696

THE COLLIERY GUARDIAN.

April 4, 1913.

economic reasons would prevent the use of spirally
reinforced concrete columns of such small dimensions. As
was expected, the square columns gave better results per
square inch than the round columns.

Table III. shows the results of tests on the first set of
posts made.

Table III.—-Compression Tests on Square and Round
Posts, Concrete Plain and Reinforced, 8 ft. Long
(Age of Concrete (1:2:5) Two Months.)

thickness of the crown is only 8 in. The depth of cover
over this culvert is to be 90 ft., not solid, but tipped
earth.

With such examples and many others it seems evident
that reinforced concrete will have an extended use in the
future for main roads when the pressures are great.

In conclusion, I should like to thank Mr. E. L. Morgan,
B.Sc., and Mr. Imam Shaban, who have carried out the
tests on the beams and posts referred to in this paper.

No.

O co

■ co

O <D

Section.

Reinforcement.

a

-c cr-

0 a ”
O J B.

1	... 2 ...8in. « 8in....	(Plain)	... 1.270

2	...	2	...8 in.	x 8in.... I.	Jin. x Jin.,7	ft.	8in. long...	I,2n6

3	...	2	...8in.	x 8in....l,	1 in. x 1 in.,	„ ...	1,300

4	... 2 ...8in. diam....	(Plain)	... 1,234

5	...	2	...8in.	diam ...1,	fin. diam, 7	ft.	8 in. long...	1,020

6	...	2	...8in.	diam ...1,	1 in. diam,	„ ...	1,068

Tests on sixteen posts of triangular cross-section and
eighteen beams show similar results, which, however,
cannot be exactly compared with the above, since by a
mistake the proportions were not exactly the same, the
mixture being a little richer in cement. The results
show, however, that there is no difficulty in making,
storing, and transporting suitable beams and posts of
concrete whose proportions are even as poor in cement
as 1: 2 : 5.

The cost of these members, when cast in steel moulds
and with the simple reinforcement described, can be
readily determined according to local conditions. The
posts, being cast vertical, needed hardly any ramming,
and from their moderate height presented no difficulties.
Both props and beams were easily handled, the beams
weighing about 1001b. per lineal foot. The slides show
the various ways in which the beams and posts failed.

The considerable increase in strength with age up to
twelve months should be very valuable in the case of
mining work. Owing to gradual settlement, the load on
the head and side trees in the headings is often found to
increase with time. But, as already stated, when great
pressures are expected, the only satisfactory method of
resisting them is by a complete shell in which the invert
supports the side walls. Here, then, are the real oppor-
tunities for the engineer in reinforced concrete work.
It is necessary to arrange for this work at the beginning
because it would be found very difficult to replace timber-
work with a reinforced concrete arch, which itself
would need to be supported on centres for a consider-
able time.

At Baggeridge the pit bottom, whose height is 60 ft.
and about one-third mile below the surface, is all rein-
forced work, and also some of the main roads, but though
reinforced the concrete is itself very thick, and it will be
seen in many cases when reinforced work is used under-
ground that, little confidence seems to have been placed
in the reinforcement. Except on the Continent it is
only in a few isolated cases where sections reinforced
with steel are made lighter than wbuld be safe with
cement only. In arch work designed for compression
only, like the original arches on the Monier system, we
have a method of construction too little used. I would
remind mining engineers who may be present of the tests
of one of the first Monier arches built in 1890. In this
instance the test arch was 32'8 ft. span, with a rise of
only 3'28 ft., the width being 13 ft. The depth at the
crown was 6 in. The reinforcement was iron wire '39 in.
and 0'28 in. diameter placed 3 in. c. to c., and 2 in. from
the soffit. The following tests were applied : first a
locomotive weighing 40 tons was placed at the crown,
then it was run off and a locomotive of 53 tons weight
was run over half the arch. Having stood these loads
successfully, a dead load of 110 tons was piled on the
half-span, the load being about 1,000 lb. per square foot
and the deflection at the centre only 0T2 in. When the
load on the half-span was increased to 2,000 lb. per square
foot the arch failed, but by the abutments yielding.
These tests show what a well-designed arch of reinforced
concrete will stand. Tests were carried out of an
arch of plain concrete, span 10 ft., rise 1 ft., width
3 ft., and thickness of ring 6 in. Loaded uniformly,
through sleepers resting on sand, it did not fail
till the total load was 60 tons, or 4,480 lb. per square foot.
The arch is one of a series of arches being tested at the
University of Birmingham, and is instanced in support
of the statement that in many cases the reinforced con-
crete arches built at present might be quite safe enough
without the reinforcement. Several examples of large
sewers and underground drains might be given to show
structures as large as mining headings carried out in
concrete and reinforced concrete. To mention but
two examples of these : the first, the great sewer in St.
Louis, and the second probably the boldest sewer con-
struction in reinforced concrete—the Ouseburne culvert
at Newcastle, where has been built in bad ground this
enormous culvert, whose diameter is 30 ft., while the

AN IMPROVED CAPEL

Messrs. Tucker and Goodwin, of the Birehills Foundry,
Walsall, have communicated to us the results of tests
carried out recently on an improved capel for winding
ropes which has recently been placed upon the market.
The general construction of the capel will be seen from
the accompanying illustrations (figs. 1 and 2). The capel
proper is formed with a recess A tapered towards the
centre and both ends; an iron core of corresponding

’^miiiiirniiiiiii ' "' '

c	, c

Figs. 1 and 2.

THE INFLAMMABILITY OF CARBONACEOUS
DUSTS.

