June 13, 1913.

The colliery guardian.

1275

dangerous condition of gob-fires and underground fires.
He knew nothing in mining which produced such
anxiety in regard to the liability to gob-fires and under-
ground fires as the avidity of some coals for oxygen, and
the presence of iron pyrites. Among the many seams
of coal in Lancashire the liability to gob-fires and under-
ground fires appertained to one or two very largely, and
only to those one or two. In one case no pyrites could
be seen; it was not visible, but the avidity of the coal
for oxygen was most marked. It would be very helpful
indeed to mining engineers if a classification of
dangerous seams of coal, such as that suggested by the
authors, could be instituted.

Mr. F. E. E. Lamplough, in reply to the questions
asked with regard to iron pyrites, said he was certainly
interpreted rightly when it was said that he regarded
both causes, the carbonaceous coals and iron pyrites, as
contributory to heat production, but he was not able to
gauge which was the more important in certain cases.
It had been held by some people that iron pyrites was
practically wiped off the slate as a cause of production
of gob-fires, but he did not think that was so. The
extraordinary rapid heating was very much greater than
with any of the slightly carbonaceous coals, and was
only stopped by the blockage of the CO2. He could
not help thinking that if oxygen had been passed
through the apparatus, the. apparatus would have gone
up in smoke in course of time with the iron pyrites.
In the apparatus it heated up very rapidly indeed, much
more so at the start than any of the slightly carbonaceaus
coals, whilst the latter, not containing pyrites, gave
eventually the greatest heat evolution, owing to their not
being choked with carbon dioxide. Attention was paid
to the production of sulphate in coals, and analyses
were made in two or three cases, but only in one case
had they ventured to draw any conclusions from them,
because in some cases the sulphate produced was so
infinitesimal that it could not be measured with any
approach to accuracy. That proved conclusively that
iron pyrites in some cases was not responsible for the
heating. For properly investigating the iron pyrites
problem, a rather different method must be employed,
in which the oxygen was continually supplied and the
CO2 stopped, and that he might be prepared to under-
take at some future time. The experiments had been
left at present in rather a belated condition. The
question of the removal of carbonates was before their
minds, but his colleague was called away to other work,
and personally he had had to carry out so me heavy work
at Cambridge, and it was impossible to go further into
the subject at the time. Many more experiments
suggested themselves at once to anybody who con-
sidered the matter clearly.

The Application of Stonedust.

In the afternoon, the discussion on the President’s
paper on “ Recent Methods of the Application of Stone-
dust in Mines,” was taken.

Prof. Henry Louis said he desired to make one or
two remarks about the historical portion of the paper.
He was rather surprised to find in the paper no reference
made to the very important paper by M. Aguillon, in
the Bulletin de la Soclete d’lndustriale Minerale, which
gave an excellent resume from the point of view of the
history of the work done up to that period. Mr.
Taffanel, in one of his reports, said that the study of the
schistification that had been suggested was one of the
first questions which they at Lievin had to solve. As
the members were aware, an experimental gallery of
quite an important size was built at Lievin, and whilst
it was being built Mr. Taffanel pointed out that in 1907
he put up a small tube for preliminary experiments, and
that those were the first experimental researches upon
the effect of stonedust in quenching an explosion of
coaldust. He confirmed that experiment in the large
gallery in 1908. Personally he rather dissented from
that point of view ; he thought that the bigger experi-
ments did a great deal more than confirm what Taffanel
did in his smaller tube, but he was simply quoting the
statement.

Mr. Tate said that at the enquiry after the Seaham
explosion, in 1880, Mr. William Atkinson, who was then
junior inspector for the Durham district, put it on
record that in his opinion the sole cause of the force and
effects of the explosion not being felt in the travelling
way was due to the presence of stonedust. He thought,
with Prof. Louis, that it was desirable to get as far as
possible the history of the subject accurately stated. In
his knowledge and experience, that was the first time
that stonedust was ever thought to have any bearing
upon the effect of an explosion.

