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THE COLLIERY GUARDIAN.

Alarch 3, 1916.

It should be added that any profit on the sale of
metallurgical coke is deducted from ;he surtax.

A Bill of this nature, after making all concessions to
patriotism, must inevitably be buttressed by heavy
penalties. Infractions of the law may be followed by
from six days’ to three months’ imprisonment, and by
fines of from 500 to 10,000 fr. Serious offences include
attempts to deal outside the provisions of the Act, the
conversion of house coal to industrial uses, privy selling
of metallurgical coke, and sales by merchants at prices
higher than those fixed by the prefects.

The operation of the Act is limited to the duration of
the war and three months following its close.

The French Parliament, in approving the scheme of
the Commission, introduced two amendments, acting in
both cases at the instance of the Government. In the
first place, it was decided to withdraw from the central
office all power of financial control, conferring upon them
duties solely of allocation; and secondly, the Govern-
ment declined to accept the provision annulling all
current contracts.

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LETTERS TO THE EDITORS.

___________________________________________________________

The Editors are not responsible either for the statements
made, or the opinions expressed by correspondents.

All communications must be authenticated by the name and
address of the sender, whether for publication or not.
No notice can be taken of anonymous communications.

As replies to questions are only given by way of published
answers to correspondents, and not by letter, stamped
■addressed envelopes are not required to be sent.

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STONE DUST AND MINE EXPLOSIONS.

Experience at Altofts.

Sirs, — In The Times Engineering Supplement of
December 31 last, “ A Mining Correspondent ” stated,
inter alia, that : “A careful perusal of Dr. Haldane’s
report on the effects of inhaling dusts applicable for
stone dusting in coal mines (Seventh Report of, the
Explosions in Alines Committee) must inevitably raise
a feeling of doubt as to the wisdom of the compulsory
introduction into collieries of stone dusting, even though
such a system might conduce to the prevention or limi-
tation of coal dust explosions.”

In the Supplement issued on January 28, Dr. Haldane,
in replying to the various points raised by the corre-
spondent in question, expressed the opinion that “ by
substituting for an explosive mixture of coal dust and
shale dust along the roads of coal mines a mixture con-
taining a sufficient proportion of shale dust to prevent
explosions, no increased danger to health will result, and
that there is sufficient evidence, both from human
experience and experiments on animals, to guide us in
respect to stone dusting in coal mines.”

In the correspondence referred to, no mention is made
of the method of distribution of shale dust on the under-
ground roadways of collieries, a most important factor,
cis it not only affects the health of the miner, but it also
gives increased safety to the mine by having in reserve
an excess proportion of shale or incombustible dust. I
should, therefore, esteem it a favour if you would allow
me to give your readers some particulars gained from
practical experience in shale dusting during the past
seven years. After the successful experiments carried
out by the Alining Association of Great Britain at
Altofts in 1908, when the explosive nature of coal dust
in the absence of firedamp and the efficacy of shale dust
in extinguishing an explosive blast were proved by
repeated experiments, it was decided to shale dust the
underground roadways in one of the Altofts mines. In
December of the same year experiments were made to
learn the best method of distributing the dust. Since
that date shale dust has been regularly and systematic-
ally placed on the roads. The shale from which the dust
was obtained formed the roof of one of the mines.
Similar shale may be found in other colliery districts;
perhaps in some mines the antidote to the coal dust
danger may lie as near to it as the dock does to the
nettle. The dust should be made from soft shale, but
flue dust should not be used, as the microscope reveals
that its particles are usually beset with vitrified points
and cutting edges.

The height and area of the roadway necessary for
haulage and ventilation requirements are obtained by
ripping ” or breaking down the shale, which is after-
wards stowed in the old workings or sent to the surface.
A quantity of the debris consists of small pieces, say,
2 to Sin. cube in size, which are collected and placed
m tubs, each holding about 10 cwt. Four or five of
these tubs are sent on each working day to the surface
disintegrator, where the pieces are pulverised. The
resulting fine dust is sent underground to be placed on
the roadways where coal dust has accumulated. Thus
there is no additional shale sent into the mine beyond
that which has been brought out, the difference being
simply one of form, the large pieces of shale (which only
presented a small cooling surface, and are too heavy to
be raised by an explosive blast) having been reduced to
dust. This dust may be raised by an extraordinary
current or blast into a cloud containing millions of super-
ficial feet of incombustible dust, which experiments have
repeatedly proved to be sufficient to reduce the tempera-
ture of an explosive coal dust flame, and so extinguish it.

During the absence of the men from the roadways, the
stone dusting is done by a youth, who stands with his
back to the air current, and throws the shale dust on to
the projecting portions of the strata with sufficient force
to dislodge the coal dust found resting there. The air
current carries away the displaced coal dust and a cer-
tain proportion of the shale dust, which by and by
become mixed, and within a short distance fall to the
floor, and are lost amongst the rough debris. The shale
dust which has replaced the coal dust assumes an angle

of repose, which tends to prevent the deposition of fresh
coal dust.

