April 28, 1916.

THE COLLIERY GUARDIAN.

807

permission to increase contract rates to cover the
increase in miners’ wages.

A meeting will be held in Burlington House,
Piccadilly, on Wednesday next, to urge upon the
Government the desirability of making natural
sciences a feature of education in the great schools.

The South Wales Conciliation Board has agreed
to help in obtaining miners and timbermen for army
tunnelling companies.

The Mansfield Eailway Company has practically
completed the new line which will materially im-
prove the facilities for the Nottinghamshire coal
traffic. The railway will be ready for service at an
early date.

The executive of the National Union of Scottish
Mine Workers expressed dissatisfaction with
Mr. Balfour Browne’s award, and decided to
ask for a further increase of Is. per day.

The point of interest in regard to
Further stone-dusting in collieries has for the
Experiments moment centred upon the relative
in Stone™ value of various kinds of. incom-
dusting. bustible material. Mr. A. S.

Blatchford has developed Prof.
Bedson’s investigations with the object of finding
the quenching effect of different substances, including
a wide range of available materials. His experi-
ments were also designed for the purpose of throwing
light upon the cause of the retarding action of these
substances upon coal dust explosions.

It is scarcely necessary to point out that it by no
means follows that the most efficient material from
the standpoint of quenching power is also the most
suitable to use for this purpose in practice. For
other considerations must be taken into account, such,
for example, as economy in use and general
suitability for the variable conditions of employment.
The value of these researches lies rather in the
theoretical than in the directly practical results
obtained. Amongst the former may be mentioned
the influence of such factors as specific heat, heat of
reaction, and the effects of decomposition of carbonates
and hydrates.

With regard to specific heat, for example, it would
appear that the quenching power of stone dust has
an important relation to this property. Other things
being equal, substances with a high specific heat
seem to be more efficient than those with a low
specific heat. This result would be just what
might be expected upon the cooling hypothesis.
Again, it was suggested in the Second Report of the
Explosions in Mines Committee that the evolution of
carbon dioxide might be a determining factor in the
quenching power of carbonates ; and, if this is so,
those carbonates with a low decomposition tempera-
ture would be expected to be more efficient than
those which decompose less readily. Mr. Blatcii-
ford, however, concludes that this property is not so
important as has been thought, and that the libera-
tion of carbon dioxide has but little influence upon
the result. The evolution of carbon dioxide from a
carbonate, in fact, appears to have considerably less
influence upon quenching power than the liberation
of steam from a hydrate, or hydrated salt. As,
however, increase of specific heat accompanies
increase in the number of molecules of water of
crystallisation, there is some difficulty in determining
which of these two properties is the more important
in regard to quenching power. Although Mr.
Bl atchford’s experiments are hardly conclusive upon
this point, they seem to lead to the conclusion that
specific heat is the essential factor, and that water of
crystallisation is mainly effective, not on account of
the liberated steam, but because its presence raises
the specific heat. Yet, against this view, we have
the fact that soda crystals, with 46 per cent, of water
of crystallisation, are slightly less efficient than
glauber salts, with only 43 per cent, of water, the
specific heats of the two substances being nearly the
same; while sodium bicarbonate, with a lower
specific heat, is nearly equal in efficiency to glauber
salts. Thus it is clear that there is also some other
influence to be considered.

This may possibly be found in the heat of reaction,
a purely thermo-chemical effect difficult to determine

under the conditions of the experiments; for it is
not so much the total heat effect of a complete
reaction that must be considered in this case as the
heat absorption over a particular range of
temperature.

Leaving aside these highly theoretical considera-
tions, however, it is of great interest to note that
from the point of view of actual quenching power
quicklime has a low value, and even ground shale
has apparently far less efficiency than certain
carbonates and hydrated salts. It remains, there-
fore, to consider what is the practical bearing of
these results upon the stone-dusting question. From
the point of view of cost and convenience in use,
certain of the substances investigated would
obviously be impracticable. Again, both the fineness
of division, specific gravity, and heat conductivity
should certainly be taken into account, and it still
remains to be proved what is the most suitable
substance to use in actual practice.

In this connection it is interesting to note that the
Bureau of Mines in the United States has been
giving attention to the question of stone-dusting, and
several pits have been engaged for a considerable
time in experimental work upon it. In the Pittsburg
district the material most in favour in the first
instance was limestone dust of such fineness that
about 75 per cent, would pass through a 100-mesh
sieve. This material was found to be very satisfac-
tory, but there is an inclination to favour the use of
a somewhat coarser dust involving less cost in
grinding. Trials in the experimental mine have
shown that material prepared by grinding in a
hammer crusher, equipped with a in. slotted screen,
is almost as efficient as the pulverised dust, provided
that about 40 per cent, will pass through 100-mesh,
and 25 to 30 per cent, will pass through a 200-mesh
screen. It is proposed to distribute this material by
means of a specially-designed rock-dusting machine,
operating by means of a blower at a pressure of 2 lb.
per square inch. This machine blows a thick cloud
of dust into the air-current, which carries it for long
distances, when it eventually settles, forming a mantle
over the coal dust deposits. Hand-dusting is, how-
ever, recommended for the first coating, because by
this means a thicker and better distributed coat can
be applied.

