April 11, 1913.

THE COLLIERY GUARDIAN.

749

apparatus have been devised capable of dealing readily with
fuel of an ash content up to and even exceeding 40 per
cent. Difficulties are only experienced when the fuel as a
whole is of an exceedingly caking nature, and, as a rule,
these can be overcome by judicious combinations of
available fuels. In firing boilers by producer-gas,
it will be necessary to gasify considerably greater
weight of fuel per unit evaporation than if the
boilers were directly fired; for, of course, one has to
provide for both boiler and producer inefficiencies, and at the
same time in many cases (where exhaust steam cannot be
obtained) to provide extra steam for blast to the producers
and for driving auxiliary machinery. The excess weight of
coal may be anything from 20 to 40 per cent, of that
required for direct firing, depending upon local circum-
stances ; but this, so far from being a disadvantage, may
result in a substantial gain; for an all-important item #in
large gas-producer plants is the recovery of sulphate of
ammonia, which is produced in quantities far in excess of
any coking system. One may safely calculate upon a yield
of 701b. per ton of fuel for each 1 per cent, of nitrogen in
that fuel; and as many of these waste fuels are su* stan-
tially as rich in nitrogen as the better qualities, containing
from 1 to 1’4 per cent., the sale price of sulphate naked at
the works being now about .£13 10s. per ton (with every
likelihood of increasing during coming years), it will be seen
that a gross return of about 9s. per ton of fuel gasified may
be relied upon. In addition to this, a considerable amount
of tar of saleable quality is produced. It may be taken that
sulphate of ammonia can be recovered equal in value to
from 8s. to 10s. per ton of fuel gasified. The cost of
gasifying 1 ton of coal is approximately 3s. 4cl. per ton, and
the profit is 6s. 4d. per ton.

Coaldust for Briquettes.

The briquetting industry is slowly developing in this
country, but, owing to an original excess supply of good
coal, this venue for the dust and small coal has been little
resorted to. The public attitude also has not favoured its
introduction, but the depletion of existing supplies will
force its consideration. As an example of the difference
between the commercial relation of the German Govern-
ment to the national resource, and the attitude of the
British Parliament, an example of a huge colliery now in
operation at Dortmund is interesting. The company was
promoted by five private individuals with a very small
amount of capital, but with a brain reserve. As soon as
the plans and schemes and general arrangements were
completed, the National Bank, after investigating the
ability of the engineers concerned and the feasibility of the
scheme, advanced the further necessary capital. A contract
for 60 years was arranged whereby the Government take
the total output of coal above a certain size, while the
financing of the mine is done at an exceedingly moderate
rate of interest. The only part of the output allowed to
the colliery promoters and owners for disposal is the residue
dust and refuse coal, which is too poor to sell in coal form.
This is sufficient for the production of 500 tons of briquettes
per day, and finds a very ready market. This case is no
rare exception, but is typical of modern Germany.

Low-temperature Distillation.

The Diesel engine, the motorcar and the oil-fired ship are
factors that have directed attention to available oil supplies
The sales of benzol in Germany for motor-car driving and
the profits that have been available from by-products at
coking centres have awakened public attention to the possi-
bility of securing oils suitable for all the former purposes
from low-temperature distillation; and at the present
moment the writer does not think that there is any develop-
ment of engineering to which more attention is being paid
than to low-temperature distillation and oil production.
While low - temperature distillation has not yet passed
definitely into history, the writer may be permitted to quote
the possible utilisation of small dust coal for this purpose
and to cite the calculated and, in certain cases, established
results.

In one method it is suggested to use highly superheated
steam, and it may interest the members to note that this
process is already being successfully operated by the
Oldham Corporation for the recovery of oils and fat from
sewage smudge. In other systems a method similar to the
Del-Monte-Everett is used, where a solvent of high hydro-
carbon has been suggested to wash out the oils from the
residual carbon in the last stages of distillation. It is also
suggested to project the dust into a retort of a similar type
to the standard coke oven, using the gas of distillation after
it has been cleared of oils, &c., as the conveying medium in
a pneumatic system.

