April 5, 1918.

THE COLLIERY GUARDIAN.

695

upon every particle of less specific gravity than the
fluid mass will float, irrespective of its size or shape.

. 2. As every particle of material, irrespective of its
size or shape, having greater specific gravity than the
fluid mass will sink, no preliminary sizing is necessary
to ensure the sinking of ali material having a higher
specific gravity than that of the fluid mass.

3. The insoluble material, such as sand, used for
producing the fluid mass can readily be washed from
the materials which have been so separated, and thus
can he recovered and returned to the fluid mass for
continuous use.

This method offers facilities for making differential
separation of materials which may be of nearly the same
specific gravity, because the fluid mass can be so adjusted
as to float one material while permitting the other to
sink, although the difference in their specific gravities
may be slight. This characteristic can be applied to
the separation of low-ash coal from high-ash, of coal
from bonv coal, or of bony coal from slate; and with
ores it may be utilised for separating waste rock from
rock that contains sufficient ore to justify crushing and
concentrat'on, as well as for the separation of ore-
bearing minerals of different specific gravities.

An apparatus in which “float and sink” tests may
readily be made on coal, bony coal and slate, consists of
a vertical box open at the top, 6 in. wide by 8 in. long
and 20 in. high. The bottom is closed by a brass plate
(4) -|-in. thick, having 48 round holes of in. diameter,
spaced 1 in. apart. Below this brass plate is a water-
tight box supplied with water under pressure from a
tank. The two boxes are fastened together with eight
bolts running from top to bottom, and the joint at the
brass plate is made water-tight by gaskets. The ver-
tical box .is provided with two glass windows and with
an overflow emptying into a bucket, in which any sand
carried out by the overflow may settle; the bucket has
an overflow pipe through which the water is discharged.

The water in the tank is maintained at constant level
by an overflow pipe and hose, so that the effective
hydraulic head—the vertical distance between the two
overflow lines—is maintained constant, but can be
adjusted by raising or lowering the tank. If the tank
be raised, increasing the agitation, the level of the fluid
mass rises, and the specific gravity of the fluid mass is
correspondingly reduced; if the tank be lowered,
diminishing the agitation, the level of the fluid mass
sinks, its specific gravity correspondingly increasing.

In apparatus of this type, agitation being effected by
hydraulic water alone, it is found that, with mixed sands
averaging 80 mesh and working under a relatively low
head, efficient ag’tation may be obtained by the use of
3 to 10 gals, of water per minute per square foot of super-
ficial area of the apparatus. When mechanical agitation is
used in combination with hydraulic water, the quantity
of water can be reduced.

In considering this method as applied to coal washing
it may be pointed out that the specific gravity of coal
is naturally increased more by high sulphur percentages
(due to the high specific gravity of the pyrite) than by
high ash. Thus, an “ash-free” coal containing 3 per
cent, of (pyritic) sulphur will have a specific gravity of
about 1’47, while a “sulphur-free” coal with 20 per
cent, of ash would have a specific gravity of T46.

As coal of relatively light specific gravity is low in
both ash and (pyritic) sulphur, the method offers a
means for separating pure coal from that which is
relatively impure, without fine crushing of the whole
mine product. Assuming the machine to be set to
produce a fluid mass of 140 specific gravity, and bitu-
minous coal (run-of-mine) be fed into the washer, every
lump and particle of low-ash and low-sulphur coal will
float, whilst every lump and particle of hiyh-ash and
high-sulphur coal will sink, together with all the bony
coal, slate, pyrites and fireclay. The coal that floats is a
very high grade finished product. The material that
sinks can be removed and passed into a second washer,
in which the fluid mass is maintained at a specific gravity
of, say, 1’60. Here, all the slate, fireclay and pyrites
sinks, and also the very high sulphur (4 to 6 per cent.),
and very high ash (15 to 20 per cent, ash) coal, but all
the coal of intermediate density will float and constitute
a product suitable for general use. If it be desired to
improve the intermediate product, this can be done by
crushing and subsequent separation in the same or
another machine.

