318

THE COLLIERY GUARDIAN

August 13, 1915.

current in the circuit, but it is clear that the greater
the resistance r of the circuit the smaller is the
sparking voltage eg for a given size of spark. Resistance
in the battery or line, or bell-windings, therefore,
diminishes the igniting power of the spark. Wet
Leclanche cells having a higher resistance than dry
cells are from this point of view safer. To ring over a
long distance is safer than over a short distance, because
the ratio rx/r is less for the same ringing current.

From observed vales of e8 the resistance of the spark
at break can be found. A common ratio of e«/E is
about 10. Thus if r = 6 ohms, r. = 54 ohms at the
moment of break. This rapidly increases as the spark
is drawn out and breaks.

Resistance Inserted Across the Spark-gap.—For the
purpose of preventing ignition of gas by a signalling
bell, the first suggestion is to bridge the spark-gap by
a resistance, but this may be in practice a positive
danger,- for by it a large part of the energy of the spark
at the trembler is handed on to the signalling point on
the wires. These wires are near the roof, and there is
probably more risk of inflammable mixtures being
formed there than at a bell in a haulage-house. When
the gap is bridged, there is no free gap at a, but there
is at b, and it has been shown by Mr. C. P. Sparks,*
and also by Dr. Wheeler, that there is danger of ignition
there equal to that at a under normal working
conditions (fig. 6).

Resistance in Parallel with the Magnetising Coils.—
When, however, a suitable* resistance is placed across
the terminals of the coils, and the gap left unbridged,
a break there gives rise to a spark of much less
magnitude. The resistance r2 may be always con-
nected (fig. 7), or it may be so arranged that it is joined
up by the movement of the armature just before
break (fig. 8), so avoiding the small current which
passes through r2 continually while the bell is ringing.
The value of r2, so as to give the best results in practice,
is found to vary from 20 to 150 ohms, depending on
the design of the bell. This resistance provides a path
for the “ extra current ” at break. In other words, the
voltage e8 at the spark-gap stops at the moment when
it begins, for the current and magnetism in the coils die
down slowly instead of being broken suddenly.
Oscillograph records such as those illustrated in fig. 9
show that the voltage across the gap ntever rises above
the battery volts, and the igniting power of the spark
is reduced, or the factor of safety increased, by at least
4 or 5 to 1; and by 10 to 1 if the voltage only is
considered.

The. effect of the suppression of the sparking voltage
is very marked. It is possible to work any bell in full
ringing in the most inflammable mixture of illuminating-
gas and air without igniting the mixture while the shunt
path is connected. Ignition occurs the moment that
it is disconnected. By having a scraping contact in the
box, it can be shown that the same increase of safety
is obtained on the signalling wires as at the trembler-
contact.

When applied for the purpose of preventing ignition
of gas, there is another important point to consider
which is not well known. It is only within the last
five or six years that the currents which will ignite gas
have been determined, and it is only as a result of long
and laborious trials that one is able to say by inspection
whether or not a certain spark will ignite gas. When
the use of a resistance across bell-coils (and not across
the gap) was first tried by the author in discussion with
his colleague, Mr. W. W. Firth, who had suggested
shunting the gap, he was able to say from previous
work—of which accounts have been given to the
Institute—'that from its appearance the nature of the
spark was completely changed, and that ignition would
not occur. This was soon verified by enclosing the bell
in a large explosion-box, and the method has never been
found to fail. The device does for electric signalling
bells what gauze does for a miner’s safety-lamp : so
long as it is in normal action, ignition cannot occur.

This arrangement, which was first demonstrated at
the Senghenydd enquiry, although it greatly diminishes
the wear at the sparking contacts, does not appear to
have ever been used on electric bells, although Mr.
H. R. Kempef recently states that the principle is well
known to telegraphists. It has the advantage that it
can be fitted to any existing bell, so making it incapable
of igniting the most inflammable pit-gas.