Several tests were made to ascertain the velocity of
the air current needed to raise the coal dust and stone
dust respectively from their seats on the ledges of the
roadway. It was found that coal dust (specific gravity
of coal 1-27) was displaced by a current of air travelling
at 1,500 ft. per minute, whilst shale dust required an air
current of 2,600 ft. per minute. The ordinary velocity
of the air current on main roadways varies from 500 to
900 ft. per minute. It may be mentioned that the
minimum velocity of an explosive blast which was
measured during the Altofts experiments was 120 miles
per hour, or four times the velocity required to raise the
shale dust from its seat; the maximum recorded velocity
was 1,300 miles per hour. From a comparison of these
velocities, it will be understood that ample ventilation
may be maintained in the mine without disturbing the
stone dust, as proved by certain roadways requiring very
little re-dusting. An examination of the dust which has
been resting on the sides of the roads for several months
shows that in a dry mine it is almost as efficacious as
newly-applied stone dust.

As the quantity of shale dust which can be distributed
on the sides of the roads is far in excess of the amount
required to extinguish flame, a part of the floor of the
roadway may be utilised by making it into a dustless
road about 4 ft. wide. This space is sufficient to allow
the men and horses to travel to and from their work,
and the floor, being kept slightly moist an 'atmosphere
free from stone dust is maintained. It must be pointed
out that the, principal danger of coal dust is due to the
finest particles of dust being blown from the loaded tubs
on the haulage roads during their passage to the winding-
shaft, and it is on such roads that shale dusting is so
necessary. In the mine in question, and at many other
mines, the men and horses travel on separate travelling-
roads, the sides of which are formed in stone or shale,
consequently such men never come in contact with the
artificially stone dusied roads. There is, therefore, no
necessity to dust artificially those roads where no coal
dust exists, as incombustible dust, whether existing in a
natural state or artificially applied, does not propagate
an explosive blast. Formerly, before the present method
of systematically distributing dust, shale dust was pro-
duced in the mine by the trampling of men and horses
breaking up the fireclay floor in the main return airways.
This dust being taken up by the air current produced a
very dusty atmosphere; yet as regards its effect on the
health of the men, no complaints were received by the
management during a period of 35 years (see Explosion
in Alines Committee Report, No. 7, 1915).

With regard to the cost of stone dusting in the three
seams in which it is used at Altofts, the following details
are given :—■

1913.	1914.	1915.

Shale dust emptied (tubs)_____ 2,069 ... 1,622 ... 873
Length dusted (yds.) ......... 29,198 23,917 ...14 655

„	„ (miles)..........	16|...	13|...	81

Length of roadway dusted per

tub (yds ) .................................	141 ... 14’7 ... 16’7

Cost of pulverising shale, in-
cluding interest on capita],
depreciation, repairs, labour,
power, and other surface
expenses....... ...................... <£224	... £178 ... £98

Cost of distributing dust under-

ground, including cost of filling

up any surplus stone dust...	£73 ... £61 ... £34

Total cost of dusting, per ton of

coal output ................ 0T08d....0T02d..,,0’058d.

From the above it will be seen that the average cost
for the past three years is about one-tenth of a penny
per ton of coal output, which a colliery expert once
observed “ may be regarded as a cheap form of insurance
against coal dust or gaseous explosions.”

In his concluding paragraph, “ A Alining Corre-
spondent ” further remarked that “ unless it can be
shown that additional invalidity, apart from mortality,
will not be caused by systematic stone dust, it will be
better to seek some less objectionable specific for the
prevention of coal dust explosions.” Alay I remark that
the use of shale dust as a preventive of coal dust explo-
sions is based on the personal experience I obtained
whilst recovering the underground roadways of the
Altofts Colliery after the explosion in 1886, which caused
the death of 22 men. Twenty miles or more of under-
ground roadways and 800 acres of goaf had to be
recovered, which requited a period of three months to
accomplish. Prior to the above explosion it was known
that large quantities of shale dust were to be found on
certain roads. During the recovery of the pit it was
noticed that there was great destruction on the roads
wherever coal dust had previously lodged, whilst on the
shale dusted roads no damage was found. The shale
dust deposits, which lay like finely drifted snow, had
evidently been subjected to whirls of an explosive blast,
but within a short distance from the last indications of
damage there was no evidence of burning. The know-
ledge thus obtained of the cooling effects of shale dust
in limiting a coal dust explosion was far more convincing
than were the Altofts experiments during 1908-11.
Besides . the experiments were on a small or miniature
scale as compared with the actual explosion or teaching
of nature. It may also be pointed out that for many
years previous to 1908 numerous attempts were made to
prevent coal dust explosions, and since that date some of
the leading scientific men in this country, France,
America, Belgium, and Germany have been engaged in
trying to discover a preventive. At the present moment
no other remedy than shale dust, except, of course, the
old one of watering, has been suggested as a preventive
of coal dust explosions. Its efficacy, as demonstrated by
the Alining Association experiments, has since been
confirmed by the Home Office or Eskmeals experiments.
It does- not damage the underground roadways, nor
interfere with the output of coal, nor, as shown by nearly
35 years’ experience by the workmen at Altofts, has
it prejudicially affected the health of the miners or boys.

