Page:Encyclopædia Britannica, Ninth Edition, v. 16.djvu/461

Rh BORING.] MINING 443 variety of gypsum, called briscale by the miners, and considered by them as affording important indications concerning the bed itself. 1 Other signs of mineral deposits are given by springs and by certain plants dependent upon the deposit or its associated minerals for part of their nourishment. The appearance of the so-called lode-lights may be explained by the production of phosphoretted hydrogen from the action of organic matter and water upon phos phates, which are so common in the upper parts of mineral veins; and one hears also of differences in the appearance of the vegetation along the line of the deposit, of places where snow will not lie in winter, and of vapours hanging over the ground. Though some writers refuse to put any value upon these indications, they should not be entirely overlooked, because the outcrop of a lode, of different nature and texture to the surrounding rocks, and which is generally a channel for water, may readily cause the phenomena just men tioned. Where the surface is cultivated and the natural springs are tapped by adit-levels or other mine-workings, these appearances cannot be looked for to any great extent. With one special mineral, magnetic iron, the position of the deposit may be traced out with some degree of accuracy with a dipping needle ; this is used in Sweden. After having acquired an idea of the position of a vein or seam by some of the surface indications just mentioned, it is necessary, before attacking it by shafts or levels, to obtain more certain data concerning it. In the case of mineral veins, trenches are dug at right angles to the supposed strike; and, when the upper part of the deposit has been cut in several places, its general course and dip can be determined sufficiently for the purpose of arranging the future workings. These trenches are called &quot; costean pits &quot; ; in some cases, instead of a trench, a pit is sunk a short distance and a little tunnel driven out. Where the mineral to be wrought occurs as a bed or mass, the process of boring is resorted to, and indeed this method is also applied in the case of veins, especially in the United States. Boring is a work of such importance that it deserves to be treated under a separate heading. 3. Boring with Rods and Ropes Diamond Drills. The object of boring is to reach a deposit by a small hole and ascertain its nature, its depth from the surface, thickness, dip, and strike. Bore-holes are also used for obtaining water, brine, and petroleum, which either rise to the surface or have to be pumped up from a certain depth, and finally for tapping water in old workings or for effecting ventilation. The methods of boring may be classified as follows: (1) boring with the rod; (2) boring with the rope ; (3) boring with the diamond drill. In the first method tools for cutting and removing the rock are fixed to rods, which are lengthened as the hole increases in depth, and which are worked by hand or by machinery at the surface. Where the ground is soft, such as sand or clay, tools like augers can be employed ; but in harder ground it becomes necessary to have recourse to percussion ; various forms of chisel are used, the simplest being made of the shape shown in fig. II. 2 The rods generally consist of bars of square iron, from 1 inch to 2 inches on the side. The length of each rod de pends upon the height of the tower, derrick, or shears erected above the bore-hole, which should be an exact multiple of the individual parts. These are made in lengths of 15 to 30 or rarely 40 feet, and with a suitable tower it is possible to de- FlG - H- Wiisela. Fig. 12. tach or attach two or three lengths at a time, instead of having to make or unmake eveiy joint. The mode of con nexion usually preferred is by a screw joint as shown in fig. 12 ; care is taken to have all the joints exactly alike, so that any two bars can be screwed together. In order to 1 Lorenzo Parodi, SulV Estrazione dello Solfo in Sicilia, 1873, pp. 7 and 24. diminish the weight of the rods, which becomes consider able in deep holes, wood has sometimes been employed. The rods are connected by male and female screws attached to the rods by sockets of sheet iron, or by a fork-like arrangement. At the surface a head is screwed to the uppermost rod by which the rods can be lifted, and they are turned by means of cross-bars called tillers. When the depth is small the rods are lifted by hand and then allowed to drop, being turned slightly at each lift so that the cutting chisel may strike a new place each time. For greater depths a lever has to be employed, the rods being suspended at one end, whilst the other end can be pressed down by men using their hands or feet. The spring pole is another arrangement, in which the elasticity of a long pole is made use of for lifting the rod at each stroke. The length of the stroke can be maintained the same while the bore-hole is deepened by means of a screw in a swivel-head at the top of the rod. With deep holes, and especially those of large diameter, steam machinery has to be employed for working the rod ; the engine may be direct-acting and stand immediately above the bore-hole, but a commoner arrangement is to employ a single-acting cylinder working a beam. Occasionally also the beam is actuated by a connecting-rod worked by a crank. The actual boring machinery has now been described, and the mere boring appears to be a very simple matter, consisting only in lifting the rod a little and allowing it to drop, the rod being turned slightly before each stroke. Nevertheless the process of putting down a bore-hole is not so simple as it seems, for there are numer ous indispensable accessory operations which take up much time. In the first place the debris have to be removed, and in order to effect this the rods must be drawn up, the swivel-head is discon nected and a cap screwed on. A length of rods is now drawn up by a hand or steam windlass and disconnected. It is well to have as many caps as there are lengths to be drawn up, and then each length can be suspended in the house. Sometimes a grip which catches the rod at the bulging joint is used instead of a cap. The next operation consists in lowering by means of a rope the shell-pump or ^_^ sludger, which is a hollow cylinder with a clack or a ball- valve (fig. 13). It is worked up and down a little till it is filled, and it is then drawn up and emptied at the surface. The operation fcj repeated, if necessary, and the boring is resumed with the rod. Occasionally a bore-hole has to be widened slightly with a tool called a reamer. Soft beds may have to be bored through with a wimble ; and, unless the rocks are hard and firm, the hole has to be lined with a tube, generally of sheet- iron. Accidents may occur, causing an immense amount Fig. 13- of trouble, such as the breaking of rods or chisel, and many in genious implements have been devised for seizing the broken rod or the fragments of tools which prevent further progress with the work. In boring at considerable depths, the weight of the rod becomes so great that much vibration ensues when the mass is suddenly arrested by the chisel striking against the bottom of the hole. Various devices have been contrived for overcoming this difficulty and pro ducing a tool which will act independently of the rod. One of the best-known arrangements is the free-falling tool invented by Kind (fig. 14). 3 The head of the actual boring-rod is held by a click or grapple ; when the main rod descends, the resistance of the water in the hole slightly stops the sliding disk D, the jaws J, J open, the head is disengaged, and the boring part falls and strikes the bottom without any injurious vibrations being com municated to the main rod. When this descends farther the head is caught again by the click. Special tools also are used for cutting an annular groove at the bottom of a bore-hole and breaking off the core, which is then brought up, with certain precautions, so as to show the nature and dip of the strata traversed. In order to obviate the great loss of time which ensues from connecting and disconnecting long lengths of rods, recourse may be had to boring with the rope. In this method, known as the Chinese method, the chisel is worked by a rope in the same manner as the sludger already described. Mather and Platt of Manchester have long used with suc cess, in many parts of England and various other countries, a system of boring by means of a flat hempen rope. _ The most important modification of late years in the 3 J. Gallon, Lectures on Mining, vol. i., Atlas, plate ix. fig. o2. Borinj with rope. Fig. 14. Messrs
 * Serlo, Leitfaden zur Bergbaukunde, Berlin, 1S78, p. 59.