874

THE COLLIERY GUARDIAN.

October 29, 1915.

the colliery company, and the total capital cost compared
with the saving in working expenses and the enhanced
income to be derived from the improved product. Finally,
an agreement would be arrived at, and the order placed with
the association. No work would be actually executed under
any fixed contract price; but, if the firm could afford to
pay for the plant, they would do so under an arrangement
whereby the association executed the whole of the work at
cost price, plus a net profit of 10 per cent. Foundations,
buildings, and such like work would be actually carried out
by workmen employed directly by the association.
Machinery would be sub-let to engineering firms, who would
execute the work to the plans of the association. In case
the colliery company were unable to find the necessary
capital for the erection of the plant, then the association
would provide the capital and take in repayment 50 per cent,
of the gross profit earned by the plant until the cost of the
plant, plus 10 per cent., was repaid; 5 per cent, interest
would be charged on any outstanding balance. Any case
of this description would be subject to the decision of the
board of directors, and for the purpose of discussing financial
questions a member or director of the firm of bankers
should be in attendance; in fact, it would probably be
desirable that the bank should be directly represented by the
appointment of a director on the board of the association.
The whole of the financial arrangements would be left to the
bank, and the profits which would undoubtedly accrue would
first be used to repay the members the amount which they
subscribed in the first instance, and would afterwards be
allowed to accumulate until a sufficient reserve of capital
was obtained to avoid borrowing, after which the profits of
each year’s working might be divided amongst the members,
a percentage being set aside for the establishment of research
scholarships in the universities and defraying the cost of
testing new ideas and inventions and other experimental
work.

Mr. E. B. Wain said the proposal struck him as
tending to destroy individual effort, which, after all,
was the basis of all progress. It would place the con-
trol of the coal trade in the hands of certain individuals,
who would act upon certain severe and definite lines.
They would have a Napoleon of the coal trade, who
would order what had to be done under all circum-
stances. We were not sufficiently disciplined to accept
such a position.

The President said Mr. Futers had broken new
ground, but his ideas were perhaps too much in
advance; they were rather Utopian. He could not
quite see every colliery in the country, or in a district,
subscribing to purchase plant for one of their number;
nor, with his knowledge of banks, could he see banking
companies lending money for Schemes, and trusting to
be paid out of profits. Supposing the plant did not
realise expectations as to economy and profit, what
would be the position of the bank or the guaranteeing
collieries in such a case? Another point would be that
it would do away -with the initiative of firms manufac-
turing plant and apparatus. He proposed a vote of
thanks to Mr. Futers for his paper.

This was seconded by Mr. F. E. Buckley, and
adopted.

Mr. Futers, in responding, said the association
would be able to assist not only in finding capital, but
in giving the benefit of experience and technical
knowledge.

Price of Coal (Limitation) Act.—The following statement
was handed to the Board of Trade at a deputation of the
Coal Merchants’ Society on October 12, 1915, with regard
to certain dubious points that have arisen under the above
Act :—Clause 3 says that “if in any proceedings any
question is raised as to the corresponding price of any coal,
the Court shall refer for decision to the Board of Trade.’’
There will be no doubt a deal of litigation saved and busi-
ness men generally will feel more comfortable if the Board
of Trade would indicate at earliest what its decision would
be on the following points :—

1.	Supposing that a contract was made between
merchant B. and colliery A., on, say, June 10, 1914, for
the purchase of coal to be delivered to the merchant over
the period July 1, 1914, to June 30, 1915. That coal is
actually offered for sale by the colliery, and bought, during
the period 1913 to 1914, although not delivered. Would
this be the corresponding price for the purpose of the Act ?

2.	If merchant B. has contracted with colliery A. for
delivery for any time coming under the Act, say
12 months forward from July 1, 1915, or six months
forward from October 1, 1915, and had no previous con-
tract with this colliery, would the amended price be
4s. over the colliery contract price to others made 1913
or 1914, according to the answer to the previous question,
or would it be 4s. over the colliery current prices from date
to date during July 1, 1913, to June 30, 1914? Further,
if so, would it be 4s. over the current price for London,
or 4s. over the highest current price obtained by the
colliery ?

The following reply has been received :—

Board of Trade (Railway Dept.),

7, Whitehall Gardens, S.W.
October 20, 1915.

With reference to the note which was handed in at
the deputation from the Society of Coal Merchants on
October 12, I am directed by the Board of Trade to say
in reply to the first question that a contract made on
June 10, 1914, for the purchase of coal to be delivered
between July 1, 1914, and June 30, 1915, may be a
contract to which reference should be made for the pur-
pose of ascertaining a corresponding price.

I am to add that, generally speaking, the date of the
contract is the determining consideration, but that the
time specified for delivery might be a relevant circum-
stance in determining whether the contracts concerned
were made “under similar conditions affecting the sale.’’

As regards the second question, I am to say that for the
purpose of determining “ corresponding prices,” contract
prices would be compared with contract prices, and current
prices with current prices, and that in the case of contracts
with new buyers, the comparison would be with similar
contracts made with other buyers on or about the same
date in the twelve months ended June 30, 1914.

