June 28, 1918.

THE COLLIERY GUARDIAN.

1301

Dr. Haldane said he was very delighted with Mr.
Storrow’s results, which came out in an extremely
nice and instructive way. With regard to the appa-
rent mystery of those two laws, why the one passed
into the other, he did not think there was really any
mystery about it if one thought what was really
happening in air. Air consisted of molecules, which
were flying about at a velocity of about one-third of
a mile per second, were colliding with each other and
glancing off. One could easily see why the ventilating
pressure should follow the ordinary rule, that the flow
or the velocity varied as the square root of the pres-
sure. Think of the work done by the fan. First of
all it imparted velocity to a certain mass of air. If
one doubled the velocity, one doubled the mass of
air; that in itself doubled the work of the fan. But
one was also imparting double the velocity to that
amount of air. The work varied as the square of
the velocity, so that the work done by the fan varied
as the cube of the velocity. That was the ordinary
law, which worked out perfectly well under all
ordinary practical conditions in considering the work
of the fan. Now think what was happening from
the point of view of the kinetic theory of gases. The
gas as it moved along had particles which were shoot-
ing out on to the edge of the tube, which, from the
microscopic point of view, was not perfectly smooth.
It did not reflect the molecules like light was re-
flected ; it had a rough surface. The molecules were
coming back into the main current from that, and
the rate at which they stepped off and stepped on,
so to speak, depended on the rate at which they
were going, which varied with the temperature, etc.
That went on whatever the velocity of the air, which,
moreover, was a mere bagatelle compared with the
velocity at which the molecules were moving, viz., at
about one-third of a mile per secend, as compared
with about 2 ft. per second for the air current. With
the one law the work varied as the cube root of the
velocity, and with the other as the square. Conse-
quently, if the velocity were lowered one came to a
point where the cube root law got so small that it
accounted for nothing, and the square root law became
relatively a much greater thing. If one increased
the velocity, the cube root law became so enormous
that it effectually swamped the other, but they were
both operating the whole time, and both held, good
at all velocities. It was only in the case of air going
through porous material, or in the case of the velocity
of the air current being reduced to something ex-
tremely small, that one got the flow varying directly
as the pressure. One had only to reduce the velocity
low enough to get it in the ordinary airways of
the mine. It had really nothing to do directly with
the size of the particles, it was the velocity of the
air current as compared with the amount of surface.
He thought the whole thing became clear from the
standpoint of the kinetic theory of gases. Anyone
who wanted to understand it would find a very good
account in Tate’s “Recent Advances in Physical
Science,” published in the ’seventies. To put the
case in other words, it was the viscosity of the air
current which came in.

Preventing Gob Fires.

