Page:Encyclopædia Britannica, Ninth Edition, v. 16.djvu/467

Rh PAYMENT OF MINERS.] MINING 449 easily be removed, but they have not made their way at present into ordinary mining. The Bosseyeuse of MM. Dubois and Franois acts on a different principle. It is a strong machine worked by compressed air. It first of all drills holes 4 inches in diameter by percussion ; a striking head is then substituted for the drill, and wedges, on the principle of the plug and feathers, are inserted into the holes ; and powerful blows with the striking head wedge off the rock in lumps. This machine is being used with success in Belgium for driving levels and crosscuts in fiery mines. Some comparative experiments between hand-labour, a percussive drill, and a rotatory drill have lately been made in one of the Freiberg mines, 1 and the results are of much interest and import ance. The actual figures are as follows, the cost including, in the case of the machines, interest, depreciation, and cost of repairs, and cost of steam-power, supposing water-power not available : Hand- boring. Schram s Drill. Brandt s Drill. 0-95 4-5 5-0 Cost in marks per metre driven &amp;lt; 120 to 77-4 to 74-34 Wages realized by the miners, in marks, per 8 j 123-5 1-85 to 2 05 85 25 3-48 to 3-66 3-76 The advantages of machine work are very marked indeed both as regards rate and cost of driving, and wages earned by the men. Brandt s rotatory drill did its work cheaper and faster than Schram s machine; but nothing is said in the original notice of the advantage of a machine driven by compressed air for ventilating workings such as advanced headings in which these drills are employed. Brandt s machine was worked with water at a pressure of 83J atmospheres, of which 56 &quot;6 atmospheres were obtained by pressure pumps provided with an accumulator, and 26 9 atmospheres by natural fall, owing to the working level being 277 metres below the pumps. The water was conveyed to the machine in iron pipes of H inches diameter inside. The diameter of the holes bored was 2 inches, and they could be bored in gneiss at the rate of 1^ inches per minute. The stretcher bar on which the machine is carried is hollow, and has a piston which can be forced out by hydraulic pressure so as to fix the bar firmly. A similar bar is sometimes used with percussive drills. 2 As a method of breaking ground the ancient process of fire-setting requires to be mentioned. Before blasting was known it was largely employed, but its use is now confined to a few places on the Con tinent where the rocks are exceedingly hard and where wood is abundant and cheap. Piles of wood are heaped up against the face of the workings and set on fire. On returning to the working place two or three days afterwards, when the rocks have cooled a little, it is found that the ground has split and flaked off, and that much has been loosened which can be removed by the pick and wedge. We finally come to water as an agent for removing rocks. Streams of water were formerly used in South Wales for working beds of clay ironstone at the outcrop. The water washed away the clay and shale and left the clean nodules of ironstone. The china clay of Cornwall is also worked by water : a stream of water is turned on to the soft mass, and the workman loosens the ground with a pick; the water carries off the particles of decomposed rock in suspension to regular settling pits. Water under pressure has rendered vast services to the miner in working auriferous alluvia. The system is described and figured at p. 746 of vol. x., so it is unnecessary here to enter into details. In the special case of salt-mines recourse may be had to the solvent action of water, directed by suitable jets, for making excavations. Modes of 5. Principles of Employment of Mining Labour. As a paying i ar g e proportion of the expenditure in mining is for actual manual labour, it is very important that means should be taken to prevent any waste in this department. Three principles are in vogue payment by time, by work done either measured or weighed, and by the value of the ore extracted. The overseers, called captains in many metal mines, are naturally paid by the month, and where strict supervision can be exercised, such as is possible at the surface, on the dressing-floors for instance, the same principle may be adopted ; but when men are working underground, and often in small gangs of only two or three persons at some distance apart, piecework of some kind is more economical and satisfactory in every way. In driving levels and sinking shafts it is usual for the 1 Jahrbuchfiir das Berg- und HiiUenwesen im KiJnigreiche Sachsen auf das Jahr 1882, p. 18, and abstract in Proc. Inst. Cic Eng., vol. Ixix., 1881-82, part iii. p. 5]. 8 Annxles des M&amp;gt;nes, ser. 5, ii. ; pi. 1, fig. 6, 1882. men to work at a certain price per running yard or fathom. The agents have to see that the excavation, whether shaft or level, is maintained of the full dimensions agreed upon, and preserved in the proper direction. At the end of a certain time, generally a month, the work is measured by the agent. From the gross amount obtained by multiply ing the price by the number of fathoms driven or sunk it is necessary to deduct the cost of the materials supplied to the men by the mining company, such as explosives, steel, candles, &c., and the remainder is divided among the persons who took the contract. When the useful mineral is being obtained the men may be paid at so much per cubic yard or fathom excavated, or at so much per ton of mineral extracted ; the overseer of course has to see, in this latter case, that worthless rock is not sent to the surface. Payment by the number of inches bored is a method in use in some countries, where the men are not experienced or enterprising enough to undertake the work in any other way. A foreman points out to the men the position and direction in which the holes must be bored, measures them when completed, and subsequently charges and fires them. The third method is that which is known as the tribute system. The miner working on tribute is allowed to speculate upon the value of the ore in a certain working area assigned to him and called his pitch. He gives the mining company all the ore he extracts at a certain pro portion of its value, after he has paid all the cost of break ing it, hoisting it to the surface, and dressing it. Thus, supposing he takes a pitch at 5s. in the, and produces marketable copper ore of the value of 50, his share will be 50 x 5s. = 12, 10s., less the cost of the materials he has been supplied with, and all expenses for winding, dressing, sampling, &c. 6. Means of Securing Excavations by Timber, Iron, and Timber- Masonry. The following kinds of timber are those most ln s- frequently employed for securing excavations underground : oak, larch, pitch pine, spruce fir, and acacia. In many mines the timber is attacked by dry rot, which gradually renders it useless, and when the timber has often to be renewed the expense may be very considerable. Various methods of preventing dry rot have been tried with more or less success, such as letting water trickle over the timber in the mine or treating it with preservative solutions beforehand. Brine, creosote, and solutions of chloride of zinc, sulphate of zinc, sulphate of copper, and sulphate of iron increase the duration of timber. It was found by experiments carried on at Commentry during a long series of years that one of the best plans was to soak the timber for twenty-four hours in a strong solution of sulphate of iron. The total cost was only |d. per yard of prop, whilst the timber lasted eleven times as long as when this simple treatment was omitted. Timber is used in various forms either whole and merely sawn into lengths, or squared up, or sawn in half, or sawn into planks of various thicknesses. Where the roof of a bed is weak it may be kept up by simple props ; but in some coal- ^^^-. -___-- . __ .. - = mines and clay- mines a better support is obtained by logs (chocks) laid two by two crosswise (fig. 38). Though a level is an ex cavation of a very simple nature, the methods of tim bering it vary considerably, because the parts requiring support may either be the j-jg roof alone, or the roof and one or two sides, or the roof, sides, and bottom. If the roof only is weak, as is the case with a soft lode between two hard walls, a cap with a few boards resting on it (fig. 39) is sufficient to prevent falls. If one sick 1 is weak the cap must be XVI. 57