(Signed) W. F. Marwood.

Experiments with Coal Dust at the Derne Gallery.*

In consequence of the length of the experimental
gallery having been doubled (to 200 m.), the force of
the explosions produced in the experiments is found to
have considerably increased, but the concrete lining has
proved strong enough to stand the additional shock.

Among the experiments carried on during 1914 were
a series for the purpose of ascertaining how far coal dust
explosions will extend in presence of zones of strewn
coal dust. To start the explosion, lOkilogs. of coal dust
were disseminated in the first 10 m. of the gallery, dust
(at the rate of 1 kilog. per running metre) being placed
on the lateral shelves beyond that point. The amount
of dust in the air of the gallery was 400 grammes per
cubic metre of space—a quantity corresponding to the
maximum explosive violence. The length of the dust
zone was increased by 10 m. after each experiment. The
igniting charge consisted of 200 grammes of gelatine
dynamite, fired from the mortar in the explosion
chamber. With a 10 m. dust zone, the dust was merely
stirred up by the explosion; and with a zone of 40m.
the flame did not extend beyond the branch; but when
the zone was increased to 70 m. the flame projected
10 m. beyond the mouth of the gallery, the distance
increasing, pari passu with the length of the dust zone,
to 40 m. with a zone of 100 m. With zones up to 60 m.
the length of the flame was about double that of the
zone, except in the case of the 40 m. zone, when it
stopped at 67 m., that is to say, the place where the
cross section of the gallery is larger than elsewhere, a
branch being intended to start from this point. As has
been observed in mine explosions, the propagation of
the explosion is checked by the sudden expansion of the
gases in the increased area. The increased effect
obtained with the longer zones is ascribed to the
damming up of the mixture of dust and air in front of
the explosion, the result being more rapid propagation,
which, in one instance, attained a velocity of 250 m. per
second.

For zones longer than 100 m., the amount of dust
per cubic metre of air space was reduced (beyond the
first 70 m.) to 200 grammes, in order to protect the
gallery from undue strain; and on these lines the zones
were extended progressively to 160 m., it being found
that any dust placed beyond this point was simply
blown out by the oncoming air. In the experiments con-
ducted under these conditions, very violent explosions
were obtained with the reduced amount of coal dust.
The appearance of two flames in close succession, each
accompanied by a sharp detonation, was frequently
observed at the mouth of the gallery.

The explosive effect appears to be influenced by the
state of the weather. As an instance of this may be
mentioned one experiment that was performed on a wet
day, with the wind opposite the mouth of the gallery.
The amount of dust used was equivalent to 400 grammes
per cubic metre for the first 30 m., and 200 grammes for
another 70 m. Instead of the usual 2-6 seconds, the
explosion lasted for some time, with repeated ebb and
flow in the front portion of the gallery; and it was not
until seven seconds had elapsed that the explosion
advanced quite suddenly, and the flame issued from the
end of the gallery with violent detonation.

In a series of experiments in which the coal dust was
ignited by a firedamp explosion, various amounts of dust
were used, ranging from 70 to 200 grammes per cubic
metre of air space. The most violent explosion that the
gallery could be expected to stand was produced by the
last-named amount, which was afterwards used in the
experiments with preventive media. Since most of
these media require a strong mechanical impulse to set
them in operation, they cannot be tested with weak
explosions;. and, moreover, explosions which, though
weak, are capable of extensive propagation by coal dust,
are so difficult to produce in the test gallery, that their
occurrence in practice was considered doubtful. Never-
theless, it was found possible to produce explosions of
this kind in the gallery by sprinkling the coal dust on the
floor alone, and not on the lateral shelves. A long series
of experiments was conducted under these latter con-
ditions, and showed that a considerably larger amount
of dust (at least 500 grammes per cubic metre) is needed
to propagate the explosion right through the dust zone;
and even then the explosion travels slowly. With 600
grammes the explosion extended to the further end of
the gallery, even when the dust zone was restricted to
100 m.; but the total time required averaged 5-7 seconds,
equivalent to a velocity of only 35 m. per second. On
increasing the dust zone to the full 200 m. of the gallery,
a velocity of 50 m. per second was attained.

The cause of this retardation is that the dust on the
floor—and especially in the first portion of the zone, that
is to say during the first stage of development of the
explosion—is not in a favourable position for being dis-
turbed by the explosion’s force, especially since, owing to
the circular section of the gallery, it occupies rather
less than half (about 0-42) the total width of the gallerv.
The result is that the dust spreads out without rising to
form the thick cloud necessary for producing a violent
explosion. When, however, the explosion was started
with an explosion of firedamp, as little as 200 grammes
of dust per cubic metre sufficed to propagate the
explosion right through the gallery, and at the same time
the velocity increased to between 50 and 91 m. per
second.

Experiments were also made on the inflammabilitv
and explosibility of two samples of coal dust from local
mines, one containing 16 per cent, of gas, and the other
containing only 37 per cent, of very fine particles. Both
were found to be explosible, but to a smaller extent than
the fine bituminous coal dust (26 per cent, of gas)
ordinarily used in the gallery. A specimen of a dusty
coal from the thick seam at the Pinghsiang Collierv.

