1270

THE COLLIERY GUARDIAN.

June 18, 1915.

experiments, which were suspended for the present,
started again as soon as possible.

Mr. J. Drummond Paton (Manchester) thought that a
solution of the varying effects which resulted in the
explosions would be found by a study of the trans-
mission of heat in the form of radiant energy. If one
considered the emissivity of the gas in the zone of pro-
duction, and also the absorption capacity of the various
shales based on radiant energy conditions, he was sure
that interesting information would be obtained. If the
nature of the gases were analysed on the basis of a
radiant energy, transmission, he thought the investiga-
tions would reveal certain information.

Mr. J. T. Winmill (Doncaster) expressed his agree-
ment with Dr. Haldane as to the necessity for further
experiment with English coal dust, because the results
given in the paper showed very definitely that there
was a, considerable discrepancy between the results
obtained on American coal dust and English coal dust,
although the point upon which they disagreed was not
very easy of determination. Dr. Haldane had
suggested that the reason might be the difference
between natural gas and the pit gas obtained in this
country, which was almost pure methane. He did not
think that that was a very reasonable explanation,
because in the 1 per cent, of gas used in the ignition test
there would only be a very minute proportion of
methane. . The figures quoted in the paper showed that
the relative explosibility of the natural gas they were
using to pure methane was about 50 to 55—5 per cent,
of the natural gas as against 54 per cent, of methane.
Therefore, he did not think that that explanation could
possibly cover the difference in the results. There was
either a very striking difference in the coals, or there
was one other possibility, viz., that there might be a
big difference in the shale dust. He could not find any
analyses in the paper of the shale dust used, but it would
almost seem that it contained very little water, because
the water in the coal was estimated, but not the water
in the shale dust. As to the shale dust used in the
Eskmeals experiments, all the experiments he had had
contained up to 10 per cent, of water, and that water
was given off extremely easily from the dust as soon as
it was warmed in the slightest degree. Probably the
large volume of water given oft when the dust was
raised in suspension and slightly warmed rendered the
coal dust far less inflammable than if the stone dust
were absolutely dry, and that might account for the
difference between the American and Eskmeals
results; but that was merely a conjecture, since no data
of the analysis of the shale dust were given.

Sir Arthur Markham (London), referring to Mr.
Winmill’s remarks, said that the tests made at Tredegar
gave exactly the result which Dr. Haldane had men-
tioned. In the Senghenydd explosion certain tests were
made to ascertain, with natural gas and with methane,
at what percentage an ignition could be obtained at
different voltages. If those experiments were based, as
he believed they must be, on the use of natural gas,
then the paper was valueless from the practical stand-
point of mining. The industry in this country was now
being asked, or would shortly be asked, by legislation,
to have compulsory stone dusting in all mines. If the
writer of the paper were correct, it would be wholly
wrong for Parliament to enact that there should be a
given percentage of stone dust in all roads, because if,
when any gas was present, it had the effect which the
author stated, the whole of the benefit of the stone dust
was lost. In regarJ to Pittsburg dust, it was said that
the mixture would not ignite when the percentage of
shale was 60 per cent. With 3 per cent, of gas, the
mixture would not' ignite under 80 per cent. Those
tests, as Dr. Haldane had said, were absolutely con-
tradicted by every single test that had been made at
Eskmeals for years past; and if the author could state
whether natural gas was used in those experiments or
not, he would relieve a great many engineers of a good
deal of anxiety, occasioned by reading the paper, as to
whether what was now proposed in this country, was not
based on an incorrect test. He did not for a moment
suggest that the Bureau of Mines in America, who had
done excellent work in scientific research, were wrong;
but if they were right in the test which they had made,
and all our tests in this country were wrong, we ought
not to proceed , by legislation to do certain acts till we
knew where we stood.

Sir William Garforth, referring to the last report of
the Eskmeals Committee, in which it was stated that
Dr. Haldane was going to make certain experiments
with respect to shale dust and flue dust, asked whether
Dr. Haldane was at liberty to say anything pn that
point. . .	,	.

Dr. Haldane replied that his report on that subject
was printed some, months ago. He supposed it had not
yet been made public. He could not say any more
about it;, he,.did not know what had become of it.

