1114

THE COLLIERY GUARDIAN

December 8, 1916.

CURRENT SCIENCE

Experiments on Earth Pressures.

In a paper read before the Institution of Civil
Engineers, Mr. P. M. Crosthwaite gives a short account
of Rankine’s theory of earth pressure, and the principles
and assumption on which it is founded, together with
descriptions of former investigations—namely, those of
the late Sir George Darwin, and Messrs. Goodrich,
Wilson, Bell, and Meem. The author concludes that of
the experiments made by these investigators to inves-
tigate the lateral pressure of earth, those in which
model walls were used are of greatest value, but points
out that if models are of any size the experimental
difficulties are almost insuperable.

The author’s experiments, a number of which are
described and illustrated in the paper, were made by
loading a plunger with known weights and measuring
the penetration when the plunger had come to rest after
the application of each weight. The materials were
enclosed in an open bucket, and their weight was
determined.

With those data the value of </>, the angle of internal
friction, can be obtained from Rankine’s well-known
formula for the safe depth of foundations—

a = g r1 ~sin-

W \1 4- sin. </>/

when d denotes the penetration, P the pressure in
pounds per square foot, and W the weight of the
material in pounds pei- cubic foot. If the formula is
true, and the pressures be plotted against the penetra-
tions, the resulting curve is a straight line, and </> as
calculated from the formula should equal the angle of
repose.

With sand, garden earth, and cinders and ashes the
resulting curves are straight lines, but it was found that
the value of </> varied with the state of aggregation of
the material—z.e., whether it was lightly poured into the
bucket, shaken in, or well pounded in. When the
material was deposited in the bucket as lightly as
possible the angle of internal friction was the same as
the angle of repose, but with more consolidation the
anyde was much greater.

From these materials the author concludes that
Rankine’s theory holds, provided the proper angle of
internal friction is used and not the angle of repose. If,
however, this angle is used it would be necessary to
introduce a factor of safety into the formula, for a wall
designed without one would be theoretically just strong
enough and no more. In Rankine’s formula there is no
factor of safety, and it is concluded that Rankine saw
this, and used the angle of repose as covering the worst
conditions that need possibly be provided for. The
author’s experiments show that, for the materials tested,
work designed by Rankine’s formula, using the angle of
repose, would have a factor of safety of 2% to 4, and he
considers that these are not unreasonable figures for
snch materials.

The experiments on clay give altogether different
results, for instead of the penetration varying as the
load, it varies as the square of the load, and the penetra-
tion curves are parabolas. Those results, which were
altogether unexpected, are completely confirmed by
larger experiments carried out by Messrs. Coode,
Matthews, Fitzmaurice and Wilson, and by Mr.
McAlpine in New York.

The author is unable to give any physical explanation
as to why the penetration in clay should vary as the
square of the load, but leaves it to the physicists. The
law must be capable of some rational explanation, and,
if true, it upsets all earth-pressure theories when they
are applied to clay; for all accepted theories assume
that the angle of internal friction is the same as the
angle of repose, and that its value is independent of the
pressure. It is suggested that the subject is worthy of
further investigation, but that such could hardly be
made by a private individual, for the work is tedious,
each experiment taking from 24 to 48 hours. Moreover,
if the investigation is to be properly carried out, physical
and chemical analyses *of the clays will be required that
could only be made in a well-equipped physical
laboratory.

In connection with the earth slides experienced at the
Panama Canal, it has been suggested that in clay and
shale cuttings there is a critical depth beyond which the
sides will not stand, and the author’s experiments on
clays clearly show that for these this must be the case.
Where </> is independent of the pressure, the depth of
the cutting cannot affect the stability of the slope, but
where the angle decreases with the pressure, it is
evident that eventually a depth will be reached beyond
which its sides will not stand.

This decrease is clearly shown in one experiment on
mud, for which the angle for a pressure of 0 25 ton per
square foot was 17 degs. — 15 min., which decreased to
2 degs. 10 min. at a pressure of 1*25 tons per square foot,
when it was little better than a liquid.

Benzol Recovery and Rectification.