But sufficient has been stated to give some idea of the
schemes proposed, and until further developments are com-
pleted it will be impossible to say which will give the finest
return. It is evident, however, that recent developments
have raised the economic value of dust, and the prophetic
suggestion of Sir W. Ramsay that the coal may yet come
from the mine in the form of a gas, or the writer might say
“dust,” in the light of the boiler-stoker system already
given, is but an indication of the possibilities in this much
neglected product of the mine. Coaldust and its treatment
is too elaborate a subject for any one section of collieries to
settle; it is a question for national investigation in an

actual mine with the best mining brains of the country
behind it, and the co-operation of our educational centres,
so that future engineers may benefit. The writer holds
that the advance of German commerce in the last 30 years
owes no small debt to the attention which German engineers
have paid to this much-neglected national asset “ coaldust.”

The Discussion.

Mr. Gerrard (who had succeeded Sir Thomas
Holland in the chair) said the members had heard
probably the widest range over a vast field, which he
had not seen approached for a long, long time. So full
of interest was the paper that it almost seemed to him
to be a fairy tale. Mining people had been told of the
dangers of coaldust in recent years, very often indeed,
but it seemed they were entirely wrong in this view,
and that there was a lot of money in the dust.

On the motion of Mr. Leonard Fletcher, seconded
by Mr. J. Lomax, the thanks of the society were
tendered to Mr. Paton for his address.

Some comments on a few points were made by Mr.
Hugh Hart-Davis, and Mr. Paton replied.

COLLIERY CABLES

, At the February meeting Mr. W. T. Anderson read
a paper on “ Colliery Cables.” A copy of the paper
having been sent to Mr. R. Nelson, electrical inspector
of mines, Mr. Nelson sent the following comments upon
the paper, which were read by the secretary (Mr. Sydney
A. Smith).

In reading Mr. Anderson’s paper I was very gratified to
note the terms in which he was pleased to refer to the Home
Office regulations governing the use of electricity in mines.
It was generous of Mr. Anderson, speaking as a manufac-
turer, to say that regulations which were designed primarily
to secure safety appeared to him to be successful also in
assisting the manufacturer by, in Mr. Anderson’s own
phrase, “ the standardisation of conditions.” I have no
doubt that it has been pointed out by others that the great
virtue of Mr. Anderson’s paper is its practical character.
With Mr. Anderson’s views in general, I should like to
express close agreement. I have merely one or two
remarks to offer on points of detail. Mr. Anderson, almost
at the outset, recommends rubber-covered cables in these
terms: “ Under normal conditions rubber (cable) is
undeniably the best, both from a physical and from elec-
trical points of view.” He appears to condemn its use only
by reason of its first cost. Later, however, he remarks, in
speaking of bitumen-covered cables, that “ these cables are,
in the writer’s opinion, ... by far the most suitable
for average colliery work.” I think he cannot mean that
rubber-covered cables are the best for “average colliery
work ”; and if so, it would be well to make this clear. If
Mr. Anderson has in mind what are usually called “ tails,”
then I suggest to him that “ making off or tailing cables ”
are obsolete below ground in mines. He himself describes
the correct procedure in that section of the paper headed
“ Boxes ” and one of the dangers to be apprehended—
namely, corrosion caused by leakage “ over the damp braid-
ings of rubber tails,” in that section headed “Bitumen
Cables.” The best sphere for rubber-covered cables, if they
have one at all below ground in mines, is in connections
between controllers and resistance grids. Mr. Anderson
mentions the matter of the proper section of high-tension
armouring where the current is transformed down at the
shaft bottom or elsewhere for use in-bye. It should be
remembered, as I think someone has already pointed out,
that the difficulty does not occur when the neutral point in
both systems is earthed. To meet an insulated neutral
point—the case of the “conscientious objector” to an
earthed neutral point—there is an alternative to Mr.
Mr. Anderson’s suggestion—namely, to fix an earth plate
or plates at the junction of the two systems and connect
it, or them, in parallel with the surface earth by means of
the armouring of the high-pressure cable alone, or, if the
circumstances are thought to require it, in parallel with
some other effective conductor. Mr. Anderson’s remarks on
corrosion are interesting and, I think, very true. I would
also support his recommendation to “share the total under-!
ground load between two or more feeders.” I have met
mine managers who claim to have “ the largest single shaft
cable on earth,” but I should be ashamed of the sample of
engineering which gave me that distinction, unless, indeed,
there was something very abnormal in my conditions. I
would not expect two old boiler plates “ thrown into a
pond” to form a good earth connection. Water has an
appreciable resistance, and I would therefore expect to find
that two buried boiler plates would give a better result.
Mr. Anderson’s last paragraph is a complete guide toproper
maintenance. He promises at the outset of his paper to
deal with fundamental principles and practical points in
connection with colliery cables. I think it must be agreed
that he succeeds very well.

