March 28, 1918.

THE COLLIERY GUARDIAN

641

wondered if in the future, or even in the present, in
America and Germany, they had a means of using
silica bricks for this particular purpose, and maintaining
their strength past the particular critical temperature
by choking the oven walls with carbon. He thought
they had, and that this was a very important factor.

Texture could be considered from other points of
view. He would like to know whether coke oven people
had in their experience noted any particular difference
in the behaviour between coke oven bricks which had
been moulded, and in which the moulded face was up
against the wall, as compared with pieces of coke oven
brick which had been dressed and the dressed face had
seen service. He would like to know if any serious
difference was to be noted. That in part was a difference
of texture. In the ordinary way a moulded surface was
attacked less than one-fifth as much as a broken
surface.

Discussion.

The Branch President had very little hopes that
many members would respond to Prof. Fearnsides’
invitation to correct his conclusions. Personally, he
(Mr. Lee) was quite certain that the texture of a brick
was perhaps more important than they had been inclined
to think, and certainly at least as important as its
chemical composition. Some of them had for many
years been analysing bricks, and thinking, in their
ignorance, that a chemical specification of a brick could
be drawn up. Indeed, this had been done, and had
been sent out, especially in the gas making industry,
some years ago; but they had overlooked the impossi-
bility of drawing up a chemical composition that would
provide a brick suitable for all the changes of tempera-
ture to which it was subjected. It used to be held
that bricks for the combustion chamber should have a
certain composition, and that those for other parts of
the setting should, and could, have a different composi-
tion; but it must be frankly admitted that they had
overlooked texture altogether. Some few prophets in
the industry did suggest that texture was an important
factor, but he was not sure that they had been listened
t<> very much and very patiently. To-day, however, he
felt quite certain that they weie willing to go along the
line Prof. Fearnsides had suggested. There could
no longer be any doubt that texture was at least as
important as chemical composition, and they could
assure Prof. Fearnsides of their gratitude for the
information he had given them.

Mr. Hughes, in proposing a vote of thanks to
Prof. Fearnsides, said that everyone present had
learned something from his lecture; and Mr. Oxley, in
seconding, said one felt certain that the important
questions raised by the professor were in safe hands and
were assured of satisfactory solution.

The Branch President said they would better
understand, after that afternoon, the importance of
maintaining, as far as possible, an equable temperature
and the risks run by undue chilling.

Prof. Fearnsides, in acknowledging the vote of
thanks, expressed the thanks of his department for
the support given by the South Yorkshire coal owners,
largely in consequence of the representations of such
societies as theirs. He did not know yet in what direc-
tion the grant of £T,000 would be best utilised, but he
could assure them that the interests of the coke oven
industry would not be overlooked. , He would have been
very grateful if some of the members had offered some
little criticism of his suggestions and conclusions, and
if any occured to them he would be very glad to have
them sent in to him at any time, because he was largely
groping in the dark ; and although he did visit coke oven
plants, and all his time was not spent in the laboratory,
yet it was inevitable that in their daily work they met
with many difficulties and problems and experiences that
would be of the greatest value to him if they would let
him know of them. What the president had said about
keeping temperatures as uniform as possible was a very
real factor in efficiency. The coke oven manager did
not want a brick which was highly refractory in the
ordinary sense of the term, but one which would stand
changes of temperature, not a static high temperature.
So far, most of the tests to which coke oven bricks were
subjected were tests which recorded the behaviour of
the bricks at very high temperatures. In his opinion
the mischief was caused in most coke oven walls
and flues, not at the static high temperature, but in the
various changes. At these changes the salt readily
added itself to the fireclay and made the latter an agent
which very actively attacked the passive quartz. He was
clear that that was one of the reasons why the salt was
so troublesome. There was another matter which would
have to be gone into very carefully—when reactions
took place between the quartz and the fireclay, gases
were given off, and it was the evolution of gas which
was responsible for the consequences, such as the
dislodging of great pieces from the sides of the wall,
although he did not know what gas it was. If, by
making the coke-oven bricks extremely dense on the
outside film, the formation of these gases could be pre-
vented within the material, they would have gone a long
way towards a solution of the difficulty. But the ques-
tion of the gas was to be got at by way of the study of
texture.

