298 On the Ventilation of Coal-Mines. {Apri, 
part of the workings. ‘The shutting of the downcast shaft for one, 
quarter of an hour would in this manner clear the mine from a 
~ very considerable quantity of gas. The exhausting pump ought 
never to be omitted at the upceast shaft; vast quantities of fire- 
damp might be extracted by it when the downcast shaft is shut; 
every stroke would extract a portion of the gas, and set another 
portion at liberty in the workings, ready to be swept out when the 
atmospheric current is again introduced. ‘These operations, regu- 
larly performed, would go a great way in preventing the overwhelm- 
ing discharges of fire-damp, which occur when the barometer sud- 
denly sinks, after having been steady for some time, and which 
arise; not from an increased production or evolution of the gas, 
but from its sudden liberation from confinement. It ought also to be 
deeply impressed on the minds of viewers, and by them on the 
minds of workmen, to take care that no unnecessary holes or ex- 
cavations be made in the roof of the mine. The collier ought to 
be made to understand, that even the mark of his pick in this part 
will contain, and retain, a portion of fire-damp, ready to expand 
into mischief at the first opportunity. 
It appears from Mr, Dalton’s experiments, that two gases, very 
considerably different in their specific gravities, as oxygen and 
hydrogen, will:miax when confined together in a close vessel. It 
occurs to me-that advantage might be taken of this fact in ventila- 
tion. A mine might be shut up for a few hours, until the mixture 
were completed. By then turning on the atmospheric current, the 
aerial contents of the workings would be hurried out before they 
had time to commix: which would have the effect of cleansing 
the mine of an enormous quantity of inflammable air. Why 
should not operations so simple, and so highly important, be exe- 
cuted on Sundays, while labour of other kinds is suspended ? 
|. From what has been said your readers will readily perceive that 
the power of complete ventilation has a certain and strongly marked 
limit. When, after every power of increasing the supply, or of 
accelerating the progress of atmospheric air, has been applied, the 
proportion of fire-damp discharged by the upcast shaft amounts to 
-i,th part of the whole quantity of air emitted by it; the ventilation 
-of that mine must be incomplete, and the mine dangerous in the 
same degree. With due precaution, however, it may still con- 
tinue to work, as allowance must be made-for the effects of, tempe- 
-rature and yarefaction; and because, being collected from distant 
quarters, the air at the bottom of the upcast shaft may be mixed to 
:the dangerous point, while the other parts of the mine may be 
considerably below it. ‘This, however, is a vast quantity of fire- 
damp, ; more, certainly, than is constantly discharged by apy pit 
in existence; and if,accidents do nevertheless frequently occur, 
long before the whole quantity evolved in the mine amounts to <;th 
part of what the shaft can discharge, they can only be referred to 
the imperfection of the system of ventilation pursued, in allowing 
the gas to accumulate, or by hindering it, from. making its. escape as 
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