Transactions . moval of these sections. The lining of the air shaft is similar tothat of the hoisting shaft. Hoisting In the mines developed according to the common practice of thepresent day in this district, the output is hmited, first, by the capacity ofthe shaft or tipple and, second, by the layout of the underground of these features have been given careful attention in the new devel-opments under consideration. 816 ENGINEERING FEATURES OF MODERN LARGE COAL MINES Two lines have been followed in the increase of the hoisting capacityof the shafts. In three of the mines conside
Transactions . moval of these sections. The lining of the air shaft is similar tothat of the hoisting shaft. Hoisting In the mines developed according to the common practice of thepresent day in this district, the output is hmited, first, by the capacity ofthe shaft or tipple and, second, by the layout of the underground of these features have been given careful attention in the new devel-opments under consideration. 816 ENGINEERING FEATURES OF MODERN LARGE COAL MINES Two lines have been followed in the increase of the hoisting capacityof the shafts. In three of the mines considered, capacity is being in-creased by the use of large mine cars and of hoisting appliances adequateto handle these cars, whereby the number of hoists necessary for largeoutput is decreased somewhat by increasing the amount of coal hoistedat each trip. In the case of the other mines the coal is hoisted in the skips hold about two mine-car loads of coal the hoisting speed canbe reduced by about Elevation of shaft bottom at Valier. Another very considerable advantage of hoisting in skips is the factthat tight cars can be used. A large part of the trouble encountered inhandhng coal in cars is due to the end doors necessary when the car ishoisted in a self-dumping cage. Moreover, such cars are always more orless leaky and a considerable amount of coal is scattered along the haulageroads, where part of it is ground into dust, part of which is suspended inthe air and part deposited on the ribs, adding considerably to the chanceof explosion. The principal advantage of hoisting in cars is that the product of eachminer is kept separate from that of other miners until it has reached C. A. HERBERT AND C. M. YOUNG 817 the surface where it can be inspected for impurities. When coal isdumped from the mine cars into skips at the bottom of the shaft, thislast advantage is sacrificed to the advantages of lower hoisting speed andsmaller number of hoists per minute. It is this
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