Mr. W. C. Blackett said that whatever might be the
opinions of people who had enquired into the causes of
explosions in mines, and whatever the work that other
people had done, he for one was satisfied that the
president was the first practically to apply the remedy

of stonedust in coalmines. The president might rest
assured that it was only a strong sense of duty that
made him take some exception to a few of the remarks
towards the latter end of the paper. Personally he did
not like the use of the specific terms that had been
employed such as “ stonedust ” and “ inert dust.” He
particularly disliked the expression “ inert dust.”
“ Inert dust ” did not convey the necessary idea, and he
thought “ incombustible dust ” was the best all round
term that could be used. There was no doubt that
colliery managers—being very ordinary mortals—would
get the cheapest, handiest, readiest and best stuff they
could for the purpose of making their mines safe, and
he therefore regretted that the president had thrown
cold water upon the use of fluedust. Speaking with
every respect, he did not think the president’s reasons
were adequate. He must bear in mind that there were
fluedusts and fluedusts. It did not seem to him that
in their application there was any need for any person
to breathe these dusts in dangerous quantities. He had
had stonemen working among all kinds of dusts ; but
the dust that was laid upon the ordinary wagon ways
was never of such a composition that it could create
physiological danger ; and to create a danger of a
physiological kind when it was not necessary and
important would do harm to the very motive the
president had at heart. The fluedusts that he had been
using were mostly burnt shales out of the coal. Their
pits looked quite white when they were dusted with the
stuff. He did not wish in any way to anticipate any
reports the committee might issue with regard to the
experiments at Eskmeals ; in fact he was not perfectly
certain he was justified in making the statement he was
about to make, but certainly the experiments at
Eskmeals had demonstrated that, so far as quenching
an explosion that had once started was concerned, the
particular fluedust in question produced better results
than the stonedust, and for this reason the president
gave it in his paper as a drawback. In one portion
of his paper the statement was made : “ Fluedust does
not possess this advantage owing to its lighter specific
gravity. Once that lighter fluedust was in position it
had the advantage that it would more readily rest than
the heavier dust and act very much more quickly in
trying to quench an explosion. There might be other
dusts—such, for instance, as the products of some of the
water purifiers which were producing lime in very fine
quality—that could be used. That, tried possibly along
with some magnesia products, would form a very fine
substance in all probability which could be put to
practical use. He was quite certain that difficulties
would be experienced in some collieries in getting suit-
able incombustible dust, and the more difficulties there
were the more prone they would be to put off the day of
using them.

Mr. A. M. Henshaw (Talk-o’-th’-Hill) felt that, not-
withstanding the demonstrations at Altofts and else-
where, and the practical proofs that stonedust was the
best preventive of colliery explosions, they were not
doing as much as they might do in applying it. It was
easily prepared, but should be ground in a proper machine
to the necessary degree of fineness. On that point the
author would perhaps give his experience and advice as
to the best machine. The claims made on behalf
of certain machines were not justified by experience,
and the plan adopted at some collieries of using the
mortar mill was very unsatisfactory. Distribution
could not be done better than by hand, but it was not
sufficient merely to dislodge the coaldust by throwing
on the stonedust. The road should be first swept and
the coaldust cleared away. An excess of stonedust, in
the first place, of 3 or 4 to 1 should be sufficient, and
could be judged by the workmen. Occasional samples
should be taken for analysis, and the ash content should
be upwards of 60 per cent., although 50 per cent, would
prevent propagation of flame. That figure would be
much exceeded by further dressings of stonedust until
the conditions became perfectly safe under any circum-
stances. Fineness was of great importance. The greater
portion of fine coaldust from the roof and sides would
pass through a mesh of 200 to the inch, and stonedust
should all pass through a 30 mesh, and a third of it
through a 200 mesh. Dust of that description would
remain in situ in ordinary air currents, but would be
easily raised by an explosion wave. He believed that
fluedust was admirably suited to the purpose in view.
He was using it with success, and had received no such
complaints as the author indicated. Though the silica
might be high in some cases, it was unlikely to be
inhaled [by the workmen, as it was not raised in the air.
It was of the necessary fineness, and contained no

carbonaceous matter, and its use entailed the minimum ' electricity, more particularly anyone who was contem-
of labour and cost. Dr. Haldane had recently inspected plating the use of an overhead line for electrical trans-

roadways treated with fluedust, and had supplied the i * abstract of this paper appears elsewhere in this
following figures :—	I issue.

Coaldust from a Roadway before Treatment.

