1126

THE COLLIERY GUARDIAN.

May 22, 1914.

The outer appearance of the cambric samples changed
very little, only a few cracks developing during the two
years of test. The weatherproof braids of the rubber
samples began to crack open after about six months of
test, and were much cracked and rotted when the test
was completed. The appearance of the rubber insula-
tion exposed by the cracking of the coverings did not
show any deterioration. The outer braid of the special
samples began to crack open in about a month and was
almost totally destroyed, by the end of the test. The
appearance of the insulating tapes exposed by the crack-
ing of the braid of these special samples did not seem
to be greatly affected.

The weatherproof covering appeared to deteriorate
most rapidly at those points where the acid solutions
evaporated. The first cracks in the covering appeared in
a line along the top of the sample. The outer covering
of the special samples was not filled with compound as
were the coverings of the other samples, and the fibres
of the covering produced a capillary action upon the
solution, raising it as high as possible, and thus estab-
lishing a point where a large proportion of the solution
sprinkled upon the sample evaporated. The effect of
this action was most evident on the vertical parts of
the sample where the. continuous evaporation of the
solution raised by the fibres made around the sample a
circular cut that extended through the outer braid of
the sample but not through the first layer of insulation.

The table on previous page gives the condition of the
outer coverings of the samples as they appeared at the
end of each periodic test.

A microscopic examination of some of the cambric
samples was made by Reinhardt Thiessen. After about
18 months of treatment with the acid solutions a piece
of 1C4, a piece of 204, and a piece of untreated insula-
tion were examined. The treated insulation as compared
with the untreated insulation was less readily cut into
sections for microscopic examination and showed a darker
colour under the microscope. The insulating coatings
that had been applied to the tapes in the course of their
manufacture seemed to have a granular structure in the
treated samples, although in the untreated samples the
structure of these coatings seemed to be homogeneous.

Tests made by Thiessen also showed that the samples of
both special and standard varnished cambric that had been
treated with the acid solutions gave pronounced acid
reactions even in the inmost layers of tape, whereas
samples of the same insulation that had not been treated
with the solutions gave weak acid reactions or none at
all.

Physical Tests.—The tensile-strength tests made of the
cambric samples indicate that the acid had penetrated
as far as the sixth layer of tape, as the breaking strength
of the first five layers of the treated samples was less
than the breaking strength of the corresponding layers
of the untreated samples. The tensile-strength tests
made of the special samples showed practically no
difference in the breaking strength of the treated and of
the untreated tapes with the exception of the first layer
of the treated samples, the strength of which was
greatly impaired. Tests made of the rubber compound
used in insulating the rubber samples showed an average
tensile strength of 624 pounds per square inch for eight
untreated samples, an average strength of 511 pounds
per square inch for 11 samples cut from 1R1, and an
average strength of 401 pounds per square inch for nine
samples cut from 2R1. The results of the different
stretch tests did not agree, and the greatest deterioration
observed was found in a sample of insulation that had
not been treated with the acid solutions.

The information obtained from measuring the insula-
tion resistance of short lengths of the cambric and special
insulating tapes showed, first, that when first unwound
the tapes of the treated samples were much lower in
resistance than the tape of the untreated samples;
second, that as the tapes were unwrapped the resistance
of the inner layers of treated tape was, in general, lower
than that of the outer layers; third, that after exposure
to the air for several hours the resistance of all treated
tapes increased to values comparable with those of the
untreated samples; fourth, that the resistance of the
outermost layer of tape seemed to be lower than that of
the next layer when first unwrapped, and this relation
seemed to exist even after the tapes had been exposed
to the air for some time, although the inner tapes, which
measured much lower than the second layer at the start,
finally became as high in resistance as the second layer.

The results seem to indicate that the moisture pene-
trated all of the layers of tape. This penetration is
evidenced by the low resistance of the treated tapes as
compared with the resistance of the untreated tapes.
The fact that the resistance of the tapes increased so
greatly when exposed to air seems to show that the acid
had not affected the insulating qualities of the tapes.
The fact that the outer tape manifested and retained
a notably low resistance seems to indicate that the acid
had affected its insulating qualities to some extent. The
fact that the resistance of the second layer of tape
showed so much higher than the others at the start may
have been due to the fact that, being nearer the out-
side of the windings, it was partly relieved of its
moisture before the measurements were made. Briefly
to sum up the results—The acid seems to have no effect
upon the insulating qualities of the tapes with the
exception of the outer layer, but the acid solution pene-
trated the interstices between the tapes, and thus
destroyed their insulating value.

A comparison of results seems to indicate that the
tap water and the acid solutions had about the same
effect on the rubber samples, but that the acid solutions
had a greater effect than the tap water on the cambric
samples, both standard and special. The plain water
undoubtedly acts to impair the insulation. The reasons
why it may effect the cambrics is easily seen, but why it
affects the rubber is not so clear. The action of the
acid solutions is greater than that of the plain water
except in the case of the rubber.

