Page:Encyclopædia Britannica, Ninth Edition, v. 16.djvu/479

Rh LIGHTING.] MINING 461 Harz blower (duck machine, Cornwall) (fig. 91) is not uncommon. This is merely an air-pump of very simple construction which is worked by the main rod of the pumps, and can be arranged so as to exhaust the foul air or force in fresh air. In working in blasting ground, boring-machines driven by com pressed air are becoming more and more largely used every day, and the exhaust air escaping from the machines is invaluable for ventilation. At the same time, on account of volley firing, the quantities of dele terious gases generated in a short space of time are very considerable ; and, in order to get rid of them speedily, the compressed air may be Fi - 91. Aspirators, utilized for working a Korting aspirator or the somewhat similar ventilator of Mr Teague, a jet of compressed air turned into a ventilating pipe, which creates an exhaust (fig. 92 1 ). Naturally this ^^,^^^^^^^^^^^^ 5 ^^, ventilator is merely brought into play at the time of blasting, and while the boring ma chinery is out of use. ^ When compressed air is Fi S- 92 - being supplied on a large scale to a mine for boring and winding machinery, it is often convenient to convey it by a small gas-pipe to working places in which the ventilation is inadequate. Of course, in one sense, it is very unecono mical to compress air to a pressure of GO or 70 Bb to the square inch for ventilating purposes only ; but, where com pressing machinery is always at work on the mine, it may be better to be a little wasteful of cheap power at the sur face than to go to the greater expense of having a man or boy to work a fan underground. iting. Mines are lighted by lamps, torches, candles, and electricity. The subject of safety lamps for fiery mines has already been discussed (see COAL, vol. vi. p. 72), and consequently the question of illuminating mines may be treated in a very summary manner. Lamps vary very much in shape and size. The Sicilian miner has a mere shallow cup of unglazed pottery ; the Saxon a small tin or brass lamp in a wooden box lined with tinplate and open in front. In the Harz the miner prefers a heavy flat iron lamp with a hook by which it is stuck into the timber or any crack in the rocks ; in France, northern Italy, and parts of Spain, the iron lamp is lenticular in shape and also suspended by a hook. In Scotland, and parts of Germany and the United States, a small tin lamp of the shape shown in fig. 93 is very common ; the hook enables it to be carried on the hat while climbing ladders, and to be fixed up underground. Olive oil and rape oil are burnt in these lamps ; petroleum lamps are employed occasionally. The miners of England and Wales still cling to the tallow candle; and when surrounded by a lump of clay it can easily and quickly be fixed in the working place or carried upon the hat when climbing. Gas brought down from the surface answers for illuminating large excavations, such as on-setting places and engine-rooms. Up to the present time the electric light has been but little used underground on account of its want of portability, and the small- ness of the spaces requiring illumination. Very often a few men only are employed in each working place, and consequently the expense incurred in fixing and shifting the lamps and maintaining them alight would be out of proportion to the value of the work executed. However, an incandescent electric lamp has been invented weighing only 10 lt&amp;gt;, which gives the light of three candles for six hours, and it may be reasonably expected that improvements will be made which will render the electric light more available for underground purposes than it is at present. When the area requir ing illumination is large, an arc-lamp may be used with advantage. 1 Trans. Roy. Geol. Soc. Cornwall, vol. x. p. 142. Among the first successful applications of electric lighting to underground excavations may be mentioned that of M. Hlavier at the Angers slate quarries. 2 In the year 1879 ho fixed two Serrin lamps in one of the large underground chambers with an area of 2400 square yards, and he found that they gave light enough for all the men at work. The total cost, reckoning everything, viz., coal, carbons, repairs, labour, depreciation of plant, and interest oncapital] is 50 francs per day ; the gas formerly in use cost 54 francs a day and gave much less light. It is evident, however, that the arc lights can only be applied with advantage in special cases where a large number of men are concentrated in one working area which can be illuminated from one or two points. The large chambers in the salt mine of Maros-Ujvar in Hungary have been regularly lighted up by electricity since 1880. The cost is somewhat greater than that of the tallow, oil, or petroleum formerly in use ; but, on the other hand, the illumination is better, the men can do more work and are more easily supervised, whilst the air of the mine is not deteriorated by the products of combustion of the lamps. 3 12. Means of Descending into and Ascending from Means of Mines, Where mines are worked by adit-levels the men access, naturally walk in along the ordinary roadways; such mines, however, are exceptional, and the men generally have to climb down and up by ladders, or are raised and lowered by machinery. The means of access to and from workings may be classified as follows : (1) steps and slides ; (2) ladders ; (3) cages ; (4) man-engines. If a lode or seam is inclined at an angle or 40 or 50 from the Steps, horizon, steps may be cut in the floors of the deposit if it is firm enough, or wooden stairs may be put in with a hand-rail. Even with higher dips steps may be arranged by directing them in a line intermediate between the dip and the strike. In speaking of con veyance underground, reference has already been made to the practice of carrying sulphur ore in Sicily and slate in Germany up to the surface by steps ; and steps may be found in other foreign mines and occasionally in Great Britain. They are much less fatiguing than ladders placed so flat that part of the weight of the body rests upon the arms. In some of the Austrian salt mines the men Slides, descend by wooden slides inclined at angles varying from 30 to 50, flattening at the bottom to destroy the velocity gradually ; the ascent is effected by steps. Ladders are very largely used in metal mines all over Ladders, the world, but they vary a good deal in different countries. The ladder consists of two sides and a series of rungs (staves, Cornwall). The sides are usually made of wood, and the rungs of wood or iron. The distance between the rungs is important; 10 inches from centre to centre is sufficient, for climbing upon ladders with the rungs 12 inches apart is decidedly more fatiguing. On the Continent wooden rungs are commoner than iron ones, and oak is preferred. Sometimes the wooden staves, instead of being round, are flat, so as to stand more wear, and iron sides may be seen in places Avhere dry rot is very bad. Platforms should be fixed at short intervals, not exceeding 3 or 4 fathoms in perpendicular shafts, so as to prevent falls from having fatal consequences. In many cases sufficient attention is not paid to the angle of inclination of the ladders. A ladder is climbed with the least fatigue when the person uses his arms simply to steady him self, and is not compelled to pull himself up by them, as on a vertical ladder, or to support much of the weight of his body by them, as happens with a very flat one. The best angle is about 20 from the vertical, and in Belgium the autho rities have very wisely decreed that no ladder shall be inclined at an angle of less that 10 from the vertical. Furthermore, of the two arrangements shown in fig. 94 Fig. 94. - M. Blavier, &quot; L Eclairage (lectrique aux Ardoisiores d Angers,&quot; Annalcs dcs Mines, ser. 7, vol. xvii., 1880, p. 5. 3 Oesterreichische Zeitscl rift fir Berg- imd Huttemcesen, 1882, No. 25, p. 296.