Fineness. Analysis

Passing through Per cent

30 mesh........ 23

30, left cn 60 ... 11

60,	„	90	...	6

90,	„	200	...	2|

2C0 mesh........	2|

Fineness.	Ash.

Passing through Per cent.

30 mesh .... 10’4

60	„	.... 13 6

90	„	  145

200	„	.... 17 5

Mixed Dust after

First Treatment with Fluedust.

Fineness.	Analysis.	Fineness.	Ash.
Passing throngh	Per cent.	Passing through	Per cent.
30 mesh		... 38	30 mesh 		, 630
30, left on 60	... 18	..	60 „			. 650
60,	„ 90	...	8	...	90 „			, 614
90,	„ 200	...	3	..	.	200 „			, 64-7
200 mesh		... 10		

He hoped the president would modify his opinion in
regard to fluedust.

Mr. J. W. Fryar said the particular point to which
he wished to make reference was that he thought a
great deal of harm was being done by trying to make
pits too safe by stonedusting. If the ordinary colliery
man was told that to make the pit safe he must have
14 to 1, or 20 to 1, or 10 to 1, he turned round and said,
“ I cannot do it; I could not maintain it if I got it
down, so I will not start.” He felt so strongly on the
question of stonedust and its efficacy that he thought
the position wanted clearing, not as to how much would
make a mine absolutely safe, but how little would make
it safe. In a group of collieries he was managing in
Nottinghamshire, he obtained a large number of samples
of dust taken from roads which had been in existence •
for anything up to 40 or 50 years. The Nottingham-
shire coalfield had been practically immune from coal-
dust explosions, and was considered an exceedingly safe
coalfield. He found that the analysis of the dust on the
haulage roads in the collieries, especially in the Notting-
hamshire Old Top Hard seam, showed an equivalent of
40 to 50 per cent, of stonedust in the dust which had
accumulated on the old haulage roads. It was evident
that 50 per cent, was a very good figure to start with.

The President, in reply, said, with reference to the
remarks that Prof. Louis made as to the claims of Mr.
Taffanel, that he (the president) had made a plain state-
ment in the paper that as far back as 1886 it was
noticed that when an explosive blast which was probably
travelling at 1,000 miles an hour or more came in
contact with very fine stone, or when stonedust roads
were reached, no destructive effects were found, although
on the coaldust roads there was the greatest destruction.
He wished the members to understand that personally
he claimed nothing except as being the instrument for
having observed what took place and then trying to
carry it out by making the experimental tube as nearly
as possible like an underground roadway. That was
done on July 30, 1908, and having obtained that
information he obtained permission from the other
members of the committee to put in a full length of
tubing and to put stonedust down in the same way that
it existed in the pit. With reference to the question of
fluedust, he wished to say at once that Mr. Blackett
had had experience with that particular dust that he (the
president) had not. He thought it was better to draw atten-
tion to the question of fluedust, because in his own case
he had simply taken the ordinary dust from the boilers.
He thought when he carried out the dusting it was very
much better for him to experiment with the same dust
that had been used in the pit than to go forward with
dust that he had not proved. That was why he spoke
more particularly with reference to the stonedust; but,
after what had been said, he certainly thought that all
collieries that had dust like the lighter dust that Mr.
Blackett had produced—a dust of a lighter colour than
the one he had been using—should try it. With respect
to what Mr. Fryar had said, he could quite understand
that when Mr. Fryar had 50 per cent, he would feel very
much safer than in having no stonedust at all. At the
same time, the members would remember the old saying
that it was better to be sure than sorry, and so long as
the dust rested on the roads in a large proportion, it
met every objection which could be brought against it.
When it was also borne in mind that it cost only £200
a year for a colliery raising 600,000 tons a year, with an
annual wage and material bill of £200,000, to stonedust
the colliery, it did not seem very much in proportion.

Aluminium Cables for Mining Work.

The following paper was then read :—“ Insulated and
Bare Copper and Aluminium Cables for the Trans-
mission of Electrical Energy, with Special Reference to
Mining Work,” by Burke wood Welbourne, M.Inst.E.E*

Mr. Robert Nelson, in opening the discussion,
thought the paper would prove most interesting to any
mining engineer who was contemplating the use of