202 On the Ventilation of Coal-Mines. [March^ 



gazometer, though this did not occur to me until after It was put to 

 work. It will readily be uudt istood by an inspection of the draw- 

 ing, wliere the shaft of the ruine is represented at A; and it may 

 here be observed, that the machine may be as well placed at the 

 bottom of the shaft as av the top, and that in either case it is proper 

 to fix it upon a IToor, which may prevent the return of the foul air 

 into the mine, after being discharged from tlie exhauster: this floor 

 may be furnished with a trap-door, to be opened occasionally for the 

 passage of buckets through it. ^ 



" B, the air-pipe from the mine passing through the bottom of 

 the fixed vessel or cylinder, C, which is formed of timber and 

 bound with iron hoops ; this is filled with water nearly to the top of 

 the pipe, B, on which is fixed a valve opening upwards at D. 



" E, the air or exhausting-cylinder made of cast-iron, open at 

 the bottom and suspended over the air-pipe, immersed some way in 

 the water. It is furnished with a wooden top, in which is an 

 opening fitted with a valve likewise opening upwards at F. 



" The exhausting-cylinder has its motion up and down given to 

 it by the bob, G, connected to any engine by the horizontal rod, 

 H, and the weight of the cylinder is balanced, if necessary, by the 

 'counterpoise, 1. 



" The action is obvious — When the exhausting-cylinder is 

 raised, a vacuum would be produced, or rather the water would 

 likewise be raised in it, were it not fur the stream of air from the 

 mine rushing through the pipe and valve, D. As soon as the 

 cylinder begins to descend, this valve closes, and prevents the return 

 of the air which is discharged through the valve, ¥'. 



" The quantity of air exhausted is calculated, of course, from the 

 area of the bore of the cylinder, and the length of the stroke. 



" The dimensions which 1 have found sufficient for large works 

 are as follow : — 



" The bore of the exhausting cylinder two feet. 



" The length six feet, so as to afford a stroke of four feet. 



*' The pipes which conduct the au: to such an engine ought not 

 to be less than six- inch bore. 



" The best rate of working is from two to three strokes a minute; 

 hut if required to go much faster, it will be proper to adapt a capa- 

 cious air-vessel to the pipes near the machine, which will equalise 

 the current pressing through them. 



" Such an engine discharges more than 200 gallons of air in a 

 minute ; and I have found that a stream of water supplied by an 

 inch and a half bore falling. twelve feet, is sufficient to keep it regu- 

 larly working. 



" A small engine to pump out two gallons at a stroke, which 

 ■nould be sufheicnt in many cases, could be worked by a povyer 

 equal to raising a very few pounds weight, as the whole machine 

 may be put into complete equilibrium before it begins to work, and 

 there is hardly any other friction to overcome that of the air pass- 

 ing through the pipes." 



