640

THE COLLIERY GUARDIAN.

March 28, 1918.

upon the impermeable strata to which the linings are
lowered. The shaft is sunk some distance below the
water-bearing strata, and great care is taken to secure
a substantial and level bed for the tubbing to stand
upon, so that the moss box may form a watertight
joint.

The arrangement of the moss box for securing water-
tightness is as illustrated in fig. 4. The lowest ring of
tubbing is of slightly smaller diameter, so as to slide
within the ring next above it, and is guided by rods as
shown in the illustration. The upper flanges of the
two bottom rings are turned inwards, and the bottom
flanges outwards. The moss packing around the exterior
of the bottom ring is held in position with strong wire
netting and pressed against the sides of the tubbing
by means of springs. When the column of lining
tubes is lowered, the moss is compressed tightly against
the sides of the excavated shaft by the weight of the
superincumbent column of tubbing. After lowering
as above, and putting in the outside lining of concrete,
the shaft is pumped out. Should the water break
through underneath the moss box, as sometimes happens,
the shaft will rapidly become flooded, and this may even
lead to its abandonment, unless the water can be
removed by pumping, and the shaft recovered by addi-
tional appropriate works.

After lowering, the moss box is generally*underset by
one or more wedging curbs and one or two lengths of
tubbing so as to make it more secure. This being done,
sinking proceeds by ordinary methods. In a deep shaft
the weight of the tubbing may amount to several
thousand tons, and, to assist in lowering and handling,
provision is made for balancing this great weight by the
water displaced. For this purpose a false bottom is
fixed by screw bolts near to the bottom of the tubbing,
and through this is carried a central tube fitted with
cocks at intervals, in order that water may be let into
the tubbing for the purpose of assisting its descent.

The Kind-Chaudron system was used at Dover
Colliery (1903) to sink through the cretaceous strata,
and previously at several other sinkings in this country.
It is more suitable for use in fairly firm strata yielding
much water than for loose surface deposits of sand and
gravel, &c., to which latter the freezing or piling
methods are best adapted.

The principal advantages of the Kind-Chaudron
system are that—

1.	All work being done under water, no pumping is

necessary, and the sides of the shaft are thus
supported by the water. The risk of life is
reduced to a minimum, as nearly all work is
done from the surface.

2.	The system has seldom been known to fail, even

though adopted only in extremely difficult
cases, and its results are comparatively certain.

3.	There is less leakage of water through the

tubbing, there being no vertical joints. The
tubbing is not easily displaced, and falls and
flows of quicksand are reduced to a minimum.

Tubbing.—The thickness of tubbing must be appor-
tioned according to the depth it occupies in the shaft,
the external pressure of earth and water and the
aggregate dead weight increasing with the depth
reached. At Dover the bottom rings of tubbing weighed
over 16 tons each, and the upper rings over 7 tons. In
very deep shafts, say 1,300 ft. by 14 j ft. diameter, the
limit of thickness of cast iron tubbing is reached at
between 4 and 5 inches. Castings beyond this thickness
are not reliable and become very cumbersome to handle,
so that it becomes necessary at the greater depths to
endeavour to reduce the thickness of the tubbing, if
possible. This can be done by reducing the diameter
of the shaft—to which, however, there are obvious dis-
advantages owing to the limitations thus placed on the
sectional area available for winding, working, pumping,
and so forth. An alternative has been suggested of
putting down a large diameter shaft within which
several tubbing cylinders of moderate diameter may be
placed side by side, the spaces between these cylinders
being filled in with concrete.

Another possible alternative is to line the shaft with
two rings of tubbing instead of one, the annular space
between the rings being filled with fine concrete. The
necessary allowance in the diameter of the shaft would
have to be made at the outset to permit of this being
done.