Shale dust can be easily applied, and by having a
pathway on the underground travelling roads kept fairly
clean, the atmosphere of the roads where the largest
amount of shale dust has been deposited can be kept
fairly free from dust.

The production of coal dust is inevitable. It will
always continue to be formed in the process of mining
and in the transport of coal, and being held in suspension
in the air current, will form part of the mine, but it is
not necessary that the dust shall remain as lodgment in
the roadways, and practically become a permanent
menace. Coal dust has been successfully dealt with for
the past seven years by dislodging it in the way described
in the foregoing remarks. Coal dust roads are no longer
a cause of dread; they are simply regarded as a danger
which ordinary precautions may avert or safely deal
with, in the same way that the workings are kept free
from water or accumulations of firedamp. Water and
firedamp offer certain difficulties, both in their volume
and the manner of their discharge, whilst the gradual
accumulation of coal dust, which is artificially produced,
persistently gives warning of its presence by altering the
sides of the roadway from grey to black.

Experience has shown that shale dust possesses those
qualities which are essential in a preventive for the coal
dust danger, namely, that it does not introduce any new
form of danger, is universally adaptable, can be supplied
at a low cost, and has on all occasions proved to be
effective.	William Garforth.

Snydale Hah, Normanton, February 29.

Re SPRING TERMINALS ON MINERS’ LAMPS.

Sirs,—We should like to point out that the recent
Home Office notice with reference to the firing of two
electric lamps in December Iasi does not apply in any
way to our make of lamp.

We have made all manner of tests with the object of
bringing together the terminals on our accumulator, for
the purpose of obtaining a short circuit, but without
effect; and we consider our lamp perfectly safe under
all conditions.

We have again submitted our lamp for further experi-
ments by the authorities, and if it is found advisable
that all lamps should be fitted with a rigid terminal, we
are already prepared with such, and can supply it at
short no:ice and small cost to those who have our lamps
already in use.

We are inclined to think that these accidents occur
not from the coming together of the terminals, but from
the spilling of acid on the top of the accumulator, and
conveying the current from one terminal to the other.

This, for several reasons, cannot happen to a lamp of
our make, because, in the first place, rubber studs are
fitted through our accumulator lids to a height of a
quarter of an inch above the level of the celluloid, and
consequently the terminals stand quite clear; further,
with our new type of valve, no leakage of acid takes
place.	George Pearson, managing director,

Pearson’s Electric Aimers’ Lamp Company Limited.
Victoria Works, Stratford, E., Feb. 29, 1916.

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PARLIAMENTARY INTELLIGENCE.
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HOUSE OF COMMONS.—February 29.

Enlisted Mining Students : Examination Facilities.

In reply to a question by Mr. Wing, Mr. Brace (the Under-
secretary of State for the Home Department) said he would
be glad to consider any request from military candidates who
might be unable to attend at the ordinary examinations for
managers’ certificates to be given special facilities for taking
the examination, but none, so tar as he was aware, had
reached the Home Office up to the present. It would not be
possible to excuse such candidates the examination altogether.

Mr. Wing further asked : (1) if the Home Secretary would
endeavour to obtain from the university authorities facilities
for mining students who completed their training by
December 31, 1914, but who had been prevented by service
in the Army and Navy from sitting for examination, to be
granted temporary certificates for two years, and be allowed
to take their examinations in sections during that period; and
(2) if he would, in the interest of mining, obtain facilities for
students who had enlisted, and at that time had not com-
pleted their training, that they should be allowed to count
their service as a part, not exceeding one year, of their
mining training, and be allowed to take their examinations
in sections.

Mr. Brace, in reply, said that under the statute, certificates
to act as manager or under-manager could only be granted
to persons who had had the specified practical experience,
anc( had passed satisfactorily the examination held by the
Board for Mining Examinations. No change could be made
in those conditions except by Act of Parliament. He could
not advise the granting of certificates to act as. manager or
under-manager of a mine to persons who had not satisfied the
responsible authority as to their competency to do so; but he
was considering with the Board whether, with the consent of
Parliament, some concession could be made, under conditions,
as to the period of practical experience in the case of men
whose time had been, interrupted by a period of active service
with the Forces. He was also considering with the Board
what arrangements could be made to secure for mining
students, who, being wounded, were unable to write, facilities
whereby their examination in such circumstances might be
oral in place of written.

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Railway Companies and Traders’ Disputes.

Answering a question by Mr. Thomas, to the President of
the Board of Trade, Mr. Pretyman said the Board from
time to time received applications from railway companies
to appoint arbitrators in order to enable the companies to
recover demurrage charges from traders who had declined
to pay the amounts claimed and disputed the reasonableness
of the charges. A number of such applications from the
Midland, Great Northern, and Great Central railway com-
panies were now pending, and the Board were about to
appoint the Railway and Canal Commission to act. It was
important in present circumstances that wagons should be