September 6, 1918.

THE COLLIERY GUARDIAN.

495

The wire support is inserted in an opening in the rear
of the box, and the balance is suspended on the
support.

The aluminium scoop is placed on one side and the
counterpoise on the other. A test swing of the balance
should be made to indicate whether the pointer swings
to the same distance on either side; if not, it should
be adjusted to swing equally on both sides. The
20 gram weight should be placed on the same side
as the counterpoise, and successive spoonfuls of the
sample should be placed in the aluminium scoop until
the balance again swings an equal distance on each side
of the centre.

The sample should all pass through a 10 mesh screen.
Before it is weighed it should be thoroughly mixed
on the rubber cloth by successively lifting opposite
corners of the cloth and rolling the sample in all
directions. The sample is then spread in a smooth
layer with a spatula, and the sample for weighing
is then transferred to the aluminium scoop on the
balance pajri by taking spoonfuls of the material at
various places so as to get a fair average of the entire
sample.

The volumeter flask, with the measuring tube re-
moved, is placed in position in the clips provided on
the board in front of the balance. The flask, espe-
cially the ground joint for the measuring tube, should
be wiped perfectly clean and dry with a cloth before
it is used. The flask funnel is inserted, and the
20 gram sample of road dust is brushed into it from
the aluminium weighing scoop. Care must be observed
that none of the sample is spilled during this transfer.
After any material adhering to the funnel has been
brushed into the flask, the funnel is removed and
25 c.c. of alcohol from a pipette is allowed to run into
the flask. The pipette is filled with alcohol by inserting
the pointed end in the alcohol can and applying suc-
tion with the mouth at the other end until the level
of the alcohol is well above the ring etched on the
stem above the bulb. The operator then removes the
pipette from his mouth antj places his finger tip
quickly over the opening before the alcohol level can
flow below the etched ring. While holding his finger
tightly over the pipette, the operator removes the
pipette from the can and by suitable manipulation of
his finger allows the alcohol to flow out slowly until
the bottom of the meniscus, the convex downward
boundary surface between the alcohol and the air, just
reaches the etched ring above the bulb. He then
inserts the tip of the pipette in the flask, and by
removing his finger entirely from the top of the pipette
allows the alcohol to flow into the flask. As soon as
the free-running stream has stopped, the tip of the
pipette is touched to the side of the flask, and the
adhering drop of alcohol is blown out at once, and
the pipette is removed before any more alcohol can
drain down. In using the pipette care must be taken
that it is filled to the mark and that no alcohol is
lost while the pipette is being transferred from the
can to the flask.

The measuring tube is next inserted in the flask, and
the volumeter is gently shaken to impregnate the
sample thoroughly with the alcohol and to allow the
air bubbles to escape. As two volumeters are usually
included in each outfit, care must be observed to use
the proper measuring tube. A number is etched on
the neck of each flask, and the measuring tube used
with a given flask must have the same number etched
on it; otherwise the results will be erroneous.

After the volumeter has been shaken, a second 25 c.c.
volume of alcohol from the pipette is introduced in
the apparatus at the top of the measuring tube. After
the mixture has stood for 30 seconds the reading of
the bottom of the meniscus is taken on the measuring
tube, and by reference to the calibration table or curve
the percentage of incombustible or of rock dust in the
sample is ascertained.

The alcohol may be recovered and used repeatedly.
It is recovered by placing a filter paper in the tin
funnel and inserting the funnel in the alcohol can.
The volumeter is placed over the funnel, the measuring
tube is lifted out, the flask is inserted over the funnel,
and the solution of alcohol and dust, poured off. The
solid matter in the alcohol is removed by the filter.
The residue remaining in the flask is washed out with
water. The flask and measuring tube are then wiped
dry with a cloth. It is advisable to make determina-
tions with the same sample until the operator is certain
that his manipulations are correct. Duplicate deter-
minations should not vary more than one or two
divisions on the instrument.