Inland Transport.—The commercial group of the House
of Commons issued last week the report of a Sub-
Committee on Transport Reform, with special reference
to inland waterways. The report points out that nothing
has been done to carry out the recommendations of the
Royal Commission on Canals, while Continental countries
have spent large sums on canal improvements. Transport
by canal for many classes of goods costs much less than
carriage by rail, and the Sub-Committee believe that the
future welfare of the country depends to a large extent
on the development of inland waterways. They recom-
mend enquiry into the railway goods clearing-house scheme
and the appointment of a committee to enquire into the
whole subject of transport.

Ten Million Pounds Iron Combine.—The directors of
the Workington Iron and Steel Company Limited, in a
circular to shareholders, state that arrangements have
been made for the amalgamation of their company with
Steel, Peech and Tozer Limited, Samuel Fox and Company
Limited, and the Rother Vale Collieries Limited. The
first-named two own the whole of the share capital of the
Frodingham Iron and Steel Company Limited, which com-
pany owns one-half of the share capital of the Appleby
Iron Company Limited. After amalgamation it is pro-
posed to acquire the remaining half. In the opinion of
the directors the proposed amalgamation will assist in
retaining for this country the leading position in iron and
steel producing industries. The consent of the Treasury
has been obtained. The loan capital of the new enterprise
is £2,500,000, and the share capital £7,680,000. To pro-
vide for the cash requirements of the combined companies
it is proposed to issue £1,000,000 A debentures. The new
undertaking will be called the United Steel Companies
Limited.

COKE OVEN MANAGERS* ASSOCIATION:
MIDLAND SECTION.

A meeting of the Midland Section of the Coke Oven
Managers’ Association was held on Saturday afternoon
at Sheffield University, when Mr. J. W. Lee presided.
He said there was no need to introduce to the members
the lecturer, Prof. W. G. Fearnsides, for he had always
been very kind to help them and he was engaged in
work at the University which was the very foundation
of their industry.

The Texture of Coke Oven Bricks.

Prof. Fearnsides referred to the conclusions arrived
at in his lecture before the association the previous
year, when he dealt with the two main constituents of
coke oven bricks, from the point of view of the geologist
and mineralogist, viz., quartz and clay. Quartz, like
most other materials, expanded when heated, but not
as rapidly as many other minerals, until it reached
575 degs. Then, quite suddenly, it changed from an
Alpha variety into a Beta and jumped up in volume.
Heated further and it ceased to expand, and modern
experiments, especially by French investigators, seemed
to suggest that it went down a very little bit, but
ultimately it took a turn and again began to increase in
volume. According to the Americans, when it reached
870 degs. it was just undergoing another change in
volume and transformation into another mineral, tridy-
mite, and afterwards at 1,470 degs. it again expanded
most abruptly and changed into crystobalite. A
peculiarity of these transformations was that they were
not gradual processes, but occurred abruptly in a series
of jerks or jumps, the mineral being liable to change in
five minutes from an Alpha variety into a Beta, and
vice versa. One might have a silica brick in an ordinary
laboratory or in an ordinary works which just
before one of these changes might be quite a
clean, respectable looking brick, and immediately
after it might collect dust from all around as the result
of an electrical disturbance, and absolutely cover itself
with dust in the same way that a piece of sealing wax
would when rubbed.

