March 9, 1917.

THE COLLIERY GUARDIAN.

485

SAMPLING DELIVERED GOAL.*

By G. S. Pope,

Sine© 1906 the plan of purchasing coal on the basis of
analysis has been adopted by the United States Govern-
ment to a large extent, so that out of a total value
approximating 8,000,000 dels, annually, moire than half
is purchased under specifications, the samples being
examined in the laboratory at the headquarters of the
Bureau of Mines, Washington, where over 1,200 samples
have been analysed and tested in one month.

One of the serious drawbacks to the general adoption
of the specification method for the purchase of coal is
the difficulty of obtaining at reasonable cost samples of
coal that can be considered fairly representative of the
commercial product delivered in wagons, railroad cars,
or ships. Therefore, the method of taking and preparing-
samples for shipment to the laboratory has been given
fully as much care as the making of the analyses and
tests, and a general plan of collecting samples fairly
representative of the delivered coal has been evolved
through various modifications and improvements based
on experience and increased knowledge of the physical
and chemical characteristics of the various coals that
are purchased by the Government. The method that is
in general use by the Government is described below.

In connection with studies of the coal deposits of the
country, of the best methods of preventing waste in
mining, and of increasing efficiency in the utilisation of
coal belonging to or for the use of the Government,
geologists and engineers of the United States Geological
Survey and of the Bureau of Mines have visited more
than 2,500 coal mines scattered through all of the coal-
producing States and territories. From, each mine twm
to eight or more samples were taken, the number depend-
ing upon- the size of the mine and its output. A study
of the analyses of these samples and of the samples taken
from cars shipped from a number of the same mines
shows that the mine samples are, as a rule, of higher
grade than the average commercial shipments, parti-
cularly with respect to containing a lower percentage of
ash, and having a correspondingly higher heating value.
This difference is due to the fact that the Government
inspector, proceeding on the basis of what can be done
by a good miner, usually removes more of the partings
of bone, slate, and other extraneous matter from his
mine samples than the average miner does in ordinary
practice, the aim of the miner being to get the maximum
number of tons past the tipple inspection, as his earn-
ings are based on his output. The average miner, there-
fore, does not always take as much care as he might in
rejecting the impurities. The difference may be caused,
too, by the presence of pieces of the mine roof and floor
in commercial shipments. The Government inspector
can readily exclude these from the mine sample, but
they often get into the commercial coal as a result of the
character of the roof and floor and of the mining methods
employed. The efficiency of the tipple inspection and
the means employed in rejecting impurities when the
coal is loaded into the railroad car are also factors that
often largely account for the difference between mine
and commercial samples. Most of the samples collected
from the mines by the Government inspectors show a
higher moisture content than commercial samples,
because of the generally moist atmosphere of the mine
and. the precaution taken to prevent loss of moisture in
the collection, preparation, and analysis of mine samples.

When properly taken, the mine samples are of great ‘
value, as they indicate the general character of the coal
and the uniformity of the coal bed, and enable one to
determine its probable value for any designated purpose,
provided due consideration is given to the character' of
the partings, the roof, and the floor, and to the possi-
bility of pieces from these, being loaded with the com-
mercial output.

Theory of Sampling.

To determine with utmost accuracy the ash content
and heating value of a quantity of delivered coal would
require the burning of the entire quantity, and special
apparatus arranged to measure the total heat liberated,
or would require crushing the whole quantity, and
reducing it by an elabor ate scheme of successive crush-
ings, mixings, and fractional selections to portions
weighing approximately Igrm., the minute quantity
which the chemist requires for each determination.
Either of these procedures is obviously impracticable if
the coal is to be used for production of heat and power.