Calibrating Volumeter.

A special calibration for a given mine where rock
dusting is practised is made in the following manner:
Representative samples of the pure rock dust and
pure coal dust are prepared, and from these samples
mixtures of coal dust and rock dust in the proportions
of 25, 50 and 75 per cent, of rock dust are made. Volu-
meter determinations are made on each of these
mixtures and on the samples of pure rock dust and
pure coal dust. The volumeter readings are plotted
on co-ordinate paper as abscissas, and the percentages
of rock dust in the mixture are plotted as ordinates.
A straight line drawn through these points is a cali-
bration curve giving the percentages of rock dust (as
received) in the mixture. From the same volumeter
readings a curve representing dry rock dust in the
mixture may be constructed by determining the
moisture in the sample of pure rock dust and calcu-
lating the percentages of dry rock dust in each of the
synthetic mixtures.

Similarly, the percentage of dry incombustible in
each of the calibrating mixtures can be calculated and
plotted as ordinates after the dry incombustible matter
in the pure coal and in pure rock dust have been
determined by the usual chemical methods. As these
curves are straight lines, it is theoretically sufficient
to establish only two points, such as would be obtained
by making volumeter determinations of the pure coal
dust and the pure rock dust. Practically, it is better
to establish several points, as described above, in order

to eliminate possible errors in the individual deter-
minations.

Determining Specific Gravity of Coal and Rocks.

As the volumeter is simply a modified specific gravity
flask, the approximate specific gravity of any coal or
rock may be readily calculated from the volumeter
reading by the formula -	= specific gravity, in

170 — x
which x — volumeter reading.

Qualitative Test for Coked Dust.

In the investigation of mine explosions it is fre-
quently desired to determine whether globules or
hollow bubbles of coke are fused material from the
partial distillation of coal are present in the dust from
the entries and rooms of a mine. Valuable informa-
tion on the extent and direction of the inflammable
wave can be obtained in this manner. A simple test
for the presence of coke bubbles is to place 0-2 or 0*3.
gram of dust in a tube tube containing alcohol, and
shake the tube. When the tube has stood a few
minutes, the coal and rock particles sink to the bottom,
while the coke bubbles remain floating on the surface
of the alcohol. The floating material is removed,
placed on a white surface, as a piece of filter paper,
and examined with a magnifying glass. The coked
material is recognised by its globular or fused
character. Usually there will be seen small hollow
bubbles or fragments of bubbles containing translucent
yellow spots at points where the shell of the bubble
is very thin. The portable outfit contains two test
tubes and a pocket magnifier for making this test in
the field.

Summary.

An investigation of the specific gravity method of
determining the percentage of rock dust, ash or dry
incombustible in mixtures of coal and rock dust, such
as are found in the entries and rooms of mines, showed
that this method was rapid and sufficiently accurate
for use in controlling the application of rock dust in
mines.

The graduated measuring tube of the original
Taffanel volumeter was not long enough to accommo-
date the entire range of incombustible from zero to
100 per cent., thus necessitating a double calibration
wjth two different weights of sample. Consequently,
a new form of volumeter that had ample scale capacity
for all percentages of incombustible was designed by
chemists of the Bureau of Mines for use with a 20 gram
sample.

With synthetic mixtures of air-dried coal and shale,
the greatest difference between the percentage incom-
bustible by the volumeter and that by chemical analysis
was 1 per cent. The same degree of accuracy was
found with air-dried mixtures of coal and limestone.

In a series of miscellaneous air-dried road dusts from
various mines, the average error in the percentage of
ash indicated by the volumeter was 3 per cent., and
the largest error 9-2 per cent.

The addition of water to the air-dried samples re-
quired the following corrections to the volumeter
reading: 10 per cent, water added, 4- 2-5; 20 per
cent., 4-5-2; 30 per cent., 4-8*1.