Coal Control and the Gas Industry.—At the annual
meeting of Scottish Gas Managers in Glasgow on
Wednesday, the president (Mr. R. W. Cowrie, of Dalkeith)
said the regulations of the Coal Controller as regards sup-
plies of coal to gasworks had met with strong criticism
and considerable complaint, which in many instances had
been well founded. Speaking on behalf of gasworks, he
thought that insufficient knowledge had been displayed
in making the allocations. A simple geographical line
distinguishing between areas seemed to have been
followed, and in many instances disregard shown to the
simple fact that gasworks processes are of a particular
technical character, demanding coals of a particular class.

English Miners’ Wages.—The representatives of the
workmen’s section of the Coal Conciliation Board for
England and North Wales met in London on Wednesday
evening to consider the proposals for a new wage agree-
ment. Mr. Stephen Walsh, M.P., was in the chair. The
men have given the coal owners three months’ notice to
terminate the present agreement, made in 1915 for three
years. The wage at present stands at the maximum of
23| per cent, on the 1911 standard, together with a war
bonus of 18 per cent, on the actual earnings, plus a war
wage of Is. 6d. per day for men over 16, and of 9d.
a day for boys under 16. The men are asking for the
war payments to be merged in the wage, for an increase
in the minimum wage, and for the abolition of the maxi-
mum percentage. The meeting was resumed on the
following day to consider the conditions deemed to be
essential in any new agreements regulating wages
within the area. The discussion showed the districts to
be unanimous that any new wage agreement for the coal
mining area in England and North Wales will have to
concede a substantial increase in the amount of the present
minimum wage, the abolition of the maximum standard,
and such a change in the conditions of ascertainment of
selling prices as will make them more clearly understood
by the workpeople.

CURRENT SCIENCE

Effect of Coal Ash on the Yield of Cement Mill Potash.

Messrs. N. S. Potter, Jr., and R. D. Cheesman
(Journal of Industrial and Engineering Chemistry)
state that the potash collected from the kiln stack
gases where coal is used for burning appears in
practically two forms, water-soluble potash and
the insoluble or slowly soluble potash. The
insoluble potash has . been attributed to two
causes: the potash in the unburned or partly
calcined raw material carried over mechanically in
the gases and to a recombination of the volatilised
potash with the finely divided ash particles of the
coal. Their analyses of the ash from the coal burned in
the kiln bring out the fact that the potash content
of the ash is considerable, and to such an extent that
it must be taken seriously into consideration in fig-
uring liberation and potash balances. The average
potash content figures close to 5 per cent. As the
coal consumption at different cement plants varies
greatly, ranging from 80 lb. coal per barrel to 250 lb.,
it is apparent that the potash entering with the coal
is considerable. Assuming the ash content to average
10 per cent., and using the above figures, it is evident
that the potash introduced by the coal lies between
0'4 lb. and 1’25 lb. per barrel of clinker. Due to
the very finely divided state of these ash particles
and the velocity of the gases in the kiln, but a very
small percentage of the ash is deposited in the kilns,
nearly all passing out with the gases. Owing, how-
ever, to the high velocity of the gases, these ash
particles will be exposed to the intense heat of the
firing zone of the kiln but a fraction of a minute,
possibly not more than a few seconds. Further, the
very nature of combustion being exothermic precludes
the possibility of a very high temperature being at-
tained by the ash particles. Such being the case,
there should be practically no volatilisation of the
potash in the ashes from the coal in the kilns.

Samples of kiln coal ash containing 4-47 per cent.
K2O were heated to a glow for approximately one
hour over the Meker burner. This showed no vola-
tilisation. Two grm. samples of this ash were then
boiled vigorously for different periods up to 24 hrs.
to determine whether this could be made water-soluble
upon boiling. After one hour’s boiling there was no
increase. While this does not reproduce the kiln
condition exactly, it is quite evident that at the tem-
perature attained by the ash in passing through the
kiln, and for the period to which it is subjected to
this temperature, no potash of the ash will be volatil-
ised. Assuming that 90 per cent, of this ash in a dry
process plant and 75 per cent, in a wet plant passes
up the flue with the gases, the effect of the insoluble
K2O in the ashes will affect the nature of the treated
dust very appreciably.