Mr. John T. Greensmith (Brodsworth Main
Colliery Company Limited, near Doncaster) in a
written communication stated the late Sir Arthur B.
Markham and the late Mr. Fryar, of Messrs. Barber,
Walker and Company, along with Dr. Haldane, had
introduced the question of research work relating to
gob fires, and undoubtedly valuable information as
the result of experiments had been gathered at the
Doncaster Coalowners’ Laboratory. He had had con-
siderable experience in dealing with gob fires at the
Brodsworth Colliery, and his remarks only referred
to the practical side of the question. Thorough super-
vision and attention to detail were absolutely neces-
sary, including the stowing up of all gate roads in
such a manner that there was no possibility of air
reaching the abandoned areas. Where falls occurred
along the coal face, and especially in the proximity
of gate packs, they should be cleared, the timber
extracted and the place made solid, using soil or sand
around the edges where the fall took place. It was
not always convenient to do that while the face was
at work, as it ought not to interfere with coal turn-
ing, but the place where the fall occurred should
be indicated, and attention to that work should not
be delayed beyond one month. A tabulated record
was kept in the manager’s office, showing the stall
number, date of fall, length of fall, distance along
the face (right or left, as the case may be), date
recovering commenced, material extracted, remarks,
and the name of the official in charge. The colliery
surveyor was responsible for maintaining that record
up to date, and it was accompanied with a plan show-
ing the course of the ventilation, position of falls
and stoppings in the abandoned area. After a fall
frequent samples of air were taken and analysed by
the chemist, and reports of such were handed to the
agent and manager. Directly a fall took place fre-
quent cross-packing was carried out in the wastes, in
order to shut off the ventilation from the affected
area and to prevent “breathing.” Careful attention
was required to be paid to the method of ventilating,
also the position of doors, levels, gateways, etc.
Special attention should also be given to those parts
where coal was being worked in close proximity to
faults, to see that stowing was efficiently done, and
that the gate packs were buried by ripping down the
roof as quickly as possible. It had been found by
temporarily connecting a district on the low side of
a fault to one on the rise side, for the purposes of
ventilation, and then gobbing off the same, that should
slight leakage take place heating was very often the
result. Keen supervision on the part of all officials
on the maintenance of straight working faces, effi-
cient packing, and withdrawal of pitwood at the
proper time played an important part in the avoidance
of falls on the working face, which after all gave
nine-tenths of the gob fire trouble. Every provision
in the way of fire extinguishers, sand, air pipes and

suitable supports was arranged prior to tackling a
fire, and the vicinity was thoughly stone-dusted be-
fore commencement. Thermometers were kept at each
suspected place, and the temperature was registered
at the end of the shift by the official in charge. An
efficient staff of officials and men on all shifts was
arranged to attend to that class of work, and on no
account were they allowed to be taken off except by
the manager’s orders. Detail was absolutely necessary
in a pit liable to spontaneous combustion, and at
Brodsworth it had been a great advantage to have
the services of Mr. Storrow as chemist under Dr.
Haldane, so that they might know exactly the state
of the atmosphere not only in the vicinity of a fire,
but by taking samples of air each shift in any sus-
pected area they knew from the analyses what was
taking place, and were able to avoid waiting until a
fire actually took hold. Apart from the question of
fires, frequent analyses were taken of air from the
returns and coal faces, and dust samples were taken,
as also analyses of various parts of the seam where
necessary.

Influence of Capillary Forces.

Mr. H. W. Halbaum (Cardiff) wrote that he had
formed the opinion that the views set forth in Dr.
Haldane’s paper and those expressed by Mr. Storrow
were surveying notes gathered on the same ground.
The one paper dealt with the solution of solids in
solids; the other dealt with phenomena ostensibly
connected with velocity and pressure, but which very
possibly were really connected with solutions due
mainly to capillary forces, and only partly due to
water-gauge. The path or paths of the “ current ”
through Mr. Storrow’s “stopping” certainly approxi-
mated to capillary ducts, and it was quite certain that
capillary forces would come into play and produce
effects which would possibly modify, or more probably
accentuate, and most certainly obscure, the real
action of the ostensible “pressure” shown by the
water gauge. It was clear that the complications
introduced by the capillary action would be most pro-
nounced when the capillary forces were largest
relatively to the total force; that was, when the water
gauges registered their lowest readings. A body
heated at one side would radiate heat from the other.
Water in the mine under normal pressure absorbed
gases, but promptly liberated them when drawn into
the partial vacuum obtaining in a pump or siphon.
In similar manner might not Mr. Storrow’s “ air
flow” through the artificial “stopping” be due to
greater adsorption of air on the side under the greater
pressure, and to the subsequent liberation of the same
on the side of the lower pressure? The question was
how to eliminate the effects of the capillary forces,
and how to determine whether those were of the
“ attractive ” or of the “ repelling ” order. After read-
ing what Dr. Haldane had told them, it was impossible
to grant that Mr. Storrow’s case was so simple as
Mr. Storrow himself appeared to think. The force
at work under such conditions was not entirely
measured by the water gauge, and he hardly expected
anyone to affirm that capillary action was confined
to liquids. Perhaps Mr. Storrow would say whether
he had tried the effect of moistening or drying the
material forming his stopping, and whether he was
sure that the same results would be obtained if the
pressures were reversed and the “current” made to
flow upward instead of in the downward direction.
It appeared likely that the papers of Dr. Haldane
and Mr. Storrow would lead them to some interesting
and valuable conclusions; but he firmly believed that
when those final conclusions were arrived at they
would still find the old law triumphant. That old
law stated without qualification that in the case of
fluid flow “the pressure varied as the square of the
velocity.” The law was a mathematical consequence
of the Newtonian philosophy. Any experiments
which appeared to contradict it should be discredited,
and always would be discredited. He was very far
from insinuating that Mr. Storrow’s work came under
that heading. The author had merely shown that
under certain circumstances the water gauge did not
represent the entire pressure. The object of the
writer’s intervention was to suggest the direction in
which they might look for, and probably find, the
balance of pressure which had escaped the author’s
observation.

