810

THE COLLIERY GUARDIAN.

April 18, 1913.

not inflammable, for the velocity of the current
is a factor of the result.

We will now proceed to consider the first
series of experiments, which were conducted in
a rectangular iron gallery, I4|in. high, 10 in.
broad, and 24 ft. long. This gallery was open
at one end, and at the other was connected, by a
short fan drift, to a Sirocco fan which drew the
air and gas from a suitably fitted chamber. The
dust was admitted into the chamber, and there-
fore on the intake side of the fan.

Generally, the arrangements were such that a
required mixture of inflammable gas and air
could be forced through the gallery at a required
velocity, and that dust could be allowed to fall
into the intake and be carried by the air-current
through the fan and along the gallery.

By experiments with an anemometer in the
gallery the velocity of the current was deter-
mined for any given speed of the fan. These
measurements were repeated at frequent intervals
during the experiments. It was found that the
addition of magnesia dust to the current made
no measurable difference in the velocity of the
current.

A sampling apparatus was fixed in he centre
of the gallery, and arranged so that a sample
could be drawn off continuously through a
narrow tube during a test. By drawing off
samples at the top and bottom of the gallery it
was shown that half-way along the gallery the
mixture of air and gas was perfect at all
velocities of the current. The Sirocco fan was
found to act as a thoroughly efficient “ mixer ”
of gases which are drawn into it together. The
source of ignition was a naked Davy lamp placed
16 feet from the fan drift. A glass window
allowed a full view of the gallery when the lamp
was placed, and for some distance on either side.

The preliminary experiments were carried out
with coal gas, but pentane was used for the
systematic experiments.

The mode of experimenting is described in the
report, and will be found in the abstract which
we give elsewhere.

In the preliminary experiments in which coal
gas was used, with velocities up to 600 ft. per
minute, a flare could be obtained. On adding
calcined magnesia or stonedust to the current no
effect was produced, except an increase in the
luminosity of the flame.

Pentane was used for the systematic experi-
ments. The “ lower limit mixture ” of pentane
and air contains, according to an experiment,
about 1*35 per cent, of pentane. The most
explosive mixture contains about 25 per cent
The lower limit of methane is, according to the
Committee’s experiments, 5’6 per cent., and the
most explosive mixture, according to Dr. Otto
Branch, contains about 9 38 per cent.*

Taking the series of experiments with mixtures
of pentane and air in the order of increasing
velocity of current, the following results were
observed:—

A.	With a velocity of 280 ft. per minute and
084 per cent, of pentane, a well-defined
“ cap ” was observed. On passing a very fine
cloud of magnesia the cap became luminous,
but no “ flare ” was produced.

B.	With a velocity of 300 ft. per minute
and 1’31 per cent, of pentane, a well-defined cap
was formed. Fine coaldust was introduced
instead of magnesia, and a brilliant flame
spread forwards and backwards, filling the
whole gallery.

C.	With the same velocity and 1'34 per
cent, of pentane, a very fine cloud of magnesia
produced no change beyond an increased

* The Investigation of Mine Air. Edited by Sir
Olement Le Neve Foster and J. S. Haldane, 1905, p. 14. ’

luminosity of the cap. In this case the
current was heated in the gallery, so that on
reaching the flame its temperature was
90 degs. Fahr.

D.	Again, with the same velocity, the gas
was gradually turned on until first a “ flare ”
was produced, and then until the ‘ flare ” was
on the point of striking back. At this latter
point, analysis showed that the percentage of
pentane was 1*69.

E.	The gas was then adjusted so that the
percentage of pentane, as shown by analysis,
was 1’57. A strong “flare” was produced,
which did not change when magnesia was
introduced.

F.	With a velocity of 610 ft. per minute, and
1’48 per cent, of pentane, a well-defined
flare, between 2 and 3 feet long, spread
forward towards the open end of the gallery
On the introduction of stonedust the flame
only became luminous (with a red glow).

G.	With the same velocity at 1’51 per cent,
of pentane and magnesia the flame became
more luminous, but no other change could be
detected.

H.	Again, with the same velocity and 1*59
per cent, of pentane and with rather more
stonedust the result was the same as in F,
when 1 48 per cent, of pentane was used.

I.	With a velocity of 680 ft. per minute
and 126 per cent, of pentane there was a
well-marked cap, and, on the introduction of
coal dust, the result was a general inflammation
as in B.

J.	With the same velocity and 1*82 per
cent, of pentane a fine cloud of magnesia
produced only a slight increase of luminosity.
In this case the flame began to show with
1‘56 per cent, of pentane, and as the gas was
gradually increased the flare extended nearly
to the open end of the gallery.

