754

THE COLLIERY GUARDIAN.

October 11, 1918

allowance is made in the results for the heat normally
absorbed in the chemical reaction. Hence the true
theoretical available calorific value of a sample of coal
containing calcium carbonate or similar decomposable
substance cannot be estimated by means of a bomb
calorimeter.

Experiments were made with the Lewis Thomson,
William Thomson, and Simplex calorimeters to
determine whether any differences could be detected
due to the presence of decomposable carbonates in the
samples of coal tested. The instruments, however, do
not admit of sufficient accuracy to register small
changes in the quantity of heat liberated. The escape
of uncooled gases which seems to be unavoidable,
renders the results unreliable. In some cases the loss
of heat in the hot gases necessitates an allowance of at
least 10 per cent. On the other hand, the experimental
errors involved in the use of a bomb calorimeter may
be reduced to about 0'25 per cent.

A second set of experiments was made using
mixtures of the same coal with varying proportions of
shale dust. As in the previous experiments naphthalene
was added to those mixtures which contained little coal,
so as to ensure complete combustion. The results are
given in Table III.

the coal seam has a calorific value of H B.Th.U. and

yields A per cent, of ash.
from 100 parts of shale.

Then S parts of ash result
Hence parts of ash are

yielded by parts of shale. Therefore, of the unit weight

A.

of the sample used in the combustion - is incombustible
8

shale. This means that

represents the weight of

mineral-free coal in the sample; and this weight of pure
coal substance produces H B.Th.U. on combustion.
Therefore, the calorific value of the ash-free coal (z.e., C)

is -----B.Th.U. The equation then becomes :—

Table III.—Calorific Values and Ash Contents.of
Mixtures of Coal with Shale.

Sample

No. .

1

7

8

Ash
per cent.

3'38

29'53

46'95

Calorific
value
B.Th.U.

14,191
9,952
7,098

Sample
No.

9

10

11

Ash
per cent.

, 64'38

68'71

90'5<i

Calorific
value
B.Th.U.

4,270

. 3,542
0

As the percentage of ash yielded by the shale dust is
very high, little decomposition of the shale may be
assumed to have occurred. Therefore, it is possible to
neglect the small quantity of heat which is lost in all
probability in the chemical reaction. Hence the graphs
drawn through points determined by the bomb
calorimeter estimations may be taken to represent
truly the relation between the calorific value and the
ash content of samples of coal from various seams,
which contain varying proportions of shale. Since in
each case the relation between the calorific value and
the percentage of ash for the same coal is expressed
graphically as a straight line, consequently the
calorific value is proportional to the quantity of com-
bustible matter in the sample.

In the purchase of coal, according to a specification,
it is usual to correct the price for variations in the
calorific value and the ash and moisture contents.
From the above it might be argued that the “ash
content ” adjustment of the price is unnecessary, as it
incidentally forms the basis of the “ calorific value ”
correction. However, in boiler practice it is found that
the increase in the evaporation which is observed with a
cleaner sample of the same coal is not directly
proportional to the decrease in the amount of inert
matter in the coal. -The evaporative power exceeds the
expected value because the fireman can use the cleaner
fuel to greater advantage. Hence the correction of the
price for variations in the percentage of ash, as well as
the calorific value is essential where coal is purchased
for industrial purposes on a specification basis.

Mathematical.

As the graph representing the relations between the
calorific value and the percentage of ash of samples of
coal from the same seam is a straight line, the problem
admits of easy mathematical treatment. Only two
points are necessary to fix the position of a straight
line, but for accuracy the points should be as far apart
as possible. In this case two such points permit of easy
determination. First, the percentage of ash yielded by
the impurity may be estimated by incinerating several
samples of shale which have been selected so as to
exclude all carbonaceous matter. The result giving the
maximum ash content is accepted as being that of shale
which is free from carbonaceous matter, and therefore
which possesses zero calorific value. Suppose this value
to be S per cent. One point through which the line
passes may now be fixed by marking off a distance L
along a horizontal axis OX, to represent S per cent.

The second point may be determined by making, say,
three estimations of the calorific value of a carefully
chosen sample of coal from the seam. Since in skilled
hands the bomb calorimeter will give very accurate
results, the mean of the three results may be assumed
to be correct. Suppose the sample of coal has a
calorific value H B.Th.U. and an ash content A per
cent., a point M is plotted to represent the above values
on a diagonal line drawn from L, so as to cut the
vertical axis OY at a point N, where the distance ON
represents C B.Th.U That indicates that the calorific
value of the coal entirely free from ash is C B.Th.U.
An assumption, however, is made that the inherent ash-
yielding material normally present in the coal is the
same as the accidental impurities in the coal. Such an
assumption is not precisely true, and therefore the
extension of the line to cut the axis OY at N cannot
be justified; but where the normal ash content of the
coal is low—say, less than 5 per cent.—the error intro-
duced by producing the line to N is negligible.

