 worked in two stages of 3500 feet each. 



The most rapid sinking record was made at the Crown Mines 

 No. 15 Shaft, where 310 feet were sunk in a month. It is circular 

 and of 20 feet in diameter. There are several interesting departures 

 from ordinary mining practice necessary even at this depth. The 

 haulage is arranged in stages of about half a mile, principally in 

 order to economise the weight of rope, and also the power for wind- 

 ing. In countries where the atmosphere is dry the sides of the shaft 

 are cooled by sprinkling water upon them, which by evaporation 

 cools the rock. It is however possible to augment this effect by 

 artificially drying and cooling the air before passing it down the 

 mine. 



When still greater depths of shaft are in contemplation, further 

 methods of cooling in addition to these would probably be found 

 necessary — for instance, the carrying the heat upwards by means of 

 brine circulated in a closed ring formed of steel pipes with a rising 

 and descending column. Though the columns might be carried the 

 whole depth of 12 miles, the hydraulic pressure at the bottom would 

 be about 12 tons per square inch, and would entail very costly pipes 

 of great strength to resist the pressure. A cheaper plan would be to 

 work in stages, each ring occupying a stage of from 2 to 3 miles of 

 the shaft, the heat being transferred from the top of one brine ring- 

 to the bottom of the ring above by surface heat exchangers and 

 refrigerating machinery to neutralise the heat drop on transfer ; 

 these may be called heat pumps and would be driven electrically. 



As the depth of the shaft increases the pressure of the air upon 

 the miners will be about doubled for every 2 to 3 miles, but 

 what is more serious is the increase of temperature of the air itself 

 caused by the adiabatic compression due to gravity, by which it will 

 be raised about 100° F. For these reasons it will be necessary to 

 place air-tight partitions across the shaft at every mile or two, and to 

 carry on the ventilation through these by means of a pump to deliver 

 the foul air upwards, and an expander to allow the fresh air to 

 descend ; these two machines would be linked together and the 

 difference in their power supplied by an electric motor (this method 

 has been often used with water and is equally applicable to air). At 

 each partition heat exchangers and refrigerating machinery similar 

 to that used for the brine would be placed. 



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