February 22, 1918.

THE COLLIERY GUARDIAN

391

tical mining. The speaker had always contended that,
in actual mining practice, the ultimate destruction of
a prop at a coal face was seldom due to the compres-
sion caused directly by the descent of the roof but to
“ buckling ” or bending and shearing created indirectly
by it. No one knew the exact direction in which the
roof exerted its pressure, and the props set to resist
it were seldom in line with the lines of force in the
roof. Consequently, compression in many cases only
resulted in tightening up, while bending and shearing,
due to the different directions of force exerted on the
props by the roof and floor, accounted for the rest in
effecting the destruction of the prop. Compression
only caused crushing, whilst bending and shearing
caused breakage and splitting; and, when it was seen
that, nearly always, a destroyed prop at a coal face
was due to its breaking, no further proof for the veri-
fication of that statement was needed. Tests must
approximate as nearly as possible to the actual working
conditions at a coal face before the figures derived
therefrom could be of practical use to mining engineers.
Mr. Booth’s tables fulfilled these conditions admirably.
Mr. Booth had stated that the strength of a prop was
independent of its length within the limit of 4| ft., and
had made no mention of the likelihood of a ratio
between the length and the diameter of the prop.
Prof. Louis’s conclusion on that point was almost
identical; for the latter, in dealing with that point
in his paper on “The Strength of Pit Props” (Trans.
Inst. M.E., 1897-8, vol. xv., p. 343), had gone into
details and had stated that there appeared to be no
relation whatever between the strength of a prop and
the ratio of its length to its diameter. As a probable
reason for the greater- liability of long props to break-
age than short ones in mining practice, Prof. Louis
thought it was due to certain weak spots contained in
the props—the longer the props the greater being the
tendency for such weak spots to be included in them.
Thus, the probability of failure depended upon abso-
lute length and not upon the ratio of length to dia-
meter. Still, in his (Mr. Lee’s) opinion, there ought
to be some relation between the length and the dia-
meter of a prop, and the probability of failure seemed
to him not to lie in the absolute length only, but also
in a definite ratio of the diameter to the length. In
theory, there was certainly no difference in the results
owing to the length of a prop when it was in true com-
pression; but, in practice, a prop was seldom in true
compression, being subject also to bending and shear-
ing and, perhaps even, torsion and, although length
did not affect the first form of stress, it played a pro-
minent part in any or all of the last three forms. That
being so, it could not technically be taken for granted
that it was so, although practical tests seemed to con-
firm the statement to the contrary. The speaker was
of opinion that a prop had its limits of flexibility, as
well as its limit of rigidity. By rigidity, he meant
the material strength of the prop to resist more or
less longitudinal compression; by flexibility, he meant
the elastic strength of the prop to resist more or less
transverse bending and, consequently, “buckling.”
Thus, when the diameter of a prop was large and its
length small, it could only be destroyed by overcoming
its rigidity, the flexibility having no share in the
result; if the reverse were the case, it would be
destroyed by overcoming its flexibility, the rigidity
being only a minor factor. So long as the rigidity was
equal to or greater than the compressive force, so long
would the prop retain its original condition and shape
without any visible sign of alteration whatever. When
that strength was overcome by the external force
applied, the prop collapsed and was crushed. That
condition could not, however, be arrived at unless the
length of the prop was comparatively small in relation
to its diameter. If the diameter of the prop remained
the same but its length were gradually increased, a
certain limit of length would be found below which
the prop would be crushed rather than bent and
broken, and above which the prop would be bent and
broken before the limit of crushing strength was
reached. The greater the increase in length the more
marked the difference should become. In such cases
he would hardly regard it as wholly due to the proba-
bility of weak spots contained in the prop, although the
latter might be responsible in certain ways. The
reason the tests had, apparently not revealed any indi-
cation of this conclusion was due to the likelihood that
“within reasonable limit,” according to Prof. Louis,
and “within the limit of 4|ft.,” according to Mr.
Booth, the length of each prop used in the tests in
relation to its diameter just afforded the suitable state
of arriving at the point where the limit of rigidity
finished and that of flexibility commenced. Thus, the
props were destroyed due either to their rigidity being
overcome when their lengths were well within the limit
of the working ratio to the diameter, or to their flexi-
bility being overcome shortly before the limit of rigidity
was about to be reached, when their lengths slightly
exceeded that ratio. Prof. Louis took the length of
a prop to be 12 diameters as the proportion in ordinary
mining practice and, in the absence of practical data
of his own, the speaker suggested that that was, per-
haps, about the length limit whereat the magnitude of
the force required to overcome rigidity and flexibility
was about equal; and, as the conditions, such as sound-
ness, individual variations in lengths and diameters,
etc., of props differed, the form of their destruction
also varied—being due to crushing in some cases and
to “buckling” and shearing in others.