The equation of the line LN may be expressed as :—

H

V = 8^A (S ~ “) v/

From this equation the calorific value of any sample
of coal from the same seam may be calculated without
reference to a graph. However, a diagram is extremely
convenient for reading off at a moment’s notice any
required values. As a rule the ash contents of the
samples rarely exceed 25 per cent., so that there is no
need to construct the whole diagram. The part giving the
ash contents up to 25 per cent, and the corresponding
calorific values is all that is required. Such a diagram
may be plotted by using the above equation. The
advantage in omitting all del ails beyond 25 per cent,
ash content is that the resulting diagram may be
constructed on an area 16 times that possible for the
complete graph. This will allow any required values to
be read off with greater accuracy.

Conclusions.

1.	For samples of coal from the same seam, the
relation between the calorific value and the ash content
may be represented graphically by a straight line which
does not usually cut the ash axis at 100 per cent., or
may be expressed in the form of an equation, such as:

where C = calorific value of the mineral free coal;
S = percentage of ash yielded by the impurity which
usually accompanies the coal in the mined samples;
y = required calorific value of a sample, and x = per-
centage of ash yielded by that sample; or:—

H
y = (s - *).

where A = percentage of ash yielded by a sample from
the coal seam; H = calorific value of the sample from
the seam, and S, y, x respectively have the same signifi-
cance as mentioned above.

2.	From numerous experiments it is concluded inci-
dentally that for the determination of the calorific
value of coal, an instrument of the bomb calorimeter
type is absolutely essential if reliable results aie to be
obtained.

3.	It is essential that, for the results to conform to*
the above relation, the utmost care must be taken in
air drying the samples before determining their respec-
tive calorific values and ash contents.

5.	The price of gas coke or breeze sold by a gas
undertaking to a factor or wholesale merchant shall
be Is. 3d. per ton less than the price chargeable to
a consumer under the provisions of this Order.

Provided that—

(i)	Where coke or breeze is dealt with by more
than one factor or wholesale merchant before
reaching the consumer or retail merchant the above
amount of Is. 3d. per ton shall be divisible between
the different factors and wholesale merchants, and
each seller, except in the case of the final sale to
the consumer or retail merchant, shall at the time
of the sale inform the purchaser how much of the
above amount is included in the price, and shall
show such amount on every quotation, sale note,
document or memorandum relating to the sale and
on the invoice in order that the maximum price may
not be exceeded.

(ii)	Where payment is not made by the consumer
or retail merchant before the date on which payment
is due to the original owner of the coke or breeze
or within 30 days of delivery of the same, whichever
is the later, the factor or wholesale merchant may
make a charge not exceeding 2| per cent, in respect
of credit to the consumer or retail merchant.

6.	Where a consumer purchases gas coke or un-
screened breeze under a contract for not less than 50
tons of gas coke or unscreened breeze per month over
a period of not less than 12 months, the maximum
price chargeable by the gas undertaking at the gas
works, that is the price prescribed by Articles 2, 3
and 5 of this Order reduced by the costs of transport
and handling,, shall be reduced by 10 per cent, and
the price chargeable by a factor or merchant in respect
of coke supplied to a consumer under such a contract
shall be correspondingly reduced.

7.	The Board of Trade may by notice under the
hand of the Controller of Coal Mines suspend the
operation of this Order or any provision of this Order
within the district of any local authority or larger
area for such times and subject to such conditions
as may be prescribed in the notice and may in like
manner restore such operation.

8.	The maximum prices and charges provided under
this Order may be increased or reduced by the Con-
troller of Coal Mines either generally or as regards
any particular class or case.

9.	All contracts for the purchase and sale of coke
and breeze existing at the date when this Order comes
into operation shall remain in force notwithstanding
anything contained herein, but the prices payable
under such contracts shall be modified so that it shall
be a price not less than, and not exceeding, the price
prescribed by this Order.

Any party to such contract may apply to the Con-
troller for*the variation of or relief against any term
or condition of such contract.

10.	Infringements of this Order are summary
offences against the Defence of the Realm Regu-
lations.

11.	This Order comes into force on October 7, 1918.

12.	In the application of this Order to Scotland the
Household Fuel and Lighting (Scotland) Order, 1918,
shall be substituted for the Household Fuel and Light-
ing Order, 1918, wherever reference to the lattef* Order
is made.

13.	This Order may be cited as the Gas Coke Prices
Order, 1918.

y

where y is the required calorific value of a sample of
coal yielding x per cent, of ash, and C and S have the
meanings respectively assigned to them above.

Calculation of the Value of C.