A very great change of opinion had occurred since he
last spoke to them in regard to the change of quartz
into tridymite, and it was now held that the Beta
quartz did not go into the Alpha at 870 degs., but that
certain material would dissolve out of the quartz and
be added to the tridymite. At the University, quartz
had been kept at a temperature of 1,000 degs. for over
a year, and the amount of tridymite which had been
formed in that time was practically negligible. On the
other hand, there was in the Don Valley a very cele-
brated material called ganister, which in the course of
ordinary burning and cooling down again (21 days)—
showed a 61 per cent, transference, whereas with a piece
of pure quartz nothing happened. A year ago he had
suggested there was some catalytic agent which did the
trick. The French workers held that there was a
comparatively large quantity of something which dis-
solved up to 60 or 70 per cent, of its whole weight of
silica, and out cf which the other constituents crystallised.
That was an important matter in the making of coke
oven bricks, because it might very well be that the
material which was in quartz might be that solvent, and
if that were so, then, with each rapid heating, more and
more tridymite would be formed. It meant that if one
had grains of quartz in a matrix and suddenly they
began to expand at 575 degs., they would squeeze up to
their neighbours, and at 870 they would decide to
make another change and, under stable conditions above
870, they would try to make another change and
squeeze their neighbours more tightly. It was for coke
oven people to see that the material was kept together
so that no gases from the ovens could escape between the
particles, and it must be ensured that when the grains
were pushing their neighbours they were not making the
whole coke oven wall a foot longer or a few inches
higher. What was wanted was for the materials to be
kept tight, but not the bulk of the material to expand.

Much less was known about the kaolin. It was the
result of a decayed or rotted granite which had lost all
its nature and all its alkalies by reason of vapours sent
up from below. He knew nothing about the actual
volume changes which affected kaolin as a mineral.
Kaolin occurred always in scales and fibres of small
particles which were too minute to individualise even
with a high-power microscope, and it was therefore
impossible to make with it the same nice experiments
which had been made during the last two years with
quartz. Hence they could only guess. There had,
however, been many most interesting guesses and
experiments with regard to its behaviour under heat.
Kaolin refused for a time to rise in temperature, and
rose exceedingly slowly, and then, when just above
100 degs., stopped. That was the water going off ; and
when near about 600 degs. the curve flattened off and it
stopped. It absorbed a lot more heat, and at 950 degs.
it suddenly had a spurt and, instead of slackening
down, got hotter quicker than one would expect; whilst
at just about 1,000 degs. it gave another curve and then
came down again. That meant there was some physical
change at each of these crests.

The behaviour of the quartz and the kaolin was such
that it about balanced when the bulk analysis was round
about 83 per cent. It would not be right to say that coke
oven bricks should have about 83 per cent, silica, but
the reason why bricks with that analysis did succeed
was largely because, with this composition, the two
expansions just about balanced.

Coming to the question of texture, the important
question to be decided—and here the practical experience
of coke-oven people would greatly assist the investi-
gator—was, should the clay and the quartz be in big or
small pieces ? In dealing with absolutely pure quartz
or kaolin, it appeared from experimental evidence that
quartz could live quite happily in contact with the kaolin
at temperatures far higher than any ever required in
coke-oven practice—they could remain in contact form
together at 1,300 degs., 1,400 degs., and possibly even
1,500 degs., and no reaction would take place. When the
time came for the ka >lin to break down and form silli-
manite, then it appeared that chemical reaction took

place at the boundary, and, if there were large quartz
grains embedded in the matrix, it would be found that
sillimanite grains grew into the places where the quartz
was—in other words, there was inter-penetration of one
into the other at temperatures of about 1,400 degs. The
ideal was a pure material; they could be clear as to that,
but they were not equally clear that it was a commercial
proposition to employ pure kaolin and pure quartz.
Pure kaolin and pure quartz formed, porcelain, and
although coke oven managers might think it would be a
fine thing to have coke oven walls made of best Berlin
porcelain, he was not at all clear that they would then
have anything they could work with. They could not
afford to use the original porcelain-making kaolin
for coke-oven walls, and they therefore used instead a
kaolin which was a substitutional material derived from
the breakdown of other materials and known as fireclay.
It always contained some small quantities of alkalies,
iron, lime and magnesia. That material would be
annexed to places where the quartz was expanding,
and where the kaolin was coming away or shrink-
ing from it. Neither feldspar nor mica in
coke oven walls ever got to the melting, point if
considered by itself; but there was something which
enabled the two materials, both of very high melting
points, to react and form a new eutectic—making a
lower melting-point mixture. It appeared to begin at
just about 900 degs. Cent., which was about the
temperature at which the tridymite change would be
likely to take place. He thought therefore that the
alkalies in the fireclay which was mixed with the silica,
in order to get the silica percentage right, was a matter
of very great importance. There was some evidence
that iron acted in a similar way. Iron, of course, was
present in one or other of two forms—ferrous or ferric.
So far as was at present known, the ferric iron was
inert, but he doubted very much whether, in coke ovens,
when gases were being delivered from the charge, it
was possible for t4ie ferric state to continue, and
therefore they were not concerned with the inert ferric
material, but with the ferrous material, which was by no
means inert. There was good evidence that the ferrous
iron acted like the alkalies, and formed a convenient
solution which helped the formation of tridymite, which
assisted the silica to do the growing, which it might
otherwise not do. Iron was sometimes present in the
clay as ferrous carbonate or ferrous silicate., and was
sometimes ready to accomplish that operation in the
first burning. Lime and magnesia acted in the same
way.

