Full text: Gray, Samuel Frederick: The operative chemist

305 
AIRS. 
for prisoners to cook individually for themselves would be 
superseded, much to their advantage. 
On the other hand, it must also be observed, that if close 
stoves acting on this principle were adopted, Count Rum 
ford’s objections to the introduction of fresh air would be 
obviated with regard to any room in which they should be 
m action, provided the opening through which it entered 
was made on a level with the ceiling. 
Air entering at this level would in the absence of open 
fires be acted upon by no other draft than the mouth of the 
funnel in the ceiling, and could not descend in currents to 
the lower region of the room. 
In a room so filled with company as to vitiate the air 
within it, the atmospheric air entering being specifically 
heavier would indeed descend and be replacedi by the 
ascending impure air, but as it would not descend by a 
stronger impulse than its difference of specific weight, it must 
be slow in its motion, and would produce no sensible current. 
Ventilation of Mines. 
The ventilation of mines is founded, in general, on the 
same principles as those of buildings. 
The air chauged by the respiration of the labourers, their 
fires and lights, is allowed to pass off by pits and galleries 
made for that purpose, and which, for the most.part, serve 
also for the passage of men and the produce of the mines. 
When a sufficient velocity of the air can be obtained by 
these ordinary means, the current is increased by making a 
fire at the bottom of the pit, or at the top, to cause a strong 
draught of air through it. Or the air is drawn out or driven 
in by machinery contrived for that purpose, and having 
channels made of boards reaching to the place where the 
men are at work. 
Besides the change produced in air by the respiration of 
the miners and their lights, some subterraneous works are 
infested with gases of a different nature, which must be 
got rid of before the works can be extended. 
The first and most common of these gases is the choke 
damp, or carbonic acid gas, which, being heavier than air, 
lies at the bottom of the works, and instantly drowns those 
that enter into it. This damp is frequently met with in opening 
old dried-up wells, and even on the floors of cellars which 
are seldom opened. Fortunately, this gas is very quickly 
absorbed by water, and it soon mixes with the air, and 
there is no danger to be apprehended out of its immediate
	        
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