MINING 381 



used to some extent; in this machine the actual reciprocating motion is produced mechan- 

 ically by an electric motor, and is transmitted by compressed air to the percussive tool, 

 the whole apparatus being practically self-contained. The Ingersoll-Rand Company 

 produce a similar machine. The percussive coal-cutter has gained from the develop- 

 ment of the rock drill, and several of the modern machines, such as the Hardy, Ingersoll 

 and Siskol, embody economical improvements in valve construction. 



A novelty has been introduced in the United States in the shape of the Hoadley- 

 Knight coal-cutter. This machine, which is of the tunnelling or breast type, comprises 

 swinging cutters rotating with great rapidity. The rotation is effected by electricity, 

 whilst the swinging and feeding movements are directed and controlled by hydraulic 

 means. The machine is especially designed for the getting of coking or gas coal in 

 which the size of the product is not a consideration. 



At the mines of the United States Coal & Coke Co., Gary,W. Va., a system of pneu- 

 matic transport has been tested r a machine cuts out the entire thickness of the seam, re- 

 moving the coal as it is cut to the outside by means of currents of air at high velocity. 



A concomitant of the increased use of coal cutting machinery has been the more 

 extensive adoption of coal face conveyors. 



MECHANICAL VENTILATORS. The principal changes in the British Coal-Mines Act 

 relating to methods of ventilation are the compulsory provision of an adequate ventilating 

 system on the surface, with, after January i, 1913, means for reversing the air current. 

 A revolution in construction has taken place in colliery fans, the principal features of 

 which are the great reduction in diameter, the adoption of high-speed engines, a quick- 

 running electric motor, and the use of short peripheral blades, in place of long blades 

 attached to the boss shaft. Another development has been the increase in the number 

 of blades, several of the modern quick-running fans having no less than 60, as compared 

 with about ten in the older type of fan. The modern inlet is nearly equal to the external 

 diameter of the fan, giving a free entry of air into the centre of the fan. In the new fans 

 the scoop blade is adopted; in the Bumsted and Chandler fan, however/the extremities 

 of the blade are curved backwards from the direction of rotation. Examples of the 

 modern type are the Sirocco and Barclay fans, and the former has given the high 

 manometric efficiency of 0.9. 



Reversing fans have been in use for some time in the American coalfields; their use in 

 Great Britain is comparatively recent. A simple method is so to arrange the fan that 

 it can either exhaust from or blow into the shaft at which it is located; or drifts may be so 

 arranged that the fan may exhaust either from the upcast shaft or from the downcast 

 shaft, by means of a kind of damper. As a modification a stand-by fan is connected to 

 the downcast shaft, which is started when a reversal of the air current is desired. The 

 other fan at the same time is stopped. In France small helicoidal fans have been em- 

 ployed, driven by the shaft of an electric motor. 



SHAFT-SINKING. A steady extension has recently been witnessed of the patent proc- 

 esses of sinking shafts through water bearing and shifting strata. In the main these 

 processes may be classified under three headings: (i) the drop-shaft system, as repre- 

 sented by the Kind-Chaudron process, the principal feature of which is the use of tele- 

 scopic tubing; (2) the freezing system, developed from the Poetsch process; and (3) the 

 cementation process, originally applied by Portier at Bethune, in the Pas-de-Calais, and 

 developed by Lombois, Saclier, Francois, Gevers-Orban, and others. 



As regards the drop-shaft system the most notable example in recent year's is perhaps 

 that at the Astley Green Colliery, near Manchester, when a depth of 3,000 ft. was attained 

 (See Pilkington & Wood, Trans. Inst. Min. Eng., Vol. 39, p. 529). 



With the freezing system, for the development of which Messrs. Gebhardt & Koenig have 

 been largely responsible, much greater depths have been reached than was at one time con- 

 sidered possible. Thus in the Campine coalfield, where the freezing process has been adopted 

 in seven of the eight shafts, the depth of frozen section has varied from 1,180 to 1, 590 ft.; 

 at Beeringen, where the latter depth was reached, 37 boreholes were necessary in order to 

 secure an uninterrupted circumference of frozen strata, and altogether eleven miles of tubing 

 were employed. In England the freezing system has been applied in seven instances in 