Sir William Garforth said that, with regard to the

academic question, he had learned far more from the
exploration work in connection with the Altofts explo-
sion in 1886 than from the gallery experiments.
Although in the latter they had the advantage of know-
ing the velocity of the flame and the pressure, and the
constitution of several of the gases evolved, still the
other was a practical test, and it was to that that he
would like to refer, in answer to Prof. Louis’s question.
In that case, the ignition of the coal dust took place at
a point about half-way along the roadway; the explosive
blast did very little damage for the first 200 yds. on the
one side, and about 150 yds. on the other, and then the
damage commenced. When it had travelled 500 yds.
the tubs were all broken to pieces, and there was one
boy whose funeral took place on two occasions, and then
for 1,700 yds. there were broken tubs, in many cases
lying under a chain, as if the chain had been put into a
state of oscillation, and then settled down on the tubs.
The evidence was very conflicting; sometimes great
destruction was found, and then for a distance very little
destruction; but he thought the evidence obtained from
actual experience must be taken to be more reliable than
that obtained from an experimental mine. Although
one knew there were those academic questions which
should be solved in order to be able to make our theories
coincide as nearly as possible with the actual facts,
still, he did not think, he could give Prof. Louis any
better information than that which he had given, which
had come from actual observation. The details of the
distances and the destruction which had taken place
were all given in the appendix to the Report of the
Royal Commission on Coal Dust in Mines, which was
published in 1891. Had Col. Blackett been present, no
doubt he would have said a good deal about retonation
waves. He might have attempted to do something
more, had the question been put some three or four
years ago, when he was more familiar with the experi-
mental work done at Altofts. As to the actual method,
they were now trying to experiment for coal dust explo-
sions in what might be called the commonest possible
way, that was to say, in the same way as, if one had a
fall of roof, one would send a man to re-timber, and if
one had water accumulating on the dip side of the
roadway, one would put a pump down and get it out.
In the same way with stone dust. They had now some
13 miles of haulage roads on which it was-necessary to
keep stone dust. More than 20 miles had been dusted,
but 13 miles were kept in an efficient state. The early
dusting had been carried out in 1912 at a cost of about
<£180 a year. The second year, 1913, it only cost £150;
and last year it had cost, so far, about £90 per annum.
That included grinding the dust and other things, the
details” of which he would be very glad to give if
required. They had always an opportunity of seeing
whether the stone dust was in proper proportion, by
putting up a couple of sheets of cloth, causing an
increased velocity in the roadway, -and then letting a
man stand about 500 or 1,000 yds. away from the
point. The men always grumbled if they had to do
repairs, and contract the roadway. Several gentlemen
present had had an opportunity of seeing the roadways
and some of the seams, and they would bear him out in
saying that they were leaving the shaft pillar, which
was, of course, already covered with stone dust; they
knew the coal existed, but until one got to the coal base
one could not see a black road—they were all grey. It
was an easy matter, after they had had several dustings
of coal dust and shale dust, to brush part of it away.
One found no angle of repose on which the coal dust
could lodge, and it showed the grey surface underneath.
It was such a trifling matter with regard to explosions,
that they were going on just as they should do in the
other matters connected with the colliery.

Prof. L. T. O’Shea said, with regard to the point
raised by Prof. Louis, Sir 'William Garforth had said that
something might be learned by referring to practical
instances of explosions, and he might refer to the explo-
sion which took place at Wharncliffe Silkstone Colliery
not so long ago. It seemed there was evidence there of
the phenomena to which the author had called atten-
tion, viz., the development of some force in the opposite
direction to which the explosion was travelling, at some
distance from the point of ignition. He understood that
the explosion originated by an ignition of gas in the face,
and was not an explosion to begin with; it was simply
an ignition which eventually, in travelling towards the
dip, developed into an explosion. The explosion then
travelled down the level at right angles to the coal face,
and in that level there was evidence of the tubs being
blown in two directions, some of them being blown inbye
and some outbye. He had had a very long discussion
on the subject with the manager of the pit, because it
had been suggested that the explosion had been in some
other direction altogether, and there certainly seemed to
be evidence of such phenomena taking place some way
from the seat of ignition.

Prof. Cadman said that Prof. O’Shea had made a very
nice point between ignition and explosion. Would he
define a little more what he meant by ignition?

Prof. O’Shea said that the question was a thorny one,
and he would rather not enter into it. He had differen-
tiated between the two, because the report stated where
the ignition was, and in the direction of the rise there
was no evidence of any violence at all;- there was con-
siderable evidence of burning,, however, and that
burning passed down the gates and cross cuts into what
was known as the slant; whereas in the opposite direc-
tion, going down to the dip, there was evidence of
considerable violence which one generally associated
with the development of an explosion. There was abso-
lutely no mechanical damage done in the opposite
direction.

Prof. Cadman thought there was little or no difference
between ignition and explosion. If violence were going
to be brought into the question, if ignition were some-
thing more than gas burning, and if explosion were
something that made a noise, it seemed to him that the
question wanted very careful consideration.

