MINING 



217 



system. In thick and highly-inclined beds it is 

 usual to remove the coal by horizontal slices, and 

 to fill the excavation with waste material. In 

 some instances blast-furnace slag is used for the 

 purpose. 



The mode of working metalliferous veins differs 

 greatly from that followed in the case of the more 

 or less horizontal coal-beds. Horizontal galleries, 

 termed levels, are driven upon the lode usually 10 

 fathoms ( 60 feet ) apart. They are rarely perpen- 

 dicularly above one another, as they follow the 

 inclination of the vein. The levels are connected 

 by means of small shafts, termed winzes. Re- 

 presented on a vertical plane, the vein will thus be 

 seen to be cut up into pillars which are worked by 

 the method of stufiinij. Of this there are two 

 varieties underhand and overhand sloping. In 

 the former the ore is gradually worked away 

 downwards from the floor of one level, the ore and 

 worthless mineral being taken out through the 

 level next below. In most districts underhand 

 sloping has been superseded by the more econo- 

 mical overhand method, in which the miners 

 stand on timber platforms and break down the 

 mineral above them. 



The great depth and size of modern collieries 

 necessitate the raising of greater quantities of coal 

 through a single shaft than was ever contemplated 

 in former times. The winding-engines of modern 

 erection are consequently of extraordinary power. 

 Thus, at Harris' Navigation Colliery the engines 

 have cylinders with a diameter of 54 inches, and 

 are capable of raising 6 tons of coal, or, with ropes 

 and the cages containing the coal-trucks, a total 

 load of 15J tons, at a speed of 32 feet per second. 

 The quantities which can thus be raised are 

 enormous. It is by no means uncommon for 900 to 

 1400 tons to lif rai-i'd from one pit in the day. 



In collieries both coal and men are raised in the 

 cages, but in the metalliferous mines the man- 

 engine is largely used. This consists of a reciprocat- 

 ing rod or pair of roils fitted with stei, by which 

 the miner is raised 8 to 14 feet at a stroke. Al- 

 though this method obviates the tax on the energies 

 of the men entailed by the climbing of ladders, it 

 i.-< by no means free from danger. Prussian stat- 

 istics show that where man-engines are employed 

 there are four times as many accidents as where 

 cages and ropes or where ladders are used. 



At the Epinac collieries in France a remarkable 

 pneumatic system of raising coal and men is em- 

 ployed. An air-tight wrought-iron tube, 5 feet 

 3 inches in diameter, is placed in the shaft and 

 fitted with a piston-cage carrying nine coal-wagons. 

 The air being exhausted above the piston, a load 

 of 3 tons of coal is raised at a rate of 19 inches per 

 second. The great cost of the installation has pre- 

 vented the method from being generally adopted. 



In almost all mines the surrounding rock contains 

 water which rapidly accumulates in the workings. 

 Where the contour of the district is suitable, tne 

 best method of draining the mine is by means of an 

 adit-level i.e. a tunnel driven in the hillside. In 

 some cases extensive areas are drained by adits. 

 Thus, the great Gwennap adit in Cornwall, which 

 i- with its branches 40 miles in length, drains 

 30 sq. m. As further examples of long adits 

 may be cited the Ernst-August adit in the 

 Harz Mountains, which has a total length of 

 14 miles and cost 85,500, and the Rothschon- 

 berger adit at Freil>erg in Saxony, which is 25 

 miles long. In cases where adits are unavail- 

 able, recourse must In- had to pumps cither of the 

 lilting or forcing type. The principal type of 

 engines is that known as the Cornisn puniping- 

 'M^'ine, which is a single-acting condensing beam- 

 n^inc working expansively. Some of these engines 

 are of enormous size, the cylinders in some cases 



being as much as 100 inches in diameter. Their 

 great cost and ponderous character have led to the 

 introduction of cheaper direct-acting engines which 

 placed underground force columns of water to 

 vertical heights of as much as 1000 feet. At a 

 silver-mine a,t Klausthal, in the Harz Mountains, a 

 pair of direct-acting rotary engines have been 

 erected, driven by hydraulic power, with a bead of 

 1959 feet. At twelve revolutions per minute these 

 IPIIIH|IS force 330 gallons of water up 750 feet. 



The ventilation of subterranean workings is a 

 problem of the greatest importance. The air is 

 contaminated by the respiration of men and horses, 

 by the combustion of lights, by the smoke of 

 explosives, and by deleterious dust. Added to 

 which, in the case of collieries, the insidious fire- 

 damp or carburetted hydrogen exudes frojn the 

 coal. Mingled with air this gas forms the 

 explosive mixture to which so many miners 

 owe their death (see FIREDAMP, CHOKE-DAMP, 

 SAFETY-LAMP). It is obvious that the venti- 

 lating current must le sufficient to dilute this 

 mixture below the firing-point and to sweep it 

 away. The general mode of ventilating a colliery 

 is to have two -shafts, a downcast and an upcast. 

 The pure air entering by the downcast shaft 

 traverses the roadways of the colliery. By means 

 of doors and stoppings, the current is caused to 

 travel in the required direction so as to reach the 

 innermost workings of the mine. It then passes to 

 the upcast shaft and returns to the surface. The 

 motion of the air-cnrrent is caused by furnaces or 

 by mechanical ventilators. In the former case, a 

 large furnace is kept burning at the bottom of the 

 upcast shaft, the air in which it heats and causes 

 to expand. In this way a volume of air is obtained 

 suitable for very extensive workings, as much as 

 120,000 to 250,000 cubic feet of air being passed 

 through the shafts per minute. In the case of 

 mechanical ventilators, the vitiated air is with- 

 drawn from the colliery by the exhausting action 

 of centrifugal fans, which may le made either of 

 large diameter to run at low velocity, or of small 

 diameter to run at high velocity. At several 

 important collieries these fans attain enormous 

 dimensions, in some cases as much as 45 feet in 

 diameter and 14 feet in width. 



Almost as important as ventilation in relation to 

 the safety of human life is the accurate construc- 

 tion and the preservation of mine-plans. In many 

 cases the plans are laid down without any reference 

 to the phenomenon of the variation of the magnetic 

 needle. Trusting to old plans constructed in this 

 way, the miner may drive straight into old work- 

 ings filled with water, the tapping of which would 

 be death to all employed in the colliery. 



The progressive legislation in connection with 

 mines (e.g. the Coal-mines Regulation Act of 

 1872, amended 1886, which prescribes for the inspec- 

 tion of mines by duly appointed inspectors, &c.) 

 has proved beneficial in diminishing the pro- 

 portion borne by the accidents to the number of 

 miners employed ; for whereas in 1850, when the 

 output of coal in the United Kingdom did not 

 exceed 50,000,000 tons, the number of miners em- 

 ployed being about 200,000, the deaths slightly 

 exceeded 10(X) in the year, in 1877, when the out- 

 put of coal was 134,000,000 tons and the number of 

 miners double that in 1850. the deaths were only 

 1200 in number. The deaths from explosions of 

 firedamp during the eleven years 1875-1885 formed 

 but 23-57 per cent, of the total deaths, the re- 

 mainder being due to falls of roof and other causes. 

 For statistics of mineral production, see GREAT 

 BRITAIN, UNITED STATES, &c. 



In England and Ireland the crown has the right 

 to all mines of gold and silver; but where these 

 metals are found in mines of tin, copper, iron, or 



