February 18, 1916.

THE COLLIERY GUARDIAN.

317

or is missing, the court shall, upon the application of
the man to whom -the certificate was granted, and upon
payment by him of a fee of Is., issue to the man a
duplicate of the certificate of exemption.

Men’s Applications.

Forms for use in making individual applications under
No. 10 of the Instructions for Colliery Recruiting Courts
will be obtainable from the Inspectors of Mines.

MINING INSTITUTE OF SCOTLAND.

A general meeting of the Mining Institute of Scotland
was held in the Heriot-Watt College, Edinburgh, on
Saturday, February 12, Mr. D. M. Mowat, president of
the institute, occupying the chair. Nominations were
received for the position of president, and for vacancies
as vice-presidents and councillors, and it was announced
that the election would fall to be carried out at next
meeting.

Compressed Air for Coal Cutters.

The discussion was resumed on the paper contributed
by Mr. Sam Mavor, Glasgow, on “ Compressed Air for
Coal Cutters.” (Colliery Guardian, September 17 and 24,
and October 1.)

The President having reviewed a number of the more
interesting points dealt with in the paper,

Mr. Sam Mavor replied to the criticisms offered at
the last meeting of the institute. In remarking on the
efficiencies of 30 and 40 per cent, referred to in the
paper, Mr. Anslow (he said) seemed to have overlooked
that these efficiencies did not refer to the system as a
whole, but to tests of individual motors working at full
load and under favourable conditions. The efficiency
referred to expressed the ratio between the energy
developed by the motor and the energy in the air sup-
plied to the motor, disregarding losses in transmission
or the air. Assuming that a compressed air plant was
in'fairly good condition, the over-all efficiency as defined
in the paper during an eight hours shift or a 24 hours
day was very largely governed by the load factor of the
plant. As had been pointed out, the efficiency of the
compressed air system was peculiarly sensitive to the
load factor. An over-all efficiency of 20 per cent, during
a shift would be a very good result, and would be diffi-
cult to attain with the fluctuating load of a coal-cutting
plant. Mr. Bryson’s question as to the effect of the
position of the orifice, etc., on a pressure gauge had been
anticipated in the course of the enquiry. Experiments
were made with the orifice facing upstream, facing
downstream, and at right angles to the direction of the
stream, and no difference could be detected on the dial
of an ordinary pressure gauge. An instrument of
greater delicacy, such as an U-tube, was required to
measure the difference of pressure due to velocity head
at the rates of flow usual in air pipes. Mr. Dixon had
referred to an opinion which was the main cause of
inefficiency in the compressed air system, viz., the
system was so simple in application that everyone under-
stood it. This view ought to be rejected. It should be
understood that compressed air, more than any other
system of power service, required close and unremitting
attention to the details as a condition of even moderate
efficiency. Mr. Black’s description of his experience
with a small compressed air pumping plant with electric
drive, was a forceful illustration of the value of measure-
ment. In this case, the measure of the power used was
presented by the bill of the electric supply company in
the convincing form of £ s. d., and the penalty of the
wasteful method was thrust home. Where the cost of
power and the efficiency of the compressor were known
—-which could be ascertained without much difficulty—
an air meter might be calibrated to record the £ s. d.
value of the compressed air delivered. The records
of a meter, which piled up the shillings like the meter
of a taxi-cab, would probably be treated with more
deference than one which gave a mere summation of
cubic feet of air. Mr. Dron’s complaint that a satis-
factory electric drill had not been produced, was irrele-
vant to the problem of raising the efficiency of the
compressed air system. Hitherto the compressed air
rock drill, despite its low power efficiency, yielded in
practice the highest commercial efficiency, and it there-
fore had held the field against all competitors, including
drills on the internal combustion principle. He (Mr.
Mavor) however, believed that the days of the com-
pressed air rock drill wTere numbered. He had seen in
operation a rock drill, with an entirely novel system of
power transmission, which absorbed only one-fifth of the
power required by a compressed air drill, and could be
used in association with any existing electric plant. This
system had features which differentiated it from all
other . attempts to compete with the compressed air
drill, and he believed it was destined to revolutionise
rock drilling in all branches. With regard to explosions
in air receivers, the cause usually attributed was the
use of oil with too low flashpoint. Explosions had,
however, occurred within compressors in cases where the
flashpoint of the oil was higher than the temperature
normally due to the degree of compression of the air.
Derangement of the water cooling system might permit
abnormal rise of temperature in compressor cylinders;
he had found that the interior walls of the water jackets
of some compressors were covered with a thick layer of
water-deposited scale, which was a non-conductor of
heat. There could be no doubt, however, as Mr. Forgie
had pointed out, that safety was to be found in the use
of oil with a flashpoint giving an ample margin above
the normal temperature due to compression. It was
true that the cost of maintaining compressed air plant
was less than the cost of maintaining electric plant, but
that applied to existing conditions whereby electric plant
received a degree of attention to its maintenance, which
was denied to compressed air. Too little was expended
on maintaining compressed air plant, and this was the
explanation of the extremely low efficiency. . Increased
outlay in. improving and maintaining the condition