Notwithstanding the fact that a certain amount of
scepticism still lingers with regard to the efficacy of
stone-dusting, it is clear that the method is to be
given a fair trial both in Great Britain and in the
United States. This is undoubtedly the right course.
Opponents of the method unfortunately confine their
remarks rather to destructive criticism than to useful
alternative suggestions. No one imagines that
colliery explosions are going to be immediately
abolished by preventive measures ; but we may hope
to diminish them to a large extent by patiently
working out the results of experimental investigation.

It has recently been stated, and with
Coal in much appearance of truth, that only
Peace Germany appears even yet to have
and War. realised that capacity for success in
modern warfare is limited ultimately
by capacity to produce and carbonise bituminous
coal, in order to secure an uninterrupted and adequate
supply of modern explosives. It follows, therefore,
from the fact of the occupation of the coal fields of
Northern France by the enemy, and from the
absence of adequate raw material in Russia and
Italy, that the Allies are mainly dependent
upon Great Britain and the United States for the.
bulk of their supplies of munitions of war. It is
equally true that practically the whole civilised world
had been dependent upon Germany for dye-stuffs
and other substances prepared from the derivatives
of coal tar. Thus both in peace and war that country
had secured a great advantage over other nations.
In peace important industries were dependent upon
foreign supplies essential to their existence, while a
state of war has placed Great Britain in positive
danger of the failure of the means for its successful
conduct.

Nor have we yet emerged from that uncomfortable
position. The huge demand for high explosives, not
only for ourselves, but also for Russia, France, and

Italy, has only been with difficulty met by the costly
expedient of exchanging British gold for American
coal tar products. It will be some months yet before
British plant will be able to cope successfully with
the demand for picric acid and tri-nitro-toluene, to
say nothing of the aniline dyes which are necessary
to maintain our textile industry. In one sense,
therefore, this war may prove a blessing in disguise,
if it should teach us the obvious lesson that, whether
for war or peace, it is criminal folly to neglect the
utmost utilisation of those resources which are lying
latent in our bounteous supplies of bituminous coal.

In a recent paper read before the Sheffield
University Gas and Coke Oven Students’ Association,
Mr. Christopher Barber showed how consistent is
the yield of benzol from British coals of various
qualities. In South Yorkshire, Derbyshire, the
Midlands and Cumberland the yield of crude benzol
is from 2 J to 3 gallons per ton of coal; in Durham
it is from 2 to 2J gallons ; while in South Wales it
is from 1 to 1| gallons only, and in this case it may
not be worth while to recover the benzol unless in
exceptionally large installations.

The deficiency in benzol in the latter case is
perhaps a fortunate circumstance, and renders these
coals pre-eminently suitable for use under conditions
where they can best be utilised in the raw state for
steam raising. The question, however, arises
whether we are doing our best to render available
the distillation products of the coals from the other
British coalfields. To this important matter much
attention is being given at the present time. We
are told that in Germany, before the war was two
months old, the use in domestic stoves of any solid
fuel other than coke from by-product recovery ovens
was prohibited by the Government. The whole of
the anthracite of the Aachen coal field is said to have
been reserved for the use of the German Navy, and
there was an immediate increase in the installation
of by-product recovery coke ovens at the bituminous
pits. In this way the production of benzene and
toluene was greatly stimulated, and the enormous
demand for these products for the manufacture of
explosives has been adequately met.

In the United States, also, the rise in the market
value of benzol and toluol has led to a rapid increase
in coal distillation plants. Before the war there was
but a single coal company in that country producing
distillation products on a large scale. The latest
statistics show that thirty-one coke making establish-
ments with 4,933 by-product ovens carbonised in the
year about 8,000,000 tons of coal, from which were
produced 4,833,939 gallons of benzol and 1,315,727
gallons of toluol. The full annual capacity of the
benzol recovery plants now in operation and in course
of construction is estimated to exceed 20,000,000
gallons. Are we doing as much to increase the out-
put of these by-products in Great Britain as we could
and should do? It is scarcely possible to answer
this question in the affirmative when we reflect that
about 100,000,000 tons of bituminous coal are being
burnt in the raw condition, whereby some 200,000,000
gallons, or more, of benzol are consigned to waste.
There is much talk of national economy in war time,
and here there seems to be a practical way of
exercising it. If the above quantity of coal were
carbonised before use, or even a considerable fraction
of this amount, our output of benzol would render us
not only independent of the United States for high
explosives, but it would also enable us to satisfy the
demands of our allies to a very large extent. It may
be urged that we have not the plant available for the
purpose, but as summer is now approaching, this
deficiency could be to a large extent made up by the
assistance of the gas works, where the retorts would,
under ordinary circumstances, be less heavily
engaged than in the winter months. It has been
suggested by a writer in the Horning Post that in
this way the normal summer production of these by-
products could be doubled, and to this extent we
might obviate, the necessity of increasing our imports
from America, and, what is more vital, avoid the
transfer of an equivalent of British sovereigns to that
country.

Of course, the matter is not quite so simple as
might appear at first sight. The question of the
disposal of the gas and coke must be kept in view.