932

THE COLLIERY GUARDIAN.

October 30, 1914.

gases, the distribution and quality of the light supplied are
now recognised as having a most important bearing on the
prevalence of the industrial disease known as miner’s
nystagmus. I am loth to think that finality in the means
of supplying an efficient light underground has been reached,
and hold the opinion strongly that much can be done in the
immediate future to improve existing conditions.

Many other points occur to me where changing conditions
might be noted, and where old methods are making way for
new ones. It is impossible, however, to deal with them
all, and I will conclude by drawing attention to a few
statistics dealing with the extent of the mining industry in
North Staffordshire as compared with four years ago, when
Mr. Hassam, in his presidential address, last put them on
record in the Transactions. The total number of persons
employed at collieries in North Staffordshire in the year 1913
is given as 31,873, compared with 27,823 in 1909. The coal
raised for the same years is, however, only 6,592,555 in
1913, compared with 6,445,178 in 1909. Taking into account
all mineral raised, the output per person employed is reduced
for the years given from 264 tons to 235 tons—equivalent to
11 per cent. The figures for 1909—in July of which year
the Eight Hours Act became law—show a reduction in out-
put per person employed of 4 per cent., as compared with
1908, and the reduction from 1908 to 1913 is nearly 15 per
cent. It is impossible to overlook the serious effect of such
a falling off in the productive capacity of the labour
employed, and as it can only be accounted for by the
operation of the Eight Hours Act and the Minimum Wage
Act, it should serve as a warning of the risks to the com-
munity at large which may result from legislative inter-
ference in the relationship of capital and labour.

In a comparatively short address I have touched upon a
variety of subjects, but I offer no excuse for so doing, as
one object I have had in view is to remind my auditors of
the infinite number of problems which have to be solved by
the mining engineer of to-day. Much information which
has not yet been communicated to the institute must be
available, and so far from there being a dearth of subjects
on which papers can be written, I feel that at no time
during the 42 years which have elapsed since the institute
was founded has there been a greater opportunity for mem-
bers to communicate their experience and views, with
benefit not only to their fellow members, but also to them-
selves.

Mr. E. B. Wain proposed a hearty vote of thanks to
Mr. Gregory for his presidential address, which, he
said, had suggested quite a number of important sub-
jects for discussion, and showed how closely in touch
with the latest mining practice their new president was.
He -was the representative of progressive colliery
management in that district, and had developed what
a few years ago was a comparatively small colliery into
one of the most up-to-date. The proprietors of his col-
liery must be very proud of their manager.

Mr. Hassam seconded. Mr. Gregory, he remarked,
was a man of very large experience, and an engineer
who kept in touch with mining progress. He had
developed the colliery of which he was manager (Sneyd
Colliery) from a comparatively small undertaking to one
of the best-equipped and most up-to-date in England.
Referring to Mr. Gregory’s remarks on electrification,
Mr. Hassam said it was very detrimental to that dis-
trict that they had no large power supply company to
provide current for the many collieries and works. The
colliery he was connected with would probably have
been electrified throughout if there had been a power
supply to draw upon, but the directors, after careful
consideration, did not think, in the circumstances, it
would pay to put down a large generating station.

The vote of thanks was unanimously accorded, and
Mr. Gregory acknowledged the compliment.

Coal Contract Dispute.—In the Commercial Court, King’s
Bench Division, on Tuesday, the action by David Evan
Howell, of Malefant-street, Cardiff, against Charles H.
Pullin and Company, of Mount Stuart-square, Cardiff, to
recover the sum of £1,298 damages for breach of contract to
supply Waterloo Colliery small coal was concluded. Defen-
dants set up a counter claim for £1,331, and the case was
fought on the counter-claim. Mr. Roche, for the defen-
dants, said the action was by the seller of the coal for the
non-acceptance of some 13,890 tons of coal, out of a total
of 21,000 tons of coal sold. There was no dispute about the
breach of contract, and no dispute about the quantity. The
only dispute was as to the difference of price at the time of
the breach. The price of coal fell in October, and what the
defendants now claimed was the difference between the two
prices—a sum of £1,331. Plaintiff said that Waterloo coal
was not supplied, byt a mixture of Waterloo ’coal and
Brithdir coal, and plaintiff claimed damages for breach of
contract in not supplying coals of the description contracted
for. The case was settled by judgment for defendants on
the claim for the non-acceptance of the coal for £550 and
costs, the £400 in Court to be paid out to defendants. If the
balance was not paid in 10 days there would be immediate
execution and costs after taxation.