of air plant would, by raising efficiency, be
very profitable expenditure. With regard to the losses
due to wire-drawing, he was in complete agreement with
Mr. Forgie. As Prof. Burns had said, there were
misconceptions as to the effects of “ wire-drawing ”
compressed air, but his own remarks did not tend to
dispel them; the statement that wire drawing did not
seriously affect the efficiency of compressed air could not
be accepted.' It was true that when wire drawn, the
compressed volume of -air expanded, but by Boyle’s law,
to which Prof. Burns referred, this was only another wTay
of saying that its pressure was reduced in the same ratio.
Difficult problems of entropy in relation to this subject
awaited investigation, but these need not concern them
at present. The practical result of- wire-drawing com-
pressed air could be stated so briefly and clearly as to
leave no room for misunderstanding. When energy was
expended in compressing, for example, 1,000 cu. ft. of
free air to 601b. per sq. in., and the air was then so
wire-drawn that its pressure was reduced.by 201b., there
remained 1,000 cu. ft. of free air compressed to 401b.,
and the energy that w’as expended in raising the pressure
from 401b. to 601b. was lost absolutely and irrecover-
ably, and that, too, in respect of efficiency, without any
compensating advantage whatsoever. That statement
was unchallengeable, and it was sufficiently concise and
clear to sweep away any misunderstanding of the
seriously wasteful results of wire drawing or throttling
compressed air? But the loss due to wire drawing did
not end here. In practice the most mischievous wire
drawing occurred in the smaller valves and piping close
to the coal face, after the air had already been lowered in
pressure by transmission from the surface. Wire-
drawing through small valves and hose pipes at the
face frequently so further reduced not only the pressure
but also the temperature of the air, that the remaining
energy had lost much in availability for useful work.
The coal cutter air-motor might run at full speed, but
with insufficient air pressure to develop the required
power. • The cutting speed was thus reduced, and the
volume of air used per square yard cut was
extravagantly increased. A practical difference between
wire-drawing air through , a restricting orifice and'wire-
drawing through long lengths of piping was that-, in the
former case, there was sudden lowering of temperature
where the air issued from the orifice, and this fall of
temperature involved loss of capacity for useful work;
whereas, in the latter case, the air, although equally
reduced in pressure at the end of the pipe line, might
have time in its passage to recover the temperature of
the mine, so that the loss of available energy would be
only that due to the reduced pressure. He strongly
recommended that a plan should be made, and kept up
to date, bearing upon the. arrangement and size of air
piping, the position of receivers, valves, etc. Such plans
were used at collieries to show the ventilating system
and the electric cable system, and if adopted for the
compressed air system would provide the manager with
a means of control.

The discussion was closed, and a vote of thanks passed
to Mr. Mavor.

Forming a Shaft Pillar in Thin Seams.

