December 17, 1915.

THE COLLIERY GUARDIAN.

1241

difficulties, owing to .the scarcity of coke, other raw
materials, and railway wagons. The Pig Iron Associa-
tion has not yet commenced selling for delivery next
year, but is expected to do so shortly, and to advance
prices in some cases. Semis are unchanged, and the
small surplus of slabs that the steel works have available
for disposal are offered at 117-120 mk. per ton ex works.
Forward selling is in progress for the coming quarter.
The scrap market is depressed, core and mixed scrap
being about 20 mk. per ton below last spring prices; and
there is little prospect of improvement. The market for
plate is very regular, the basis price for fine plate being
still 180-185 mk., ex works, higher rates being obtained
for export. Skilled workmen are becoming so scarce
that some works are reported to be refusing orders for
very fine plates, and others require four to six weeks for
delivery. Medium plate is quoted at 160-170 mk. ex
works, and is in good request. Latterly there has been
a tendency to weakness in the price of heavy plate, the
output being apparently in excess of the demand, and
offers of a little below 150 mk. have been made for the
inland market. Pickled, high-grade, and tin plates find
a ready sale. The bar market has weakened, the basis
price for open-hearth mild steel bars having receded
temporarily by 10-15 mk. per ton. The demand for
building material and girders is quiet.

MINING INSTITUTE OF SCOTLAND.

A general meeting of the Mining Institute of Scotland
was held in the rooms of the Institute, 39, Elmbank-
crescent, Glasgow, on Saturday afternoon last, Mr.
D. M. Mowat (president) in the chair.

Mr. James Lorimer, under-manager, New Cumnock,
was admitted to the membership of the institute.

Intimation was made of the fact that the council of
the institute had decided to appeal to the members for
contributions towards a scheme for raising, in the name
of the institute, a sum of £500, in aid of the work of
the British Red Cross Society at the front.

Lining Shafts with Concrete Z-Blocks.

Discussion was resumed on the paper contributed by
Mr. Marcel Gillieaux, on “Lining Shafts with Con-
crete Z-Blocks.”

Mr. J. B. Thomson said his difficulty was in seeing
how the buntons could be fixed in such a system of
walling as that described by the author. In the ordi-
nary system of brick walling, the usual custom was to
build in wall pockets. In such a method of walling by
brick, that could be easily enough done by measurement
and plumbing, but in the method of hanging the
Z-blocks described, he did not think it would be practic-
able—although it might be possible—to fix in these wall
pockets.

Mr. James Hamilton said this system did not seem to
have been in use anywhere. At all events there was no
mention in the paper that it had been put into actual
practice at all.

The President observed that if the author decided to
reply to the points raised, he might be able to give
further additional information as to where these concrete
blocks were in use.

The discussion was thereafter closed.

Compressed Air for Coal Cutters.

The meeting then proceeded to discuss the paper read
by Mr. Sam Mavor, Glasgow, on “ Compressed Air for
Coal Cutters.” (Colliery Guardian, September 17 and
24, and October 1.)

The President remarked that although compressed
air was not largely used just now in Scotland, the paper
showed the importance of seeing to every single item of
possible loss in mining from the beginning to the end.

Mr. Sam Mavor said there was no doubt that elec-
tricity had played a considerable part in the large expan-
sion of machine mining in Scotland, and while no new
compressed air plants had been laid down in this country
—certainly not for coal mining—there were still a certain
number of old plants in use, that the subject dealt with
came to be of interest to the members of the institute.
It was probable that those users of electric coal cutters
who read the paper would be filled with a sense of satis-
faction and relief that so far they had not had anything
to do with compressed air. The president, however,
had very wisely pointed out that some of the points
touched upon in the paper might quite well be applied
to other branches of mining—those points which dealt
with the avoidance of wastage and the need for economy.
The paper was not intended at all to discourage the use
of compressed air. Its scope might be summed up in a
few words as being : firstly, an exposition of the nature
and extent of the losses that are prevalent in relation to
the use of compressed air plants; and, secondly, sug-
gestions were offered in the paper with a view to the
stoppage of such waste.

