April 20, 1916.

THE COLLIERY GUARDIAN.

753

7,410,000 cu. ft. in part of the Gemeinschaft Mine. In
one English mine it is estimated that the open space in
old workings amounts to 36,000,000 cu. ft.

Below are given the results of some of the many inves-
tigations of the relation between atmospheric changes
and variations in methane in mines.

Investigations in British Mines.

Galloway’s observations in Scotland did much to
establish the belief that there was an important relation
between barometric change and the volume of gas given
off by mines, and although his investigation was not
extensive, it led to the passage of the Mines Regulation
Act in 1872, which required barometric observations at
all collieries. Experiments in German mines by
Schondorff and Nasse in 1875 to 1877 showed that the
methane content in the returns was greatly increased
in periods of low pressure, especially in those mines
where there were extensive areas of old workings with
poor ventilation.

-The enquiry into the ventilation of coal mines in
England in 1908, by Cadman and Whalley, of the Royal
Commission of Mines, resulted in finding that in many
mines a diminution of atmospheric pressure was reputed
to have caused more mine gas to appear in the work-
ings, but no precise determinations were made.
Redmayne states that sudden diminution of atmospheric
pressure causes large amounts of gas to come out of old
workings, and also increases the discharge of blowers.

Investigations in Prussian Mines.

The Prussian Commission investigated the effect of
atmospheric influence on methane emanation at the Ath-
Gouley Gemeinschaft mines, near Aix-la-Chapelle, and
at the Gabrielle mine, near Karwin, in Austrian Silesia.
At all three places a close relation was found, so that
the results were confirmatory.

The investigations at the Ath-Gouley and Gemein-
schaft mines were conducted in 1885 by Hilt. Both
mines work the Grosslangenberg bed, which is very
gaseous. The Ath-Gouley mine contains large areas of
old workings, but the Gemeinschaft mine was in fresh
dip workings, which gave off much gas. In each mine a
split of the return air was sampled every morning at
5 o’clock, and the volumes of methane and carbon
dioxide were determined. One week the samples were
taken four times a day, and for another week samples
were taken in two different parts of the Gemeinschaft
mine where the workings were particularly fresh. Air
from workings in another bed (“ Meister ”) was included
in this last series. These latter samples were taken to
determine whether the variations in mining from day to
day and' during parts of the day would account for the
changes of methane content in the return, but the rela-
tion was not established.

Hilt thought that the experiments proved absolutely
that variations in atmospheric pressure affected the
emission of -gas in both mines. The barometric
variations were small at the time of the tests, but their
effect was plainly discernible in corresponding variations
in methane content, especially in the returns of the Ath-
Gouley mine. A rise in barometer was followed by
diminution of the volume of methane and carbon
dioxide, and a fall in barometer by an increase in the
volume of methane, and always within 24 hours. The
more rapid the rise or fall the greater was the variation
in the percentage of gas. Moreover, the outflow of
methane showed a tendency toward equilibrium, for
when, by reason of a considerable fall in barometric pres-
sure, the flow had risen much above the mean, it
appeared to have a tendency to decrease. The absolute
pressure was found to be of less importance than the
relative changes, especially when the changes were
rapid. In tests made at the Ath-Gouley pits, in a
region of old workings having open spaces aggregating
9,110,000 cu. ft., comparatively slight variation of
atmospheric pressure caused variations of 70 per cent, in
-the mean volume of gas in the returns, and these varia-
tions appeared to be independent of the amount of coal
being mined. The opinion was stated that at this mine
a great decrease of atmospheric pressure might double
the volume of methane. In the longwall and dip.work-
ings of the Gemeinschaft mine, where most of the gas
was from solid coal, the effect of changes of atmo- ■
spheric pressure was much less marked and it was
somewhat modified by the variations in the mining
operations. One notable irregularity in this mine
was a great increase of methane on two successive
days, with only a slight fall of barometer, and as there
were no old workings this increased flow must have come
from the face. Doubtless,some crevices were opened, or
a body of coal entered which contained an increased
volume of gas.

Mallard and Le Chatelier reviewed Hilt’s report, and,
although they agreed that some relation was proven, they
claimed that it was in returns receiving air from exten-
sive areas of poorly ventilated old workings. They
thought, however, that the test in the new workings
appeared not to show any relation, for there was more
discordance than concordance in the relations in the
fresher workings at Gemeinschaft, and not very close
relation in the workings in the Meister bed, notably in
one of the most rapid falls of barometer. They pointed
out that this is to be expected in fresh workings where
the gas is given off under pressure. Mayer, who made
extensive researches on gas evolution in mines in
Polnisch-Ostrau, concurred in the idea of increased
emanation of methane caused by diminished atmospheric
pressure, but believed that old workings are principally
affected, and in no case is the increase likely to be
dangerous in a well-ventilated mine.

Investigations in Austrian Mines.