Pitch.

In the course of a paper read before the Liverpool
Section of the Society of Chemical Industry, Mr. W.
Mansbridge defined pitch as the black, fusible residue
left after the distillation of some organic matters.
Distillation might be destructive, in which case they
got a tarry material of the pitch order, or it might
be fractional, not tarry, when the volatile products
were collected, and there would remain a residuum
which was called asphaltum, which might be of a
dark brown. It was always fusible under the
influence of heat. Pitch, as met with in commerce,
was of various characteristics, according to the raw
material from which it was produced. One refinery
listed no less than 14 grades of pitch obtained from
crude oil. Each raw material yielded some pitch of
definite character, and suitable for some special uses
to which it might be put. Coal tar pitch was well
known. Blast-furnace pitch was not so well known.
Next in order came the mineral oil obtained from the
Texas oil field, and somewhat later the Galician and
Roumanian oil fields were developed, and as these
gave a pitch with an asphaltum basis they gave a
good return to the refiner. The Mexican fields and
some of the Californian fields gave a crude oil which
yielded a pitch on distillation. Oil pitches were now
used to an enormous extent, especially in America,
for architectural work, road making, insulating, and
general waterproofing purposes, and as an anti-
corrosive paint for steel work. Closely allied to the
pitches made from crude oils were the mineral
bitumens or natural asphaltums, gilsonite, and
Columbian, being suitable for the varnish maker.
They entered into the finest black japan enamels
whenever a very beautiful varnish was desired. Then
there was stearine pitch, the residue in the distil-
lation of tallow, palm oil, and fatty acids. Being
entirely soluble in petroleum spirit, this stearine pitch
was very useful in varnish making. Cotton-seed
pitch was in a grade by itself, and was obtained by
distillation. An elastic rubber-like pitch obtained
from American decorticated seed would vulcanise,
and had many of the characteristics of rubber,, but
was not rubber. Egyptian cotton-seed oil pitch, on
the other hand, was quite brittle. Elastic cotton
pitch was extensively used in vulcanising and for
electric cable making, but was apt to decentralise
and break down. The harder kinds of cotton pitch
were extensively used in the manufacture of water-
proofing paper. Bone pitch came from the tar
obtained in bone black making. It was the blackest
of all pitches, and was used by the colour-maker to
deepen the colour of his enamels. Gilsonite was one
of the most brilliant of the asphaltums, and was sold
as 99 per cent, pure as regards ash.

The testing of pitch is in a very unsatisfactory
position, there being no really well thought-out
scheme. The melting point is the first test approved
by most users; they must have a melting point, so
there are three or four ways of taking that melting
point; none of them, however, being satisfactory.
The lecturer described Wendri ver’s apparatus for
ascertaining the melting point, and apparatus he had

AND TECHNOLOGY.

himself devised and used. Each was based on the
principle of using a thermometer within a test-tube
set vertically in a second test-tube or cylindrical glass
container, a small piece of the pitch to be tested
being stuck on the lower end of the thermometer, and
heat applied below the containing tube or vessel. The
first dropping of the pitch, on melting, was regarded
as the melting point, the degree at which this
occurred being noted and regarded as the melting
point of the pitch being tested, the “first drop” of
the pitch being noted and taken as the determining
point. The specific gravities of pitches, he said, were
very useful, but they varied greatly, according to the
district the crude oil came from. On the whole,
specific gravity was not much of a guide, except as
regards coal tar, stearine, and other pitches as a
class. Solubility was amongst the most useful tests
that could be applied. Petroleum spirit (ordinary
motor spirit) gave about the same result as 640 ether.
Benzine of 90 per cent, dissolved quantities, and
carbon di-sulphide and carbon tetra-chloride were
useful as solvents. The method adopted was to weigh
out 9, 10, or 20 grms., dissolve it in the solvent
required by boiling, pour it into a graduated glass,
stir it and leave it all night. In the morning the
sedimentary portion of bitumen could be poured off
and weighed.