Discussion was resumed on the paper read at the last
meeting of the institute, by Mr. James Black,
Shettleston, on “ Forming a Shaft Pillar .in Thin
Seams. ”

Mr. R. W. Dron (Glasgow) wrote that he had recently
formed shaft pillars on the system described by Mr.
Black, and was satisfied that the results obtained fully
justified the innovation. In laying out the pillars, his
method was first to lay down a pillar of sufficient size to
provide for the protection of colliery buildings. In the
case of normal coal measures strata, lying at a moderate
inclination, he took fully one-third of the depth from,
and marked off that distance around, the outside line of
the buildings to be protected. The workings within this
area were then regulated so as to allow of the extraction
of about 20 per cent, of the coal, and the shape of the
pillar was altered where necessary so as to leave in
rectangular blocks of coal. The roofs and pavements
he had dealt with had been fairly strong sandstone, and
at a depth of over 1,200 ft. there had been no trouble
with crush or creep. He had not had similar experience
with soft roofs and pavements, or with soft coal, but
was inclined to think that under such circumstances
there would be less trouble with the longwall places
than there would be with places nine or ten feet wide.
It would be very interesting if some of the members
who had experienced difficulties in maintaining roads
through the shaft pillars could give their views on this
point.

It was agreed to continue the discussion on this paper
at next meeting.

Mr. Henry Briggs then read a paper entitled “ A
Device for the Rapid Estimation of Oxygen and Black-
damp in Mines,” which will be given in next week’s
issue.

The Morning Post understands that an arrangement has
been made between the British Government and the Italian
Government for the supply and transport to our Ally of
coal, for use in her Navy, in the manufacture of munitions,
and on the State railways. It is understood that the
Admiralty have been asked to purchase the necessary
quantity of coal for the Italian Government, but it has
been impossible, in view of the needs of the British Navy,
to satisfy the demand from the Welsh coal fields, and it
has therefore been necessary to enquire whether for Italian
use types of coal from the Northumbrian and Scottish mines
would not be serviceable. The question of transport is one
of considerable complexity, and a committee is at present
engaged in assessing the number of vessels which are not
required in the work of the British or Allied Governments,
or in the transport of war material to Allied countries.
When this work of assessment is complete, it is hoped to
allocate to each of the different Governments a certain
number of vessels at Admiralty rates for the carriage of such
goods as coal.

THE GERMAN AND AUSTRIAN COAL
AND IRON TRADES.

We give below further extracts from German
periodicals that have reached us, showing the course of
the coal and iron trades in Germany :—

Coal Syndicate Report for December and the Whole of 1915.

Total coal raised in December, 6,429,689 tons
(5,661,200 tons in December 1914), or 255,908 tons
(233,452 tons) per working day. Calculated distribu-
tion, 4,730,490 tons (4,469,072 tons), being 188,278 tons
(184,292 tons) per working day, or 63-91 per cent.
(62-95 per cent.) of the participation. Total coal dis-
tribution, 6,303,161 tons (5,839,695 tons), or 250,872
tons (240,812 tons) per working day. Deliveries,
including local sales, miners’ house coal, and supplies
to pits’ own iron works : Coal, 3,507,238 tons (3,622,478
tons), or 139,592 tons (149,381 tons) per working day;
coke, 1,547,938 tons (1,114,147 tons), or 49,933 tons
(35,940 tons) per working day; briquettes, 295,750 tons
(355,843 tons), or 11,771 tons (14,674 tons) per working
day. For the whole of 1915, the total coal raised
amounted to 73,984,097 tons (84,809,916 tons), or
245,183 tons (281,060 tons) per working day; calculated
distribution, 58,047,597 tons (64,666,066 tons), being-
192,370 tons (214,303 tons) per working day, or 65-44
per cent. (73-00 per cent.) of the participation; total coal
distribution, 74,988,085 tons (83,411,307 tons), or
248,544 tons (276,425 tons) per working day; deliveries,
including local sales, miners’ house coal, and supplies to
pits’ own iron works—coal, 43,031,721 tons (55,146,642
tons), or 142,607 tons (182,756 tons) per working day;
coke, 17,418,150 tons (14,816,139 tons), or 47,721 tons
(40,592 tons) per working day; briquettes, 3,970,243
tons (3,917,774 tons), or 13,157 tons (12,984 tons) per
working day.

