616

THE COLLIERY GUARDIAN.

September 18, 1914.

and. temperatures were taken near the air inlet. The
temperature rose slowly to 80 degs. Cent., and remained
constant at this point lor about 20 hours. By stopping
the air current and raising the temperature of the bath,
the coal in the flask was heated to 84 degs. Cent.; but
when the air current was started again, the tempera-
ture quickly fell to 80 degs. once more, at which point
it remained constant for a further 24 hours, after which
the experiment was stopped.

It is important to notice that both the rate of heat-
ing and the temperature at which the break occurs in
these experiments give most ample confirmation of the
thermal value of the heat of absorption of oxygen found
in Part III. From the value there found the break is
calculated to occur very close to 80 degs. Cent., which
is the point found by experiment; whereas, from the
figures found by Lamplough and Hill, the break should
occur at about 98 degs. Cent. This confirmation is to
a large extent independent of methods of measurement,
heat insulation, etc., and must therefore be taken as
very strong additional evidence for the value given in
Part III.

Experiment No. 4.—This was a repetition of experi-
ment No. 1, air being substituted for oxygen. During
the heating of the coal, in order to dry it, a small quan-
tity of oxygen is unavoidably absorbed, and this
diminishes considerably the initial rate of heating.
Several experiments were made with dried coal, start-
ing from room temperature, and it was found that they
would heat slowly in an air current, temperatures as high
as 65 degs. Cent, being reached. Such an experiment
is, however, very tedious, and therefore in the experi-
ment now described the coal was heated initially to
50 degs. Cent. The rate of heating was then such that
the experiment could be watched throughout its course.
Table IV.—Rate of Heating of Dried Hard Coal in Air.

Time, in hours.  0 		Temperature, in degs. Cent.  	 52	Time, in hours.  16 		Temperature, in degs. Cent.  	 85
2 			 55	20 			 94
4 			 59	24 			 112
6 			 64	28 			 137
8 			 70	30 			 150
12 			 76		

The coal heated very rapidly to 150 degs. Cent., at which
point the experiment was stopped, so as not to destroy
the apparatus by the firing of the coal.

From the experiments described in this paper it is
clear that both the Barnsley Hards and Softs are
capable of firing readily in favourable circumstances.
There may be, however, a considerable difference as to
what constitutes the necessary conditions, depending on
the physical circumstances of the mass of coal. If the
heap is a small one, the writer has already pointed out
that the conditions must be very “ exact ” indeed. The
heat insulation must be good, and the air current must
be regulated to a nicety, otherwise, owing to evapora-
tion of water, the air current will cool the coal after
it reaches 80 degs. Cent. (170 degs. to 180 degs. Fahr.),
instead of causing it to heat. This is a matter of
experience, for surface stacks below a certain size will
not fire. Fayol, too, has pointed this out, and has
devised many excellent experiments in support. He
also showed that some of his small heaps of heated coal
would only fire if the air current were carefully regu-
lated, but he gave no explanation of this.

In a large mass of coal, however, the conditions are
very different, for evaporation of water may actually
help the initial heating. A narrow break, for instance,
fills gradually with coal dust because of the breaking up
of the roof and sides. Air leaks slowly through the
break, and heating slightly a small portion of coal near
the entrance of the break becomes deprived of its
oxygen, but passes on charged with water vapour, which
condenses further in the break, and heats the coal on
which it condenses. By the time fully oxygenated air
passes freely to it, this second portion of dust has
already risen a few degrees in temperature. By the
effects of alternate evaporation and condensation a
cumulative heating effect is produced at some distance
into the break, until a portion of coal reaches such a
temperature that free heating can occur. Under these
conditions, too, no break in the heating curve will occur
at 80 degs. Cent., for the air reaching the heated coal
will be saturated with moisture, so that until the coal
reaches 100 degs. no break will occur in the steady rate
of heating. At this temperature it has been shown that
the rate of oxygen absorption is so high that it would
easily evaporate the water long before the power of
absorption had been lost by the coal. Thus, 3-8 per
cent, of its weight of steam condensing on a mass of
coal could raise the temperature of the coal to .100 degs.
Cent. If oxygen were then to reach the coal, it could
evaporate off all the condensed water together with its
own combined water (taken at 6 per cent.), after which
it would start heating at the rate of 1-5 degs. Cent, per
hour, a rate which would double itself in about six
hours, and continue to increase more and more rapidly.
Such conditions may well occur in a break through
which air can percolate, and it appears that under these
conditions • successive evaporation and condensation of
water may actually increase the liability to fire instead
diminishing it, as in the case of a small heap.