Messrs. P. D. Walmsley and H. A. Mor fey presented
a paper on this subject before a recent meeting of the
Manchester District Institute of Gas Engineers.
Previous to the commencement of the war, they said,
practically the whole of the benzol produced in this
country was obtained from by-product coke ovens, and
a present estimate of the supply from this source was
about 38,000,000 gallons per annum. The coal
carbonised in gasworks would point to a potential yield
of about 60,000,000 gallons per annum. The usual
apparatus in use for the extraction of ammonia
from coal gas—Livesey washers, tower scrubbers or
mechanical rotary scrubbers—were all suitable for the
extraction of crude benzol; but an important point to
bear in mind was that the washing with the extracting
oil should take place after the gas had been cleared of

AND TECHNOLOGY.

ammonia. Otherwise the greater part of the ammonia
left in the gas at the point where the oil washing took
place would be lost, owing to the absorption by the
wash-oil. Although no statistics could be given, io was
obvious that the benzol-absorbing capacity of the wash-
oil would be reduced. The extracting medium generally
favoured is creosote oil obtained in the distillation of
coal tar, the specific gravity of which is usually from
5 degs. to 9 degs. Twaddell. It should be as free from
naphthalene as possible, and can be obtained with so
low a naphthalene content as not to deposit more than
5 per cent, by weight when the distillate from 200 degs.
to 300 degs. Cent, is cooled to 45 degs. Fahr., and main-
tained at this temperature for 30 minutes. Further, it
should be quite free from water. Anthracene oil, or
“ green ” oil, is also a suitable medium for use, after
having the anthracene removed by filtration or settle-
ment. Shale oil and blastfurnace creosote have also
been used. The amount of wash-oil to be debenzolised
in the stills per ton of coal carbonised depends entirely
upon the degree of saturation of the benzolised oil,
which, in turn, is governed by the efficiency of the oil-
scrubbing plant. An average degree of saturation
would be about 3 per cent, which means that for every
ton of coal carbonised (assuming a yield of 3 gallons per
ton) the oil to be debenzolised would be 100 gallons,
and if 4 per cent, saturation is aimed at, the oil
would be 75 gallons. The loss of creosote oil in
distillation is approximately one-fifth of the crude
benzol recovered. It is important that the oil for
washing should be as free from water as possible,
as the presence of water considerably reduced its
absorbing capacity. In dealing with the benzolised oil,
the direct-fired still is preferable for small makes, up to,
say, 50 tons of coal carbonised per day, inasmuch as it
is cheaper to instal, and, if necessary, it can be adapted
to tar dehydration. Its disadvantages consist in its
control, which necessitates constant attention m the
firing, though in cases where the still is fired by gaseous
fuel this would be considerably reduced. For makes of
over 50 tons of coal carbonised per day, the steam-
heated still is to be preferred, owing to its ease and
efficiency of control, in addition to its practically
automatic action, which necessarily means small labour*
cost in operation. It is remarkably flexible; and its
efficiency is not impaired when dealing with quantities
of wash-oil between wide limits. The space occupied is
small. A complete plant (excluding storage tanks)
capable of dealing with the benzolised oil from 300 tons
of coal carbonised per day can be erected on a site 20 ft.
square. The cost, also, as the size of the plant increases,
does not increase to such an extent as does the cost of
the direct-fired plant.

Aluminium as a Detartarisei*.

In the Comptes Rendus M. Schloesingfils mentions that
whereas the ordinary constant-level water bath used in
laboratories is liable to become encrusted with lime salts
when supplied with tap water, so that, eventually, the
feed pipe gets completely choked, this drawback can be
removed by coating the interior with aluminium paint,
in which case the apparatus can be run for three years
or more without having to be cleared out. Experiments
have shown that this effect is due to the presence of
metallic aluminium, and that the mere suspension of
powdered aluminium in a boiler reduces the deposition
of boiler fur by more than 50 per cent., whilst a similar,
though smaller, effect is obtained with granulated
aluminium, the best results, however, being furnished
by painting the inner walls with aluminium powder
mixed with resin and oil of turpentine.

THE GERMAN AND AUSTRIAN COAL
AND IRON TRADES.