Mr. Frank Anslow wrote that, by stating the highest
and lowest over-all efficiency he had encountered in his
investigations, and proceeding to say that, under more
or less ideal conditions, an over-all efficiency of 30 per
cent, might be expected, Mr. Mavor had whetted their
appetite for further knowledge. It would be of interest
if the author would give his opinion as to the over-all
efficiency he considered reasonably obtainable in an
average installation, working under average conditions,
assuming all the aids to efficiency which he had recom-
mended had been adopted. In the recent case of a test,
taken over a shift of eight hours, on an installation con-
sisting of a number of small pumps and haulages, the
over-all efficiency was estimated to be 27 per cent. The
efficiency of the compressor plant, i.e., the ratio of the
electric horse-power input to air delivered at the receiver
was, by actual measurement, ascertained to be 65 per

cent., thus leaving an efficiency of 43 per cent, to cover
all losses from the receiver onwards. The air at the
point of using was not measured, but calculated from
the duty performed, and, while these calculations were
made from careful observation, he personally believed
an over-all efficiency of 20 per cent, would be nearer the
mark, which, for such an installation, appeared to be
quite reasonable.

Mr. Thomas Bryson wrote that in dealing with the
measurement-of pressure and volume of compressed air,
the author raised certain important questions in relation
to the form of the instruments used for these purposes.
Mr. Mavor had frankly admitted that : “ Owing to the
fragmentary nature of these tests, made without the
precision of adjustment upon which a claim to accuracy
could be based, they are not offered as authoritative, but
as presenting, the results of actual observations under
the particular conditions of the test.” To generalise on
the basis of a single test was not a sound proceeding, and
consequently the author’s attempt to overthrow a rule
which had long been considered as fundamental did not
seem to be justified on scientific grounds. A mathematical
analysis of the curves shown in fig. 7, would show that
they were very different from the curve given in fig. 8,
and they supported the contention that the fall of pres-
sure was proportional to the square of the velocity of
flow. He (Mr. Bryson) had analysed these curves,
which were obtained from tests “ with the pressure and
sizes of pipes used in collieries,” and he found that the
author’s contention regarding the truth of the accepted
rule was unsound.

Mr. James Black (Shettleston) said he personally
considered this paper was nothing short of a revelation
to users of compressed 'air in the pits. He felt sure that
if the advice tendered by the author was heeded, and
the remedies which he had suggested carried out, con-
siderable economy would be effected. It had always
seemed to him (Mr. Black) that at a colliery where the
power used was obtained from an outside source, and
had 'to be paid for directly, considerably more economy
was exercised in its use. Indeed, nothing compelled one
to consider economy more readily than a huge account,
which was perhaps 50 per cent, more than it should have
been had the power used been efficiently employed.
Only recently a case came under his observation which
corroborated the very point the author wanted to make.
Not long ago he installed temporarily <a compressed-air
driven duplex double-acting pump, of the Worthington
type, to discharge about 50 gals, per minute at a head of
200 ft. As the compressor was being driven by a motor,
it was quite an easy matter to get at the amount of power
that was being consumed; and he was rather astounded,
on making investigation, to discover that that small
pump was costing £200 per annum in excess of what an
electrically driven pump, of similar capacity, would have
cost. If, then, there was a loss of £200 per annum
on a small machine like that, there was clearly need
for investigation, as the author had indicated, in
collieries where compressed air was being extensively
used.

Mr. R. W. Dron (Glasgow) said that electrical
engineers had not yet been able to design an electrical
machine capable of assisting a coal cutter, like a punch-
ing machine, or qualified to work as rock drills. Many
of the compressed air plants were being used for these
purposes, and were doing good work. Although the
compressor system might be inefficient, so far as the cost
of power consumption was concerned, the loss was com-
pensated for by the advantage of being able to use these
auxiliary machines. After all, the difference between
electricity and compressed air was only represented by
the extra cost of fuel. Since, then, the actual fuel con-
sumption of a coal cutter was such a small item correla-
tively to the total cost of the cutter itself, the
indictment against air compressors was not so serious as
some speakers had endeavoured to make out.