As practically all samples of road and rih dusts in
mines (except lignite mines) contain less than 12 per
cent, of water, in addition to that contained as
moisture in the air-dried sample, an average correc-
tion of 4-1*2 may be applied to the volumeter reading
of the calibration curves established from readings for
air-dried samples. These corrected curves are to be
used when undried samples are tested at the mine.

The average probable error in using the volumeter
on undried or “as received ” samples of mixtures of
coal dust and shale dust, or of limestone dust, is 2 per
cent., and the maximum error is 3-5 per cent., the
appropriate calibration curve being used for each
material in the rock dust mixture.

The average probable error in using the volumeter
with undried or “ as received ” road dusts from various
mines is 5 per cent., and the maximum error in some
samples may reach 11 per cent.

Derbyshire Oil Fields.—It is understood that the Govern-
ment experts are to prospect for oil in the Codnor Park
and Pye Bridge districts, and preparations are being made.
The little hamlet of Pye Bridge, which is a few miles
distant from Alfreton, fathers the enormous petroleum
oil industry, for the first stream of oil was discovered in
1847 in a little coal pit, long since closed, belonging to
Messrs. James Oakes and Company, the well-known coal
and iron masters. The stream produced about 300 gallons
daily, and then ran dry.

Economy in the Use of Steam Coal.—There is in
Germany the most stringent necessity for economy in the
use of steam coal, and therefore coke or a mixture of
coke and steam coal or less valuable fuel must be employed.
After pointing out the desirability of employing either
forced or induced draught in such cases Zeitschrift fur
Dampfkessel und Maschinenbetrieb refers to a special
arrangement brought out by Eberhard and Company of
Cologne. This consists of pipes perforated with small
holes and fixed below the grate bars, which effect the
cooling of the firebars and also cause an increased volume
of air to be delivered to the grate by means of the
steam jets which create an increased draught. These
steam jets can easily be shut off when not required, and
the apparatus employed merely as a firebar cooler by open-
ing small steam jets below the injection fittings. The
whole apparatus is very inexpensive, and can be fitted very
easily to any steam boiler. Another important method of
effecting economy is to separate the combustible portion
from the ash, and this may be as high as 30 per cent, of
the total. A special apparatus known as the “ Phonix
Separator ” has been invented by M. Muller, in which
chalk and water are used for the separation of the lighter
coked cinders from the heavier clinkers. Instead of this,
the lime sludge, which is a waste product from the
“ Permutit ” process of water softening, may be employed.
The objection which has been raised to the use of the
“ Permutit ” process on account of the soda which passes
into the boiler with the feed-water is not of serious
moment, as trouble may be avoided by frequent blowing-
off and the substitution of steel or iron fittings for the
usual gun-metal fittings.

INFLUENCE OF ASH IN ANTHRACITE.*

By F. G. Philo.

The value of coal as fuel depends not alone upon
the total number of heat units, or B.Th.U. per lb.,
but upon the fraction of the total heat contained
which can be produced under actual conditions of
combustion and operation. The B.Th.U. value of one
coal as represented by a calorimetric determination
may be higher than a second actually, but the lower
B.Th.U. coal often shows a higher actual fuel value.
This can be seen when it is considered that the calori-
metric determination does not include the moisture
in the coal as fired, the amount and composition of
the ash, whether it contains excessive slag or clinker-
forming constituents, or there are present such im-
purities as sulphur compounds, which in spite of their
heat-producing properties are often the cause of par-
tial corrosion of the boiler, the breeching and the
bunkers.

The sample of coal tested by the calorimeter is
usually burned in an atmosphere of pure oxygen, a
condition much different from that in practice, where
an atmosphere of only 21 per cent, of oxygen exists.
It follows that the most practical way to determine
the relative fuel value of different coals is to burn
a considerable amount of each grade upon the grates
and in the furnace under operating conditions, and
note the characteristics accompanying each grade.