We give below further extracts from foreign periodicals
that have reached us, showing the course of the coal and
iron trades in Germany and Austria :—

Fuel Traffic on the Rhine-Herne Canal in October.

The total shipments of coal, coke and briquettes on
the Rhine-Herne Canal during October amounted to
407,474 tons (190,980 tons in October 1915), of which
51,471 tons (20,990 tons) were from Arenberg Prosper ;
70,343 tons (56,183 tons) from the State collieries;
32,537 tons (16,370 tons) from Bismarck; 17,971 tons
(15,203 tons) from Concordia; 11,209 tons (8,025 tons)
from Friedrich der Grosse; 6,078 tons (1,890 tons) from
Hibernia; 22,138 tons (6,641 tons) from Koln-Neuessen ;
12,697 tons (9,000 tons) from Kbnig Ludwig; 10,240
tons (4,333 tons) from Konig Wilhelm ; 42,066 tons
(9,459 tons) from Mathias Stinnes; 5,171 tons (3.873
tons) from Minister Achenbach ; 12,864 tons (2,319 tons)
from Nordstern; and 92,337 tons (32,000 tons) from
Wanne-West.

Austrian Coal Coal Output in the First Nine Months
of 1916.

The total output of coal amounted to 13,239,442 tons
(12,080,441 tons in 1915); briquettes, 151,912 tons
(155,750 tons); coke, 1,915,731 tons (1,374.770 tons).
The Ostrau-Karwin district produced 8,166,689 tons
(7,103,018 tons) of coal, 22,503 tons (22,438 tons) of
briquettes, and 1,857,562 tons (1,332,664 tons) of coke);
Kladno, 1,915,297 tons (2,102,920 tons) of coal; Pilsen,
906 803 tons (879,040 tons) of coal and 53,609 tons
(57,313 tons) of briquettes; Galicia, 1,403,012 tons
(1,193,347 tons) of coal; and other districts 847,641 tons
(802,118 tons) of coal, 75,800 tons (76,000 tons) of
briquettes, and 58,179 tons (49,106 tons) of coke. In
brown coal the total production was: Coal, 17,656,9 16
tons (16,362,196 tons), and briquettes, 176,955 tons
(190,047 tons), of which Briix-Teplitz-Komotau pro-

duced 11,392,440 tons (10,607,262 tons) of coal and
2,891 tons (2,991 tons) of briquettes ; Falkenau-Elbogen-
Karlsbad, 3,026,508 tons (2,709,445 tons) of coal and
174,064 tons (187,054 tons) of briquettes ; Trifail-Sagor,
899,239 tons (922,005 tons) of coal; Leoben and Fohns-
dorf. 702,414 tons (675,804 tons) of coal; Voitsberg-
Kbflach, 442,146 tons (465,176 tons) of coal; and other
districts, 1,194,201 tons (1,093,504 tons) of coal.

Deliveries of the Austrian Iron Works in September.

The Austrian ironworks delivered in September: Bars
and sections, 57,415 tons (41,428 tons in 1915); girders,
6,603 tons (6,920 tons); heavy plate, 9,684 tons (3,938
(tons); and rails, 7,370 tons (6,245 tons).

Coal Market in South Germany.

At the end of November the difficulties of traffic at
all unloading ports had become acute, supplies being
very short and great care having to be exercised in
distributing the available quantities so as to minimise
stoppages in industrial works, especially those engaged
on war orders. An improvement is expected as soon as
the wagons required for the transport of agricultural
products are released; and measures are also being
taken to restrict passenger traffic on the railways and to
divert goods traffic to the waterways, in order to relieve
the pressure. The industrial demand for fuel is urgent,
washed nuts being in special request but only insufficiently
available. It has also been difficult to secure smalls in
substitution, the same also applying to briquettes, the
manufacture of which has had to be reduced on account
of the coal being needed for coking. W orks which have
omitted to arrange for burning coke instead of coal are
likely to be in serious difficulties for fuel. Gas works,
too, are finding it difficult to obtain supplies, especially
those using Saar* coals, owing to the shortage of railway
wagons. The Saar trade in industrial and house coals
is also suffering from the same-cause ; and this circum-
stance has led dealers who have stocks in hand to sell to
the highest bidder, so that large consignments have been
sent from the Upper Rhine ports to Austria-Hungary.
The Swiss demand for fuel continues high, but the
congestion of traffic is delaying supplies, especially
those from Belgium. The house coal trade is suffering
from insufficient means of transport, but most con-
sumers have enough in hand for their immediate needs.
Dealers have to give precedence to munition works over
domestic requirements; and the same applies to house-
hold briquettes, the Brown-Coal Briquette Syndicate
having notified the trade that only 40 per cent, of the
contract quantities can be supplied, whereas, for in-
dustrial use, a full quota is allowed.

