December 29, 1916.

THE COLLIERY GUARDIAN

1275

to 30s., and ordinary steams 28s. to 29s. Monmouthshires
are relatively firmer, and range from 28s. to 30s.,
according to quality. The small coal market has a
stronger tendency, best bunkers being 19s. to 20s.
ordinaries 17s. to 19s., and cargo qualities 14s. to 16s per
ton. Bituminous coals show no change, No. 3 Rhondda
large being 28s. to 30s., and No. 2 27s. to 28s., with other
grades in proportion. There is no alteration in the best
brands of patent fuel, which are still quoted up to 37s, 6d.,
but secondary grades are 35s. to 36s. Cokes are in strong
demand and without change. Pitwood is still quoted at
49s. to 50s. per ton.

IRON.

Official figures last week again showed an increase of
production over shipments, and stocks now stand at about
170,000 boxes, or about 200,000 less than at the corre-
sponding date of last year. It is almost impossible to
obtain raw material except for Government contracts,
and only about 35 per cent, of the mills are at present
working. From week to week labour is becoming
more scarce owing to the drafting of men into the
steel works, and the general condition of the trade is un-
satisfactory. For Class A and B certificates there is still
some amount of competition, and rates are on the basis of
28s. to 30s. per box for standard sizes. The stock of large
plates is becoming depleted, and as much as 70s. has
recently been paid. Steelmakers generally are exceptionally
busy, and works are operating night and day in producing
material for munition purposes. There is a good demand
for light section rails at prices varying from <£15 to .£15 10s.
per ton. Welsh pig iron and steel bars are nominal, and
there is no alteration in the iron ore market.

Llanelly.

COAL.

There is hardly any alteration to report as to the
condition of the local coal market. Although it had been
agreed to resume work at the pits on Wednesday, there
were many absentees, and it is feared that the output for
th^ week will be far below normal. There is a weakness
noticeable for many sorts, but it is anticipated that as a
result of the cessation of work over Christmastide the
market will regain some of its firmness. Large anthracite
coals at present show the most weakness, whilst the other
kinds are going none too well. Large steams for inland,
however, however, are be ng keenly sought after, but
throughs and smalls for export are difficult to dispose of.
Manufacturing fuels are none too plentiful, and sellers for
the most part have as much as they can do to satisfy
customers’ requirements. This week’s quotations are
approximately as follow :—

Prices f.o.b.

Anthracite:—

Best malting large...

Secondary do. .......

Big Vein large.......

Red Vein do..........

Machine-made cobbles...
Stove nuts............

French do.............

Paris do..............

Machine-made beans ...

Do. peas.........

Culm .................

Duff..................

Other sorts:—

Large steam coal......

Through-and-through...
Small ................

Bituminous small coal...

Current L’st week’s1 Last year’s

prices.
29/6-32/
27/6-30/
25/6-28/
24/ —25/
37/6-40/

prices.
29/6-32/
27/6-30/
25/6-28/
24/ -25/
37/6—40/
37/6-39/6 37/6-39/6
38/ -40/ j 38/ -40/
37/ -39/ ! 37/ -39/
28/6-29/6 i 28/6-29/6 i 32/ -34/
20/ -22/ ! 20/ -22/ 1 19/ -20/
—■ 10/6-11/6 ; 7/ - 7/6
6/ - 6/6 | 2/ - 2/6

prices.
35/ -37/
33/ -35/
35/ -37/
33/ -35/
43/6-45/
! 44/6-47/
, 47/6-49/
! 44/6-47/

10/6-11/6 i
6/ - 6/6 '

27/ -28/6 27/ -28/6 1 22/ -24/
19/6-22/ ; 19/6-22/6 , 14/6-16/6
13/6-17/ ; 13/6-17/ j 6/ - 8/
17/ —19/6 17/ -19/6 ! 15/6-16/6

THE LONDON COAL TRADE.

Thursday, December 28.

