February 28, 1913.

THE COLLIERY GUARDIAN.

433

conical so as to securely hold the detonator / containing
the fulminate e.

On explosion of the composition p and the consequent
short-circuiting of the two electrodes c, d by the depres-
sion of the tongue i, the electric current flows much
more strongly through this short circuit to the remaining
fuses than it would do had it to pass through all the
platinum bridges, and it therefore makes it absolutely
certain that all the fuses in series explode.

Fuses constructed on this principle need not all be
equally sensitive, although the irregularity in that
respect has hitherto been the main cause of missfires or
partial missfires when firing in series. Even if one fuse
were so extremely sensitive as to fire before the others,
which would cause a break in the circuit with ordinary

C

O

Fig. 1.

m

f

fuses, it would not cause a break with fuses constructed
on this principle, as the firing of a single fuse would
short-circuit it and allow the current to pass with
increased force to the remaining fuses, and, were many
of the fuses much more sensitive than the others, no
break of the circuit could occur because, as each fuse
explodes, more current flows to the remaining fuses, and
the least sensitive cannot fail to fire.

In speaking of one fuse exploding after another, the
interval or intervals between the explosion of the various
fuses is so infinitesimal that no difference in time would
be noticeable between the explosion of one fuse and
another, as all the fuses, even up to 100, would explode
within a fraction of a second.

This type of fuse has been perfected only after several
years experimenting, and machinery has been con-
structed for automatically making and assembling the
various parts of the fuses, so that the cost will be only
a fraction more than that of fuses of the ordinary type.
The inventor and patentee is Konrad Schaffler, of
Vienna, also inventor and patentee of the “ Sterling ”
blasting machines, constructed on an entirely new
principle less than 10 years ago, which are now the
standard type, not only in this country but throughout
the world, with the exception of the United States,
where a heavy tariff shuts them out.

Institution of Civil Engineers.—The council have
arranged for several of the offices on the ground floor of the
new building to be opened for temporary use as reading
rooms, and the current journals and the library books, as far
as practicable, will be available until such time as the
permanent library can be completed, and the books removed
into it. The rooms will be open from 9.30 a.m. until 5.30 p.m.
daily, Saturdays 9.30 a.m. until 2 p.m. The annual con-
versazione of the institution will be held in the Royal
Albert Hall on Wednesday, June 25; but the council have
decided to defer for the present making arrangements for
the annual dinner, in the expectation that it may be
practicable to hold it later in the year in the new building.

NOTES ON MINE GAS PROBLEMS *

By George A. Burrell, Chemist to the United
States Bureau of Mines.

The Bureau of Mines has accumulated considerable
data regarding mine gases as a result of the analysis
of gas samples collected in different mines and
of experimental work performed in the laboratory.
Some of the observations are presented here regarding
the explosibility and physiological effects of mine atmo-
spheres, also regarding flame extinction and afterdamp.

Explosibility of Firedamp.

The limits of explosibility of firedamp have been
worked out by different investigators, and results which,
in the main, are in accord with each other, have been
determined in the laboratory. Some differences have
been published, but these are mainly due to the fact that
different experimenters have performed the work under
different conditions. Sufficient emphasis has not always
been placed upon the decided effect experimental con-
ditions exert on the results. The size and shape of the
vessel employed; nature of source of ignition, i.e.,
whether flame, small electric spark or large electric
flash; ignition of mixture from above or below;
moisture in the mixture; and temperature and pressure
—all may have some influence in determining the limits
of explosibility or extent of inflammation in mixtures of
combustible gases with air. A partial burning in a
mixture of a combustible gas with air always takes
place when the ignition temperature is reached, whether
an explosive proportion of combustible gas be present
or not. The extent of this burning will depend upon
some of the conditions just referred to. But explosive
limits in the sense in which the terms are generally used
mean limits between which self-propagation of flame
takes place without help from the source of ignition
other than the ignition of the mixture at one point. The
smallest quantity of any combustible gas which when
mixed with air (or oxygen) will enable self-propagation
of flame to take place is termed the lower limit of
explosibility of the gas. It is of vital importance to
mining men, of course, that the correct limit of
explosibility of methane with air be known.

Low Explosive Limit of Methane-air Mixtures.

More recent work has shown that this value is about
5’50 per cent, methane, and not 6 per cent, as is some-
time stated. Even 0’50 per cent, is of significance.
Modern ventilation aims to keep the methane in mine
air as far removed from the explosive proportion as
possible. One per cent, of methane in return air is
considered a large quantity; | per cent, is sometimes
tolerated. If the explosive limit for methane is 5 5 per
cent., and a mining management calls 6 per cent, the
low limit of explosibility, they are 0’5 per cent, nearer
the explosive proportion than they think.

Coquillon ignited methane-air mixtures in a closed
vessel by means of an electric spark, and placed the
lower limit of explosibility at 5’8 per cent, methane. Le
Chatelier and Mallard and Boudouard have placed the
limit at 6 per cent. Eitner determined the lower limit
of explosibility of methane to be 6T per cent. Clowes
obtained 5 per cent, as the low limit of explosibility
when the gas was fired from below with a flame, and
6 per cent, as the limit when the gas was fired from
above. Teclu found the lower limit of explosibility to
be between 3’20 and 3 67 per cent. Teclu’s values are
quite outside of the others mentioned here. The most
recent values are those obtained by Burgess and Wheeler,
who place the lower limit of explosibility between 5’5 and
5’7 per cent. No discussion of the different methods of
experimentation will be given here, the object being
only to convey the idea that exact duplication of results
by different experimenters has not always followed.