A series of tests extending over six months was made
in 1885 by Koehler, in the Gabrielle mine at Karwin, in
Westphalia. The mine is a very gaseous one, with an
average of about 24 per cent, of methane in the main
return, equal to about 800 cu. ft. a minute. Five-gallon
samples of this air tvere taken daily, and also samples of

the air in a return from districts entirely in fresh work-
ings in the Karl bed. He found that the proportion of
methane increased with barometric fall, and that the
more abrupt the fall the greater was the rate of increase.
He confirmed Hilt’s observation that the amount of
methane does not depend upon the absolute pressure,
but on the rapidity of change. If, after the rapid diminu-
tion of pressure, there was little or no further change,
there was only a gradual increase of methane, whereas
if, after a rapid increase of pressure, there was little or
no barometric change, there w’as a slight decrease of
methane content. Therefore the time of maximum gas
content did not precisely coincide with that of minimum
pressure. The curves of barometric pressure and volume
of methane showed 105 concordances and 85 dis-
cordances.

Koehler made an important test to determine the
effect of artificial rarefaction of the air on methane
emanation. The intake was sealed, while the upcast
fan continued to run, so as to diminish the air pressure
in the mine, which amounted to 2’5 mm., or about
one-tenth inch. Increases, ranging from 20 to 41 per
cent in the Karl bed, and from 50 to 90 per cent, in the
upcast, were observed.

As this mine contained large areas of old workings, the
great increase of methane in the air from the main
upcast may have been in large part derived from them.
The workings in the Karl bed, however, were all fresh,
and the increase of methane from them was probably
due to increased emanation from the solid coal when the
atmospheric pressure was diminished. There are some
possibilities of error in these diminished-pressure
observations, because air volumes are not very
accurately measurable with anemometers running slowly.

In 1888, Koehler made another series of similar
observations in the Kohlscheid mines, near Aachen. The
barometer pressures were taken at noon and midnight,
and the amount of gas was determined morning and
night. A gasometer installed behind the fan of the
ventilating shaft of the Ath-Gouley mine, and placed in
such a manner as exactly to fill itself in 12 hours,
furnished average samples of the composition of the
air in the mine. For taking the amount of gas, a
Coquillion firedamp meter was used, and the analyses
furnished by that apparatus were controlled by experi-
ments at the laboratory of the Aachen School of Mines.
The comparison of the curves of methane and atmo-
spheric pressure is very instructive. Thus, for January
1889, during the first fortnight, to the lowest pressure
(737 mm.) corresponded a maximum holding power of
3'9 per cent, of methane, which became nil when the
pressure returned to 770 mm. During the second fort-
night, the variations of the curves also agreed. In
February a fall of pressure showed itself by an increase
of methane up to 7 per cent., and ended by disappearing.
Then, the pressure rising, the methane decreased. Some-
times considerable barometric falls appeared to be
without effect, but, generally speaking, the maximum of
pressure coincided with the absence of methane. In
summer, escapes were much more marked, and the pro-
portion of 8 per cent, was even exceeded at the end of
July. The phenomena were not simultaneous, one or
two days being necessary for the alteration of the sub-
terranean air to attain its maximum, but there were cases
observed in which the action was in some way
immediate.

Conclusions by Behrens.

Behrens, in a review of the observations made by
himself and Koehler, at Karwin and Hibernia,
Westphalia, states the following conclusions :—(1)
Increasing atmospheric pressure retards the escape
of firedamp; diminishing pressure accelerates it; (2) the
greater the increase in atmospheric pressure per unit
of time, so much the more is the liberation of gas
diminished; the more the pressure falls per unit of time,
the larger is the escape of the gas; (3) if the barometric
pressure, having attained a certain height—the result of
which has been to diminish the escape of firedamp—
remains at that level for some time or permanently,
the percentage of gas gradually increases again, though
without -attaining the original figure, so long as the
increased pressure continues. The diminution in the
outflow, induced by a permanent increase in the atmo-
spheric pressure, is less when the gas pressure in the
coal is high, and greater when the gas pressure is low.
Conversely, when the atmospheric pressure falls—which
condition is accompanied by an increase in the escape
of gas—and then remains at this point, either for some
time or permanently, the percentage of gas gradually
decreases again, though it does not recede as low as the
original level, so long as the pressure remains constant;
the increased outflow of gas, due to the permanent fall
in th$ pressure, is smaller when the gas pressure in the
coal is high, and greater when the gas pressure is low;
(4) should a sudden rise of atmospheric pressure be suc-
ceeded by a more gradual increase, a slow acceleration of
the gas outflow ensues; on the other hand, when a rapid
fall in the barometer is followed by a more gradual one,
the retardation of the gas outflow proceeds slowly; in
no case, however, do the maxima or minima of the
barometric curves correspond to maximum or minimum
rates of outflow of the gas.

Tests at Hanover Mine.

In 1885, Broockman made an investigation at Hanover
mine No. 2, near Wattenscheid, Westphalia, to deter-
mine the effect of variations in atmospheric pressure on
the volume of gas from a “ blower.” The blower was
connected to a tube, and the gas was burned so that a
comparison could be made of variations in height of
flame with variations in pressure as recorded on a
barograph. The results showed a close connection
between the two, indicated by an increased flow of gas
at the time of diminished atmospheric pressure, as in
the tests of mine air at Karwin and other places.

