January 5, 1917.

THE COLLIERY GUARDIAN.

teury Conciliation Board, the London Retail Coal Prices
Committee, and the supply of coal to the poor.

Taking the year ending July, the estimated output of
the whole of the mines of the United Kingdom is :—
281,135,000 tons for 1914; 250,368,000 tons for 1915;
254,748,000 tons for 1916; and 282,200 is given as the
number of miners who have joined the Colours since the
outbreak of the war. For the first half of 1916, the
Board of Trade returns show the following statistics of
coal raised in mines in the United Kingdom
128,135,000 tons for 1916, January to June 30;
127,620,000 tons for 1915; and 139,994,000 tons for 1914.

Life’s wheels stand still with many prominent mem-
bers of the London trade, and amongst those who have,
passed away during the year, and who have been well
known on the floor of the London Coal Exchange, may
be enumerated :—Mr. John Lamont, of Messrs. Lamont
and Warne; Mr. Batt, of Geo. Hinchlifie and Company;
Mr. C. E. Parker, Wigan Coal and Iron Company;
Mr. John Lea Smith, late of Rickett, Cockerell and
Company; Mr. H. Copson Peake, of Walsall Wood
Colliery; Mr. T. W. Kennett, Messrs. Stephenson,
Clarke and Company; Mr. F. D. Lambert, of Messrs.
Lambert Brothers and Company; Mr. Albert Usher, of
Messrs. A. Usher and Company; Mr. Hugh W. Russell,
for many years representing the Coal Exchange on the
Court of Common Council; and Mr. Thos. Williamson,
of West Hallam Colliery.

There have been no outstanding features in connec-
tion with the London coal trade during the year, but it
must be remarked that the Price of Coal (Limitation)
Act has been wonderfully beneficial/ No serious labour
troubles have taken place. The aggregate outputs are
considerably down, and the tonnage proportionately
lower, but collieries have worked full time throughout
the year, and the Government proposal to release cer-
tain men at the front, to work again at the coal face,
makes the outlook far more satisfactory, and has already
led to a distinct recovery in the tonnage. Loaded
wagons in stock at the colliery sidings have become a
thing of the past, and the general public commencing, as
they did in May and June last, to 'anticipate the winter
demand, had a steadying influence upon the trade

PNEUMATIC CONVEYOR FOR SLACK.

The principle of the pneumatic conveyor, introduced
(for grain) some 30 years ago by Duckham, has since
been applied to other granular materials, including
slack, owing to its convenience, the absence of dust,
small space and little attention required. An installa-
tion of this type has recently been set up, at the works
of the Deutsche Solvay Company, Bern burg, for dis-
charging fine-grain brown coal from railway wagons,
which is accomplished at the rate of 15 tons per hour,
without dissemination of dust, and without leaving any
remainder to be removed By hand.

As shown in the illustration, an iron mast, set up
by the railway track, supports la movable conveyor pipe
by means of a jib. This pipe can be slewed, and can
also be moved up and down by means of a winch at the-

Pneumatic Conveyor for Unloading Slack.

ill

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foot of the mast. The suction nozzle terminating the
pipe is guided to and fro by hand. From the mast, the
conveyor pipe passes to a hopper, which is of large
dim ens,tons on account of the low specific gravity of the
brown coal; and this hopper communicates with a
second one (to the right), in which the dust arising
from the coal is deposited. The mouths of both are
closed by pocket-wheel valves C, which are kept in con-
stant rotation to discharge the contents of the hoppers.
A vertical air pump communicates with the conveyor
pipe through the hoppers; and the discharged air is
passed through 'a system of bag filters before being
expelled into the atmosphere by a fan. A worm con-
veyor, underneath the valves C, delivers the coal to the
fines. The same type of device might also be applied
to, the removal of ash and flue dust from producers,
furnaces, etc.—Stahl und Eisen.

Tax on French Mining Concessions.—In the discussion on
the Vote of Credit for the first quarter of the current year, the
French Chamber of Deputies increased the tax on mining
concessions which have been left unworked for a period of
five years to 5 fr. per hectare. The object of this measure
is to ensure that valuable mineral resources shall not be left
undeveloped, since if present holders of concessions are
unwilling to pay the tax, they can abandon their rights, and
the State can re-issue the concessions to others.