Unemployment Insurance.—Pursuant to paragraph (5) of
the Unemployment Insurance (Umpire) Regulations, the
Board of Trade gives notice of the following decisions by
the Umpire : The Umpire has decided that contributions are
payable in respect of workmen employed in an insured trade
in a district which is rural in its character who usually follow
in that district some occupation other than an insured trade
—(a) from the commencement of such employment if—(1) the
workmen are employed at such a distance from their homes
as to require them to travel by rail; or (2) if they have been
employed anywhere in an insured trade for a total of 13
weeks in the two years preceding the commencement of the
employment; (3)' otherwise, after the employment, has
amounted to 13 weeks in an insured trade. The Umpire
has decided that contributions are not payable (except by
agreement between the employer and workman) in respect
of workmen employed in an insured trade in a district which
is rural in its character who usually follow in that district
some occupation other than an insured trade, provided that
all the following conditions are fulfilled :—(a) the workmen
are employed so near their homes that they do not require
to travel by rail; (6) the workmen have not been employed
in an insured trade for more than 13 weeks in the two
years preceding the commencement of the employment; and
(r) the employment has not amounted to more than 13 weeks
in an insured trade.

Explosions in Mines Committee : Sixth Report.

The Effect of Small Percentages of Gas on the Inflammation
of a 1 :1 Mixture of Coal Dust and Incombustible Dust.

It has already been shown in our Fifth Report that a
mixture in equal proportions by weight of coal and
incombustible dust cannot be ignited by a charge of
24 oz. of blasting power fired from a stemmed cannon
in our large gallery when the atmosphere contains no
combustible gas. It remained to be seen what pro-
portion of combustible gas would, if present in the air,
render such a mixture ignitible.

Several series of large scale experiments have been
made to determine this question, using, in the earlier
series, coal gas as the combustible gas, and, latteily,
firedamp obtained from Cymmer Colliery, Glamorgan-
shire.

We commenced our experiments with coal gas, of
which we had an abundant supply from the gas making
plant at the Eskmeals experimental station. These
tests were supplemented by laboratory tests with dif-
ferent combustible gases in order to determine the
relative effects of methane and of the coal gas used for
the experiments in the galleries.	'

But since coal gas acts very differently from methane,
we did not consider the coal gas experiments decisive
of the question until we had thoroughly checked them
by large scale experiments with methane.

We found that it was a matter of some difficulty to
obtain such quantities of methane as we required. We
finally succeeded in securing an adequate supply of
nearly pure firedamp from Cymmer Colliery, and we
are now able to give the results of direct determina-
tions of the percentages of methane that must be pre-
sent in the air to render a 1 : 1 mixture of coal dust
and incombustible dust ignitible by a cannon shot,
using methane from a natural source.

The experiments made with coal gas have, however,
a certain value, inasmuch as they demonstrate, in a
way that laboratory experiments are unable to do in a
convincing manner, the differences that exist between
coal gas and methane in respect to their ignitibility and
their facility for propagating flame. We therefore think
it desirable to include in this report the results obtained
with coal gas.

The average analyses of the combustible gases used
were as follow :—

Coal	Cymmer

Coal gas.	firedanip.

Per cent, by volume.