Tables I. and II. show the results of tests during
which over 20,000 tons of No. 3 buckwheat coal were
fired and over 500 chemical analyses were made.

The coal used was fired into the same type of
furnace and upon the same “sawdust” grate, having
small circular air spaces ranging from 3/32 to i in. in
diameter. The area of the air spaces represented about
8 per cent, of the total grate area. Forced draught
was used, and an average pressure of 1 in. of water.
As practically no coal fell through the small openings,
the fuel losses in the ashpits represented these, due
to the combustible carried with the ash at cleaning
periods, which in this plant occur once every six hours.
It was found practically impossible to economically
burn out more combustible after it had been burned
until it represented about 18 per cent, of the material
left on the grates after “pushing back.” This fixed
ratio of combustible to refuse mainly accounts for the
rapid rate in which the losses in the ashpits increased
with the higher ash coals. The percentage of the total
combustible lost was calculated from the following
formula: —

Per cent, total combustible lost =

(per cent, ash in dry coal) x (per cent, comb, in dry refuse)
7 (100 — per cent, in dry coal) — (100 — per cent A
x	combustible in dry refuse).	/

With anthracite as fuel, the value of the combustible
in the refuse is almost the same as that of an equal
weight in the coal fired, so no correction was applied.

Table I.—Comparison of the Calorimeter Value and
' Actual Value of Different Ash Coals.*

Per cent.	Calorimeter value	Actual value	Actual value.
ash in	per lb. dry coal.	per lb. dry coal.	Cal. value
dry coal.	B.Th.U.	B.Th.U.	per cent.
14	12,220	11,755	96*2
16	11,920	11,420	95'8
18	11,640	11,080	95*2
20	11,350	10,714	94*4
22	11,080	10,348	93*4
24	10,800	9,936	92*0
26	10,510	9,459	90*0
28	10,240	8,949	87*4
30	9,950	8,000	80*4
* The “ actual value ” of a		pound of coal is here taken to	

mean the difference between the total B.Th.U. contained in
1 lb. of dry coal fired and the B.Th.U. in the combustible in
the dry j efuse per lb. of dry coal fired.

Table II.—Calorimeter and Actual Values of
Different Ash Coals as Compared with 14 per
Cent. Ash Coal as a Standard.

Calorimeter value. _______Actual value_____

7 Cal. val. of 14 per cent. \ 7 Act. val of 14 per cent. \
x ash coal. / x ash coal. /

Per cent, ash.	Per cent.	Per cent.
14			100*0	100*0
16	97*5	96*9
18			95*3	94*1
20	92*9	91*0
22	90*7	88*3
24	88*4	84*5
26	86*0	80*5
28	83*8	76*1
30	81*4	68*1

The tables will be found useful in calculating the
penalties to be imposed for high ash when coal is to
be purchased on specification. Although the actual
values given will not apply to all sizes and kinds of
coal, the actual loss curve will be about the same.
Of course, in computing the economic value of the
different coals, 'due allowance must be made for the
transportation costs, costs of handling the coal and
refuse, and the increased depreciation and main-
tenance charges against the grates and stokers that
accompany high ash and clinker. The reduction of
the capacity of the boiler and the furnace must also be
borne in mind, especially in plants where the boilers
are required to operate at high overloads.

* Power.

German Capital in Rumanian Lignite Mining.—The
Disconto-Gesellschaft, the banking house of S. Bleichroder,
and the Banca Generale Romano, Bukarest (founded by
the two foregoing concerns), have jointly acquired a
number of lignite mines in Rumania. The mines in work-
ing comprise about 80 per cent, of the total present
Rumanian lignite production. According to a German
paper, it is intended to increase the output considerably
by more intensive mining, and so far as possible to make
Rumania within a reasonable time independent of the
import of German pit coal. This will not only confer
a great economic benefit upon Rumania, but will also bring
considerable relief to the German railways, which have
hitherto had to supply the occupied Rumanian territory
with German coal.