The method actually employed is to select portions
from all parts of a consignment or delivery of coal, and
to systematically reduce the gross sample, obtained by
mixing these portions, to quantities that the chemist
requires for making ash determinations or that can be
burned conveniently in the calorimeter, an apparatus for
■determining the heating value. The gross sample should
be so large that the chance admixture of pieces of slate,
bone coal, pyrites, or other impurities in.an otherwise
representative sample will affect but slightly the final.
results. Increasing the size of the gross sample tends*
toward accuracy, but the possible increase is limited by
the cost of collection and reduction. In reducing the
gross sample by successive crushings and halvings or
fractional selections, the object is to procure a small
laboratory sample that, upon analysis, will give approxi-
mately the same results as the gross sample itself, or,
in fact, the entire quantity of coal from which the gross
sample was obtained.

Practical Considerations : Moisture.

At one time the specifications used for the purchase of
coal were on the British thermal unit “ as received ”
basis; that is, payment for delivered coal was directly
affected by the moisture content of the sample received
by the laboratory; but from experiments made, it is
known that the moisture content reported by the labora-
tory may be as much as 5 to 10 per cent, lower than
that actually contained in excessively wet or high

* From United States Bureau of Mines Bulletin 116.

moisture coal at the time of weighing. For this reason
the Bureau of Mines recommends that the heating value
in coal specifications should be on the “ dry coal ” basis.

The fact is recognised that the amount of moisture
contained in coal produced from day to day from the
same mine, or group of mines working the same bed, is
largely accidental, and is a matter over which the buyer
'and seller have only slight control. However, in order
to place a negative value on high-moisture coals, and to
protect the Government against the delivery of coals con-
taining excessive amounts of moisture, the specifications
require the bidders to specify the maximum moisture
content in coal offered. This value becomes the standard
of the contract.

If coal of uniform British thermal unit “ dry coal ”
value is delivered on a contract, the contractor receives
the advantage on any delivery in which the moisture
content approaches• the maximum specified, because he
is paid for the weight of water contained in the coal in
excess of a normal amount, whereas if the coal is very
dry, containing less than the normal amount of moisture,
the purchaser receives the advantage.

For example, coal is delivered under a contract in
which the standards are 14,300 British thermal units per
pound “ dry coal,” and a maximum moisture-content of
3’5 per cent. The heating value of a ton (2,2401b.) of
” dry coal ” would be 32,032,000 British thermal units.
Assume that the average moisture content of deliveries
for a year is 2-5 per cent., then for every 2,2401b. of
” dry coal ” having a heating value of 32,032,000 British
thermal units, the purchaser is required to pay for 56 lb.
of water at the same rate per ton a<s for “ dry coal,” but
as this percentage of moisture in . average deliveries is
inherently a constituent of the coal, it is considered as
part and parcel of the coal by both the purchaser and
the seller. If the coal delivered contains 3’5 per. cent,
moisture, to procure 32,032,000 British thermal units
11 dry coal,” the purchaser has to pay 1 per cent, more
for coal because of the excess water above the normal
amount, whereas if the coal contain's 1’5 per cent,
moisture, the purchaser pays 1 per cent. less. As the
variations .in moisture content, 1-5 or 3’5 per cent., are
largely accidental, the season of the year being partly
responsible for them, it is equitable that the purchaser
and seller should share the uncertainty. The purchaser
justly has a right, however, to demand that the seller
shall guarantee a maximum moisture content, as a
means of enabling the purchaser to compare one coal
with another, as a guarantee that the seller will observe
precautions against delivering coal that is unduly wet,
and as a basis for adjusting the price of exceptionally
wet coal.

The determination of the moisture in. coal delivered .
from stock piles is often of great importance, for the
proportion of moisture contained in the small sizes,
which pre most abundant near the centre of a stock pile,
and which absorb the rains and melting snows in districts
of heavy snows, may be from 10 to 15 per cent, higher
than when stocked. It is apparent, therefore, that
special moisture sample determinations are necessary
for equitable adjustment of payment on - account of
excessive moisture in coal which is stocked in piles
exposed to the weather.