The author ventures to submit the device to the con-
sideration of those concerned with the management of
coal mines, as a contribution to the safety of under-
ground working.

Partnerships Dissolved.—The London Gazette announces
the dissolution of the following partnerships :—A. Lawrence
and C. Lawrence, corn and coal merchants, at Holdenhurst-
road, Bournemouth, under the style of A. J. Lawrence and
Sons; A. T. Pugh and G. C. Ilett, engineers and metal
workers, at Winchelsea Works, Hesketh-road, Forest Gate,
Essex, under the style of Arthur and Company; Ben Preston
and C. B. Young, machine makers, at Batley, Yorkshire,
under the style of Benjamin Preston and Sons; E. Bowden
and J. E. Bowden, boiler cement manufacturers, at Mer-
chants’ Exchange, Bute Docks, Cardiff, under the style of
E. Bowden and Company.

Hull Coal Exports.—The official return of the exports of
coal from Hull to foreign countries for the week ending
Tuesday, August 3, is as follows:—Archangel, 800 tons;
Alexandria, 7,599; Amsterdam, 1,677; Assens, 2,213; Buenos
Ayres, 4,438; Christiania, 1,120; Dunkirk, 801; Dieppe, 843;
Fecamp, 1,778; Gefle, 4,259; Granville, 737; Gothenburg,
2,577; Honfleur, 593; Halmstad, 1,205; Harlingen, 3,081;
Havre, 2,232; Iggesund, 655; Oxelosund, 1,789; Reykjavik,
994; Rotterdam, 2,525; Ronne, 1,088; Rouen, 44,341; St.
Nazaire, 2,066; Treport, 1,093; Tuborg, 1,195—total, 91,699
tons. The above figures do not include bunker coal, ship-
ments for the British Admiralty, nor the Allies’ Governments.
Corresponding period, August 1914, total, 67,934 tons.

* Journal of the Institution of Electrical Engineers, 1915,
vol. liii., p. 389.

1 Electrical Review, 1915, vol. Ixxvi., p. 886.

MINING INSTITUTE OF SCOTLAND.

A general meeting of the Mining Institute of Scotland
was held on (Saturday afternoon in the rooms of the
institute, 39, Elmbank-crescent, Glasgow, when there
was a large attendance. Mr. J. Balfour Sneddon
(Mid-Calder), presided in the absence of the president.

The following gentlemen were at the outset admitted
to the membership of the institute :—Messrs. J. A.
Daniel, Institution of Mining and Metallurgy, 7,
Finsbury-circus, London; David Forsyth, under-
manager, Coatbridge; and George Russell, assistant
mining engineer, Lugar Ironworks, Cumnock, Ayrshire;
Associates—Messrs. David Stevenson, mines rescue
station, Cowdenbeath; and George Welch, mines rescue
station, Coatbridge; Student—Mr. Maurice Berman,
mine surveyor, Lochgelly, Fifeshire.

Training Engineers and Colliery Managers.

The' discussion was resumed on the papers read by
Mr. R. W. Dron, mining engineer, Glasgow, on “ The
Training of Mining Engineers,” and by Mr. John
Gibson, Kilmarnock, on ” Some Notes on the Education
of the Colliery Manager.”

Mr. D. M. Mo Wat (Coatbridge) the president of the
institute, in the course of a. written communication, said
he did not think there was any difficulty in a candidate
for the colliery manager’s certificate obtaining a very
complete knowledge of the theoretical side of his pro-
fession during the years he was working at a mine, which
latter training enabled him to acquire what was
absolutely essential—an acquaintance with practical
mining.

