268 
MINUTES OE PROCEEDINGS OE 
frequently occur at the time of considerable barometric disturbances, 
which must unquestionably affect the rate of diffusion of the fire-damp 
into air and the rapidity of air circulation in a mine. They also point 
out that when the external temperature rises very considerably, the 
natural ventilation, due to the higher temperature of the air in a mine, 
is liable to cease, by the external atmospheric temperature becoming 
equal to, or perhaps exceeding, that in the mine. They consider that 
of 233 explosions which occurred in 1872, 58 per cent, were due to 
disturbances of atmospheric pressure, and 16 per cent, to excessive 
heat of the weather; and they have similarly traced the proportion in 
which the same meteorological changes have contributed to bring 
about explosions in other years.* 
Since the employment of gunpowder as a means of rapidly removing 
coal, or overlying shale, has come into considerable use, there can be 
no question that an additional and a very serious source of danger has 
been imported into the working of collieries. That the explosion of 
a charge of powder in a blast-hole, or the “ firing of a shot/'’ has by no 
means unfrequently resulted in the production of a fire-damp explosion, 
has been clearly established by careful enquiry. This has been ascribed 
to two causes—one of them the direct ignition of the explosive gas- 
mixture by the flame from the shot, the other the dislodgment of 
fire-damp from cavities or disused workings by the concussion produced, 
and its ignition by some naked flame or defective lamp in the 
neighbourhood. If a shot takes effect properly (i.e., if the force is 
fully expended in breaking the coal or rock at the seat of the charge), 
there is seldom flame produced; but if the tamping which confines the 
charge in the blast-hole is simply blown out of the latter like a shot 
from a gun (which not unfrequently occurs when the rock is very hard 
or the tamping is not sufficiently firm, or when the charge of powder is 
excessive), the powder-gas issuing from the blast-hole will produce a 
flash of fire as obtained with a gun; and if the fire-damp were in the 
immediate neighbourhood, it would no doubt be ignited thereby. But 
this combination of conditions is not likely frequently to occur; the 
second cause above given is therefore more likely to be fruitful of acci- 
-dents : but the existence of a third cause, to which the majority of 
explosions connected with blasting in collieries is most probably 
ascribable, has been very clearly established by the careful enquiries. 
* Reference must be made here to an ingenious application, made by Mr. Ansell, of the laws of 
diffusion and osmose for detecting the presence of fire-damp in coal-pits. Two or three forms have 
been given by Mr. Ansell to the detector apparatus; perhaps the most simple consists of a ball of 
thin india-rubber, filled with air and fixed upon a stand under a lever which slightly presses the 
upper surface of the ball. If from any cause the lever is raised, it liberates a spring which sets a 
bell in vibration, or brings an electro-magnetic alarum arrangement into operation. If this appar¬ 
atus is placed where fire-damp exists to an important extent, the light carburetted hydrogen passes 
through the pores of the india-rubber ball, and as the air in the latter passes outwards at a much 
lower rate, the ball soon distends, exerting sufficient pressure on the lever to bring into action the 
signalling arrangement, which, if electric, may be placed at any convenient distance from the fire¬ 
damp detector, being connected with the lever by means of conducting wires. It would appear as 
though a detector of this nature could be made of important service in fiery mines ; but its employ¬ 
ment does not seem as yet to have passed beyond the experimental stage. 