Mr. J. T. Forgie (Bothwell) observed that there was
no doubt the cost of air compressing plant was very
much greater than electrical power, but on the other
hand, air compressors had a distinct advantage so far
as the charges for maintenance were concerned. When
they narrowed the question down to the main point, the
relative costs per ton of coal, his belief was that,
generally speaking, the advantage was in favour of
electricity. Most of the compressor plants in Scotland
were old; and while it was, perhaps, a great mistake
to be so conservative, there was a natural reluctance to
scrap old plant and introduce a newer type. Many
improvements had been effected on the newer types of
compressor plants, and the wastage complained of might
be reduced if the older compressors were discarded. At
the collieries with which he (Mr. Forgie) was identified
they had often gone into the question of power costs
as between electricity and compressed air, and the
advantage always lay with the former, particularly at
those pits where they produced the current for their own
immediate use. There were several points in the com-
pressor system which, if given attention to, would
greatly improve the supply of compressed air power, and
considerably reduce the cost of that power to the users.
In the first place, if they were installing a new plant,
they should get a thoroughly efficient engine—either
compound or condensing. That was one feature which
appealed to him, because, in many of the older plants,
the engines could be considerably improved, and
economy thereby increased. Then they seldom saw on
the surface at any colliery where there was a compressor
plant, sufficient storage capacity or ample facilities for
cooling. Perhaps the most important point of all was
in reference to the pipe line. It was a matter of
difficulty in mines to get a perfect pipe line, and it was
also somewhat of a problem to maintain the pipe line
near the workings. Further, in nearly all the com-
pressed air installations in Scotland the pipes themselves
were too small.

Further discussion on the paper was adjourned till
next meeting.

Forming a Shaft Pillar in Thin Seams.

Mr. James Black (Shettleston) read a paper on
“ Forming a Shaft Pillar in Thin Seams.”

When a pair of shafts have been sunk to a seam of coal,
it is necessary (before commencing to work the seam in the
ordinary manner) to leave a pillar of sufficient size to pro-
tect the shafts and property on the surface from the effects of
subsidence. The usual method of forming a shaft-pillar in
such seams is to drive places of only the width of the road
in the required directions, from the shafts to the pillar
boundaries, and then to connect these roads by others, which
form off the pillar, and at the same time to open out the
seam by longwall working. In some cases, only single
roads are driven in the required directions through the
shaft-pillar; but it is common practice, particularly in the
case of large pillars, to drive these roads in pairs, and
connect them at intervals by cross-cuts for the purpose of
ventilation. This system, whether the roads be driven
singly or in pairs, has several serious drawbacks, which are
well known to all colliery managers who have had experi-
ence in work of this description.

The ventilation of these narrow roads necessitates the use
of long lengths of “ bratticing ” in some form or other,
which is always expensive and difficult to maintain, but
seldom satisfactory. Generally speaking, it is practically
impossible to ventilate these places /in a proper manner. In
forming a shaft-pillar in /a mine which it is intended to
work with naked lights, an important point is raised.
Previous to the passing of the Coal Mines Act of 1911, it
was left pretty much to the discretion of the management
whether safety lamps or naked lights should be used in a
mine. Neither an occasional ignition of firedamp, nor even
a small explosion, which resulted in trifling injury, were
deemed sufficient to warrant the introduction of safety lamps
into a naked light mine. The passing of this Act, however,
changed matters considerably as regards ignitions and small
explosions of gas, and nowadays such occurrences may result
in the Home Office authorities promptly prohibiting the use
of naked lights. If, during the operation of forming the
shaft-pillar in what is intended to be a naked light mine, fire-
damp is given off to any appreciable extent, and the
ventilation is defective, for the reasons already stated, the
manager is confronted with a rather delicate and difficult
problem. Will he carry out the work with naked lights, and
thus incur the risk of ignition or explosion, with its
subsequent penalty, or will he dispense with naked lights
and introduce safety lamps? If he should adopt the former
course, his path is a thorny one indeed, and he will be lucky
if he succeeds to such an extent as to evade the attention
of the Home Office. If he chooses the latter course, he may
find it necessary, when the shaft-pillar has been formed,
and there is consequently adequate ventilation, to obtain
the permission of the Home Office before introducing naked
lights. In view of this, and in the interests of safety, as
well as for other reasons, it is, therefore, imperative in
opening out seams intended to be worked with naked lights
that the system adopted should permit of efficient
ventilation.

