August 2, 1918.

THE COLLIERY GUARDIAN.

229

of a one ton car travelling through. It was designed
to withstand a water pressure of 1,000 lb. per sq. in.,
but when tested at 200 lb. was found to leak some-
what badly. Cementation was then resorted to, and
the dam most effectively sealed.

Rectifying Defective Boreholes.

Sometimes boreholes, for the purpose of obtaining
domestic water, are required to pass through one or
more rock strata containing inferior or corrosive

Fig. 7.—26 Cross cut E.R.P. Mines. Cemen-
tation of Open Fissure.

Showing woodeii wedges, also release and injection
boreholes.

£ LEGATION

B

Da I VE

Fig. 8.—28 W. Drive, E.R.P. Mines. Fissures,
with Concrete Dam and Rubble Filling.

Water pressure, 4001b. per sq. in.

SOUTH WALES INSTITUTE OF
ENGINEERS.

The ordinary general meeting of the South Wales
Institute of Engineers was held at Cardiff on Friday,
July 26, the President (Mr. J. Fox Tallis) in the
chair.

The Late Mr. G. G. Hann.

At the outset the President referred to the sudden
death of Mr. G. G. Hann, manager of the Britannia
Colliery, Pengam, a member of the council, a former
winner of the institute’s gold medal, and a compara-
tively young man who had accomplished much, and
gave promise of even greater things.—Dr. Henry K.
Jordan, as the oldest member of the council, paid a
warm tribute to Mr. Hann, the youngest member
of that body.—Mr. Joseph Shaw, K.C., chairman of
the Powell Duffryn Company, said it was the greatest
blow he had ever received when he was informed of
the death of his friend and colleague, Mr. George Hann.
The Powell Duffryn Company had sustained a great
loss. He (Mr. Shaw) had looked forward to the time
when Mr. Hann would be at the top of the whole con-
cern—a position for which his talents eminently fitted
him. He had a grip of the big things in the engineer-
ing world, and possibly no man in South Wales \had
grasped the possibilities of electricity, and especially
in its application to coal mining, to the "extent that
he had. A motion of sympathy with Mrs. George
Hann and with Mr. E. M., Hann, the father, and
other relatives, was adopted.

A vote of condolence with the Dowager Lady
Rhondda and the Viscountess Rhondda on the death
of Viscount Rhondda, a member of the institute for
many years, was also passed.

The following were elected to the institute: Mr.
P. Kenyon, manager and director of William Kenyon
and Sons Limited, Dukinfield, Cheshire; Mr. W.
Morgan, Raglan Engineering Company Limited,
Briton Ferry ; Mr. H. H. Pennington, Llanbradach;
Mr. W. Daniel, Blaenavon; Mr. J. L. Evans, Ton
Pentre; and Mr. W. M. Thomas, Forestfach, Swansea.

Gas Firing Boilers.

Discussion was resumed on Mr. T. M. Hunter’s
paper, “Some Notes on Gas Firing Boilers.”
(Colliery Guardian, May 31, 1918, p. 1097).

The President endorsed the principle enunciated by
Mr. R. James that more power was got out of gas
consumed directly in gas engines than when used under
boilers, and expressed the opinion that there was a
great future for the gas engine, which had been
viewed with a little prejudice in the past.

Mr. W. D. Wight said the idea of applying gas
under boilers was very old, and, like the proposal to
use the gas in the gas engine, was a very good idea,
but the difficulties in its practical adoption had been
such that it had been slow to develop. Great im-
provements had been effected in appliances for burn-
ing coal. By an improved appliance in the furnace
he was getting excellent results in steam generation
for a very common anthracite. The troubles and
difficulties in the way of using gas in gas engines
more than counteracted the economy, and in his
opinion there was more hope in the direction of burn-
ing gas under boilers. Many important improve-
ments had been effected in the steam engine—the
steam turbine, uniflow engines, etc.—all reliable and
economical; and if still further improvements could
be effected in the fuel burning and in the generation
of the steam in the boiler, he felt sure that steam
as a motive power would hold its own for many years
to come.

Mr. G. D. Budge asked the author of the paper
whether he thought it would pay colliery companies
to use gas producers and convert the coal into gas
before firing in boilers, in view of the rapid advance
made in the recovery of sulphate of ammonia. He
believed this part of the problem was entirely changed,
and that the large proportion of sulphate of ammonia
which could now be made from these producers would
entirely change old ideas on the subject.

The discussion was adjourned.

Mining Electrical Engineering.

Consideration was resumed of the paper of Mr.
Chris. Jones, M.I.E.E. (Colliery Guardian, May 31,
1918, p. 1094.)

Mr. Forrest (deputy electrical engineer, Birming-
ham City) said it was significant that the author had
hardly mentioned direct current at all, but had dealt
entirely with alternating current generation and dis-
tribution. Presumably he was satisfied that the alter-
nating current system was the better one for general
use in mines, in spite of the difficulty of motor speed
regulation, the wattless currents, and a rather more
complicated arrangement of switchgear. In this he
(Mr. Forrest) felt sure he was right, although, as
the paper made clear, the ideal method of utilising
electrical energy had not yet been evolved. He was
interested to learn of the author’s satisfactory expe-
rience with static condensers for the improvement of
power factor, and wTould be glad to have some further
information as to their cost, construction, and guaran-
teed temperature rise when dealing with the maximum
rated current. They appeared to be ideal pieces of
apparatus for use in mines where over-excited syn-
chronous motors (or rotary condensers) or even phase
advancers of the Kapp or other well-known types
would be entirely out of place. In calculating the
capacity, in microfarads, of the static condensers, for
use at any point, did the author aim at obtaining
unity power factor at the point when the motor or
motors were running at full load? The capacity of
the static condenser, not being adjustable, would
draw a leading current of a fixed amount from the
mains, and with the motor or motors running at light
load, the leading wattless component of the current
might occasionally predominate.