Trade has been exceedingly quiet during the week. The
London Coal Exchange practically closed on December 22.
The decision of the London merchants not to meet on
Wednesday practically suspended all market operations for a
week. Fortunately, the majority of depots and wharves
have a fairly good stock in hand, and thus have been
enabled to cope with all the pressing needs and requirements
of those who left the ordering of the coal supply until a very
late hour in the Christmas week. The reports from the
depots show, however, that comparatively few householders
waited until the eleventh hour to secure a good supply, and
consequently the extra pressure has not been so heavy as in
former years. The railway companies also must have
worked heroically to bring forward the delayed loaded
wagons, for all the London merchants speak favourably of
the extra number of trucks brought through, in the first few
days of the week before Christmas. The current week has
been largely given up to bringing forward Government stores
and the increased “ troop trains,” so that very little tonnage
was expected, and very little has come forward. The
shippers, who have been largely instrumental in sending coal
to France, report that a critical period has recently been
satisfactorily passed. Gas companies and electrical works
had barely two days’ supply to fall back upon. The miners
in the Nord district patriotically agreed to work an extra
hour each day, and 2,000 to 3,000 miners were released from
the front; and this, with the tonnage sent over from Eng-
land, has practically overcome the difficulty. Twenty-four
vessels arrived in the River Thames for Friday’s market,
and since then no returns have been made, but a good
number of boats have been signalled as coming up the river.
Colliery representatives have practically ceased taking
orders, and await the resumption of work after the holidays.
The scarcity of empties at the various collieries has con-
siderably hampered the working, and some excitement has
been caused by the old question of “ pooling ” all the
wagons having revived. Steam coals are exceedingly
scarce, and shippers report that the export trade has been
quiet. Holiday conditions still continue in the London area,
and a good deal of congestion on the various railway lines
is apparent. Prices remain normally the same, but all
current quotations are recognised as being subject to accept-
ance from day to day. Slacks continue plentiful, and gas
companies appear to be well provided for. The Welsh coal
market has been more buoyant owing to the arrival of a
better number of vessels, but all best Admiralties are
reserved for Government use.

GAS ANALYSIS IN MINE FIRES *

By George A. Burrell and Frank M. Seibert.

The United States Bureau of Mines is conducting an
investigation of the factors involved in the origin and
spread of mine fires, and of the means by which such
fires may be prevented, limited, or extinguished; and in
this connection the authors have made gas analyses and
recorded observations on the condition of the atmosphere
in mines.

When an entire mine, or a section of it, has been
sealed to exclude air from a fire, the sampling of the
atmosphere within the sealed area becomes desirable
in order to determine the effectiveness of the stoppings
or dams in excluding air. If the stoppings are tight,
the fact is shown by a depletion of oxygen in the atmo-
sphere behind them.

Another reason for the systematic collection and
analysis of samples of air from the sealed area is to
obtain information regarding the advisability of remov-
ing stoppings. Disastrous consequences have sometimes
followed the premature re-opening of sealed areas; more-
over, fires have burned vigorously after external air was
thought to be entirely excluded. Hence, stoppings are
sometimes left in place for many months, and when
they are eventually removed much uncertainty is
sometimes felt as to the result.

When a burning section of a mine has been success-
fully sealed, the atmosphere within changes in compo-
sition. It loses oxygen, and cannot support combustion.
Then the coal, or wood, cools, until re-admission of air
cannot cause a blaze, and finally the temperature of the
fire zone becomes normal. The cooling requires con-
siderable time, because in a mine the embers and the
hot coal are so excellently insulated that they cool
slowly. The principal changes in composition of the
atmosphere in a coal mine during a fire are as follow :
Oxygen is consumed in the burning of coal, and is
absorbed by coal that is not on fire; carbon dioxide is
produced; methane accumulates; and carbon monoxide
and hydrogen form when the oxygen supply becomes
insufficient for complete combustion.

Atmospheric Changes in the Burning Mine.

The atmosphere in a burning section of a coal mine
loses oxygen not only by the combustion of the coal
but by oxygen being absorbed by the coal. This
absorption appears to be mainly a chemical combination
between the oxygen and certain unsaturated hydro-
carbon compounds in the coal, and the rapidity with
which it takes place depends upon the nature of the
coal. The action may be so rapid that the fire plays
only a minor part in depleting the oxygen of the air in
the burning section. This is particularly the case when
the area on fire is very small in proportion to the area
enclosed. That such .absorption takes place is fortu-
nate, because the removal of the oxygen in an enclosed
section is hastened, and the atmosphere more rapidly
becomes incapable of supporting combustion.