SPECIFIC GRAVITY STUDIES
IN COAL/

By M. L. Nebel.

The investigations detailed in this report were con-
fined to Illinois coal, chiefly bituminous and high in
moisture; and both the effect of moisture on specific
gravity, and the methods employed for determining
specific gravity, are described at length.

With regard to the practical uses to which a knowledge
of the specific gravity of coal may be put, the author
deals with the following(1) The calculation of the
tonnage of coal in the ground over a given area;
(2) the calculation of the tonnage of quantities of
broken coal, such as the coal stored in large bins or in
stock piles; (3) the comparison of coals by the rapid
estimation of the ash and moisture content; and (4) the
determination of the adaptability of coal to the removal
of its impurities by washing processes.

Tonnage of Coal in the Ground.

It is often desirable to estimate the number of tons in
a given area underlaid by coal beds of a known or to be
determined thickness. The volume of solid coal can be
easily calculated, kno wing the thickness of the beds and
the area they cover; and the tonnage may then be found
by multiplying the volume in cubic feet by the weight
per cubic foot, and dividing by 2,000.

. tom^ = W ’

in which V = volume in cu. ft., and W = weight
per cu. ft.

Since the weight per cubic foot of coal is equal to the
specific gravity of the coal multiplied by the weight of
a cubic foot of water (62*5 lb.), the formula becomes

To^e =

(S = specific gravity).

It is necessary to know the specific gravity of the coal
with reasonable accuracy if the estimate of tonnage is
to have any value. An error of only a small amount in
the specific gravity might cause the amount of coal
recovered from a given area to fall millions of tons
short of the estimated recovery. This fact was recog-
nised by the commission appointed to investigate the
waste in coal mining in Pennsylvania in 1890. This
commission in its report stated that “. . . a variation
of 1 per cent, in the specific gravity would reduce the
total number of tons of coal in the ground 195,000,000.”

The importance of selecting the proper value for the
specific gravity is evident when it is remembered that
the specific gravity of any coal may be represented by
a number of widely differing values, each perfectly
correct for the condition which it represents. For
example, the apparent specific gravity of a fresh coal
may be 1*33, while after the coal has dried out it may be
only 1’20. This difference of 0’13 in the specific gravity
makes a difference of about 1,020 tons per acre for a
bed of coal 6 ft. thick, or over 650,000 tons for an area of
only 1 sq. mile. This difference is far too great to

be neglected, and it is therefore necessary to select thA
proper value for the specific gravity.

In selecting this value it should be remembered that
the fresh specific gravity represents the condition in
which the coal exists in the ground; the apparent
specific gravity represents any condition of the coal at
any stage in the drying process, while the dry and unit
values represent only theoretical conditions that are
never attained practically, and therefore can be
neglected in this connection.

The most practical value for use in the calculation of
tonnage in the ground is one that represents the con-
dition in which the coal exists when it is marketed,
since the calculated weight will correspond to the
weight upon which the price received for the coal is
based. In the State of Illinois, coal that is marketed is
usually settled for on the basis of weights at the mine.
The coal is weighed as soon as it is placed in the
railroad car ready for shipment. Only a short time
elapses between the mining of the coal and weighing it,
and therefore the coal when weighed is practically fresh.
It is not exposed to the air long enough after being
mined to lose sufficient moisture to affect its weight
appreciably. Since the coal is sold on a practically
fresh basis, all calculations of tonnage in the ground
should be based upon the fresh specific gravity of the
coal.

* From University of Illinois Bulletin No. 89.

Tonnage of Broken Coal.

In calculating the tonnage of a known volume of
broken coal it is necessary to know not only the specific
gravity of the coal, but also the amount of void spaces,
or the amount of increased volume occupied by the Coal
when it is broken. For bituminous coal, such as that
found in Illinois, this increase in volume probably varies
from 60 per cent, for large sizes to about 80 per cent, for
small sizes. Assuming that the coal in question is in
small sizes, the tonnage can be calculated by the
formula:—

m	625 VS

Tonnage =

in which V = volume in cu. ft., and S = specific
gravity.