Dr. Haldane said that Mr. Halbaum seemed to
think that whatever was the observation of the water
gauge it must be wrong. He agreed with Mr. Halbaum
so far that the two laws held good at all velocities,
but, as he had explained, the work done varied as
the cube of the velocity in one case, and in the
other as the square, and the consequence was that if
one lowered the velocity the direct law pressure be-
came entirely predominant. If one increased the
velocity it was the cube root law. It was really quite
intelligible, and did not contradict the Newtonian
philosophy. But if one said that the Newtonian
philosophy was going to hold good whatever the
observations might be with the water gauge, and that
the water gauge must read something else than what
it did read, then it converted the Newtonian
philosophy into sheer nonsense. They were only con-
cerned with what the water gauge did say; what it
ought to say according to the Newtonian philosophy
was another thing. If it did not say that, so much
the worse for the Newtonian philosophy, but there
was no real contradiction. He thought there was no
real contradiction between anything which Mr.
Halbaum had said and with what had been said in
the paper with regard to capillaries. Of course, when
one began to analyse what happened when the mole-
cules hopped off and hopped on the tube, so to speak,
they stuck against the side owing to capillarity; every
surface attracted the molecules of gas, as Mr. Graham
had shown so distinctly with regard to coal. If the
surface were perfectly smooth, and the particles were
simply reflected from it as light was, then there would
be no direct law at all. But they were not; they
stuck on the surface. That was the capillarity which
Mr. Halbaum referred to.

Mr. J. T. Storrow, in reply, thanked Dr. Haldane
for his exposition of the behaviour of the two laws;
it was put very clearly, and much better than he
himself could possibly have done. With regard to
Mr. Mowat’s question in respect of the fissures in
the coal as the face left the goaf, that was to say,
as the face advanced, in the pits with which he had
been connected they always got the weight on to the
goaf as quickly as possible. They were all pits liable
to spontaneous combustion, and therefore the fissures
were closed up as soon as ever they could possibly get
them closed. If, however, they found places that did
not close up by Nature’s remedy, weight, they had
to stop them up with fine materials—generally soil—
as soon as possible. He had no experience of any goaf
which was in any way loose except right on the
face. The soil was put in in its natural condition.

Mr. D. M. Mowat thought it would be interesting
if Mr. Storrow would try a further experiment to
see what the resistance would be in the same tube
if it were filled with wires, that was, to reduce the
continuous interstices, taking a foot of the tube and
ramming it full of wires of small diameter to see how
the resistance varied in that case. That would be
more in the nature of a crevice or a crack which passed
from one road to another, not a space which was con-
solidated near the face, but more in the nature of
a continual break in the strata.

Mr. Storrow thought the suggestion was a good
one, and said it would be very interesting to do some
experiments on those lines by taking a single capillary
tube as a base and working from that.