Mr. Frank J. Moffetts, B.A., M.I.E.E. (Birming-
ham) urged, in view of the ability to interconnect
colliery power stations with each other and with the
systems of public supply authorities, that the fre-
quency should be standardised. In the past there had
been a large range of frequencies, but the tendency
now was to adopt either 25 or 50 periods, and this
was by far the most common. When each supply
system was kept isolated, each station was obliged
to have a certain amount of spare plant, and often,
at week-ends, was running at a very poor load factor.
Further, it was often exceedingly difficult to arrange
for the overhauling of the station plant, owing to
the need for continuous running. If a number of
power stations were interconnected, great advantages
at once accrued. The static condensers mentioned
by Mr. Jones should prove of value, more especially
underground, where it was often impossible to instal
synchronous motors, phase advancers or rotary con-
verters. As regards cables, in his opinion there would
be a considerable extension in the use of higher pres-
sures underground in the near future. The erection
of heavy low pressure cable where they fed plant
. at a considerable distance inbye, was an arduous
undertaking when these were of large section. The
comparative figures given by Mr. Jones for cable to
transmit 600 kw. at 3,300 volts and at 400 volts proved

Fig. 9.—Plan of 26th Level Cross-cut to the South Circular Shaft.

Showing scheme of keeping two pilot boreholes in advance of cross-cut face during its course through the probable water zone, (a) Recess for Diamond drill.
(b) Boreholes—to be at least 20 ft. in advance of face of cross-cut. (d) Brickwork dam to withstand pressure of 1,000 lb. to sq. in., built as a precautionary measure.

water. In such cases the usual method is to line these
boreholes with metal tubes, but these tubes frequently
become corroded at the point of contact with the bad
water, with the result that they become useless and
the good water is polluted. In this case the upper
feeders of bad water can be successfully closed off by
means of cementation.

Rendering Impervious Foundations of Dam Walls, Etc.

It frequently occurs that at the site of a dam the
rock foundations are of such a nature as to be unsuit-
able of withstanding the pressure of the water behind
the dam. This in the usual way is overcome by deep
excavations, which consequently greatly increase the
cost of the dam. It is intended to treat by means
of cementation the pervious rock foundation at a
dam site in the Mazoe Valley, Rhodesia, and there
is little doubt but that the operation will be quite
successful and so greatly reduce the expenditure on
this dam. Briefly, the rock foundation is treated with
cement introduced through a system of drill holes.
Foundations of engines and machinery generally when
ruptured can be very effectively strengthened and
solidified by cementation work.

Having regard to the great demand for coal, the Derby-
shire Miners’ Association and the coal owners have agreed
that the 50,000 miners in the county shall confine their
August Bank Holiday to Monday, instead of the customary
four days.

Mr. T. Sugden said that, in theory, gas used direct
in the gas engine gave more economy, but, as Mr.
Wight had remarked, there were practical difficulties
in the way. At some electrical power stations, where
gas engines had been given full trial, steam was being
reverted tc in the form of steam turbines, and the
gas engine had a long way to go before it displaced
the steam turbine. Then they had to remember
the large amount of capital that was invested in
the steam engine and the steam turbine when they
talked of scrapping these things. He had no doubt
however, that there would be a greater use of gas
in connection with boilers, because it was much
cleaner, much more easily handled, and dispensed
with a lot of labour. He believed that a useful and
practical direction in which to employ gas-fired boilers
was in processes of recovering the by-products of coal,
working through mains at a high pressure.

Mr. W. A. Chamen said that in spite of the improve-
ments that had been effected—and a great deal had
been done by designers—they were still without a
satisfactory gas engine on a large scale. There were,
of course, special circumstances in which it was found
advisable to use gas engines, in spite of expensive
maintenance—cases where coke oven waste gases could
be utilised, or at chemical works—but even in these
instances their use did not appear to be on the in-
crease. They had not yet arrived at the time when
gas engines could be designed and made for the g nera-
tion of electricity using, say, 10,000 horse-power, and
even probably 5,000 horse-power.

the advantage of adopting the higher pressure.
Motors of 100 horse-power, and of even less size, could
now be built to run satisfactorily at 3,000 to 5,000
volts, and consequently there was no need to use
transformers in such cases.

Mr. E. B. Wedmore, M.I.E.E., believed that, in
the light of developments that were bound to take
place, consideration of the frequency which would be
standard for electrical power distribution in that part
of the country in which the individual mine was
situate outweighed all other considerations, whether
the individual installation was large or small. He
welcomed, too, Mr. Jones’s references to improvement
of power factor, a subject which would be found of
considerable practical and financial importance, and
would receive increasing attention. The author had
touched on the use of current-limiting reactance. It
was clear that where it was contemplated that the
plant might reach a capacity of 1,000 k.v.a., or more,
consideration must be given to impedance in circuit.
It should not be necessary to employ external re-
actances, but the switchgear manufacturers must be
given particulars of the conditions to be met, so as
to ensure that the switches furnished had a proper
rupturing capacity. If rated with a factor of safety
suitable for mining work, small distribution switches
on the market for medium and high voltage circuits
had a rupturing capacity from, say, 5,000 to 15,000
k.v.a., according to design and size, but there were
some fancy ratings in use which should be avoided.
There was no difficulty in obtaining generating and