In the Bureau’s laboratory an explosion could not be
obtained when a mixture of methane and air containing
less than 5 50 per cent, methane was subjected to the
action of a small |in. spark from an induction coil.
The latter was driven by four dry cells. The mixture
was placed in a 100 cubic centimetres spherical vessel
over mercury. An explosion could not be obtained with
0’10 per cent, less methane when the pressure was
increased from 1 to 2 atmospheres. With 5’50 per cent, of
methane combustion was not quite complete. Analysis
of the products of combustion showed, however, that
only a trace of combustible gas remained unburnt.
Pure methane was prepared by the action of alcohol
and methyl iodide on a zinc-copper couple.

A number of experiments have been performed in the
Bureau’s laboratory, in which a flame has been used as
the source of ignition. In some of those experiments a
spherical flask, having a capacity of 1 litre, has been

* A paper presented, by permission of the Director of the
Bureau of Mines, at the winter meeting of the West
Virginia Coalmining Institute, Parkersburg, W.Va.,
December 1912.

used. Some burning followed under these conditions
when as little as 4’75 per cent, methane was present.
Ignition was effected from below. The burning extended
as a cone about one-half of the way to the top of the
flask. Inflammation in the mixture increased with
increasing percentages of methane. All mining men
have of course noticed this behaviour in mixtures of
combustible gases and air. With very small percentages
the inflammation starts as a cap on the flame of the
safety lamp. The inflammation spreads from the source
of ignition as the percentage of combustible gas is
increased. Finally, conditions are right for a projection
of flame throughout the mixture. At about 5’50 per
cent., the low limit of explosibility, the flame extends to
all parts of the mixture but travels comparatively
slowly, and can be followed by the eye. With increasing
proportions of methane, the explosion becomes more
violent. It was observed that the partial burning in a
mixture containing less than 5’50 per cent, methane
depended upon the several factors such as nature of
ignition, shape of container, &c., but that complete
explosion could not be obtained under several different
conditions of experiment tried when less than 5’5 per
cent, of methane was present. In determining the low
explosive limit of methane-air mixtures, the products of
combustion were examined to ascertain the completeness
of the combustion. In the experiments that follow,
this was not done unless otherwise stated. The term
explosion will be retained to mean conditions when the
flame filled the container, as far as could be seen by the
eye. Inflammation will mean only a partial filling of
the container by the flash. The foregoing remarks are
preliminary to a brief account of some experiments
regarding explosibility of firedamp, which are not so
! well known.

Effect of Carbon Dioxide on the Explosibility of
Firedamp.

In explosions, as well as flame extinction and physio-
logical effects, the influence of carbon dioxide in mine
air has usually been over-estimated. Carbon dioxide
always occurs in mine gas mixtures in which explosive
amounts of methane are present, and there is always a
greater oxygen deficiency than is produced when the
methane is added to air for simple laboratory experi-
ments. The following experiments show something
about the explosibility of methane in the presence of
excessive proportions of carbon dioxide and when the
oxygen is considerably reduced. In the Bureau’s labora-
tory, when 2’5 per cent, of carbon dioxide was present in
a mixture, an explosion followed when the methane was
raised to 5’83 per cent.

With 5 0 per cent, carbon dioxide an explosion
occurred when the methane was raised to 6’25 per cent.
With 10 0 per cent, of carbon dioxide an explosion was
obtained when the methane constituted 6’6 per cent, of
the total. A small spark from an induction coil was
the source of ignition. The presence of carbon dioxide
narrows the explosive limits, but it will be observed
that even 10 per cent, only raised the low limit to 6’60 per
cent.

Effect of Reduced Oxygen on the Explosibility of
Firedamp.

A spherical flask having a capacity of 1 litre was
used in the following experiments. A mixture of the
following composition was experimented with :—

Per cent.

Carbon dioxide ................ 0	03

Oxygen...................... 1400

Methane........................ 9	40

Nitrogen ..................... 76	57

When this mixture	was exposed to a flame from

above, inflammation occurred. The flame spread down-
ward to the middle of the flask and out toward the
sides, where it died. The eye could easily follow the
course of the wave. When the mixture was ignited
with a flame from below, it exploded with considerable
force. As far as the eye could see, the flame filled the
entire flask.

Further experiments were made in which the oxygen
had been reduced to 13 per cent. This mixture had
the following composition :—

Per cent.

Carbon dioxide............... 0	03

Oxygen ................... 13’00

Methane.................... 9’40

Nitrogen .................. 7757

The above mixture was placed in a cylindrical vessel
having a capacity of 2,750 cubic centimetres. Two
copper terminals were quickly broken to produce tho
flash, which took place in the centre of the vessel. A
current of 7’5 amperes, at a pressure of 220 volts, was
used. A fat spark about J in. long could be obtained.
On the break of the contact the inflammation spread
upward almost to the top of the jar.

With 151 per cent, oxygen and 9’4 per cent, methane
a quite violent explosion was obtained under the same
conditions of experimentation. Experiments were alsa