668

THE COLLIERY GUARDIAN.

March 13, 1911.

however, is less than last year, whilst the proportion of
good papers has shown a decided improvement.

As regards the individual questions, No. 21 was
attempted by 245 candidates, in most cases with a fair
measure of success, though many of the drawings were
extremely bad ; attempts at representing such appliances
as fans in perspective should be severely discouraged,
and students should be made to understand that machines
are best shown by plans and elevations. Next in order
came Questions 22 and 25, attempted in each case by
just over 200 candidates; the main fault in many
answers to No. 22 was that candidates, although
asked specifically to describe bord-and-pillar working,
appeared to think themselves at liberty to work the
seam in question by Welsh stall, longwall, or any other
method that they happened to prefer. Question 23 was
attempted by 181 candidates ; it was often well answered,
but too many had got hold of the erroneous idea that a
hydraulic method necessarily implies the use of hydraulic
cement. Question 26 was attempted by 159 candidates,
but no less than 65 of the answers gained no marks
whatever, the candidates in question having evidently no
idea how to calculate the quantity of air passing
through an airway. Question 24 was attempted only by
just over 100 candidates, and was often very badly
answered; more attention is evidently required to the
subject of colliery surveying. Question 28 was attempted
only by 74 candidates, and, of these, 40 obtained no
marks at all for their answers, as they described coal-
washing machines other than the particular type that

0	0	0	7 0

for

test Firing.

T<£]

Fig. 1.—View of Apparatus as a Whole.

SnitcF



was asked for. Teachers should be urged to pay more
attention to the very important subject of coal-washing.
Question 27 was attempted only by 31 candidates, thus
showing how very few were acquainted with the modern
applications of electricity to mining.

The examiners conclude :—“ It seems clear that the
weakness of candidates, in addition to the specific
points above referred to, lay mainly in drawing and in
arithmetical calculations. Candidates ought to be
trained to read the questions through carefully and to
answer the precise points to which the question is
directed. They should be taught that answers not
exactly to the point gain them no marks whatever.”

Grimsby Coal Exports.—The exports of coal from
Grimsby during the week ended Thursday, 5th inst., as
shown by the official returns, totalled 12,587 tons, com-
pared with 14,327 tons during the corresponding week last
year. The shipments were as follow:—To Aarhus, 1,358
tons ; Arendal, 625 ; Dieppe, 989 ; Fredrikstad, 2,001 ;
Gothenburg, 607 ; Hamburg, 1,471; Malmo, 2,858 ; Rotter-
dam, 398 ; Skien, 205 ; Windau, 2,075. There were no
coastwise shipments.

Hull Goal Exports.—The official return of the exports of
Goal from Hull for the week ending Tuesday, March 3,
1914, is as follows :—Alexandria, 2,635 tons ; Antwerp, 449 ;
Amsterdam, 595; Aalborg, 250; Bordeaux, 1,622; Barce-
lona, 2,151; Bilbao, 1,343; Bremen, 653 ; Boulogne, 1,521 •
Christiania, 2,552; Christiansund, 50; Copenhagen, 176;
Esbjerg, 1,364; Genoa, 1,144; Ghent, 3,062; Harlingen,
1,004; Harburg, 566; Hamburg, 2,844; Konigsberg, 300;
Libau, 5,833; La Pallice, 2,208; Leghorn, 197; Malmo,
1,780; Novorrossick, 2,522; Oxelosund, 6,705; Port Said,
5,672; Reykjavik, 785; Rouen, 7,459; Rotterdam, 192;
Reval, 2,985; Stockholm, 155; total, 60,774 tons. Corre-
sponding period, March 4, 1913, total 66,418 tons.

SELF-TESTING ELECTRICAL SHOT-FIRER *

In shot-firing by electricity it is advisable to test the
apparatus to see whether the resistance is normal and
the current generator in good working condition, with a
view to preventing miss-fires and their attendant
dangers. This can be easily and simply effected by
means of the combined apparatus illustrated in the
drawings. When the shots are ready and the wires
have been attached to the terminals, the apparatus is
connected up with the wires at a suitable distance from
the face, by means of the terminals k1 k2, the resistance
switch on the left being then operated by means of a
detachable key. The total resistance of the apparatus,
in ohms, will be indicated on the upper scale of the
meter. If the indication shows that the apparatus is in
good working order, the key is taken out and inserted in
the testing and firing switch on the other side. By
turning the key from the zero position to “ testing,” the
battery is switched on to the meter, the voltage and
amperage being then indicated on the lower scale. On
these being found normal, the key is turned to “ firing,”
thus connecting the battery up to the shots and firing
same. The resistance switch and the testing and firing
switch are arranged in such a way that, on being
released, they return automatically into the switched-off
position.

The apparatus consists of two superimposed boxes,
the lower box containing the dry battery, the cells (each
4J volts) being arranged in threes in insulated cases.
One group of cells is made independent of the others,

and serves exclusively for supplying current to the
tester. Insulated wires from the poles of this group
lead through insulation bushes to the contacts of the
resistance meter, whilst the poles of the other groups
are soldered together. The outer casing is made of
strong sheet iron, strengthened with angle iron.