The rapidity with which coal absorbs oxygen is shown
by experiments performed by Porter and Ovitz. During
the first day after mining, 10 kilogs. (22 lb.) of coal from
Connellsville, Pennsylvania, absorbed nearly one-half
the oxygen in 10 litres of air. Slightly more than one-
tenth as much carbon dioxide was produced as would
have been obtained had all the oxygen absorbed com-
bined with carbon to form carbon dioxide.

Parr and Barker also have shown that the absorption
of oxygen by coal occurs rapidly, especially with freshly
mined coal, and that the absorption is very noticeable
even in samples of coal that have been mined two years.

Deficiency of Carbon Dioxide in Sealed Area.

The fact that oxygen is absorbed by the coal in mines
is confirmed by the authors’ analysis of many samples
of mine air. A very large proportion of carbon dioxide,
more than 4 or 5 per cent., in the atmosphere of a
sealed section of a mine, is unusual except near the fire.
Even in places where the oxygen has been entirely con-
sumed, no large quantity of carbon dioxide has been
found by the authors. A fire in a coal mine increases,
of course, the total quantity of carbon dioxide produced,
but if the samples collected from a closed section repre-
sent fire gases diluted by the atmosphere of those parts
of the section that are not on fire, the carbon dioxide
found is by no means proportionate to the oxygen con-
sumed in the fire. This deficiency of carbon dioxide
results from 'the absorption of oxygen by the coal with-
out (as is largely the case in the combustion of coal in
a boiler furnace) the formation of a proportionate
quantity of carbon dioxide.

In some mines methane escapes from the coal in
large quantities, and under extreme conditions the atmo-
sphere in some places may contain 50 per cent, or more
of methane in a very short time after becoming stag-
nant. On the other hand, samples collected from work-
ings in which the air had been stagnant for several
months did not contain methane enough to form an
explosive mixture, even if the proportion of oxygen had
been sufficient.	w

Formation of Methane by Mine Fires.

In a mine fire methane is undoubtedly formed from
the burning coal, and such methane is added to that
escaping from pores and cracks in the coal not on fire;
but because the area on fire may be small as compared
with the total space enclosed, the proportion of methane
produced by the fire may be small throughout the larger
part of this space. In one instance, samples collected
directly over a fire contained only about 1 per cent,
more methane than samples collected behind a stopping
2,000 ft. from the fire.

Usually the oxygen supply in a burning section of a
mine is quickly reduced; then incomplete combustion
begins, and hydrogen and carbon monoxide form at the
fire. Carbon monoxide is so poisonous that deadly pro-
portions are liable to be present in all parts of the

* Coal Trade Bulletin.

section. Samples of gases collected by the authors near
a fire, where the coal was intensely hot and the oxygen
content of the mine atmosphere was only 2 per cent.,
contained 1*5 per cent, of carbon monoxide. The part
that carbon monoxide plays in gas explosions during
mine fires has aroused considerable conjecture, but the
data thus far accumulated by the United States Bureau
of Mines indicate that the danger from the formation of
explosive mixtures of carbon monoxide, or of hydrogen
is subordinate to the danger from methane, because in
some mines methane accumulates rapidly in any place
where the atmosphere becomes still, and enough is soon
present to form an explosive mixture with an inrush of
air. ' The explosive limits of a mixture of carbon
monoxide and air lie between about 14 per cent, (low
limit) and 75 per cent, (high limit) of carbon monoxide.
The limits for a mixture of methane and air lie between
about 5*5 per cent, (low limit) and about 13 per cent,
(high limit) of methane. These limits apply to ignition
of the gas at ordinary temperatures and pressures by an
electric spark. Other methods of ignition, changes in
the shape of the containing chamber, differing pressures
and temperatures, change them somewhat. For
example, the explosives engineer of the Bureau of Mines
has found that mixtures of natural gas and air used in
testing explosives could be partly inflamed by the flash
of a blown-out shot of black powder when as little as
4*07 per cent, of gas was present, whereas the authors,
using an electric spark, and confining the gas-air mix-
ture in a Hempel explosion pipette, could not ignite a
mixture containing less than 4*8 per cent, of gas, and
with this percentage of gas obtained only a slight inflam-
mation throughout the mixture. The explosion was not
strong until the mixture contained 5 per cent, of gas.