Partnership Dissolved.—The London Gazette announces
the dissolution of the following partnership :—W. S. Squire
and F. J. Tolman, ironmongers, at Terminus-road, East-
bourne, under the style of Squire and Company.

Immingham Coal Exports.—According to the official
returns for the week ending September 11, the coal exported
from Immingham totalled 31,038 tons foreign, and nil to
coastal ports, compared with 30,649 tons foreign and coast-
wise nil during the corresponding period last year. Ship-
ments :—Foreign : To Rotterdam, 7,711 tons : Ronne, 917;
Stockholm, 1,430; Roxsund, 1,495; Skutskar, 2,061; Gefle.
3,303; Aalborg, 1,583; Malmo, 2,494; Bombay, 501; Gothen-
burg, 2,887; Reykjavik, 1,176; and Bagnoli, 5,480.

Working Steep Seams at the Montrambert Colliery.*

By F. ARGUILLERE.
(Continued from page 564.)

The method of working at present pursued is that of
forward stalls in inverted steps (gradins renversees), this
having been adopted as the most suitable, both as
regards getting down the coal and packing the goaf,
more especially in view of the compact nature of the
coal and the absence of gas. It also presents the
advantage that each hewer is protected from the falling
coal brought down by his next higher neighbour.

The height of the working face is determined by a
number of factors, first among them being the character
of the rock. If the roof be at all inclined to cave in
locally, the debris is a source of danger to the men at
the face, since it rolls down to the bottom of the slope,
and, if the latter be long, the falling rock may break
down the timbers and entomb the men. Where, on the
other hand, the walls are sound, the height of the steps
may vary between 7 and 16 feet, whilst in Westphalia

Mill1
iiimiiii

Fig. 11.

it is often 22 to 45 feet in a 3 ft. seam. At Montrambert
there is little risk of the coal falling, since the seams
are thin and the coal itself is held firmly between roof
and floor. On the other hand, a very high face with a
large number of steps brings difficulties in the way of
providing the hewers in the middle steps with props.
High steps necessitate frequent shifting of the
scaffolding, and if they exceed 12 to 15 feet a fall of the
scaffolding would be dangerous. Whilst high steps
facilitate getting down the coal, tbe removal of the
latter is facilitated by keeping down the height of the
face; and at the same time a better classification is
obtained, this being particularly the case where the
false roof and floor part easily and the coal contains
layers of slate. Packing is also easier when the face is
of moderate height, and there is less risk of the stowing
material knocking down the props in its descent.

The length of the face, which is determined by the
overhang of the steps, is fixed by the angle of slope
adopted for the packing, to which the face must be
parallel. With a slope of 45 degs. (the natural angle of
repose) the overhang of the steps is equal to their
height; and though longer steps would afford more
shelter to the hewers, the unsupported empty space in
the rear would be increased, and the angle of the
packing would have to be lowered. Moreover, in seams
with a dip of about 50 degs., the won coal, instead of
rolling down over the packing, would slide in the
channel formed by the packing and the lower wall of
the seam, the edge of this channel, at the same time,
approximating to the line of greatest dip of the seam,
and the overhang of the steps decreasing. As soon as
the dip of the seam becomes equal to the natural angle of
the packing the latter will take the line of maximum dip,
the coal will slide down on the lower wall alone, and tbe

Ax

Fig. 12.

steps will come so close together as to form a continuous
face or forward stall in a steep seam. It is therefore
necessary to arrange the disposition of the face in each
seam and portion of seam, so as to meet the require-
ments entailed by the existence of the several factors in
question. Hence, the height of the steps ranges between
7j ft. and 13 ft., and the number at each face is either
two or three, the total height of tbe face varying between
17 ft. and 38 ft.