Increased Price of Heavy Plate in Germany.

The Heavy Plate Association has raised the price of
5-6 mm. plate by 35 mk. per ton, so that, on the basis
price of 195 mk., this plate now costs 230 mk. per ton,
ex Essen.

INDIAN AND COLONIAL NOTES.

Africa.

Cape Town Coal Trade.—During the whole of last year the
coal imported from British collieries into Table Bay docks
only amounted to 4,004 tons, as compared with 28,310 tons
in 1914, and 51,504 tons five years ago. Most of the coal
now used at Cape Town is brought overland from the Trans-
vaal and Natal collieries at a flat rate of 14s. 2d. per ton.
Last year the total tonnage carried overland from the Trans-
vaal collieries was 168,038 tons, as compared with 137,698
tons during the previous year, an increase of 22 per cent.
From the Natal coal fields there was, however, a considerable
increase, only 26,214 tons being carried overland in 1914, as
compared with 52,098 tons last year, an increase of 98 per
cent. Twelve months ago the overland railway rate was
brought down to the Transvaal level, and since the reduction
the Natal collieries seem to have devoted more attention to
the bunkering trade at Table Bay docks. The price for
bunker uoal at Cape Town ranged last year from 26s. 6d. for
Transvaal coal trimmed into bunkers, to 28s. for Natal coal,
but the South African railways propose to add 6s. to the
railway rate for bunker coal, leaving the rate for coal for
local consumption at 14s. 2d. as before. Since the end of
last year there has been a remarkable increase in the tonnage
of coal carried overland to Cape Town from the Transvaal
and Natal coal fields. Even before many of the steamship
lines had abandoned the Suez route in favour of the Cape,
the Transvaal collieries had more than doubled the consign-
ments of bunker coal to Cape Town, whilst from the Natal
coal field the consignments had more than trebled. The
actual tonnage of Natal coal bunkered at Cape Town in
1914 increased from 160,139 tons to 205,193 tons in 1915,
whilst the bunker coal brought from the Transvaal increased
from 113,189 tons in 1914 to 139,740 tons in 1915. Coming
to the coal production of the Cape Province, notwithstanding
the frequent announcements of the discovery of excellent coal
near the Karroo, the production is still confined to the inferior
coal from Indwe and the Stormberg beds. Even the South
African railways found it unsuitable for locomotive purposes,
but, to prevent the collieries from closing down, consumed
last year 30,488 tons. The price paid at the collieries for
this inferior coal was 11s. per ton, a price double that paid for
some of the Natal coals, which for locomotive purposes is
quite double the value of these inferior Cape coals. In 1914
the total tonnage of Cape coal carried over the South African
railways amounted to 51,154 tons, whilst last year it fell to
45,841 tons, and as soon as the railways decide to discontinue
the use of Cape coal for locomotive purposes, it is to be
feared that the output of the Cape coal fields will shrink to
even more insignificant proportions.

South African Coal for the British Admiralty.—Some time
ago the Transvaal Coal Owners’ Association offered 100,000
tons of coal free at the mines for the use of the British
Government during the war, and the offer was gratefully
accepted. Naturally the only coal of service to the Imperial
Government for use on transports, etc., would be the coal
obtained from the associated collieries in the Middelburg
district. The whole of the gift has been supplied, and was
obtained from the following collieries :—Anglo-French Navi-
gation, 9,884 tons; Cassel Collieries, 7,291: Clydesdale
Middelburg Colliery, 4,251; Coronation Colliery, 8,502;
Douglas Colliery, 4,528; Middelburg Steam Coal and Coke