K.	With the same velocity and 1*95 per
cent, of pentane, the gas was turned on until
the flare came out of the open end of the
gallery in a roaring flame. The introduction
of a fine cloud of magnesia had no visible
effect, and the flare did not strike back. In
this case the gallery was heated from the fan
drift onwards, so that on reaching the flame
the temperature of the current was between
96 and 100 degs. Fahr.

L.	With a velocity of 1,000 ft. per minute
and 140 per cent, of pentane, a “ cap,” but no
flare, was visible. This cap became luminous
on the introduction of magnesia.

M.	With the same velocity and 1*67 per cent,
of pentane, a flare was produced, but no
change could be detected on the introduction
of magnesia. In this case the gallery was
heated.

N.	Again, with the same velocity and 1’92
per cent, of pentane, the gas was turned on
until the mixture was highly explosive, and a
large flare burnt from the lamp, and reached
the open end of the gallery. The introduction
of magnesia caused no change, and there was
no striking back.

The Committee’s conclusions, from the result
of these experiments, appear to be legitimate.
They are:—

1.	That the addition, under the described
conditions, of incombustible dust does not
confer any increase of inflammability, either
in mixtures below the lower limit of inflam-
mation, or on explosive mixtures travelling at
various rates.

2.	That the initial temperature of the
current within the limits of 42 degs. Fahr,
and 90 degs. to 100 degs. Fahr, appears to make
little difference.

Experiments B and I also tend to show
that a non-inflammable mixture of inflammable
gas and air becomes explosive upon the
introduction of a coaldust cloud into the current.

Further experiments were conducted in the
same gallery with modifications which had the
effect of rendering the mixture of gas and air less
perfect, and constituted an endeavour to account
for the phenomena witnessed by Abel.

The second series of experiments were con-
ducted in an iron tube, 50 ft. long and 1 ft. in
diameter. Mixtures of ordinary lighting gas
and air were used, and an electric spark as the
means of ignition.

With a velocity of 450 ft. per minute and
5*2 per cent, of coal gas, a cap was formed, but
no explosion took place. The introduction
of calcined magnesia made no difference.

With a velocity of 315 ft. per minute and 7'4
per cent, of coal gas, on passing the spark, a
flame travelled slowly with the air current, and
for a short distance toward the fan. The
mixture continued to burn (at the point of
union between the 1 ft. tube and the fan drift)
after the spark had been cut off, showing that
an explosive mixture had been obtained in which
the normal speed of propagation of flame was
equal to the velocity of the air-current. (We
have already referred to the experimental
significance of this phenomenon.) The intro-
duction of calcined magnesia produced no
explosion—only increased luminosity.

With a velocity of 315 ft. per minute and
9 3 per cent, of coal gas, an explosion took place,
the speed of travel of the flame over the last
25 ft. of the tube being 54’3 ft. per second. With
magnesia in suspension, the speed was only
30*3 ft. per second.

A similar experiment, with a higher percentage
of coal gas and a velocity of 125 ft. per minute,
gave corroborative results.

These experiments point to a retarding effect
on the rates of travel of the flame, as a conse-
quence of the presence of magnesia.

A third series of experiments were made with
a vertical glass tube with the object of testing
the results obtained by MM. Mallard and Le
Chatelier. In view of the qualification to
their “ confirmation ” of Abel’s results, “ that the
flame thus produced ia not propagated automati-
cally in a similar mixture beyond the path
traversed by the incandescent particles,’’
MM. Mallard and Le Chatelier’s results
appear to have rather the reverse effect.

Perhaps the most interesting and promising
series of experiments were those conducted in
a spherical explosion vessel of about 4 litres
capacity.

On this occasion the inflammable gas used was
ethane. These experiments certainly appear to
afford conclusive evidence of the retarding effect
of magnesia dust upon the rate of propagation
of flame through an explosive mixture of gas
and air.

We venture to think that, by this report, the
Committee will have attained their present
object—namely, the removal of any apprehension
that may exist of an increase of danger of gas
explosions resulting from the introduction of
stonedust into mines.

Trade Summary.

The London coal market has had a very brisk trade
during the past week, and the volume of trade doing has
been exceptionally large. The shipping trade continues to
absorb very large consignments, which would otherwise
find their way into the metropolitan area. Prices have
advanced somewhat for house coal, and all special quotations
have been withdrawn, the winter prices remaining firmly in
force. Double-screened nuts and slacks are unusually
strong, and all manufacturing coals are in good demand.

Prices at Newcastle are weak. The stoppage in Belgium
has affected the market, customers being inclined to await