September 25, 1914.

THE COLLIERY GUARDIAN.

667

THE COUNTER-CURRENT THEORY OF
EXPLOSIONS.

During his recent visit to this country Mr. Samuel
Dean, of Delagua, Colorado, informed us that he had
prevailed upon Dr. Wheeler to carry out an experiment
at Eskmeals with the object of testing the “ counter-
current” theory advanced by Mr. John Verner in the
United States.

In the Coal Age of August 22, Mr. Dean gives
some interesting details of the experiment. Mr.
Verner found* that when a shot is fired, say at the face
of an entry, the air and what dust there may be present
are driven away from the face by the expansive force of
the heated and burning gases from the shot. This
expelling force, however, is instantly checked apparently
through the effects of a growing depression at the face,
caused by the rapid cooling of the gases there and their
consequent rapid shrinkage in volume. This depression
is immediately filled by an inrush or backrush of air
along the bottom toward the face, while the heated

used containing 70 per cent, coal dust and 30 per cent,
incombustible dust (fuller’s earth). This was done to
slow down the explosion and allow more time for
observing the air actions at the mouth of the gallery.
Across the mouth of the tube a board, 6 in. square, was
supported by four >coil springs, and from the board a
rod 6 ft. long projected out into the open. There was
a white mark on the rod, which passed through a
stationary upright painted black. The rod moved back
and forth as the air movements forced the board out-
ward or inward. Half a-pound per linear foot of mixed
dust was strewn along the gallery to within 20 ft. of the
mouth, and 1J lb. of black powder, stemmed with 8 in.
of dry clay, was fired from the cannon placed 50 ft. from
the closed end of the gallery.

A whistle was blown immediately before the shot was
fired, and the first action observed was a cloud of dust
blown out of the mouth of the gallery. This was
caused by what might be called the concussion wave
from the cannon; there was no flame in this dust cloud.
Then immediately there was an air inrush, then an

NEW BELT-CONVEYING COAL-LOADING PLANT
AT PORT TALBOT.

An interesting coal-conveying installation, the first
to be completed at any of the Bristol Channel ports,
has recently been put into service at Port Talbot. This
plant, designed, manufactured, and erected by Messrs.
Spencer and ’Company Limited, of Melksham, Wilts,
for the Port Talbot Railway and Docks Company,
replaces the ordinary type of hydraulic wagon hoist.

There are two patent truck-tipping gears provided for
dealing with any size of truck by end-tipping, the
double set being for the purpose of allowing any truck
to be tipped at once no matter which end the door
happens to be, thus doing away with the necessity of
marshalling by means of turntables. These tipping
gears are worked by hydraulic pressure, and are both
fitted with patent anti-breakage aprons, rail-shifting
apparatus, and complete automatic controlling gear.
Between the two tipping tables is placed an intake
hopper with a capacity of approximately 20 tons, the

‘if

rite

11

Fig. 1.—General View of Conveyors at Port Talbot.



,/

/

Fig. 2.—Side Elevation of Conveyor to Rail Level.



gases in the upper part of the entry keep on their course
outbye. The force and volume of the inrush of air
along the bottom vary considerably in the different
observations, the conditions in this respect being
evidently determined by the size of the depression near
the face. In view of this, Mr. Verner thought, it might
be rightly concluded that, if the inrush of air along the
bottom is of sufficient volume, and carries with it
sufficient dust, and if it reaches the heated gases near
the face before they are cooled below the ignition
point, then inflammation with explosive effects may
trke place.

The experiment at Eskmeals was carried out in the
small gallery 3 ft. 3 in. in diameter. A mixed dust was

* Trans. Inst. Mining Engineers, vol. xlvi., part 2.

outrush with little dust, then another inrush, then an
outrush with flames, which appeared first at the top of
the mouth of the tube. The final movement was an air
inrush. The second air inrush was very strong, accom-
panied by a loud sucking or whistling noise as. the air
rushed into the tube. It will be noted that the observers
were able to count two inrushes before the flame
appeared, and in a longer gallery there would doubtless
be many more.

Dr. Wheeler's pressure diagrams from violent explo-
sions show the pulsations clearly. It appears that
during an explosion the pressures in front rise and fall
in an alternating manner. The peaks of the diagrams
show when the obstructing pressure is greatest, and the
fall is probably caused by air rushing under the advancing
explosion wave to fill the partial vacuum behind.

sides of this hopper being fitted with screens for taking
out the small coal if desired. The large coal passes
direct to the conveyor, and the small coal is delivered to
an elevator which raises it to a sufficient height to
discharge direct into railway trucks for removal.

These screens are so arranged that they may either be
worked or not, as desired. The hopper is specially
designed to deal with large or small coal, and so that
there may be a minimum of breakage. The coal passes
direct from one hopper to a band conveyor, a regulating
valve being fitted at the discharge opening.

The conveyor is 210 ft. long by 3 ft. 6 in. wide and
troughed, and is capable of dealing with 700 tons of
coal per hour. It is driven by means of an electric
motor of 80 b.h.p. This motor, with its gear for driving,
is situated between the intake hopper and the quay in a