As regards the drying of tape insulation, the facts

seem to indicate that the tape insulation will dry out
if no moisture is applied to the insulation and if the
atmospheric conditions are favourable.

Discussion of Results.

The results of the tests show little difference between
the action of the two solutions. Both solutions had
about the same effect upon the cambric and the special
samples. The rubber samples that were treated with
solution No. 2 did not show as well as the other samples
in the tensile strength tests, but otherwise the effect of
the two solutions seemed to be the same.

The results seem to indicate that sprinkling the acid
solutions upon the samples is the method of application
best adapted to hastening the deleterious action of the
solutions. This conclusion is based upon the observa-
tion that the parts of the samples that were allowed to
remain moist all of the time were seemingly not impaired
as much as those parts that were alternately wetted and
dried. So far as could be discovered neither bedding
the samples in coal dust nor letting acid solution drip
on them increased the severity of the conditions.

Although the acid may have promoted the entrance of
moisture between the layers of tape of both the cambric
and the special samples, it was not discoverable that the
acid had actually affected the tapes beyond the first one
or two layers. So far as could be seen the acid had no
destructive effect on the rubber insulation or on the
lead sheath of the paper insulated telephone cable.

The paper insulated, lead sheathed, telephone cable
having been tested merely to determine the action of the
acid on the lead is not considered in the following state-
ments regarding the relative resisting power of the insu-
lations tested. The rubber insulation undoubtedly
withstood better than the cambric and special insulations
the treatment accorded to all. The percentage of
decrease in insulation resistance was far less in the case
of the rubber samples than in the case of either the
cambric or the special samples, and at the end of the
test the insulation resistance of the rubber samples was
comparatively high (more than 20,000 megohms). The
breakdown voltage of the rubber insulation held up well
also. The cambric samples were the most affected by
the treatment, for although both cambric and special
samples decreased in insulation resistance to less than 2
per cent, of their original values, the breakdown strength
of the special samples was well maintained throughout
the test, whereas all but one of the cambric samples
broke down on high potential during the test.

The insulation resistance of the cambric and the special
samples decreased because moisture penetrated between
the layers of tape that constituted the insulation of those
samples. The results obtained from measuring the
resistance of the various tapes and the evidence of “dry-
ing out ” that was observed in several tests indicate that
moisture was the chief cause of the failure in insulation
resistance. The result of the microscopic examination
indicates that the presence of acid promoted the entrance
of the moisture. The reason is not so clear for the
failure of the rubber insulation. The results of the water
test of the rubber samples seem to show that the treat-
ment with pure water decreases the insulation resistance
as rapidly as does treatment with acid solutions. Yet it
is hard to believe that the deterioration of the rubber
was due to the effect of moisture alone, and it seems
more reasonable to consider that the rubber became
impaired by the combined effect of temperature, exposure
to air, and exposure to the action of the acid solution.

The principal fruits of the investigation were the data
made available for organising future tests. The effect
of plain water was shown to be sufficiently great to
warrant in future work a control test treated with water
alone. It will also be advisable to make a test of samples
exposed to the air but not treated with water or acid
solutions. The method of applying the solutions will
probably not be changed in future tests, but the electric
potential will be continually impressed upon the samples
while they are under treatment.

MANCHESTER GEOLOGICAL AND MINING
SOCIETY.

The monthly meeting of this society was held on
Tuesday, May 12, 1914, at the offices of the society, 5,
John Dalton-street, Manchester. Sir Thomas H.
Holland (president) was in the chair.

The President said that before they took the paper
which was down for reading, and which evidently had
attracted a good many members, there were one or two
small items of business to be got through, and one or
two announcements to be made. Some time ago he
directed attention to the proposal to raise a capital fund
for the Institution of Mining Engineers, and it was
arranged that the seven societies comprising that insti-
tution should contribute their share, according to mem-
bership, of the £15,000 required. The share of the
Manchester Geological and Mining Society was .£1,263.
They had already received £1,260 7s. 4d. That left
£2 12s. 8d. to be offered by some generous member at
this meeting, and that would close the account at once.

He had also to announce that they had been invited to
join the Mining Exhibition, which would be held in the
Exhibition Hall, off Deansgate, Manchester, from the
12th to the 27th of June. The exhibition is to be on
lines similar to those on which the exhibition was held
in 1911, and the committee in charge of the exhibition
had offered to reserve a day for members of this society.
The day that suited the members of the council best
was Tuesday, June 23. He would like, further, to call
attention to the fact that the London meeting of the
Institution of Mining Engineers had been altered to the
4th and 5th of June, and that the dinner would be held on
Thursday, the 4th of June. As this would be the 25th
anniversary of the institution, it was hoped Manchester

would be well represented at the meeting. He had been
asked to announce, also, there would be a conference on
metallurgy in Edinburgh on Tuesday, September 8
next, and four following days. If any members were
interested in the subject,or wished to take part in the con-
ference, they might get full particulars by applying at
the offices of the conference, Metallurgical Office, South
Kensington.