Mr. R. W. Dron (Glasgow) wrote that the main object
in writing his paper was to emphasise the fact that if
progress was to be made in the future organisation of
the mining industry, it was necessary that encourage-
ment should be given to young men to undergo a proper
course of scientific training. His further contention
was that the training should be taken during the period
of life when the mind was most receptive. If the youth
so trained had even a moderate endowment of brains
he should at least prove himself an exceedingly useful
tool in the hands of Mr. Blake Walker’s ” shrewd,
forceful, practical man,” but if, by chance, he had the
brain power, plus the scientific knowledge, his qualities
as a potential profit-maker would soon assert themselves.
Not only in mining, but in every other industry in this
country the failure to appreciate the importance of
proper scientific training had been a source of national
weakness. The Sheffield University scheme was an
encouraging indication of progress, and the results would
be watched with great interest. It was to be hoped that
the institution would ultimately rise to the standard of
making a university degree or approved diploma a sine
qua non for full membership, but such a reform would
require to be made in progressive stages to allow time
for the rising generation to adapt itself to the new con-
’ ditions. There might be differences of opinion regarding
an apprenticeship supplemented by properly defined
courses at a university or technical college, but this
was just one of the points where the institution as a
body should be able to give guidance, both to the
authorities and the students. There could be no question
about the value of the education given on evenings and
Saturday afternoons at such centres as Glasgow and
Edinburgh. An apprenticeship to a mining engineer,
supplemented by such courses, was at least the next
best thing to a full university course. Practical work
in the pits must, of course, follow on the apprenticeship,
but two years of this manual labour should be ample.
One part of the paper which had not received much
attention in the discussion was the suggestion that some
portion of the practical training should be received in
the workshop. The writer’s view was that whilst the
mining engineer could not become an expert mechanic
or electrician, he ought to have a practical knowledge of
how these tradesmen went about their work. Mr.
Robert M’Laren, H.M. inspector of mines, seemed to
be of the opinion that the mine manager might be spoiled
by over attention being given to the scientific side.
Assuming that there was this danger, it was all the more
important that a separate body of men should receive
scientific training. It was certainly remarkable how
this country had been able to muddle through in spite
of her neglect of proper training and organisation, but
it was a grave mistake to assume that any past success
had been a result of that neglect. j

Mr. John Gibson (Kilmarnock), who is just recovering
from a nervous breakdown, and was unable to attend the
meeting, submitted a written communication, in the
course of which he explained that the chief use of the
paper which he contributed lay in the discussion it had
evoked. The subject bristled with difficulties. Thus,
for the man of poor general education, the oral point of
the examination was necessary, yet there was a feeling
against jt. Mr. Wm. Smith, in his criticism, stated
the case for the oral with perfect fairness, but he was
wrong in assuming that he (Mr. Gibson) said anything
to the contrary as a personal opinion. Another difficulty
. of the question generally was tiiat criticised by Mr.
Robert Martin regarding differences in sizes of collieries.

Two men, A and B, both pass the same examination.
A took charge of a small, shallow colliery, employing
40 or 50 men. B took charge of a big, deep colliery,
employing 2,000 men. The work in each case differed
so much that it might be said to differ in kind—not in
degree—yet both men were, so far as the examination

was concerned, qualified alike. Tt would be hard, how-
ever, to suggest remedies for such difficulties. Prof.
Hardwick said he (the author) had made a ” sweeping
condemnation ” of the present system, but did not
explain the remedies proposed. That criticism was fair
and the omissions were caused through compression.
The remedies he proposed were :—(1) To produce a man
of much wider knowledge on general matters by a
curriculum, in which would be included the subjects
mentioned; (2 ) to produce a more efficient man by a
training, in which experience and information would be
given, not by haphazard, as at present, but on a carefully
thought out and co-ordinated system; (3) to increase
efficiency and give time for the better education by
cutting out all matter that taxed only the memory of the
student, e.g., the Mines Act, etc. Both Prof. Louis
and Prof. Hardwick had contended thd?t the purpose
of the examination was to find if the candidate could
manage a mine safely. He (Mr. Gibson) submitted,
however, that the examination was also intended to find
if he could economically manage a mine. This was as it
should be, because if the mine could not be made to
pay, it might be shut down, and the need for safety
disappeared. The introduction of a comparison of
Scottish and English passes had called forth some
criticism. He admitted that there was much force in
the contentions of Mr. Smith and Mr. Hamilton that
the data were insufficient. Mr. Hamilton seemed to
regret the introduction of the topic, but he would remind
him that the education systems of these countries
differed very much, and it was of the utmost importance
that their respective efficiencies should be at all con-
venient times passed under scrutiny. He was of opinion
that the results of examinations for mine managers’
certificates afforded such opportunities. Mr. Hamilton
expressed the opinion that the candidates in both
countries were pretty much on a level, but the fact
remained that Scotland had a much higher percentage
of candidates per thousand persons employed than
England had. This, he was of opinion, showed that the
training commenced in the elementary schools—in other
words, it was largely a matter of general education.