Mr. T. G. Lees (Nottingham) wrote that the subject
was worthy of the closest attention of colliery managers
in the present difficult times. Many collieries were
unable to get sufficient prop timber of the particular
size, as regarded diameter, most suitable for their
requirements. Home-grown trees were, generally, not
so economical as the foreign-grown, as there appeared
to be more taper and also knots in the former, and
it was difficult, in cutting up a tree grown in this
country, to obtain so many props of the required dia-
meter, the tops being too thin and the butt ends too
thick. On the other hand, the foreign timber varied
very little in diameter from the thick end upwards.

The practice of splitting trees to obtain prop lengths
of adequate strength had been adopted at many col-
lieries recently. It very often happened that the butt
ends of trees were too thick to use otherwise than by
sawing them up, and short ends might be very usefully-
split into four pieces by running the saw down them.
The point to be borne in mind in that method of
supplying prop wood was that sufficient cross sectional
area should be allowed when the tree was split to be
fully equal to the area of a round prop of the cor-
responding length. It was quite easy to provide a
table showing the size of trees that might be sawn
down allowing for the sawgate to guide the sawyer
as to the sizes from which he must cut suitable props
corresponding to round props of, say, 4 in., 4|in.,
o-Jin., etc., diameter. The experience at Newstead as
to the relative strength of sawn props compared with
round props of the same area practically confirmed the
author’s estimate, i.e., there was a loss of about 23 per
cent. The writer showed, diagrammatically, other
methods of utilising the thick ends of trees. Taking
a tree 8 in. in diameter, two props and a benk bar
might be obtained by sawing through the centre of the
tree for about two-thirds of its diameter- to obtain the
two props and then cutting a cross section of the tree
at right angles to the original cut. Again, taking a
12 in. diameter tree, four props and two benk bars
could be cut, by sawing through the tree once through
the middle and twice, at right angles to that cut, at
intervals of one-third and two-thirds, respectively, of
its diameter, the four corner pieces forming the props
and the two inner pieces the benk bars. The results
shown in Tables I. and III. were rather surprising, the
load per sq. in. in Table III., with props 4 ft. 6 in.
long, showing slightly higher than for 18 in. props in
Table I. It would be interesting to continue the
experiments as to the comparative strengths of props
of varying lengths of the same diameter. The advisa-
bility of not using freshly felled timber for props, as
indicated by comparing Tables VI. and VII., was
generally borne out in practice.

Mr. Geo. S. Bragge (Birmingham) wrote saying he
assumed that the props tested were foreign timber.
His experience of English timber had not been very
favourable, probably owing to the timber being green.

Mr. Mark Halliday referred to Mr. Booth’s finding
that the strength of a round prop was independent of
its length within the limit of 4 ft. 6 in. He said he
took it that none of the props collapsed by bending,
but all by crushing. So far as he was aware, the
accepted theory of long columns took into account the
radius of gyration, and that figure did not enter into
the strength of short columns in any ivay whatever. It
appeared to him that they must look somewhere else
for the reason that a quartered prop was not as strong
as a round prop.

Replying, Mr. Booth said he thought Mr. Leach
made some suggestion as to the pressure of the roof.
That could hardly have anything to do with his experi-
ments, as the conditions were the same in each ease.

Mr. Leach interposed that Mr. Booth’s pressures
were all at right angles to the axis, but in the pits
that was not so. The props might be all right for Mr.
Booth’s tests but not for the pit tests.

Mr. Booth continued that he was prepared to
accept Prof. Louis’s idea that the fixing of the ram
might have something to do with the results obtained.
As to Dr. Atkinson’s remarks, the speaker had had no
previous experience with cut props until the necessi-
ties of the present time compelled him to try them.
Provided they were carefully cut and not cut from
timber with diagonal sun cracks, his experience was
that they were quite satisfactory. Mr. Lee, in his
lengthy contribution to the discussion, had raised no
question for the speakei- to answer. Mr. Halliday’s
question was really outside the scope of the paper, as
the tests were entirely practical; perhaps Prof. Louis
could answer the point raised by Mr. Halliday at
some other time.

On the motion of the President, Mr. Booth was
accorded a vote of thanks, and the discussion was
adjourned until next meeting.

OBITUARY.

The death occurred last week at Lydney of Mr. George
E. Elsmore, for 26 years secretary of the Lydney tin-plate
works of Messrs. Richard Thomas and Company.

Mr. Robt. Peel, of The Towers, Durham, who has died
at the age of 56 years, studied mining at the Durham
College of Science, Newcastle, under the late Prof. J. H.
Merivale. He served his apprenticeship as a mining engi-
neer with his father, the late Mr. John Peel, and after-
wards at Lord Durham’s collieries at Lumley. In 1892 he
was appointed manager of New Brancepeth Colliery, and
in 1914 became managing director. He was a magistrate
of Durham county, a member of Durham Board of Guar-
dians and of Brandon Urban District Council, of which
latter body he was chairman for four years, and was one
of the governors of the Johnston Technical School,
Durham.