Modern Developments in Hydraulic Stowing.

Discussion followed the reading of Mr. J. Drummond
Paton’s paper on “ Modern Developments in Hydraulic
Stowing and Suggestions for Application of same in
British Collieries.” (See page 1121.)

The President, in expressing the thanks of the meet-
ing to Mr. Paton, said he was sure all present would
acknowledge that the paper was one of great and
unusual interest. Prof. O’Shea was present, and might
think that the paper and the attendance were average
examples of the meetings and papers of the society. He
hoped that was the case, for they could not have had
better material for Prof. O’Shea to form his opinion
upon. The paper just read was evidently one that
would make a very distinct mark in the literature of
mining in this country, and add greatly to the value
of the Transactions of the institution.

Prof. O’Shea said he did not know that he could say
very much on the subject, because he spoke rather as
an amateur in the matter, than as one who had a great
acquaintance with the subject, either of hand or sand-
stowing. About four years ago he was in Silesia, and
saw what was going on there in the way of sand-stow-
ing. The manner in which the material was carried
down the pit had been very graphically described by
Mr. Paton, and had vividly brought back to his mind
what he saw there. One remarkable feature in regard
to sand-stowing he saw when he was at Myslowitz last
year; they took the whole of the coal out of a seam 17
metres thick, with buildings on the surface, and the
subsidence was practically nothing. The manager of
the mine, who took him round, told him this question
of sand-stowing was the salvation of the Silesian coal-
field, because, owing to the thickness of their seams
they had to leave so much of the coal unworked in order
to support the surface. Otherwise, the subsidence
would be enormous. Another point was the question of
dealing with gob fires. This was a very important ques-
tion, so far as Yorkshire was concerned now the develop-
ment of the Doncaster coalfield was taking place in
areas that were liable to spontaneous combustion. At
the Myslowitz pit the manager told him that on the
Friday before he entered the mine there was a gob fire.
It was then Tuesday, and they had a fear the fire
would prevent his going down the pit; but by directing
the sand-stowing at the fire they put it out, with the
result that the visitors went down the pit and knew
nothing of the fire until they came up again. That
fact gave one the impression that this was a practicable
method for preventing spontaneous combustion. In
Westphalia the seams were all very great inclines, but
a large number of the Yorkshire seams were much less
inclined, and he thought it would be well if they had
some information as to the method applied in those less
inclined seams.

Mr. N. Williams (Manchester University) said he
did not know much of this question, save what he had
learned by reading what had been done in the United
States, and Mr. Paton had not referred to that part of
the world. As to the pipes used in America, those most
efficient were the wood stave pipes, spirally wound with
galvanised wire and coated with tar and sawdust. These
pipes were very adaptable, and largely used in Penn-
sylvania for incline roads. Cast iron pipes were used
extensively on flat roads and permanent travelling ways
for pressure over 1001b. per square inch. The joints
were made by a sleeve, and packed and made water-
tight with oakum, and every 48 ft. flanges were put in,
so that they could be turned. Where the inclination
was more than 15 degs. semi-circular cast iron troughs
were used for conveying the flushing material. The
water was filtered through the dam by means of
launders. Passing to the space to be filled the launder
was covered every 15 ft. or so by wire mesh. The water
settled in settling ponds in old roadway. The sludge in
these ponds was cleaned occasionally, and conveyed by
hutches to lower workings. He wished to ask Mr.
Paton if, when blast furnace slag was used, the material
was treated to neutralise its acidity and bad effect on
the pipes. At the Robinson Mine, Transvaal, it was
treated with lime.

Mr. Geo. B. Harrison, H.M. inspector of mines, said
he did not know anything of this question from the prac-
tical point of view; but if it could be used in one hun-
dred mines in Germany, and in so many other countries
of the Continent, no doubt it could be used here in this
country, if it were found advisable to do so. There
were many points that kept occurring to his mind as to
why it should be advisable to do so. As to gob fires,
they, it was said, would be a thing of the past if this
system were adopted. Then as one travelled in the
train one saw heaps of material that might be used for
hydraulic stowing, and it was obvious from land subsi-
dences that such stowing would have been very useful
in some of the mines of this country. It seemed to
him that it would pay owners to have recourse to this
process; even if it cost a bit more at the time it was
done, it would pay them in the end. The surface land
being made more serviceable, the owners and royalty
owners would get their money back in time, and a thing
that would go on paying all the time would stand a
great cost in using. Those persons who had read the