For example—one of the seams is 5 to 5J feet thick
with a dip of 70 degs., regular and firm clay schist roof
and lower wall, and the coal in three layers separated
by thin partings of fine material. The face is divided

* From the Bu leti'i of the Societe de 1’Industrie
Minerale.

up into three 13 ft. .steps, and there are thus only six
faces in a stage of 70 yds. The coal from steps 2 and
3 (fig. 11) simply rolls down the goaf into tubs at
the bottom, whilst that from step 1 is collected and
removed on the right. The coal is mostly small, and
therefore its descent over the surface of the goaf (a
height of about 30 ft.) causes no trouble. In this method
of working—the simplest of all—three hewers can fill
55 to 60 tubs holding 8 cwt. each.

In another typical instance a vertical 5 ft. seam of
hard coal, free from parting, is enclosed in firm sand-
stone, with about 2 ft. of clay schist on the lower wall.
The coal is very difficult to get down, and its hardness
enables it to stand the long slide down the goaf; but
the uneven surface of the roof and presence of clefts
makes low steps (about 10 ft.) necessary, in view of
obtaining good support from the timbers. Here three
hewers can fill 40 tubs, and two men 30.

A third example is afforded by a vertical 6| to 8 ft.
seam with firm clay schist roof and floor. The top
layer of coal is good, but small, and the bottom layer is
of second quality and smaller, a 2J ft. band of drossy
coal forming a false floor. In this case there is no need
for recessing the levels ; and, indeed, the goaf has to be
partially packed along them in order to reduce the reach
of the roof timbers (fig. 12). The face is in two 7 ft.
steps, since any greater height would give an unduly
large empty space and endanger the cross timbers
unless the roof timbers are very strong. The thickness
is sufficient to give a good output fro tn the step; the
coal does not break up; loading is very easy, and the
good coal can be separated from the bad on the
platform at the base. Moreover, packing is greatly
facilitated by the absence of a third step, for, in places
where the conditions are less favourable, the upper slice
of each step has to be supported by a flank of packing
laid against the lower wall, and with three steps this
would be expensive. At these faces two hewers can fill
40 to 45 tubs.

Finally, another 6J ft. seam dips at 80 degs., with a
loose schist roof and a 2 ft. firm schisty false floor, the

Fig. 13.

coal being separated into 5 J ft. of good top coal, and
1 ft. of drossy coal below, with 4 inches of schist parting.
The face is divided into three steps, the thickness of the
packing between two levels being insufficient with two.
To prevent the coal from breaking, and to facilitate
screening, the third step is slightly reduced (fig. 13),
and the packing is advanced, leaving a 2 ft. passage for
men and ventilation. This reduces the height of fall
of the coal, and each step has an independent loading
point. Three hewers can fill about 50 tubs, two men
about 35 to 40.

The various modifications have several points in
common. For instance, a greater output (by some
15 per cent.) per man can be obtained by setting only
two hewers to work at a three-step face, since the hard
coal face ripens better, the overhang of the steps can be
kept more uniform without delaying tbe strongest
workman of a gang; and, finally, because two men work
together better than three. The hewer works with a
light pick, marking a vertical cut from above downward
and utilising his own weight and that of the pick with
a minimum of effort. Each step is timbered in a
manner similar to that of a level in a medium thick
seam, roof timbers being put up first, followed by cross
timbers, timbers on the lower wall and struts. The
cross timbers are usually horizontal, to firm the whole.
The roof timbers are shouldered to fit on the cross
timbers of the next lower step or level, so that a con-
tinuous line of timbers extends all the way up the face,
an arrangement necessary in steep seams to prevent
slipping, especially where the rock has been recessed at
the bottom of the face.

The packing is supported at the base by a screen of
old jointed props resting on horizontal timbers, thus
forming a compressible joint above the cross timbers of
the level. The packing is arranged in sloping banks,
two or three in number, according to the condition of
the rock.

Grimsby Coal Exports.—According to the official returns
for the week ending September 11, the quantity of coal
exported from Grimsby totalled 18,933 tons to. foreign
destination, against 20,152 tons foreign, and 461 tons to
coastal ports. Shipments:—Bergen, 1,560 tons; Chris-
tiania, 1,946; Copenhagen, 1,242: Gothenburg, 576;
Helsingborg, 2,228; Korsoer, 901: Karlshamn, 644; Malmo,
3.269; Oxelosund, 1,408; Rotterdam, 1,282; Skanov, 849
Skive, 742; and Ystad, 2,286. Coastwise, nil.