Again, it is necessary to know which value of the
specific gravity to use. In such a case, the manner in
which the coal has been stored will affect its moisture
content and consequently its specific gravity. Three
cases should be considered:— (a) When the coal
has been stored under water; (5) when it has been
stored in a tight bin, and (c) when it has been stored iu
an exposed stock pile.

Under-Water Storage.

Coal that is stored under water undergoes practically
no deterioration, and its condition is practically the
same after a long period of time as when freshly mined.
Its specific gravity should not change, and consequently
in calculating the tonnage of a given volume of coal
stored under water the fresh value of the specific gravity
should be used.

Closed-Bin Storage.

Coal that is stored in a closed bin should lose its
moisture very slowly, but after a considerable length of
time—for instance, several months or years—a large
proportion of its contained moisture would probably be
lost, especially if the coal were handled much during
the process of transferring it to the bin. Under such
conditions it would probably be necessary to obtain
samples of the coal and actually determine its apparent
specific gravity in order to obtain a reliable value upon
which to base any-calculations of tonnage.

Storage in Exposed Piles.

Coal that is stored in exposed piles will lose moisture
in dry weather and gain moisture in wet weather, and
its specific gravity will vary accordingly. It is probable
also that the specific gravity will not be the same on
the surface of the pile as in the centre or at the base,
because evaporation of the moisture takes place more
rapidly at the exterior. Under such conditions it would
be almost impossible to estimate with any degree of
precision the average specific gravity of the coal from
any known values. Samples should be selected from
different depths in the pile and the apparent specific
gravity determined. On such an average value the
estimate of tonnage should be based.

Comparison of Coals.

If the specific gravity of two coals of the same type
and of the same moisture content, such as two bitu-
minous coals from different parts of the same bed or
even from different beds, are compared, it is probable
that the one having the higher specific gravity has also
the higher ash content. They can be more conveniently
compared if the moisture is entirely eliminated by
calculating the dry specific gravity. By comparing the
dry specific gravities of different coals of the same type
a great deal might be learned about the other properties
of the coal, especially the ash content. Since the heat
value varies inversely as the ash content for a given coal,
some idea might also be obtained as to the relative heat
values of the two coals. Such a comparison could not
be made between two types of coal such as a bituminous
and an anthracite, or a bituminous and a lignite, but
for the same types of coal valuable comparisons could
be made. By eliminating all the impurities and using
unit value of the specific gravity it might even be
possible to draw valuable conclusions as to the
relative heat values of different coals. Such a possi-
bility is only suggested, but it may be worth further
consideration.

Specific Gravity and Coal Washing.

Before an attempt is made to remove the impurities
from coal by washing, the properties of both the coal
and its impurities should be investigated to determine
whether the coal is adaptable to washing, and which
sizes give the best results. The common method of
testing is the “ float and sink ” test, by means of which
the impurities are removed from the crushed coal by
immersing it in a heavy solution, such as a solution of
calcium chloride or of zinc chloride, in which the im-
purities sink and the clean coal floats and can be
skimmed away. The object of washing the coal is
twofold: first, to reduce the ash below an arbitrary
maximum, which depends upon the purposes for which
the product is to be used, and secondly, to reduce the
sulphur content to a minimum, especially if the product
is to be utilised in, manufacturing metallurgical coke.
By testing with solutions of different specific gravity,
one can be selected which will separate float coal with a
little less than the maximum allowable ash. If the
sulphur in the float coal has at the same time been
reduced to a minimum, the coal is suitable for the
manufacture of metallurgical coke, otherwise it is not.
However clean the float coal may be, the sink material
must contain only a small amount of coal if the separa-
tion is to be a commercial success. If the sink contains
much coal the loss in the tailings will reduce the profits
realised by the increased price of the clean coal until
the washing is no longer economical. The lighter the
coal and the heavier the impurities, the cleaner will be
the separation. If float and sink tests are carefully
made by a standard method of procedure'they give
valuable comparative data.	.

Specific gravity tests may be used to advantage in
determining the adaptability of coal to washing. They