190 The Ventilation of Coal Mines. [April, 



of temperature would have to be quadrupled. The amount of 

 current varies with the square root of the depths of the upcast 

 shaft; thus, to double this, the shaft or chimney must be made 

 of four times the original height. Again, the resistance of an air- 

 current increases with the square of the velocity, and inversely as 

 the area of the spaces traversed. These facts show that a furnace 

 being constructed for the purposes of ventilation, and placed under 

 the best possible conditions, cannot, in cases of sudden emergency, 

 be greatly augmented in power. 



The principles for securing the greatest advantage from the heat 

 of a furnace are, — first, to maintain as high a temperature as pos- 

 sible in the upcast shaft ; and secondly, to place the source of heat 

 ■ — the furnace — at the bottom of the shaft, supplying the fire with 

 air which has not passed through the workings. It has been often 

 argued that greater ventilating power can be obtained' by using the 

 return air rather than fresh air to urge the combustion of the coal. 

 This is no doubt true, and in many collieries it may be safely 

 applied ; but there is always greater safety in exciting the fire with 

 fresh air, and directing the return air into the heated shaft, without 

 allowing it to pass over the incandescent fuel. 



The shaft is a chimney : the higher you can heat that chimney, 

 the more rapid will be the current moving up it. At Hetton col- 

 lierv, 190.000 cubic feet pass bv the furnace in each minute. At 

 Haswell colliery, 100,917 cubic feet ; and at Wallsend, 122,000 

 cubic feet. In these large collieries the extent to which ventilation 

 is carried is necessarily greater than in less extensive works, where 

 the liabilities to the presence of explosive gases are less. In the 

 West Eiding of Yorkshire, for example, we find the rate at which 

 air passes the upcast shaft is, — at Ardsley Main, 30,957 cubic feet; 

 and at Daiiey Main, 30,780 cubic feet. 



Some years since, Mr., now Sir Goldsworthy Gumey. intro- 

 duced what has been called steam-jet ventilation. He found that a 

 jet of steam issuing under pressure, at high velocities, dragged the 

 air forcibly with it. At Seaton Delaval, where this system was ad- 

 mirably applied, the rate of the air-current was found to be 82,320 

 C. F., and 74,391 C. F., as the average of a great many sets of 

 experimental trials. 



Mechanical ventilation must now receive consideration. The 

 machines adopted for the ventilation of mines, although varying 

 considerably in structural details, may all be referred to one or other 

 of two great classes, namely: — 1. Those exhausting the air by 

 direct expansion and compression in a cylinder or chest ; and, 

 2. Those producing a vacuum by centrifugal action. The latter 

 includes the various kinds of fans, while the former is represented 

 by the piston and cylinder machines. 



The oldest machine of the first class is that which, under the 

 name of the Harz air-pump in Germany, or duck machine in Corn- 