All this meant that whatever impurity there was in
the fireclay was likely to set going change which they
knew about, and which might otherwise be delayed to
much higher temperatures. Eutectics had always a
lower melting point than their constituents. The
impurities in most cases were not in the silica, because
silica could be obtained pure. The impurities were
generally in the fireclay. If they used, big pieces of
silica—and this was where texture came in—the part of
the big pieces of silica in contact with the surrounding
fireclay was a small portion of the whole. If the
silica were fine and the texture finely ground the big
pieces of silica were much more likely to survive the
long course of treatment by impurities than if they were
very fine. He was not prepared to recommend one or
the other, but it was a matter for each, knowing his own
practice, to decide whether the difficulties which were
caused by a coarse-ground material were greater than
the certain gradual attack of the small pieces. It
appeared that if they had a very pure fireclay, ora
fireclay which was almost kaolin, and very pure silica,
the finer the material was ground the more chance
there was of getting uniform behaviour when the whole
mass was heated. If, on the other hand, they had a
matrix which was chemically active, being itself quite
stable per se, but chemically active with respect to the
silica, then it was pretty clear that they should go for
the big pieces in the active matrix.

Prof. Fearnsides asked for the guidance and assist-
ance of those engaged in the coke oven industry in this
matter, to enable investigators to pursue their experi-
ments in these directions. • Texture was a matter which
must be controlled by the composition of the materials
used, but it must also be controlled by the conditions
under which those materials had to be worked. One of
the most important things in coke oven construction, it
seemed to him, was that the oven should be gas-tight,
and that it should retain and send along the ducts the
materials which come from the distillation of the coal.
If they could not have a material which was absolutely
gas-tight, they should have the pores of the material as
fine, as near capillary dimensions, as possible, and
as devious as it was possible, so that the pressure acting
on the one side would have lots of friction to overcome.
It seemed that, other things being equal, the nearer they
could get to complete compactness the better would
they be able to hold the gases. However, when they
got near to complete compactness another matter came
in. The coke oven would be heated from the flue, going
continuously, and though it might be said the tempera-
ture was constant, he feared it was not always so. He
suggested that the place where the flakes generally
came off was where the quartz was passing from the
Alpha to the Beta stage, and there was an instantaneous
local change in volume of more than one-half per cent,
in relation to the rest. It was his belief that the
shattering took place there, and that the pieces came
off where the change in the quartz took place. It was
within his knowledge that there were certain natural
clays containing 33 per cent, of silica, some of which
had been used and were free from this particular trouble,
and it was also within his knowledge that they con-
tained, -after many firings, quite an appreciable quantity
of tridymite. He did not say it was cause and effect,
but it was a fact which had some bearing on the matter.
In making town gas, various sorts of retorts had been
tried, including silica retorts. When first put in, these
showed a gas leakage which was wasteful in the extreme
and which, if continued, would have been intolerable;
but it was found that after a time, provided the settings
and other things were right, the walls became coated
themselves with a kind of carbon which filled up
the pores and made them much more compact. He