The collieries having a sales agreement had a coal
production of 493,920 tons (363,402 tons) in December,
and 5,175,377 tons (5,275,982 tons) during the whole
year. Their total coal distribution for December was
453,025 tons (333,564 tons), and for the year 4,652,687
tons (4,851,838 tons). Of this the amounts distributed
on Syndicate account were 196,457 tons (104,967 tons)
and 1,921,852 tons (1,934,644 tons) respectively. The
total coke distribution was 117,950 tons (114,519 tons)
and 3,313,798 tons (1,520,549 tons), and the distribu-
tion for Syndicate account 61,021 tons (88,571 tons) and
792,930 tons (1,003,587 tons) respectively. The sales
of briquettes were : December, 4,298 tons; whole year,
36,764 tons, all conducted through the Syndicate.

German Coal Output in 1915.

The total , coal production in Germany during 1915 is
stated to have amounted to 146-712 million tons, as
compared with 161-535 million tons in 1914, and 191-511
million tons in 1913; the Prussian output being 139-786
million tons, against 153-006 million tons in 1914. The
brown coal production was 88-370 million tons (83-947
million tons in 1914, and 87-116 million tons in 1913);
Prussia’s share being 71*829 million tons (67-424 million
tons in 1914. The coke production fell from 32-168
million tons in 1913, and 27-325 million tons in 1914, to
26-359 million tons, of which Prussia produced 25-942
million tons (26-788 million tons in 1914). Coal
briquettes were produced to the extent of 6-392 million
tons (5-949 million tons, and 5-824 million tons in the
two previous years); and brown coal briquettes to the
extent of 23-350 million tons (21-449 million tons in
1914, and 21-418 million tons in 1913).

Deliveries by the Steel Works Union in December.

The total distribution, calculated on weight of raw
steel, amounted to 264,970 tons, as compared with
24,750 tons in the previous month, and 268,189 tons in
December 1914.

German Production of Medium Steel in December.

The report of the German Iron and Steel Makers’
Association gives the output of medium steel in the
Customs Union during December as 1,162,895 tons
(1,192,682 tons in November), or 44,726 tons (40,707
tons) per working day. Of this total, 567,454 tons
(565,084 tons) consisted of basic steel, 14,886 tons
(15,912 tons) of Bessemer steel, 472,614 tons (498,773
tons) of basic open-hearth steel, 19,300 tons (24,089 tons)
of acid open di e ar th steel, 42,400 tons (45,044 tons) of
basic cast steel, 23,934 tons (22,111 tons) of acid cast
steel, 7,733 tons (8,390 tons) of crucible steel, and 14,574
tons (13,279 tons) of electro steel. Rhenish Westphalia
produced 665,306 tons (688,233 tons); Silesia, 103,467
tons (109,903 tons); Siegerland .and Hesse-Nassau,
24,445 tons (27,421 tons); North, East, and Mid-
Germany, 44,374 tons (41,844 tons); Saxony, 21,528 tons
(22,691 tons); South Germany, 10,899 tons (11,947
tons); Saar district and Bavarian Rhinepfalz, 92,283
tons (94,239 tons); ■ Elsass-Lothringen, 104,089 tons
(101,893 tons); and Luxemburg, 95,774 tons (94,511
tons).

German Hoop Iron Prices.

The Hoop Iron Association has advanced the price of
this article, by 10 mk. per ton, to 180 mk.

Company Reports.

Gewerkschaft Oespel, Kley.—In the first quarter, 51,939
tons coal, 7,630 tons coke, and 6,075 tons briquettes
were produced, the sales amounting to 51,539 tons coal,
8,916 tons coke, and 6,076 tons briquettes. Against a
trading profit of 28,269 mk. were liabilities on interest
and loans which necessitated a call of 35,439 mk. on
the shareholders.

Gewerkschaft des St einkohlenb erg works Lothringen,
Gerthe.—In the first quarter of the present year, 175,880
tons of coal were raised (192,615 tons in the previous
quarter and 265,260 tons in the first quarter of 1914).
Coke production, 74,315 tons (68,003 tons and 78,310
tons respectively). Working profit, 451,662 mk. (388,672
mk. and 901,122 mk.). Dividend, 250 mk. (250 mk.
and 500 mk.) per share.