During the period occupied in driving these narrow roads
through the shaft-pillar, only -a very small output of coal
is obtainable. The yield of coal per fathom of roadway
driven is very small, and consequently the price paid for
driving is extremely high if reckoned at a rate per ton of
coal produced. In the case of thin hard seams, the cost
per fathom for driving these roads approximates closely to
the cost per fathom required to drive a stone-drift through
favourable strata. All the debris produced from the
brushing has to be drawn to the surface and emptied on
the dirt heap. Apart from this source of expense, which
in most cases is not inconsiderable, it must always be
remembered that any ground covered with debris must be
restored at the end of the lease, or restoration damages paid
to the landlord. It seems to the writer that this method
of forming a shaft-pillar in thin seams has little to recom-
mend it, and is adopted solely because it is the outcome of
custom. In the earlier days all seams were worked by
the stoop-and-room method. When the longwall system
was introduced, its application to a seam commenced only
when the boundary of the shaft-pillar was reached. The
method of driving through the shaft-pillar was carried out
in the same manner as in the older system of stoop-and-
room. Instead of driving places of only the width of a
road, a decidedly better and far more economical method,
in the writer’s opinion, is to drive pairs of longwall places
through the shaft-pillar in the required directions.

By adopting this method, the disadvantages inherent to
the ordinary system are eliminated. The ventilation of the
working places can be carried out without the slightest
trouble or expense, and in a thoroughly efficient manner.
The brushing or ripping can be stowed at the working
face—this being a great advantage when compared with
drawing it to the surface. The output of coal per man
employed is certain to be greater; and, as a larger number
of men can be employed at the working face, the output
from the colliery will be considerably larger, thus reducing
materially the cost of driving through the shaft-pillar. The
advantages of this system are so obvious to the practical
mind as to be almost beyond question. In view of this, the
question naturally arises as to why it is not generally
adopted. The writer’s investigations lead him to believe
that the principal reason is the apprehension of danger
arising from the excavation of the considerably larger area
of coal from the shaft-pillar. The writer considers that the
dangers apprehended are more apparent than real, particu-
larly in the case of thin hard seams. In deciding upon the
size of a shaft-pillar, the crushing resistance of the coal is
never taken into consideration, so far as the writer is aware.
Its limits are defined with the object of ensuring that not
only the shafts, but also the property on the surface which
it is desired to protect, will be within the area not affected
by subsidence. The greater the area occupied by surface
buildings, the greater are the distances of the pillar
boundaries from the shafts. Briefly expressed, the writer’s
contention is that, in a great many cases, in thin seams, a
much larger area of solid coal is left, in the form of a shaft-
pillar, than is actually necessary for support.

Discussion on the paper was adjourned till next
meeting.

A meeting of the Institution of Petroleum Technologists
will be held on Tuesday, 21st inst., at 8 p.m., at the house
of the Royal Society of Arts, John-street, Adelphi, W.C. The
chair will be taken by the president, Sir Boverton Redwood,
Bart., D.Sc., F.R.S.E.; and the following paper will be
read : “ The Uralsk Province and its Oil Fields,” by F. A.
Holiday, A.R.C.Sc., F.G.S., M.A.I.M.E.