The President moved a very hearty vote of thanks
to Mr. Storrow for his paper, and proposed that the
discussion should remain open till the next meeting.
Perhaps before that Mr. Storrow would carry out the
task of the experiment referred to by Mr. Mowat,
if he had the time and inclination to do so.

The vote of thanks was carried by acclamation.

Oxidisable Constituents of Coal: American Notes.

The President said there were two other subjects
on the agenda open for discussion, first, the paper by
Mr. J. Ivon Graham on the “Oxidisible Constituents
of Coal,” * which was discussed at the Newcastle meet-
ing, and the other “American Notes,” f by Mr.
Samuel Dean.

Mr. J. Ivon Graham said that Mr. Mowat had
mentioned the question of the oxidisation of wood, and
had pointed out that there seemed to be a similar
behaviour to the material which was found to be
insoluble in pyridine, and which was now generally
considered to be a degradation of the products of
cellulose. He though that showed that one got the
same type of oxidation in the case of dry wood as
in the case of coal. It showed that similar bodies
were present in the two, that was to say, in the wood
and in the cellulose degradation products which were
supposed to be present in the coal.

The President said that the discussion on that
paper, and also on “American Notes,” would be con-
sidered closed.

Votes of Thanks.

He moved a very hearty vote of thanks to the presi-
dent and council of the Royal Geological Society for
the use of their rooms for those meetings. They could
not be more comfortably housed.

Mr. J. B. Sneddon had much pleasure in seconding
the motion. He supposed it was a case where their
gratitude might be considered to be a lively sense of
favours still to come.

The vote was carried by acclamation.

Mr. W. D. Lloyd thought they would all agree with
the resolution which he had to propose. Every
member of the institution owed a great debt of grati-
tude to the president for the energetic and inde-
fatigable way in which he had carried out the duties
of the office during the past two years, and the way
in which he had spared the time to attend the meet-
ings. He was sure they would join with him in
carrying a vote of thanks to the president for pre-
siding, which he had much pleasure in proposing.

Mr. Stanley Atherton seconded the motion, which
was carried by acclamation.

The President said he was much obliged for the
motion and for the kindly terms in which it had
been proposed. It was a pleasure to him to do all
he could to further the objects of the institution.

* Colliery Guardian, September 14, 1917, p. 491.

+ Colliery Guardian, September 14, 1917, p. 493.

Queensland Coal Production, 1917.—The total output
amounted to 1,048,473 tons, valued at £597,360, compared
with 907,727 tons, valued at £389,348, for 1916, an in-
crease of 140,746 tons in quantity, and £208,012 in value.
The average value of the coal at the pit’s mouth (Ils. 4-7d.)
was 2s. 7-8d. higher. The greater part of the increased ton-
nage is due to the larger output of some of the principal
collieries in the Ipswich district. The output of the
Darling Downs collieries was very little more than in
the previous year, while that of the collieries in the Mary-
borough and Rockhampton districts and at Mount
Mulligan in the Chillagoe district was somewhat less
than in 1916. The yield of the collieries in the Clermont
district increased by about 18,000 tons.

Motors for Pit Locomotives.—An advantage of alter-
nating current compared with direct current in the opera-
tion of pit locomotives is that small transformer stations
permit of an efficient distributing scheme, and are cheaper
than converter stations. A new arrangement brought out
by Brown, Boveri and Company permits a high-speed
double-geared motor to be accommodated in locos of 50
to 60 cm. gauge. If the motor may project beyond the
frame of the locomotive the gauge may be yet narrower.
Five types of motor have been produced for 110 to 750 volts
at 1,250 r.p.m., 50 cycles, with gauges 450, 500, 500, 550,
600 mm., and corresponding horse-powers 6, 10, 15, 20, 25.
The motor pinion is placed immediately behind the arma-
ture. With 70 cm. driving wheels the speed ranges from
6-2 to 15 km. per hr., and the draw-bar pull per axle
from 450 to 1,090 kg.