As the necessary proportion of carbon monoxide has
not been detected in the afterdamp gases the authors
have examined, they believe that the possibility of explo-
sions from the formation of carbon monoxide and air
mixtures is remote. Still, a point would undoubtedly be
reached at which the addition of less than an explosive
proportion of carbon monoxide to be a non-explosive pro-
portion of methane would result in the formation of an
explosive mixture. The production of hydrogen in a
fire area seems to be even less than that of carbon
monoxide; hence the danger from the formation of
explosive mixtures of hydrogen is still more remote.
Other combustible gases, such as ethylene (C2H4), may
be produced by a fire in a mine, but seemingly they
are formed in such small proportions that their value
in indicating the progress of the fire, as shown by gas
analysis, or their importance as factors in explosions,
need hardly be considered.

Experiment shows that the flame of a candle or of a
miner’s open lamp is extinguished when the oxygen con-
tent of the surrounding air falls to about 16 or 17 per
cent.; and the authors obtained the following results by
placing flames in a gastight bell jar, and allowing them
to burn out :—

Composition of Residual Atmospheres that
Extinguished Flames.

Percentage composition
of atmosphere.

Flame.	CO2. Oa. N2.

Wolf lamp .............. 3'00	...	16*50	...	S0'50

Acetylene lamp.......... 6*30	...	11'70	...	82 00

Natural gas*............ 3'25	...	13'90	...	82'85

Candle.................. 2'95	...	16*24	...	80'81

*CH4, 82; C2H6,16'4; N2,l*5; CO2, 0'1 per cent.

Although a mine fire that is well under way when
stoppings are built may continue to bum in an atmo-
sphere containing less than 15 or 16 per cent, of oxygen,
yet the above results afford some basis for estimating
the amount of inleaking oxygen required to keep a fire
burning, or to cause a smouldering fire to burn more
strongly. The following instances are instructive :—

A fire in a heavily timbered stope in a metal mine
had been brought under control by sealing the section,
but as air was slowly admitted to re-open the section,
the fire blazed when the oxygen content of the atmo-
sphere reached 17 per cent. A fire in a timbered airway
of an anthracite mine burned more vigorously when the
atmosphere of the airway contained approximately 17
per cent, of oxygen. In each of these cases, of course,
the fires had smouldered in an atmosphere containing
a smaller percentage than this.

Conclusions as to the approximate length of time a
sealed mine or section of a mine should remain clo-sed
after a fine has been brought under control are hard to
reach, because conditions differ at different fires.
However, it is certain that analysis of a sample of the
atmosphere in the mine or section will show whether
the fire is well sealed, and will enable more intelligent
conclusions to be drawn regarding the length of time
that stoppings should be kept up. When the oxygen
in an area is almost or entirely consumed, combustion
necessarily must cease, and the question then is how
long the embers can retain heat sufficient to cause them
to re-kindle on the admission of air.

Precautions in Sealing.

In sealing any part of a mine certain precautions are
observed, for it is a matter of common knowledge that a
fire continues to burn for some time after stoppings are
built, and the heated gases, unless they can escape
readily, exert considerable pressure on stoppings. More-
over, an inrush of air after the cooling of the imprisoned
atmosphere must likewise be guarded against, or the fire
may start afresh; again, dangerous explosions may
result if the outflow’ of gases from a fire is checked too
suddenly. At some fires the precaution has been
adopted of having a pipe with an elbow, placed in the
upper part of the dam, so as to dip into a vessel con-
tinuously supplied with water from a pipe fitted with a
tap. The overflow from the barrel is allowed to run off.
By this arrangement the outflow of gas is checked
gradually, and is finally stopped when the pressure of
the water over the outlet of the escape pipe equals that