Home Office Report.

In consequence of the two serious dust explosions
which occurred in November 1911, at a provender mill
in Glasgow, and an oil cake factory in Liverpool, a
series of experiments has been carried out at the Home
Office Experimental Station, at Eskmeals, by Dr.
Wheeler, the chemist attached to the Explosions in
Coal Mines Committee, with samples of all kinds of
carbonaceous dust—so far known to the inspectors—
which are liable to be generated on premises under the
Factory and Workshop Acts, with a view to determine
their degree of inflammability and capacity to transmit
explosions. The results of the experiments are given
in a report by Dr. Wheeler, which has just been
published by the Home Office [Cd. 2662]. Experiments
were made with 66 samples in all. The samples were
not specially selected, but were in all cases ordinary
samples taken by factory inspectors from beams, ledges
or other projections in the course of their inspections.

Two methods of testing have been employed; one for
the purpose of discriminating between harmless and
dangerous dusts, the other with the intention of
ascertaining the temperatures at which inflammation of
the dangerous dusts takes place readily. As a result
of these tests it has been found possible to divide the
dusts into three classes, namely :—

Class I.—Dusts which ignite and propagate flame
readily, the source of heat required for ignition being
comparatively small; such, for example, as a lighted
match.

Class II.—Dusts which are readily ignited, but

,..w

...

■

Fig. 3.



shape C is formed with a slot B, in which the middle
strand of the rope is laid, the remaining wires being
wrapped round the core in the manner shown in the
photograph (fig. 3). This is then inserted in the recess
A, the capel being then clamped in the usual way by
means of rings. The obvious advantage of the method
is that it obviates the necessity of bending back the
wires and thereby increases the resistance of the rope as
a whole.

The tests referred to were carried out at Lloyd’s
Proving House, Oradley Heath. The first test was made
with a 1T\ in. six-strand plough shear steel rope made by
Messrs. Haggie Bros. Limited, Gateshead-on-Tyne,
which broke under a load of 32 tons. In the second test
a if in. lock-coil rope was tested to destruction, breakage
occurring at 30 tons 10 cwt., whilst in the last test a rope
of similar dimensions broke at 31 tons 7 cwt. In this
case the rope had been previously in use at the Sandwell
Park Colliery and was reduced in diameter-A-in. and
lengthened 2A in. under strain in a distance of 26 in. In
no test were the capels broken or the ropes drawn.

The inventor is Mr. H. Weetman, of Walsall.

Grimsby Coal Exports.—During the week ended March 28
the exports of coal from Grimsby totalled 22,089 tons in the
foreign trade and 364 tons coastwise, the shipments being
as follow :—Foreign : To Aarhus, 882 tons ; Assens, 1,215;
Bandholm, 1,220; Dieppe, 960; Esbjerg, 321; Gothenburg,
2,543; Hamburg, 2,102; Havnefjord, 627; Helsingborg,
1,728; Hoganas, 601; Karrebecksminde, 1,003 ; Landecrona,
4,023; Langesund, 427 ; Malmo, 1,351; Ronne, 722;
Rotterdam, 724, and Savona, 1 640. The coastal shipments
were: 102 tons to London and 262 to Whitstable.

Examinations under the Coal Mines Act.—An examina-
tion for first- and second-class certificates of competency as
manager and under-manager of mines will be held on
May 27 next at Edinburgh, Newcastle, Sheffield, Wigan,
Cardiff, and Birmingham. An examination for certificates
of qualification as surveyor of mines will be held at the
same places on May 28. Candidates must, on or before
April 12, send their names and state the district in which
they are employed to the secretary (Mr. W. W. Ware) at
the Home Office, Whitehall, London, S.W., from whom all
particulars can be obtained.

which for the propagation of flame require a source of
heat of large size and high temperature (such as an
electric arc), or of long duration (such as the flame of a
Bunsen burner).

Class III.—Dusts which do not appear to be capable
of propagating flame under any conditions likely to
obtain in a factory; either (a) because they do not
readily form a cloud in air, or (&) because they are
contaminated with a large quantity of incombustible
matter, or (c) because the material of which they are
composed does not burn rapidly enough.

In Glass I., sugar, dextrine, starch and cocoa were
found to be the most dangerous, sugar exceptionally so.
Sugar ignites when projected as a cloud against a
surface heated to below red heat, and, when ignition
has taken place, the flame travels throughout the dust-
cloud with great rapidity. Of Class III. ten dusts are
all more or less readily inflammable, but they showed no
signs of being capable of propagating flame. It is
possible, however, that other samples of the same
materials, less contaminated with incombustible matter,
or in a finer state of division, might be found capable of
propagating flame.

In Test No. l.if ignition occurred, the temperature of
the platinum coil was lowered 10 or 20 degrees Cent-
and a fresh trial made ; and so on until two temperatures
were obtained, differing by 10 degs. Cent., at one of
which inflammation took place, whilst at the other the
dust-cloud passes over uninflamed. The mean
temperature was then taken to be the ignition-
temperature of the dust under the conditions of the
test.

The ignition-temperatures observed, which are relative
and refer only to the particular set of experimental
conditions employed, are given in a table. It may be
mentioned that the ignition-temperatures of most
bituminous coaldusts, as determined in the same
apparatus, lie between 1,000 degs. and 1,100 degs. Cent.
So far as possible the different dusts (all of which were
dried during one hour at 107 degs. Cent.) were obtained
of the same degree of fineness by passing through a
200-mesh sieve. In some cases this was not possible