Page:The American Cyclopædia (1879) Volume XI.djvu/593

 MINE 575 and hoisting them in cars, buckets, or cages, or by means of an ingenious arrangement called the man machine or FaJirlcunst. What- ever method is adopted, every mine should be provided with ladders in good repair, since other means may fail at a critical moment. In its simplest form, the fahrkunst is a con- tinuous piece of wood, iron, or wire rope, ex- tending from the top to the bottom of the shaft, and provided at regular intervals (8 to 24 ft.) with small platforms, upon which a miner can stand. This frame is so placed in the shaft, and supported by counter weights (and, in inclined shafts, friction rollers), that a regular reciprocating motion, like that of the pumping rods, can be imparted to it. The machinery is so arranged that the stroke is exactly half as long as the distance between the platforms on the fahrkunst, and at the end of the stroke in each direction there is an in- stant's pause. During this instant the miner can step from the machine upon a fixed plat- form in the side of the shaft. As the fahr- kunst is kept constantly running, a miner wishing to ascend by means of it has only to step upon it as it begins an upward stroke, step off at the end of that stroke, wait until the down stroke brings opposite to him the platform next above, then step upon that, and be carried another lift higher. At the same time, another miner may descend upon the same machine, by stepping on for the down stroke, and waiting during the up stroke. The double fahrkunst has two such frames or rods, running reciprocally side by side; and here the miner steps across from one to the other, always finding opposite to him, as the plat- form on which he stands pauses in its move- ment up or down, a platform on the other frame, just about to commence its movement in the same direction. The moving platforms are usually small, holding but one person con- veniently. When two miners pass each other, one steps upon a ladder placed between the two frames. In Belgium the moving plat- forms are so large as to fill the whole shaft, and take several workmen at a time. The rate of working may be seen from the following statement, calculated for a shaft of 800 ft. : Double FAHRKUNST. Stroke. strokes per minute. descends in 500 men In Ordinary double. . Swift 10ft. 10 " 5 10 8m. 4m. 1 h. 47 m. 54 in. Large Belgian 10 " 5 8m. 27m. The Belgian machine is here assumed to be carrying four men on each platform. On lad- ders one man usually descends 800 ft. in about 30 m., and ascends in an hour. The time allowed for 500 men is about 2 hours to descend and 5 hours to ascend. The waste of strength involved is also to be considered. When miners are hoisted in the cages, the av- erage velocity being about 15 ft. per second, 558 VOL. XL 37 and the average load four men, about 3^ hours are required to lower or raise 500 men in a double vertical shaft of 800 ft. ; or when the load is six men, 2 hours. At the Comstock mines, Nevada, 12 men descend at once, at a rate varying from 400 to 800 ft. per minute. Some of these mines are more than 1, 600 ft. deep. IV. PROTECTION OF THE WORKS AND WORKMEN. Arrangements for the protection of the miners and works include timber or other supports, ventilation, and drainage. Shafts and perma- nent ways are carefully protected, if neces- sary, with stout timbering, masonry, or even cast-iron linings. Pillars of rock left stand- ing, piles of waste material packed in the empty spaces, and posts, stulls, lagging, &c., suffice for stopes. In some mines the tempo- rary supports are iron columns, or even screw- jacks, which can be removed without damage and used again. Ventilation is necessary to remove explosive and inflammable gases (car- buretted and sulphuretted hydrogen and car- bonic oxide, which are also poisonous), and simply poisonous gases, such as sulphurous acid, carbonic acid, and quicksilver or arsenic vapors. Natural ventilation is secured by having two openings to the mine, at one o"f which (called the intake or downcast) fresh air enters, while the foul air escapes at the other (upcast). The difference in altitude be- tween these openings, and the difference in temperature between the entering and the es- caping air, determine the strength of the natu- ral ventilation. It is likely in temperate cli- mates that the air in the mine will be warmer in winter and cooler in summer than that out- side. Hence the draft will be in winter out through the highest opening, and in summer the reverse, while periods of stagnation will occur in spring and autumn. The natural draft may be assisted by wise choice of the localities for the openings, or by use of weather caps and chimneys over the upcast ; but these aids are not effective except where the intake is an adit. Artificial ventilation is effected by in- creasing the difference of temperature between the entering and the escaping air, so as to render the currents comparatively independent of the weather, or by increasing mechanically the difference in density. In the first class of instances, either the escaping air is warmed, or the entering air is cooled ; in the second class, either the escaping air is rarefied by suction, or the entering air is condensed by blowing. The escaping current may be warmed by connect- ing the upcast with the chimney of a steam boiler above ground, or with a special furnace above ground, or by means of a furnace in the shaft, or near the bottom of it, or by introdu- cing steam jets into the shaft. The jets have a mechanical as well as a thermal effect ; but the total effect per pound of coal consumed is less than that of the furnace. The cooling of an entering current of air is sometimes effected by allowing water to fall into the downcast, and is also an incidental effect of the water