The specifications provide for the collection of “ special
moisture samples ” if, in the opinion of the Government
officials sampling it, the delivery contains moisture in
excess of that guaranteed by the contractor. If the
analysis of the special sample shows a moisture content
in excess of the contractor’s guarantee, a proportionate
deduction is made from the price to be paid for the coal.
These “ special moisture samples,” representing coal as
delivered, should be preserved in such a way as to
minimise moisture loss, , the sample being placed in a
tight container, and stored in a cool place before it is
reduced. Moreover, the sample should be reduced and
transmitted to the laboratory as soon as practicable.

Ash and Heating Value.

The heating value of coal from the same mine or'from
a group of mines operating the same bed of uniform
character is directly influenced by the percentage of ash,
z.e., earthy matter and impurities that do not burn. As
the proportion of ash inherent (sometimes termed
“ intrinsic ash ”) in the coal substance, as a rule, does
not vary widely in coal from the same bed, the heating
value is largely determined by the amount and character
of the free (sometimes termed “ extraneous ”) impurities
■—-and hence the manner in which coal is cleaned and
prepared at the mine may greatly affect the heating
value of commercial shipments. In collecting samples,
therefore, it is of utmost importance that the samples
should contain within reasonable limits the same propor-
tion of impurities as the delivered coal from which they
were taken.

As the specifications provide for adjustment of price
according to the ash content or the heating value, or
both, it' is evident that samples taken from delivered
coal should show, by analysis, practically the same ash
content and heating value as the delivered coal. In
other words, the sample should contain the same pro-
portion of slate, bony coal, pyrites, and other impurities
as the quantity delivered, in order that the price adjust-
ment based on the analysis may be fair to both purchaser
and seller. Obviously, it is important to guard against
any accidental admixture of sand, cement, clinkers, or
other foreign matter while the sample is in storage, .or
while it is being prepared for transmittal. The gross
sample should contain the same proportion of lump.and
fine coal as the delivered coal, for it has been determined
that fine or slack coal may have an ash content, or a
heating value, different from lump coal from the same
shipment.

Volatile Matter.

The volatile matter of coal, as shown in analyses,
generally contains some inert non-combustible matter,
the proportion of which may range from 1 to 15 per
cent. The character of the volatile matter in any given

coal, and the temperatures at which it is given off, bear
directly on the design and operation of furnaces for burn-
ing the coal efficiently and without smoke. The propor-
tion of combustible and non-combustible constituents
in the volatile matter, and the character of the combus-
tible constituents, differ in different coals, and, there-
fore, the heating value of a coal cannot be determined
from a proximate analysis. Moreover, different coals
with the' same proportion of volatile matter may not
behave alike in the furnace. In order to determine the
comparative value of two coals for the same purpose, it
is important to know both their chemical composition
and their heating value. Hence the specifications
recommended by the Bureau of Mines provide that before
final 'awards of contracts, practical service tests may be
made to decide the relative suitability of coal offered.

In the specifications the contractor is required, in addi-
tion, to giving the name and the location of the mine or
mines producing the coal and the name of the coal bed
worked, to specify the volatile matter content and other
proximate analysis determinations of the coal he pro-
poses to furnish. The volatile matter content he
specifies becomes the standard of his contract, and
delivery of coal with a different percentage of volatile
matter, indicating the substitution of a coal other than
that offered, may result in the coal being rejected, and
the Government purchasing coal in the open market (the
contractor being charged with the difference, if any, in
cost) or in the contract being cancelled. Since the
character of the volatile matter and its heating value are
not necessarily indicated by the volatile matter deter-
mination, and because this determination is made by an
empirical method, no corrections in price are made for
variations in volatile matter.

(To be continued.)

THE IRISH COAL TRADE/
Thursday, March 8.

Dublin.