The value of C cannot be determined by direct
experiment, as the coal always yields a certain
amount of ash. It can be obtained by drawing
a graph as explained in the preceding sections;
but even then it is only possible to read off
the value, of C in an approximate manner, unless the
diagram is constructed on a very large scale. The
calculation of the value of C, however, may be made
readily from the actual calorific value determinations.
Thus, suppose a selected representative sample from

GAS COKE PRICES ORDER.

The following is the text of the Gas Coke Prices
Order, a summary of which appeared in our issue
of October 4 : —

1.	This Order applies to all sales of gas, coke or
breeze in the United Kingdom for such industrial
and other purposes as the Household Coal Distribu-
tion Order, 1917, or the Household Fuel and Lighting
Order, 1918, do not apply to.

2.	(a) The maximum price of ordinary large gas
coke delivered to a consumer by road vehicle shall
in any district be the second highest price fixed under'
the Household Fuel and Lighting Order, 1918, for
sales of coal in such district.

(5) The maximum price of unscreened breeze de-
livered to a consumer by road vehicle shall be 40 per
cent, of the corresponding price of ordinary large
gas coke.

3.	(a) The maximum price of ordinary large gas
coke or unscreened breeze delivered in railway wagon
or barge load or cargo to a consumer, or to a retail
merchant for delivery by road vehicle to consumers,
shall be less than the price prescribed under Article 2
of this Order by 12s. per ton in the case of deliveries
within the Metropolitan Fuel Area as defined in
section 124 of the Household Fuel and Lighting Order,
1918, and in the case of deliveries in the rest of Great
Britain by such amount as has been fixed by the Local
Fuel and Lighting Committee for the district in
respect of loading, cartage and delivery of coke, or,
where ho amount has been so fixed, by 10s. per ton.

(5) Where the transport charges .by rail, barge
or ship as the case may be are not paid either in
whole or in part by the gas undertaking from whose
works the coke or breeze is supplied, the maximum
price shall be reduced by the amount by which such
charges to the destination are not borne by the gas
undertaking; provided that in the case of coke or
breeze delivered into barge at gas works within the
Metropolitan area the amount by which the maximum
price for coke or breeze delivered at destination shall
be reduced shall be 2s. 6d. per ton in respect of the
service of lighterage plus any additional cost of
transport by rail.

4.	(a) Additional charges may be made for the
services of breaking, screening or washing coke or
breeze provided that any dispute as to the cost of
such services shall be submitted to the Controller of
Coal Mines, whose decision shall be final and con-
clusive for all purposes. Any such charge shall be
shown separately on the invoice.

A notice, dated September 30, has been issued by
the Controller of Coal Mines under Article 7 of the
Gas Coke Prices Order, 1918. This Order suspends
during the period from the commencement of the
Order up to and including October 31 in the counties
of Derbyshire, Nottinghamshire, Leicestershire,
Staffordshire and Warwickshire, in order that the gas
undertakings in those districts may have an oppor-
tunity of submitting applications for an increase in
maximum prices under Article 8 of the Order; pro-
vided that full particulars in support of such appli-
cations shall be furnished by such undertakings on
or before October 16, and that the decision of the
Controller of Coal Mines as to the prices to be charged
by such undertakings under the Order shall in all cases
operate as from October 7, being the date of the com-
mencement of the Order.

Coal Conservation in Chicago.^The Electrical Review
of Chicago states that coal conservation to an astonishing
degree is the result of the discontinuance of 24 privately
operated plants in Chicago, and the consequent operation
of their systems by central station service. The estimated
saving in coal occasioned by this change reaches the
excellent total of 54,840 tons a year. By these plants
taking over central station service a total daily require-
ment of 2,172,000 kw. hours has been added to the
Commonwealth Edison Company’s operating system—a
figure that approximates an addition of nearly 17,000
horse-power.

Dublin Fuel Shortage. — A consultation between the
Dublin Industrial Development Association, the E.L. Com-
mittee and the Irish Coal Controller has resulted in
the following proposals for e'conomy in lighting. If
the proposals are adopted, the Controller has agreed to
supply enough coal to carry them into' effect, even if
he has to commandeer it from other sources. The pro-
posals include the closing of shops at 5 p.m., or, alter-
natively, to close between 3.30 and 5.30, and to remain
open until 9.30 p.m.; offices to close at 4 p.m.; private
houses to be rationed as follows: 1, 2 or 3 rooms, 110 units
per annum; 4-6 rooms, 160; 7-9 rooms, 210; over 9 rooms,
250 units, or two-thirds of the supply in 1914; theatres
to close by 10.30 p.m.; picture theatres to close between
3.30 and 5.30; outdoor theatre lighting to be prohibited,
and the total lighting to be reduced by 25 per cent, com-
pared with 1914; factories to have preference for energy
for power purposes, but factory lighting is not to be
more than 80 per cent, of the pre-war lighting. It was
stated that the contractor would not enter into any con-
tracts for coal this year, owing to the critical position.