Carbon dioxide ......... 010	...	O 'JO

Ethylene hydrocarbons 3*75	...	0*20

Carbon monoxide ....... 5’95	...	0*20

Hydrogen ............. 52*75	...	nil

Methane............... 30*65	...	96 40

Ethane ................ 3*40	...	nil

Nitrogen (by difference) 3*40	...	2*30

The firedamp was compressed into cylinders at the
colliery and sent to Eskmeals, where it was stored in a
1,000 ft. or a 750 ft. gas holder. As the analysis shows,
it contained no hydrogen and no paraffin hydrocarbon
other than methane.

The difference of composition of coal gas and fire-
damp as revealed by the above table is very striking.
Thus, for example, in coal gas there is over 50 per
cent, of hydrogen, whereas in the firedamp used by us
there was none. There are also present in coal gas
large proportions of ethane and the paraffin hydro-
carbons.

These differences in chemical composition, especially
the absence of hydrogen, account 'for the much milder
behaviour of firedamp than that of coal gas.

Both the large gallery (7 ft. 6 in. in diameter) and
the 3 ft. gallery were employed for the serveral series
of experiments.

Method of Experiment in the Large Gallery.—The
mixtures of gas and air were made in the following
manner : a gas main leading from a 1,000 ft. gas holder
entered the gallery on the intake side of the fan (vide
Fifth Report, fig. 3, showing plan of gallery). Gas and
air were drawn together through the fan and forced
along the gallery towards the open end, the gas and
air stream being maintained during five or 10 minutes
before attempting to ignite the mixture of coal dust
and incombustible dust that had previously been
strewn along the gallery.

The percentages of gas present in the air (which could
be altered by regulation of the gas or air supply to the
fan) wTere determined by analyses of samples taken
near the cannon just before firing, and by calculation
from the known quantities of gas and air passing.
Satisfactory agreement was obtained between the two
results.

Immediately before firing the cannon a plate valve
between the main gallery and the “ return ” to the fan
was closed, so that the experiments were made in a
still atmosphere in a gallery closed at one end; that is
to say, under conditions comparable with those obtain-
ing during experiments Nos. 338, 354, 355, and 356
described in our Fifth Report. As in those experiments
also, the cannon was placed 50 ft. from the closed end
of the gallery, and pointed into a tube 3 ft. in diameter
and 10 ft. long, open at both ends, in which a quantity
(about 301b.) of the 1:1 mixture of coal dust and
incombustible dust was strewn.

The 1 : 1 mixture was also strewn on shelves and on
the floor along the gallery for a distance of 150 ft. from
the cannon. At the end of this 150 ft. length of dusted

gallery a plate was removed from the side, leaving an
opening to the outer air 7 ft. 6 in. in diameter. When
ignition of the mixture took place flame travelled along
the gallery and issued from this opening.

Method of Experiment in the 3 ft. Gallery.—By a
suitable arrangement of valves and mains the volume
of gas necessary to give the percentage required in the
atmosphere was run into the gallery which already con-
tained the mixed dusts and the charged cannon. One
end of the gallery, that nearest the cannon, was sealed
by an iron plate, and the other end closed by an oiled
paper diaphragm.

The mixture of gas and air was circulated during two
hours by means of a small fan working in a by-pass main
5 in. in diameter that extended the whole length of the
gallery. This by-pass was shut off from the gallery
just before firing the cannon.

The cannon was placed 50 ft. from the sealed end
of the gallery, and pointed towards the paper diaphragm
350 ft. distant.

Results of Experiments.—The results obtained in the
two different galleries, fullers’ earth being used as the
incombustible dust and the 1 : 1 mixture being present
at a rate per linear foot equivalent to about 1 oz. per
cu. ft. of air,* agreed very well amongst themselves.
They showed that when coal gas was the combustible
gas 2-3 per cent, in the air was insufficient to render
the 1 : 1 mixture ignitible by the cannon shot, the flame
from the shot being merely extended to a length of about
40 ft. When 2*5 per cent, of coal gas was present,
however, flame travelled throughout the gallery.