Sir William- Garforth said that Mr. Fryar had
carried out a great deal of practical work in connection
with stone dusting, and had given very valuable infor-
mation at last year’s meeting. His experience with
•stone dusting in the last 12 months would be interesting.

Mr. J. W. Fryar (Eastwood, Notts),, speaking
of the stone dusting work carried out at Bentley
Colliery, said he had not anything to say on
the subject in reference to the last 12 months
which was in any way different from the experience
stated at the last meeting. They had gone on in the
same way, and had kept their places stone dusted, and
so far had had no trouble. He might once again call
attention to the Nottinghamshire coalfield, and to the
fact that that coalfield had an average of about 43 per
cent, of stone dust naturally in the dust’in the mines,
and point out that the circumstance that that coalfield
had not had a dust explosion in its history was a very
good basis to work upon in legislation for the safety of
English coalfields. One could hardly get any better
illustration than practically the whole life of one coal-
field.

Mr. J. D. Morgan, in a written communication,
expressed his appreciation of Mr. Rice’s paper. He
(Mr. Morgan) had recently designed an electrostatic
flame indicator, which had been found very useful in
laboratory experiments on gas and dust explosions, and
it occurred to him to suggest that a similar indicator
would be more reliable than those employed by the
author. A full account of that instrument was given in
Engineering of January 8, 1915. He was interested to
observe the author’s remarks on super-dusting. The
diminishing effect of excess on the explosibility of coal
dust was the subject of a communication by him (Mr.
Morgan) to the Institution in March last, and in the
discussion Mr. Henshaw had cited a case in his mining
experience in which excess of dust appeared to have a
retarding effect on an explosion. The author stated
that retardation had been observed by him when the
excess had been placed close to the firing cannon, and
that under no other condition had super-dusting proved
to have a noticeable retarding effect. That was a some-
what puzzling statement; it was hardly conceivable that
the explosibility of a given dust depended on the posi-
tion in which it was placed relatively to the igniting
medium. Perhaps what * the author desired them to
understand was that at a position in the gallery remote
from the cannon there was insufficient atmospheric dis-
turbance to raise an excess of dust, and that it was for
that reason that no retardation was experienced. The
curves at fig. 6 were extremely interesting, but unfor-.
tunately they were not very fully explained in the text.
It was noticed that as abscissae the values plotted were
the ratio of volatile combustible to the total combustible
in the dust, and for ordinates was taken the quantity
of inert matter necessary to prevent explosion. At first
sight there did not appear to be any rational connection
between the quantities chosen. The crucial question
was : Why the ratio of volatile to total combustible?
There was an opinion in this country that the relation
between the volatile and the total combustible consti-
tuents of coal had no definable connection with
explosibility. That was certainly his own opinion at
present, and he believed it was also that of others. As
against that opinion, there was the remarkable regu-
larity of the author’s curves, and it would be very
surprising to find that the regularity was accidental. He
would also ask the author if he had observed whether the
roughness of the walls of his gallery had any increasing
effect upon the violence of a coal dust explosion. Atten-
tion had been drawn to the possibility of that pheno-
menon in his (Mr. Morgan’s) paper to the institution
to which he had referred. There seemed no doubt that
the surface of the gallery had a modifying effect upon
an explosion, but direct proof by investigation on a
large scale appeared to be wanting. The author had
had experience of a smooth gallery, and one made to
imitate a mine roadway; he would doubtless be able to
say, therefore, whether any effect had been noticed
which was attributable to the character of the surface
of the gallery.

Mr. H. W. G. Halbaum (Cardiff) wrote that, in his
opinion, Mr. Rice’s paper was a most valuable record.
It demonstrated the practical utility of the principle
that the air current itself was the best selector of dust,
and the success of the plant proved conclusively that it
was sufficient to break up the mass by a purely hammer-
like action, leaving the air current itself to select the fine
dust required. That principle of the automatic selec-
tion of dust by the air current was evidently capable of
extension to the case of stone dust, as well as to the
case of coal dust. He would like .to ask Mr. Rice to
state precisely what was meant by, say, a “ 240-mesh ”
screen. The first paragraph of the section entitled
“ Point of Ignition ” would greatly surprise some
authorities in this country, if one might judge by the
hostile reception they accorded not so long ago to a
suggestion that an excess of coal dust might ’ have an
influence analogous to that exerted in other cases of
combustion where one of the agents was much in excess
of the other. Personally, he had never been able to
agree that chemical laws acted differently in different