1867.] The Ventilation of Coal Mines. 191 



wall, has for centuries past been almost the only artificial ventilation 

 employed in metal-mining. It consists of a square wooden box, 

 oj>en at the bottom, which is moved up and down by a reciprocating 

 rod, in a cistern partly filled^with water ; a pipe communicating with 

 the working of the mine rises in the centre of the cistern, a little 

 above the level of the water, and is stopped by a valve opening 

 outwards. As the box rises, a partial vacuum is formed within it, 

 into which the foal air from below rises as soon as the difference of 

 pressure is sufficient to overcome the small resistance offered by the 

 weight of the valve. At the return stroke, the aspired air is com- 

 pressed and drawn out, either through a second pipe communicating 

 with the external air, or, what is more generally the case, through 

 discharging-valves fixed on the top of the box. The use of the 

 duck machine is generally confined to ventilating the end of a 

 single gallery, and for such purposes it is well adapted, being of a 

 simple and inexpensive construction. The power necessary to drive 

 it is usually obtained by attaching it to the main rod of the pump- 

 ing-engine. 



Machines upon this principle have been constructed for colliery 

 Ventilation, of very large dimensions, one of the most important 

 examples being that erected by M. Devaux at Marihayes, near 

 Seramy, in Belgium. It has two wrought-iron cylinders or bells, 

 12 feet in diameter, and 8-J feet high, which are put in alternating 

 motion by a horizontal steam-engine, one rising as the other 

 descends. The cistern is annular, of about 10 inches greater 

 diameter than the bell. The interior space or air-chamber is closed 

 at the top, the air-way being formed by sixteen large balanced 

 valves, opening outwards, a corresponding series being fixed in the 

 roof of the bell. 



A modification of this machine, called by the inventor and 

 patentee, Mr. W. P. Struve, an " airometer," has been in use for 

 some years past in South Wales ; the bells are, however, without 

 valves, and are driven by a rotary motion of a reciprocating engine. 

 The intake and discharge valves are in connection with outer 

 cylinders of masonry, one set being placed below and the other 

 above the bells. The whole arrangement is, in fact, an imperfect 

 form of double-acting blast cylinder, having a water-joint instead 

 of tight packing on the piston ; but the valves being placed verti- 

 cally instead of horizontally, allows them to be made much tighter, 

 thus giving an advantage over the more perfectly constructed 

 Belgian machine. 



An airometer at Westminster colliery, Denbighshire, with a 

 single bell of 17 feet in diameter and 6-J- feet stroke, making eight 

 double strokes, was found to draw 23,608 cubic feet per minute, 

 the average pressure being about 1*41 inches of water. 



The single-acting blowing cylinder, with a tightly fitting piston, 

 similar to that formerly employed in forges, was at one time used 