Unloading Bulk Cargoes.

A novel system for transferring bulk materials
from vessels to cars, which has been installed on one
of the piers of the Baltimore and Ohio Railroad at
Baltimore, is described in The Times Engineering
Supplement. This plant conveys the load to the cars
instead of requiring the services of an engine, and
shunting is reduced to a minimum. The system com-
prises an electrically operated car-loader with a belt
conveyor and receiving hoppers, and was installed to
unload ores, coal, and other bulk materials from
vessels and transfer the loads to the cars auto-
matically. The receiving hopper, the car-loading
machine, and the conveyor are placed on the centre
track of the pier, and the cars are shunted to the
two outside ones, which extend the whole length of
the pier and provide room for 38 cars. The hoppers
are motor driven to permit ready movement from
one hatch to another as may be necessary for unload-
ing the vessels.

The main conveyor is a 30 in. belt extending the
whole length of the pier, and is driven by a motor
placed at the shore end. The loading machine, which
is motor driven and is mounted on trucks running
on the centre track, also travels the whole length of
the pier, the conveyor belt passing through it. An
intermediate conveyor is employed between the load-
ing arm and the machine, and is movable in a hori-
zontal plane through an arc of 270 degs., the loading
arm having the same range of horizontal motion as
well as a vertical movement sufficient to clear the
side of the largest open car. The system is operated
electrically, and with the exception of the hopper
traverse and the speed of the hopper conveyor, which
must be set at the hopper, a single operator in a cabin
on the loading machine has entire control. A three-
wire system strung along the timber bulkheads
separating the outside tracks from the conveying
apnaratus and the middle track, supplies the power,
while a fourth wire interlocks the main belt control
and the control on the hoppers, thus permitting the
whole equipment to be started and stopped from the
operator’s cab.

In operation the load may be transferred from
the vessel to the hoppers, which have a capacity of
20 cu. yds., by a gantry, locomotive, or ship’s crane.
Each hopner has a two-speed feeder or conveyor that
delivers the materials to the main conveyor, which in
turn discharges to the loading machine. This two-
speed feeder and an adjustable gate enable the flow
of material to the main conveyor to be controlled, and
permit a capacity load to be delivered at all times
irrespective of the nature of the material being
handled. From the main belt the materials are
delivered to the cars through the loading machine
by 20 in. belt conveyors on both the intermediate
conveyor and the loading arm. The loader is placed
in position by closing a switch in the cabin, after
which the belts from the intermediate conveyor and
the loading machines start. When these have
attained a certain speed the main belt begins to move,
a centrifugal control ensuring the proper sequence
in starting. Wire ropes extending along the buck-
heads on each side of the conveyor enable the
operation to be stopped from any point, should that
become necessary, by tripping the circuit-breaker in
the drive house. The circuit-breaker must be reset
before operations can be resumed. A drum control
is provided on the hopper for the traverse, with two
drum controls on the loading machine, one for the
traverse and the other for the horizontal motion of
the intermediate conveyor. The loading arm is
moved to its various positions by hand, the work being
done by the man directing the loading of the cars.
Horizontal motion is secured by pushing or pulling
the arm to the desired position, and the vertical
movement by a worm operated through a hand
ratchet. This arrangement has resulted in loading
box cars in 10 minutes, and open or gondola cars in
less.

A large company is being formed at Gothenburg for
the purpose of manufacturing peat fuel, etc. The
maximum capital of the company has been fixed at
2,250,000 kr.

Messrs. W. H. Bowater Limited, colliery proprietors,
Exchange Buildings, Stephenson-place, Birmingham, have
opened an office at Royal Exchange Chambers, Leeds,
under the management of Mr. T. K. Fox, who has been
connected with the Micklefield Coal Company over a
period of over 21 years, and who is also a past chairman
of the Coal Trade Benevolent Association.