In a distance of one mile,—which is an ordinary run on each side of the slope in our large collieries,—four boundaries may be laid off, and the first entirely worked out before the last is started, including the pillars of the upper level, which can be of no value whatever after the excavation of the coal below them, except for the purpose of keeping up the water, which may be effectually done, at small expense, by the mode represented in figure 143.
This is an adit or drain cut partially in the bottom slate in the gangway of the upper level, and securely timbered or arched before the withdrawal of the upper-level pillars. This drain, being small—about 3 X 4 feet—and made secure with the refuse timber of the upper-level gangway, will resist all pressure that will be brought upon it on the extrac tion of the pillars, since the weight will be evenly distributed on the falling of the roof and the entire subsidence of the boundary. But, even if this plan was not adopted, it would be economy to pump the water of the upper level from the lower one, rather than leave so much available and valuable coal to waste.
The plan of ventilation suggested in the plan here proposed is simple and effective.
Each boundary is complete in itself, and supplied with a column of pure air from the main gangway or inlet air-course; these currents sweep the face of each breast, passing in the nearest and most direct way to the return air-course, and thus reaching the upcast shaft, or slope, without mixing their impurities with any other portion of the mine. The number of boundaries at work at the same time would not affect this arrangement: each one receives its column of fresh air, and empties its impurities into the return air-course, which does not pass into any part of the working portions of the mine.
In this respect, the plan may be illustrated by the drainage of a city. Each street and house has its respective channels communicating with the main ones, and the sewerage from each house passes away without injury to its neighbor. But in the systems of ventilation hitherto in use in our anthracite mines, the impurities of one chamber pass into the next throughout the entire mine; and no matter how thorough the ventilation may be, it is more or less defective in this respect.
But the benefits resulting from the plan here proposed are numerous, and none is of less importance than the one mentioned.
FIRST.—The mode of dividing or splitting the air relieves the tension of the column, and the power required to propel it. Instead of dragging the entire column through all the intricacies of the mine, a portion of the weight and friction is relieved at each boundary. We think this so manifest that further proof will not be needed. Pt is
found to work so well in the English mines that "splitting the air" is now a permanent part of their system.
SECOND.—The danger from gases and the resulting explosions is rendered far less imminent, and accidents are confined to their own locality; the operations of the mine are not materially affected, nor the lives of all the workmen endangered, as by the old system, with the "after-damp." Tumn.—The air traverses comparatively short distances, "sweeping" each face with its fresh currents, and depositing its impurities in the common return air-course, without carrying its obnoxious vapors into other working portions of the mine.
The realization of these desirable improvements in our ventilation would not only secure the results specified, but the benefits to follow are of more consequence, in the security to life and health and the saving to capital and property.
But the improvements are not confined to the ventilation: the mode and plans pro posed insure economy in the mining of coal, not only in the cost of digging it, but in the great items of dead loss by waste in pillars, &c.
FIRST.—It enables the miner to develop his mine by the earliest and best method known, and, consequently, to realize profit from investments in the shortest time possible consistent with permanence and order.
SECOND.—It secures labor at less cost, and an increase of work from a given number of hands, from the fact that pure air is supplied in abundance, and that there is less danger to life from explosion and foul air.
THIRD.—The amount of coal obtained from a given area is increased by nearly one third, without additional expenses in "dead work," or original expenditure, or the ordi nary expenses of the drainage and superintendence of a colliery; thus benefiting the landed proprietors largely, and the operators or miners perhaps not less.
We think the preceding explanation, with the aid of the engraving or plan, will enable most of our practical readers to comprehend the plans proposed, and the im provements therein presented. It will be very difficult for the inexperienced to follow us intelligently, since no subject is more abstruse and intricate than that of mine-venti lation and economic mining. We have met people who had not the first idea of scientific mining, who assumed it to be a simple matter, and, as recently stated in a prominent "guide-book," "only digging a hole in the ground ;" but those who know most about it, and have had most experience with extensive mines and explosive gases, know it to be as difficult a business as men can engage in, and one of the least understood.