The Branch President mentioned that, since the
last meeting, one of their members who had been fore-
most in the formation of the association, Mr. B. W.
Haigh, of Barnsley Main, had been married, and it was
the wish of the council that that event should not go
unrecognised by the association, and it had therefore
been intended that afternoon to ask his acceptance of a
little gift, but as he was not present this would be
forwarded, with an expression of the congratulations
and best wishes of the members.

The next meeting of the Section will be at Leeds, on
April 27.

The formation of a national council for the whole of
the iron and steel trades of the country, whose duty will
be to remove labour troubles and to regulate conditions
of employment on the lines proposed by the Whitley
Committee, is being considered. The Ministry of Labour
has already seen some of the interests concerned.

ELECTRICAL OSMOSIS AND COLLIERY
CABLES.

[ Specially Contributed. ]

Osmosis is the action which takes place when two
liquids of different specific gravities are separated by
a porous diaphragm. The classical experiments of
Nernst—one of the fathers of the modern science of
chemico-physics—will perhaps explain it best. Nernst
placed a certain quantity of a sugar solution in an
ordinary glass jar, such as is used for chemial experi-
ments. Above the sugar solution, and pressing down
upon it, was a disc of porous earthenware, and above
the disc a certain quantity of pure water. Notwith-
standing the presence of the diaphragm, and the fact
that the liquid below it was denser and of a higher
specific gravity than the liquid above, the sugar solu-
tion gradually worked its way up into the water, and
in doing so forced the diaphragm up a certain dis-
tance. As Prof. Thornton has pointed out in a recent
paper, if an electric current is caused to pass through
the two liquids, from one to the other, one of the
liquids will flow into the compartment of the other, in
the direction in which the electric current is flowing.
Fig. 1 illustrates Prof. Nernst’s original experiment;

W ater.

be

ft

Dense Liquid.

Fig. 1.—Nernst’s Experiment.

Liquids of unequal densities.

and fig. 2 the same modified by the action of an elec-
tric current. The action of electrical osmosis, or
endosmosis, as it is sometimes called, is perhaps better
illustrated by fig. 3, in which there is a glass jar con-
taining water, and a porous earthenware jar (similar
to those used in Leclanche cells) also containing water.
A carbon plate is immersed in the water in the glass
vessel, and another in the water in the porous jar; and
both are connected to a source of electric current, as
shown. When the circuit is complete, including the
water in the two compartments, the water will flow
from the carbon plate connected to the positive side
of the source of current towards the negative plate;
and it is quite practicable for the whole of the water
to be carried from one compartment to the other.
Moreover, the direction of flow of the water will follow
the direction of flow of the current if the latter is

Fig. 2.— Effect of
Current on Flow of
Liquid through
Diaphragm.

Fig. 3.—Effect of
Current on Flow
of Water through
Porous Cell.

reversed. Another interesting illustration of this
action arises in the working of wet Leclanche cells.
When a battery of cells is first put to work, there is
very little liquid inside the porous jars, and so the
internal resistance of the cell is comparatively high;
when the battery is started, the sal ammoniac solu-
tion is carried from the outer jar into the porous jar,
and the resistance of the cell gradually falls. The
effect is very striking, where a battery of new cells is
put to work a signal, the signals being very weak at
first, and gradually gaining strength as the battery
is used.

Effect on Colliery Cables.

The insulation of electric cables used in mines is
subject to two sources of trouble, in which electrical
osmosis plays an important part. Paper insulated
cables, it will be remembered, owe their insulation to
the presence of a carefully chosen resinous oil, with
which the fibrous manila paper is impregnated; with
continuous electric currents, the leakage current that
always passes through every insulating envelope (in
this case the oiled paper) carries the oil with it: in
the positive cable, from the conductor to the lead tube;
and, in the negative cable, from the lead tube to the

conductor. Fig. 4 shows this diagrammatically. This
action tends to rob the manila paper of its protective
resinous oil, and lays it open to the attack of any
moisture that may enter through a crack in the lead
tube, through an uncovered end of the tube, or in any
other way. This is part of the explanation why paper-

Fig. 4.—Section of Positive Cable. Current
Carrying Oil over to the Lead Tube.

covered cables so readily give out when cracks occur
in the lead tube. In addition to the above action, the
flow of the main current in the positive conductor will
carry the ’oil towards the outer end of the cable, whilst
the current in the negative cable will carry it towards
the inner end of the cable. Two serious results follow
from this, particularly in the case of shaft cables: the
flow of the oil lowers the pressure upon the oil above,
and causes a portion of the latter to assume the
vaporous condition; and the pressure developed by the
vapour tends to stress the lead covering of the cable,
and to cause cracks and other openings, that would
not otherwise have arisen. Some years ago, a case
was reported of a paper-covered shaft cable which
burst, near the pit bottom, from this cause.