When firedamp was used, sufficient had to be present
in the air to give 4*6 per cent, of methane before the
1 : 1 mixture of coal dust and incombustible dust
became ignitible; 4*5 per cent, of methane in the air
only caused the flame of the cannon shot to be extended
to a length of about 40 ft.; smaller percentages than
4-5 caused no appreciable lengthening of the flame of
the cannon shot.

We are therefore warranted in concluding that unless
the proportion of methane in the air reaches 4-6 per
cent, its presence will not interfere with the beneficial
operation of a mixture of 50 per cent. (1:1) of incom-
bustible dust with coal dust.

It will be seen that this quantity, 4-6 per cent, of
methane, is not much below that which laboratory
experiments have indicated as required to form a lower
limit mixture with dust-free air, namely, 5*6 per cent.
(vide Third Report).

. From the manner in which the flame travelled in the
3 ft. gallery when sufficient methane was present to
enable the 1 : 1 mixture of coal dust and incombustible
dust to propagate flame, it seemed possible that, on
such a large scale, and when ignited by a cannon shot,
the 4-6 per cent, of methane alone, without the dusts,
might be capable of propagating flame. Experiments
showed, however, that this was not the case, though
the flame from the cannon shot was extended to a
length of 50 ft.

On the other hand, it must be noted that when 4-6
per cent, of methane is present in the air, it requires
but a small quantity of combustible dust also to be
present to render the atmosphere explosive. Flame was
propagated throughout the 3 ft. gallery when it con-
tained, in addition to the 4-6 per cent, methane-air
mixture, only 101b. of the 1 : 1 mixture of coal dust and
incombustible dust sprinkled along the floor. This
quantity of 1 : 1 mixture was equivalent to about 0*05 oz.
of coal dust per cu. ft. of air. As confirming the
deductions drawn in our Third Report, we may men-
tion that a similar quantity (101b.) of incombustible
dust, no coal dust being present, did not render a 4’6
per cent, methane-air mixture capable of propagating
flame when a cannon was fired in the mixture in the
3 ft. gallery.

The Watering of Coal Dust.

We have tried a number of experiments to deter-
mine what quantity of water is required to render coal
dust non-ignitible. Information on this head can be
derived from Bulletin No. 425 (“ The Explosibility of
Coal Dust ”) of the United States Geological Survey,
which was referred to in our Fifth Report (p. 7). From
the American experiments, which were made with arti-
ficially prepared dust from a bituminous coal containing
about 35 per cent, of volatile matter and about 5 per
cent, of ash, it was concluded that the total moisture-
content of the dust must approach 30 per cent, to
insure that it should be incapable of progagating flame.

We have repeated these experiments, using not only
coal dust containing merely its natural ash, but mix-
tures of coal and incombustible dust, and have deter-
mined the quantities of water that it was necessary to
mix intimately with the dusts in order to render them
incapable of ignition by a stemmed charge of 24 oz. of
blasting powder. Our results are in accordance with
those obtained in America.

The large gallery was employed for these experiments,
the cannon being placed, as in the previous experiments
with incombustible dusts, 50 ft. from the closed end
and pointing into a tube, 3 ft. in diameter and 10 ft.
long, open at both ends. This tube contained 251b.
of the mixture to be experimented with, which was also
distributed on shelves along each side of the gallery,
and on the floor, at the rate of 11b. per linear ft. for
150 ft. The coal used was a bituminous coal contain-
ing about 35 per cent, of volatile matter (exclusive of
moisture) and about 5 per cent. ash. It will be
observed, therefore, that we so atranged the experi-
ments with wetted coal dust as to be as nearly as pos-
sible under similar conditions with regard to ignition

* That is to say, aj a rate of 4 lb. per linear ft. in the
7 ft. 6 in. gallery, or at a rate of } lb. per linear ft. in the
3 ft. gallery.