Mr. Gerrard said they all congratulated Mr. Ander-
son on receiving such a high compliment from such a
high authority as Mr. R. Nelson.

Mr. Anderson then replied to comments upon his
paper. He said that Mr. Hart-Davis’s plea for a copper
shield under the armour of high tension shaft cables, to
bring their load-carrying capacity into line with the low

tension requirements below ground; was hardly feasible
except in the case of lead covered cables. In the event
of pit water getting inside the armour, galvanic action
would probably arise. Otherwise the suggestion was
distinctly sound, if only to avoid the danger set up by
mechanical bonds between sheathing and an auxiliary
earth wire. He agreed with Mr. Hart-Davis that
sufficient attention had not been given to lighting
circuits below ground, but the new rules would tend to
cure that. For the rest it must be remembered that
their pressure seldom exceeded medium pressure, and
that falls were of very infrequent occurrence in the
districts immediately round the shaft, where lightning
circuits are usually run. With Mr. Ernest Long’s plea
that all colliery cables should be armoured (with the
exception, of course, of trailers) the writer was in entire
accord. Wooden casing had been mentioned by him in
his paper, but dismissed as impracticable. His remarks
equally applied to the split telegraph poles mentioned
by Mr. Long. Rule 12 (D) happily put this suggested
method entirely out of court. It was a method which
was quite opposed to the spirit of the new rules, in that
it allowed to a greater extent than any other of the
possibility of surroundings becoming charged up to a
dangerous extent without a fault declaring itself. In
vertical casing of the ordinary type or in grooved poles,
unarmoured and therefore mechanically weak cables
must either be a tight or a loose fit. In the former they
were almost invariably damaged in the malleting in, in
the latter they are unsupported—both insurmountable
objections.

Mr. G. S. Corlett queried the advisability of using
bitumen cables for extra high pressures in shafts, but
he (Mr. Anderson) had no hesitation in saying that for
normal conditions, with the exception, of course, of
rubber cables, which were not feasible on account of
cost, bitumen cables without hygroscopic material of
any kind in their internal construction were the best*
He was inclined to agree with Mr. Corlett in his remarks
that it was not (electrically) necessary to increase the
high tension armour as an earth connection to a low
tension system below ground, and realised that an earth
on the low tension might not affect the armouring of
the high tension system, but would probably be confined
to the underground portion of the installation.

For systems in which the neutral point is unearthed.
Mr. Nelson had, in his contribution to the discussion,
suggested a method which was both practical and
economical.

The writer could not agree with Mr. Bolton Shaw
that the clamp method of single suspension was good
for paper lead covered or for any other type of cable
and under no circumstances would he recommend its
use. As regards hydraulic pressure being set up at the
bottom of paper cables, this could not occur in cables
the insulation of which was impregnated layer by layer
and not in bulk.

The writer had purposely refrained from any mention
of aluminium for mining work, as he considered its use
impracticable. The greatly increased weight of the
metallic sheathing necessary to cover the enlarged
conductors would far outweigh any gain in the weight
of the conductors enclosed, and it was mere waste of
time to discuss the merits of unarmoured cables.

If size and weight had already not ruled this metal
out of the question the cost would certainly do so, as at
present day prices for insulated conductors, copper
worked out the cheaper of the two. Indeed, the only
form—load for load—in which aluminium could be
; considered from motives of economy, would be in
' the case of bare overhead lines. Regarding wood
impregnation, happily white ants had not to be catered
for in the treatment of wood for preservation in this
country, and for pit conditions of exposure to air and
moisture the writer could not imagine a finer pre-
servative than creosote.

Mr. S. H. Lee suggested that three locomotives (two
I to lower and one as a standby) used to instal a six-ton
cable were far from necessary. With this the writer
could not agree. The stresses and safety factors to be
catered for were impossible to gauge by ordinary calcu-
lation. Mr. Lee’s plea for a recessed groove for cables
in shafts was not likely to meet with support. Its cost
would certainly not be justified. In his paper he had
endeavoured to treat the various classes of cables upcn
their merits. With regard to bare rubber sheathed
trailing cables, he was inclined to think that though
; their initial cost was great, they had a great future
before them. As regards the ready smothering of an
arc in this class of cable, mentioned by Mr. Lee, this
was simply a matter of the quantity or the radial thick-
ness of material. It was not even essential that the
material should be airtight, so that, for instance, a thick
padding of fibrous material might be equally efficacious.
To thread long lengths of cable behind the timbering of