The discussion was closed, and the authors thanked
for their contributions.

Rescue Brigades—Resident versus Non-Resident Systems.

The meeting thereafter proceeded to discuss the paper
by Mr. Henry Briggs, kof the Heriot-Watt College,
Edinburgh, on “ The Resident Brigade System versus
the System of Non-Resident Brigades.”

Mr. James T. Forgie (Bothwell) said it would be
expected of him to state his views in regard to this
paper, particularly as he had been the chairman of the
committee of the Lanarkshire Coal Owners’ Association
which had dealt with the rescue brigade question in the
Lanarkshire area. First of all, he should like to say that
the paper presented by Mr. Briggs was a most fair and
equitable one, and gave an impartial survey of the two
systems. Mr. Briggs and the others associated with
him in the east of Scotland had gone in for what might
be termed the old system, and quite naturally Mr. Briggs
wanted to praise it as highly as possible as being the
better method of the two. The whole subject of rescue
operations was considered by the committee of the
Lanarkshire Coal Masters’ Association, and viewed by
them not in any ” dog-in-the-manger ” way, but with
an extreme desire to arrive at the best scheme possible
in the interests of safety. The Lanarkshire coal owners
did not do anything so long as the proposals regarding
rescue work were voluntary, but once the whole question
came to be embodied in legislation, they were forced to
take active steps. At considerable length Mr. Forgie
proceeded to say that it was a matter of opinion at the
present moment whether the old or the new system was
the better, because they had not as yet in Scotland had
sufficient experience to enable them to come to a definite
conclusion on the point. If, unfortunately, the necessity
should arise—perhaps more than anyone he hoped it
would not—they in Lanarkshire believed the system
which they had adopted, which was the newer one of the
two, would prove to be the more useful and advant-
ageous. If rescue brigades and stations were thought
by the Government, the miners, and the country in
general, to be desirable for the safety of those working
underground, then the Lanarkshire Coal Owners’
Association held to the view that no question as to
expense should be allowed to interfere with the system
being made as perfect as possible. In Lanarkshire they
were firmly convinced that a series of central stations
where men trained and skilled in the handling of
apparatus could be summoned at any moment was to be
preferred to any other arrangement. The cost of
equipping and maintaining in the Lanarkshire area the
central stations at Coatbridge, Larbert, Lesmahagow and
Bathgate would no doubt be greater than that of keeping
together at each colliery a separate rescue brigade and
station, but as against that they were ensuring ihe
maintenance of far more efficient and capable rescue
brigades. Mr. Forgie adduced a number of reasons for
favouring the central station system in preference to the
establishment of local colliery brigades.

Mr. Robert Wilson (Giffnock) said that from the
experience gained at his colliery, he was disposed to
think that the arrangements in vogue permitted of his
own rescuers being at the seat of a fire or explosion much
more quickly than trained men could come from any
central station.

Mr. A. H. Steele (H.M. inspector of mines) asked
how a rescue brigade at a central station would be
affected in the event of two or three disasters occurring
simultaneously.

Mr. Forgie replied that when their four central
stations were completed the Lanarkshire Coal Owners’
Association felt that one or other of their teams could