62 On the Ventilation of Coal- Mines. 



will pump out of the pit and its workings in that time 6000 feet 

 of contaminated air : consequently an equal volume of pure at- 

 mospheric air will descend by the down-cast pit, and be circu- 

 lated through the air courses. 



If the extent of the under-ground workings be equal to a mile ; 

 400 yards in the direction of the rise ; and the height of the ex- 

 cavated opening, after allowing for the space occupied by the 

 pillars in a vehi six feet in thickness, be taken at four feet, — this 

 tvill give a total excavation of 25,000,000 of cubical feet, or a 

 magazine of air of this extent composed of the fatal gas, atmo- 

 spheric air and carbonic acid gas : this quantity, though great, 

 would by means of the engine be entirely removed in three days, 

 and the void replaced by pure air. 



I shall now proceed to show that a supply of 6000 feet of 

 fresh air per minute, is much more than is necessary for the exi- 

 gencies of the under-ground workings, so far as combustion and 

 respiration are concerned. 



According to the accurate experiments of Messrs. Allen and 

 Pepys, a man requires olO cubical inches of atmospheric air 

 in one minute for the purpose of respiration. Let us suppose 

 that one hundred men are necessary to carry on the work of the 

 mine, and that 200 candles are required to give sufficient light 

 to all the departments of the work : let the quantity of air ne- 

 cessary for each candle be taken at twice the quantity requisite 

 for a man ; let the complement of the horses be taken at 30, 

 and the quantity of air necessary for their respiration be esti- 

 mated as equal to that consumed by the men and candles. 

 These items of waste taken collectively will not amount to more 

 than 200 cubical feet per minute. Whereas the engine has 

 powers to replace into the mine in the same space 30 times as 

 much, or 6000 cubical feet. 



As tlie subject occurs to me at present, only two objections 

 are likely to be urged to this mode of ventilation ; namely, its 

 fii"st cost and subsequent expense ; and the probability of its be- 

 ing urged, that an upcast pit with a funnel will produce equal 

 effects, and at a smaller expense. 



If the former objection be urged, I hope it will occur to the 

 coal-owner, that the investment of 1000/. of extra capital, toge- 

 ther with the weekly wages of two boys and the consumption of 

 20 tons of small coal per week that would otherwise go to waste, 

 or in the best situations be not worth more than 40^., are mat- 

 ters of comparative small importance and expense compared with 

 the ruinous derangement which takes place throughout the whole 

 of the work when an explosion occurs. 



if the second objection which I have anticipated be urged 



against 