The meter is also housed in a sheet iron box, screwed
on to the battery box, the two being separated by a
layer of wood and insulating material provided with
four insulation bushes, a, b p and 2, for the passage of
the wires. To prevent unauthorised opening, the box is
sealed in two places. The meter is covered by a J in.
sheet of glass, and the observation opening at the top is
also covered in the same way.

To facilitate illustration of the arrangement and
working of the apparatus in recording the various
measurements and in firing the shots, the circuit of the
resistance meter, and the parts for testing the battery
and firing the shots have been omitted from fig. 1, and
are shown separately in figs. 2 to 5.

For measuring the resistance, a weak current of about
0 006 ampere is sent through the apparatus, to which
current the firing device will not respond, the rotary-
coil galvanometer, serving as ohmmeter, indicating the
resistance of the apparatus in ohms. This current, which
is supplied by the separate battery e (figs. 2 and 5),
passes through the resistance w (750 ohms), and is
thereby reduced to 0’006 ampere. It then flows through
the rotary coil d, and is shunted (its course being
marked by the double arrows) vid the contacts 1 and 2,
to the terminal &2 of the shotfirer, and back vid kx to
the coil. The main circuit passes from the battery e,
through the contacts 3 and 4, direct to the coil d, and
back through the resistance w. This gives a kind of
Wheatstone bridge, so that the resistance of the main

* O. Dobbelstein. Gluckauf.

circuit, which is practically nil, can be compared with
the resistance of the shotfirer, and read off on the
galvanometer.

The switch diagram, fig. 4, and the corresponding
details, fig. 5, illustrate the testing of the battery and
the subsequent ignition. To test the battery the switch
s on the right hand side of the apparatus (fig. 4) is
turned into the middle, or “ testing position marked
by dotted lines. The main current from the batteries
el and e2 then flows through the coil d, and the series
resistance v w to e2, whilst a divisional current passes
through the testing resistance p w interposed in the
shunt circuit. The resistance v w sets the volt-ampere
meter to the desired tension, whilst the amperage also
present in measuring the tension is compensated by the

Fig. 3.—Resistance
Tester.

vn/-

f o J

Fig. 5.—Battery Tester
and Shot-firer.

Fig. 2.—Switch
Diagram.

e,

Fig. 4.—Switch
Diagram.

ppj

testing resistance in the shunt circuit. The testing
resistance is adapted to the ordinary resistances in the
shot-firing apparatus.

The battery having been found sufficiently powerful
for the igniter, the switch is turned to “ firing,”
whereupon the current from the battery e1, passes
through the bush z and the terminal kx to the firing
device, passing back through k2 and the switch s to the
battery e2.

The apparatus, which is made by the Rheinisch
Westfalische Industrie-Bedarfsgesellschaft, Essen, has
been tested at the experimental gallery of the Bergge-
werkschaft, and has been in practical use for some con-
siderable time at the Massen, Graf Schwerin and
Frohliche Morgensonne collieries, with satisfactory
results. The dry batteries show only a slight decrease
in voltage after six months’ use, and the whole apparatus
remains in good condition.

Coaldust Removal at Tirpentwys Collieries.—In the
Western Mail, Mr. William Brace, M.P., gives an account of
the system adopted at the Tirpentwys Collieries, Pontypool,
for clearing the dust from the roof and sides. The first
part of this process, as practised by Mr. Nicholas and his
staff at the Tirpentwys Collieries, is to divide the roadways
into given sections or lengths. At the end of these sections
a perforated screen is erected, care being taken that the
area of the roadways at these points is sufficiently extensive
to allow the ventilation to travel through the screen
practically unimpeded. The screen is of a zinc material
thoroughly perforated. It is made up of three layers of
perforated zinc sheeting, with a very small division between
each sheet, so that should any of the dust which was
being forced from the roof and sides escape through the
first screen it would be effectually imprisoned by the second
or third screen. At the side of the screen there is a small
dust-tight door let in to enable men to pass through the
screen if necessary. The top and sides of the screen are
also designed to be dust-tight. On the top of the screen
there is a spray waterpipe running the entire length of the
roadway, and this permits the screen to be continuously
swept with water during the period the dust is being driven
along the roadway by the blast. The process employed for
sweeping the dust from the roof and sides is a blastpipe
with a pressure of 80 lb. to the square inch. The pipe is so
constructed that it will easily penetrate between the laggings
over the timber, and thus every hole and crevice is cleared of
the fine, dangerous dust accumulations. To ensure that no
dust so removed shall find a lodgment in the roadway again,
the section being cleaned is previously subjected to a com-
plete watering of the floor, so that any dust falling to the
floor of the roadway is quickly converted into mud or slush.
Following the man with the blastpipe is another man with
a scraper, whose duty it is to collect the dust-mud into
heaps and place it in a tram, either sending it to the surface
or gobbing it. The system is inexpensive, and any person
can undertake the work, as it calls for no special or expert
skill from the operator. Should anyone be working inside
the section being treated it will not affect them, as the
screen prevents the dust travelling into the workings.