Mr. John Oilerton, secretary of the Blainscough Colliery
Company Limited, died on Wednesday last week at his
residence, Rose Mount, Coppull, near Wigan. The
deceased was in his 64th year.

The funeral of Mr. Walter Mayhew, of Duxbury Hall,
who was director of the Garswood Coal and Iron Company
Limited, Wigan, took place at the Ghorley Cemetery on
Saturday last -week, when Mr. W. Clark, general manager
of the Garswood Coal and Iron Company, was present as
representing the board of directors of the firm. Mr. W. H.
Hewlett, J.P., of Standish, the managing director of the
Wigan Coal and Iron Company Limited, who is a brother-
in-law of the deceased, was among the mourners. The
deceased, who was in his 80th vear, was a former Mayor
of Wigan.

Exports of Coal Products.—The exports of coal products
(excluding dyes) in January were valued at £242,557, com-
pared with £244,771 a year ago, and £275,640 in January
1916.

MILITARY HONOURS.

Among the new D.S.O.’s is Second-Lieut. A. R.
Latch, aged 27, of the firm of Latch and Batchelor
Limited, and son of the late Mr. Arthur Latch, of
The Firs, Edgbaston. Aftei’ serving for some months
as a private in the Worcestershire Regiment, he was
commissioned in the Tank Corps, and was wounded in
the battle for Cambrai in November, in which action
he was awarded the D.S.O. for gallant services. He
showed great skill and determination in this action,
and later he went in a disabled tank to the assistance
of an isolated battalion, and by his action was suc-
cessful in breaking up a counter attack, relieving the
situation, and, although wounded himself, being the
means of killing a large number of the enemy and

2nd Lieut. A. R. Latch, D.S.O.

capturing numerous prisoners. Second-Lieut. Latch
married the second daughter of Mr. A. Cecil Wright,
of Brandwood House, and Borth, Cardiganshire (High
Sheriff of Cardiganshire), to whom we are indebted for
the above particulars.

LABOUR AND WAGES.

South Wales and Monmouthshire.

The decision of the Coal Controller as to the payment of
the war wage settles a dispute at the Powell Duffryn pits.

The workmen at Bargoed held a mass meeting which
had been called to consider the attitude of the company in
“ refusing to pay the fifth of bonus turns to night workmen
and the war wage granted by the Controller.” The meeting
was adjourned to consider the Controller’s reply.—A
further meeting was held on Saturday, when Mr. Lewis
reported that the matter had been put right —Mass
meetings of the men held on Sunday at Bargoed, Pengam,
New Tredegar and other places passed resolutions to pro-
ceed to work as usual on Monday.

The colliery examiners of South Wales held a meeting in
Cardiff on Saturday, and a report was presented as to the
joint board of employers and examiners. This report was
considered to be unsatisfactory, seeing that at some of the
collieries the war wage had not been paid in full, whilst in
two collieries no payment at all had been made on this
account.

The railwaymen of South Wales held a mass meeting in
Cardiff on Sunday and passed a resolution strongly protest-
ing against differentiation which had been made in regard
to shopmen in the recent wages increase. Some of the shop-
men had received 12| per cent, on day rates and 7i per cent,
on piece work ; but those in the engineering departments,
also the carpenters, blacksmiths, etc., had not received the
advance. Strong protest was made against this, and a
deputation was appointed to wait upon the management of
each of the local lines.

The executive council of the South Wales and Mon-
mouthshire Iron and Steel Works Association met in
Cardiff on Saturday and discussed their application for 20
per cent, increase of wages, a circular having come from the
Ministry of Labour. The council decided that the matter
should stand in abeyance for a month, and that meanwhile
other matters should be dealt with:—(1) The subsidy of
iron and steel manufacture because of the increased cost of
coal and coke; (2) the award of 12J per cent, bonus to some
sections of workmen and only 7i per cent, to others.

Several matters of importance came before the Federation
executive at its meeting on Friday, the first being that of
the five days week proposal. As to this, a letter was read
from the Coal Controller, who said he did not approve of
applying generally the principle of curtailing work ; but
he suggested that men should be transferred from pit to
pit or to other work of national importance. The executive,
after considering the letter, resolved to bring the matter
again before the Controller. A letter from the Ministry
of National Service dealt with the idea of removing colliers
to other employments; and the executive decided to call
for volunteers, resolving in this connection that the men
should register locally, and that all applications should go
through the general secretary, the men being further
advised not to take any steps till they heard from
Mr. Richards, who would have full instructions posted at
the pit top as soon as practicable. As to engagement of
men in the Army for tunnelling work, the Miners’ Federa-
ation of Great Britain recommended obtaining a wage
agreement with payment to start from enlistment.

The point which has been at issue between employers
and men as to the war wage also came before the executive .-
were the men entitled, as they claimed, to six payments of
war wage for working five nights ? On afternoon and night
shifts, they had previously been paid six for five; and they
held that this should apply in the case of the war wage ; but