Business locally continues to be active, a return of wintry
weather being favourable to the house coal trade. There is
no change in prices of any of the qualities. The country
trade is fairly good, deliveries by the canals being effected
freely since the disappearance of the severe frost. Freights
are somewhat easier, but considerable difficulty is now being
experienced in getting in supplies. Quotations in the city
are as follow: Best Orrell, 44s. per ton net; Yorkshire
brights, 43s.; best Wigan, 42s.; best slack, 36s.; retail
prices, 2s. lOd. to 3s. per sack of lOst.; steam coal, from
about 40s. per ton; best coke, 44s. per ton. Prices of Irish
coals are about to be revised, so that no quotations are
available just at present. The coal vessels arriving during
the past week amounted to 65, as compared with 78 the week
previously, the total quantity of coal discharged upon the
quays being 23,000 tons, as against 32,000 tons in the
previous week. It is stated that the Government has con-
sented to build the connecting line between the Wolfhill
Collieries, Queen’s County, and the main line of the Great
Southern and Western Bailway at Athy., and when this is
constructed the mines will be further developed, and the coal
placei} upon the markets throughout the country.

Belfast.

The trade generally remains quiet, for reasons previously
given, viz., the laying in of large stocks by the principal
consumers early in the winter, and these are not yet
exhausted. In retail directions, demand for house coal is
somewhat better, owing to a return of cold weather. Fair
stocks are held by the local merchants. Prices are
unchanged, as follow : Best Arley house coal, 43s. 6d. per
ton; Orrell nuts, 42s. 6d.; English house, 41s. 6d. ; Scotch
house, 39s. 6d.; Orrell slack, 39s. 6d. Approximate prices
of steam coals are : Scotch, 35s. per ton; best English and
Welsh steam coal, 40s. per ton. Gas coke runs from about
37s. 6d. to 40s. per ton; and foundry coke, from 60s. to 64s.
per ton delivered. .

Miner Woodcutters. — Notices 'are being posted at the
South Wales collieries regarding the scheme agreed upon by
the joint local pitwood cutting and transport committee of
the Coal Conciliation Board, which has already acquired a
considerable area of woods on which work will begin imme-
diately. The rate of pay is 7s. 6d. a day, plus a weekly
lodging allowance of 7s'. 6d. to single men, and 10s. to
married men or those single men supporting families. Piece-
work is provided for, railway fares are to be paid at the
beginning and end of the employment, and reasonable faci-
lities given to men for visiting their families. A six-day
week of 45 hours is guaranteed. Existing house coal privi-
leges of colliers are retained, and volunteering for this
service is not to break the continuity of employment at the
collieries, the men being guaranteed re-engagement in their
former positions. Volunteers will retain their military
exemption cards.

Miners for Active Service.—At a meeting of the. executive
council of the Miners’ Federation of Great Britain, at the
Imperial Hotel, Bussell-square, London, on Thursday, it
was reported that an important concession had been granted
by General Geddes, Director of Becruiting, with reference
to the recent Order under which the miners are to be
recruited for military service. Under an agreement, which
has been approved by the executive, an effort is to be made
to secure the voluntary enlistment of 20,000 men from the
collieries. If this number is not raised by a certain date,
the men who have already received notices are to be called
up to complete the 20,000 demanded. As the result of
negotiations between the miners’ executive committee, the
Coal Control Board, and General Geddes, the agreement
referred to was offered by General Geddes, on behalf of the
War Office, the full text being as follows “ March 8,
1917. General Geddes agrees that if a general volunteering
scheme among colliery workers is agreed to, he will send
out a general wire of instructions to the military representa-
tives to suspend the calling up of all those who have received
notices calling them to the Colours and who have not yet
joined up and been posted, and if at the end of two months
from this date the full 20,000 have been secured, the men
who have not received notices will not be called up. If the
full 20.000 have not been secured, the men who have now
received notices will be called up to complete the number.
It is clearly understood that volunteers will join up at once,
without waiting for two months, or any other period.”