Heise and Herbst have shown that notable pressures of
the gas are obtained only by boring several metres back
into the solid, and that near the face the pressure is only

slightly in excess of the air pressure. This refers solely
to the pressure of the free gas, and not to the gas in the
pores of the coal, which escapes too slowly to affect an
ordinary gauge.

Investigations of the Austrian Firedamp Commission.

The Austrian Firedamp Commission made many
observations to ascertain the relation between gas
emanation and changes of atmospheric pressure. The
tests were made simultaneously for four weeks in six
districts, some in gaseous mines, others in non-gaseous
mines, some in mines with old workings, and others in
mines without old workings. Samples were taken three
times a day, and data obtained as to the amount of coal
mined, surface of coal exposed, number of men and
animals working, and other details. In some of the
returns in gaseous mines the samples contained 14 per
cent, of methane, or 7,469 cu. ft. per ton of coal
extracted, and in less gaseous mines the methane content
in the return air averaged 0'3 per cent., or 519 cu. ft. per
ton of coal extracted.

In five districts in gaseous mines without old workings
no concordance was found between barometric changes
and the amount of methane. In mines in a slightly
gaseous district, however, the volume of methane varied
from 12| cu. ft. a minute when the barometer was
low to 11 cu. ft. when it was higher than the average.
On the other-hand, in mines containing extensive old
workings the proportion of methane closely followed the
the changes in atmospheric pressure.

The effect of barometric changes on gas emanation
from very gaseous fresh coal was tested by measuring the
volume of methane from bore holes. It was found that
the volume produced from these in equal given times
showed no relation to the variations of atmospheric
pressure. This latter test, however, did not show
fairly the conditions at the exposed surface of the coal,
where ordinarily most of the gas has been given off, and
therefore the pressure is far less than in bore holes.

Investigations in French Mines.

The French Coal Gas Commission (1887) gave con-
siderable attention to the question of the effect of baro-
metric changes. The Commission was doubtful as to there
being any material effect or enough to be a factor of
danger in properly ventilated mines. Le Chatelier,
however, believed that old workings were susceptible.
Chesneau made daily tests for 11 months in 1886 at the
Herin mine at Anzin, at a place where only a small part
of the air could come from old workings, even with great
barometric change. The methane content of this air
averaged about 0'8 per cent., or equivalent to an outflow
of about 118,570 cu. ft. a day. He found 81 days of
concordance between gas emission and barometric fall,
46 days of discordance, and 51 days of independence.
He concluded that for a bed that yields a permanent
and relatively regular outflow of gas sudden barometric
falls cause a notable increase in the emanation of
methane.

Tests at Lievin.

In 1907 Morin made an extended investigation to
ascertain the relation between atmospheric pressure and
gas at Lievin. A long time previously he had noted
such relation, especially in certain galleries not well
ventilated, and also along some of the returns.

The tests at Lievin were continued for two months.
In shaft 13 the percentage of gas was determined every
hour, with the unfortunate exception of Sundays; and
in three shafts every eight hours. At shaft 13, the
upcast from an area of nearly 200,000 sq. yds., includ-
ing extensive worked-out areas, carried 16,800 cu. ft. of
air a minute with remarkable uniformity. The samples
of air were collected by displacement in water-filled
bottles. Except for a small area in an underlying bed,
there were no workings above or below. From the
results obtained, Morin concluded that : Even slight
variations in atmospheric pressure may induce varia-
tions in the escape of methane, and other things being
equal, when the atmospheric pressure remains constant,
the liberation of methane is uniform. When atmo-
spheric pressure increases the escape of gas diminishes,
and conversely. Maximum atmospheric pressure corre-
sponds to minimum percentage of gas, and vice versa.
In some tests a decrease of 1 in. in the height of the
mercury column increased the proportion of methane
50 per cent.

Atmospheric Conditions in Old Workings.

As the air tested came from a district comprising a
large area of old workings, it appeared likely that the
old workings might act as a great reservoir and give a
large outflow of gas at times of diminished atmospheric
pressure. Even where the old < chambers were filled
with gob, and the surface had settled more or less,
the amount of free space was large. Morin found that,
when certain old workings were pumped out, the volume
of water, when measured, showed that the voids
amounted to 30 per cent, of the original excavation. A
careful estimate of voids in workings in the Du Souich
bed, workings which covered nearly 200,000 sq. yds.,
and were nearly 5 ft. high, showed a total of 4,028,000
cu. ft. It was found that, if differences in the volume
of gas coming out of the mine under different pressures
were all supposed to be caused by the open workings,
the volume of pure methane in the voids in the mine—
if the voids were assumed to be filled—would range from
107,660 to 10,266,100 cu. ft., the larger volume corre-
sponding to a longer period of time. This result could
be explained only by the hypothesis that the gas and
air might be in strata of varying composition, those mix-
tures richest in gas occupying the highest levels. Under
such a condition, a slight diminution in atmospheric
pressure might affect only the mixtures poor in gas
occupying the low^er levels, whereas further diminution
would bring out mixtures containing more gas. How-
ever, careful sampling of the air in the old workings did
not reveal such a condition, which, moreover, is not
consistent with the laws of diffusion.