On Ventilating Mines or Hospitals. 121 



We are here unacquainttil with the rapid production of 

 those gases which occasionally in the colherics are the cause 

 of such dreadful tffects; such a^ hydrogen gas, or the fire- 

 damp; carbonic acid^or the choke-damp ; the inconvenience 

 we experience takes place gradaiUy as we recede from ihe 

 openings to the atmo-phere, and seems to arise solely from 

 the causes which I have before assigned, though it is found 

 to come on more rapidly in certain situations than in others. 



The moit obvious remedy, and that which is most fre- 

 qnentlv resorted to, is the opening a communication either 

 to some other part of the mine, or to the surface itself; and 

 as soon as this is done, the ventilation is found to be com- 

 plete, by the currents which immediately take place, often 

 with considerable force, from the different degrees of tem- 

 perature in the subterranean and upper atmospheres ; and 

 these currents may be observed to change their directions as 

 the temperatures alternate. 



The great objection to this mode of curing the evil is, the 

 enormous expense with which it it most comn)oiilv at- 

 tended. In driving a long level, or tunnel, for instance, it 

 may happen to be at a great depth under the surface, and the 

 intervening rock of great hardness; in such a case every 

 shaft which must be sunk upon it for air atone, .where not 

 required (as often they might not) to draw up the waste, 

 would cost several hundred pounds; or in sinking a shaft 

 it mav be necessary, at an expense not much less, to drive 

 a level to it from some other fnr this purpose alone. 



To avoid this, recourse has been had to dividmg the shaft 

 or level into two distinct parts, communicating near the 

 part intended to be ventilated, so that a current may be 

 produced in opposite directions on each side the partition ; 

 and this, where room is to be spared for it, is often effectual 

 to a certain extent. It is found, however, to have its limits 

 at no very great distance, and the current at best is but a 

 feeble one, irom the nearly equal states of heat in the air 

 on each sride. The only scheme besides these, that ] know 

 of. has hiiheito been to force down a voluine of purer air, 

 through a system of pipes placed for the purpose, and a 

 variety ((f contrivances have been devised for effecting this; 

 most of them are so o'd that they may be found described in 

 Agricola's work De Re Melallicd. The most common are 

 by bellows woiked by hand; by boxes or cylinders of va- 

 rious forms placed on the surface with a large opening 

 against the wind, and a smaller one communicatinu- with 

 the air-pipes by a cylinder and piston vi^orking in it, which 

 when driven by a sulHcicnt force has great power. But the 



cheapest 