* From Gluckauf.

China, was also examined for the explosibility of the
dust. In point of coke, gas, and moisture content, this
specimen was almost identical with the standard dust
used in the gallery, except that the ash content was
14-7 per cent., in place of 7-4 per cent. The results of
the tests were practically the same as those furnished by
the local coal dust.

Experiments with Wet Zones.—Wet zones are exten-
sively used in Westphalia for preventing the spread of
explosions, and are generally regarded as a valuable
means to this end, though they are liable to cause
“ creeping,” and are inconvenient and unhealthy to the
miners. Their effect is to prevent any floating coal
dust, so that there is nothing to feed the flame, any dust,
moreover, that is driven forward by the explosion being
deposited on the wet walls. The evaporation of the
water also lowers the flame temperature, whilst the
floating spray has a direct extinctive action.

Experiments with wet zones were carried on before
the gallery was lengthened, but were, as a rule, unsuc-
cessful. In the lengthened gallery the zones are
arranged to begin about half way along, so that the
explosion has 100 m. in which to develop and attain
considerable power. Coal dust is placed on the lateral
shelves, at the rate of 400 grammes per cubic metre of
air space, for the first 70 m., and at the rate of
200 grammes for the next 30 m., the same quantity
being strewn on the floor for another 60 m. The -water
is sprayed from nozzles, as in ordinary mining practice,
one of them bein£ arranged so as to form a water curtain
occupying the full cross section of the gallery. Three
nozzles were used at first, one at 102, another at 107,
and a third at 113 m. from the explosion chamber,
enabling a wet zone, 15 m. long, to be produced between
the 97th and 112th metre, or 103rd and 108th metre,
according to the direction in which they are turned.
This zone is shorter than those in practice, but on
the other hand the free zone is also shorter than is
usual in a mine, and therefore the force of the explosion
is less. The water issues under a pressure of eight
atmospheres, which gives a powerful spray impinging
against the sides of the gallery. The nozzle taps are
turned on 1| minutes before the exploding charge is
fired, and are left open during the explosion. This zone
was insufficient, however, to arrest even a purely coal
dust explosion, no difference being produced by the
inclusion of the water curtain. The sole effect was to
retard the explosion, so that it took 1-8—2-1 seconds to
reach the mouth of the gallery, instead of about half
that time; and the detonation at the mouth was less
powerful. The extension of the zone to 24 m., by the
provision of a fourth nozzle at 122 m., also failed to
arrest explosions, though a suspensory effect was pro-
duced, the explosion then breaking through the whole
zone and nearly or quite reaching the mouth of the
gallery. Replacing the nozzles with rose heads, which
discharged more water, had little effect. These heads
were therefore taken off, and the water was allowed to
issue from the open ends of the 1 in. pipes, at the apex
of the gallery, splash boards being mounted half way up.
Of course, these conditions could not be copied in
practice, the volume of water being so great as to flood
the floor for a long distance; but the object was to
obtain an intensive wet zone. At first only one jet of
water (at 107 m.) was turned on, which watered about
10 m. of gallery; but this failed to arrest the explosion
completely, though so far weakening it as to cause it to
die down within the next 40 m. This zone entirely
failed to stop a firedamp explosion with a coal dust
charge of 200 grammes per cubic metre provided the full
length of the gallery, the explosion reaching the mouth,
with powerful detonation, in 1-3 seconds. Even when
three jets were used, the explosion traversed the whole
gallery in 1*8 seconds, with its power unimpaired, a cloud
of dry, unconsumed coal dust issuing in front of the
flame. In these circumstances it was decided not to
proceed further by extending the wet zone, the system
having proved unsuitable in conditions approximating to
those of practice. The chief reason for the failure is
that the amount of water vaporised from the sides of the
gallery by the explosion flame is not enough to quench
the latter, which is large in volume and travels at very
high velocity. On the other hand, the high pressure
developed by the explosion prevents any water issuing
from the nozzles and pipes during the passage of the
flame.

Different conditions would arise if the wet zone were
situated close to the seat of the explosion, since, in the
absence of firedamp, the explosion would not then attain
its full power and velocity, and the water would be
able to extinguish the flame. Experiments are still
being conducted with concentrated wet zones produced
by storing water in troughs, which are overturned by the
force of the explosion. So far as they have gone, these
experiments give better results than the wet zone
described above.

Experiments with Stone Dust.—Several methods of
employing stone dust for checking explosions have been
proposed. According to one, the dust is plentifully
strewn over the floor, sides and timbering of a gallery,
so as to form a long zone; whilst in another—corre-
sponding to concentrated water zones—large quantities
of the dust are piled up at one or more points in the
sectional area of the gallery, so that they may all act
at once on the explosion flame. This latter method was
tried, as likely to be the more effective. The simplest
way to prepare such a concentrated dust zone is to place
the dust on transversely-arranged boards or shelves near
the roof, since the dust is then more easily dislodged by
the explosion than when contained in boxes or troughs
which must be overturned or destroyed before the dust
can come into action.

Barrier shelves on this principle were arranged half-
way along the gallery, where the latter is of square