The other source of trouble is the peculiar, and often
exasperating, action of water vapour. It will be
remembered that the capacity of air for carrying water
vapour varies with the temperature, increasing very
rapidly as the latter rises, and vice versa. Warm air
can carry a considerable quantity of moisture, and
when it impinges upon a metal surface, such as the
lead covering or armour of a cable, that is at a lower
temperature than the air itself, a certain amount of
moisture is deposited upon the lead covering of the
armour; and, in the case of the negative cable, will be
carried by the electric osmotic action inwards to the
conductor. Prof. Thornton reports a case where, on
cutting a cable, more than a gallon of water that had
been carried into it in this manner was drained out.
The action of the water, under electrical endosmosis,
is rather complicated; but it is bound to lead to
leakage faults, and sometimes to disconnections.

Action of Alternating Currents.

One advantage of the use of alternating currents in
underground mining work is the fact that electric
osmotic action is absent, and, in addition, the heat
produced by the currents which flow into and out of
the dielectric tend to dry up any moisture that may
have got in. After one of the electrical exhibitions at
the Crystal Palace in the 90’s, Messrs. Siemens showed
a very interesting experiment at their works during a
visit of the Institution of Mining Engineers. They
had a short piece of insulated cable, through which
alternating currents could be passed, and a thermo-
meter was placed with its bulb embedded in the insu-
lation. The temperature was carefully noted when
there was no current passing through the conductor;
and when the current was switched on, the tempera-
ture was seen to rise until the usual limiting conditions
were reached. Prof. Thornton mentions an interest-
ing experiment recently made with underground cables
buried in damp ground in the neighbourhood of New-
castle - on - Tyne. When continuous currents were
allowed to flow through the cables, the leakage current
rose to 1 ampere in 45 hours, with a pressure of 240
volts, and moisture collected at the negative cable,
accompanied by the evolution of steam. When the
current flowing through the cables was changed to
alternating, the leakage current fell to zero in a few
hours, and faults which had previously been frequent
were eliminated.

FUEL EXPORTS TO DENMARK.

The Controller of Coal Mines has issued a Direction,
which will have the effect of increasing the price
payable by Danish buyers for cargoes of coal, coke oven
coke, and patent fuel for export to Denmark the ship-
ment of which is commenced on or after Monday,
March 25, by 10 kroner per ton.

The Directions affect shipments in pursuance of all
contracts made with buyers abroad on or after
October 15, 1917 (to all of which the Instruction of
October 12, 1917, as to the inclusion of a clause
providing for variation of the price in accordance with
any directions of the Controller of Coal Mines applies).

The charge of 10 kr. per ton specified in the
Directions does not form part of the price recoverable
by the exporter or the owners of the colliery, etc.,
through the Board of Trade, but will be accounted for
by Messrs. Hambro directly to H.M. Government.

Sellers are to observe the following instructions as to
notifying Danish buyers :—

(i.) In the case of deliveries under existing con-
tracts to which the charge is applicable (i.e., contracts
made with buyers abroad on or after October 15,
1917), the buyer is to be informed that a further sum
of 10 kr. per ton is payable on all cargoes the ship-
ment of which is commenced after March 24,1918.

(ii.) In quotations for new business the price is to
be quoted on the basis of the Directions of January 31,
1918, plus the separate charge of 10 kr. per ton.

(iii.) The charge of 10 kr. per ton is not to be
included in the amount specified in the telegraphic
notification of loading or the invoice forwarded to the
Board of Trade, but will be added by the Board of
™ Trade when arranging for payment by the buyer.

The Direction does not affect shipments under
contracts made with Danish buyers before October 15 last.