1330

THE COLLIERY GUARDIAN.

June 20, 1913.

Inasmuch as a large number of constrictions, such
as were represented by the props and bars in the
demonstrations, so complicated the phenomena as to
render the pressure curves obtained hardly intelligible, the
effect was tried of introducing one constriction at a time.

The constriction was obtained by bolting on to the
inside of the gallery an angle-iron ring having a 6 in.
flange. This reduced the diameter of the gallery at the
point where the ring was fixed from 7 ft. 6 in. to
6 ft. 6 in., the amount of surface exposed at right angles
to the direction of movement of the explosion being
11 square feet.

In the series of experiments to be described the point
of ignition was 400 ft. from the open end. The method
of carrying out the experiments was in each case exactly
the same as in the case of experiment No. 119, of which
details have been given.

The first experiment of the series (No. 123, June 22,
1910) was with the gallery clear of all constrictions. A
slowly-moving inflammation was all that was produced.
The pressure curve traced by the manometer most
distant from the point of ignition, 350 ft. (No. 6, fig. 6),
showed a maximum pressure of only 21b. per square
inch, and that pressure was attained but slowly.
Moreover, the curve shows no signs of any sudden rise
of pressure such as accompanies 44 explosive combus-
tion.” The effect of introducing a single constriction
at a point 200 ft. from the point of ignition (experiment
No. 142, August 26, 1910) was to raise the maximum
pressure produced to 10 51b. per square inch for the
same distance of travel; this maximum pressure was
attained about one second after ignition, as against one
and a-half seconds required when no constriction was
present. The pressure curves, which are described later,
indicated the beginning of 44 explosive combustion ” at a
point about 350 ft. from the point of ignition. A single
constriction, therefore, shortens in a remarkable degree
the distance that has to be travelled before 44 explosive
combustion ” begins.

A second similar constriction was now introduced at
a point 250 ft. distant from the point of ignition
(experiment No. 144, August 30,1910). The maximum
pressure, which was attained about three-quarters of a
second after ignition, now reached 21 lb. per square
inch, and the curves traced by the manometers both at
350 ft. and 300 ft. from the point of ignition showed the
abrupt increase in pressure that we regard as indicative
of explosive combustion.

When a third constriction was made, at a point
300 ft. from the point of ignition (experiment No. 139,
August 23, 1910), the maximum pressure produced was
55 lb. per square inch, attained about two-thirds of a
second after ignition.

In order to bring out the important features of these
experiments it is not necessary to reproduce all, or the
whole of any one, of the pressure curves traced during
each experiment. We have already shown that for a
considerable period after the time of ignition the
pressure curve traced is merely that due to the igniting
cannon, and is of no particular interest from the point
of view of the development of the coaldust explosions.
To avoid confusing diagrams, therefore, those portions
of the curves that were due to the igniter pressure are
omitted in fig. 6. Further, although in each experiment
records were obtained of six manometers (fixed, 100,150,
200, 250, 300, and 350 feet, respectively, from the point
of ignition), the curves of chief interest are, as can
readily be understood, those traced at the points most
distant from the point of ignition, after explosive
combustion had been attained. These curves only,
therefore, are reproduced.

Examination of these curves shows the effect of
constrictions very clearly. The curve at the top (fig. 6)
shows the pressure recorded at the manometer most
distant from the point of ignition (350 ft.) when the
gallery was clear of all obstructions. It is obvious that
the result was merely a slow inflammation. The
diagram below this curve reproduces two curves traced
during experiment Nd. 142, in which one angle-iron
constriction was fixed at a point 200 ft. distant from the
point of ignition. No. 5 curve is that obtained at a
point 300 ft. from the point of ignition and No. 6 that at
350 ft. distance; this latter curve, therefore, corresponds
with No. 6 curve in experiment No. 123, when the
gallery was clear. It will be seen that there are distinct
signs in No. 6 curve of experiment No. 142 of the sudden
rise of pressure indicative of the beginning of 44 explosive
combustion”; this occurs after an interval of 97-
hundredths of a second from the time of ignition.

The next two curves, Nos. 5 and 6 of experiment
No. 144, show the result of introducing a second
constriction at a point 50 ft. distant from the first. In
this case there are indications of the beginning of
44 explosive combustion ” in curve No. 5, at a distance of
only 300 ft. from the point of ignition.

Lastly, the two curves Nos. 5 and 6 of experiment
No. 139 (in which three constrictions had been intro-
duced) both show the sudden rise of pressure due to
44 explosive combustion ” which has apparently begun to
be developed (as shown by curve No. 4) within 250 ft.
distance of the point of ignition.

Summarising, the influence of constrictions on the
development of the explosion as shown by this series of

experiments was as follows :—		Interval of time
	Maximum	between ignition
Number of	pressure	and attainment of
constrictions.	developed.	maximum pressure.
	Lb. per	Hundredths of
	square inch.	a second.
None 	  One, 200 ft. from the point	2-0	155
of ignition	  Two, 200 and 250 feet from	10*5	103
the point of ignition ... Three, 200, 250, and 300 feet from the point of	21’5	74
ignition 		57*0	66

The most striking comparison is perhaps obtained
from experiment No. 119, already described, and No. 137
(July 28, 1910). In the former, it will be remembered,
the point of ignition was 500 ft. from the open end of
the gallery, and the gallery contained no constrictions.
In the latter three constrictions were introduced at
points 300, 350 and 400 ft. from the point of ignition.
Except for the presence of these constrictions the
experimental conditions in experiment No. 137 were the
same as in No. 119.

The pressures recorded by the manometers along the
gallery were as follows :—

Experiment Experiment
No. 119 No. 137
(clear gallery), (three constric-

Pressure. tions). Pressure.
Lb. per sq. in. Lb. per sq. in.

230

830

1520

300 ft. from point of ignition 4*5

400 ft.	„	„	6’5

450 ft.	„	„	16’0

The essential parts of the four curves recorded by the
manometers most distant from the point of ignition in
experiment No. 137 are reproduced in fig. 7. If these
curves are compared with the corresponding curves of
experiment No. 119, which are reproduced in fig. 4, the
remarkable effect produced by offering a slight obstruc-
tion to the passage of the explosion at but three points
along its path, 50 ft apart, will be appreciated. We do
not propose at this stage to discuss the theory of con-
strictions in augmenting the intensity of explosions of
gas and coaldusts ; but we would point out that the
effect of such constrictions in the gallery and,
presumably, of obstructions in the roadway of a mine is
not necessarily to increase the ultimate violence of which
a coaldust explosion is capable, but to enable it to obtain
violent proportions at a much earlier period than in a
smooth gallery.

Experiments which are now being carried out at
Eskmeals illustrate and confirm many of the experi-
mental conclusions above set forth. We hope shortly
to give an account of them.

Wrongful Imprisonment in the Mine.—A case of con-
siderable importance to those engaged in the mining
industry came before Lord Justice Vaughan Williams and
other judges in the Appeal Court on the 12th inst. The
appellants are the Weardale Steel, Coal and Coke Company,
who desired to set aside a judgment given by Mr. Justice
Pickford at the Leeds Assizes awarding John Thomas Herd,
a hewer employed at the defendants’ Thornley Colliery,
Durham, 20s. on a claim for false imprisonment. The case
for the plaintiff at the assizes was that he went down
the pit to do a seven-hour shift. He refused to do certain
work, not only because he considered it unsafe, but because,
as he alleged, it did not come within the terms of his
employment. Having put down his tools, he desired to
ascend, but was refused permission for two hours. For the
purposes of the allegation of false imprisonment being
argued, the parties agreed that the plaintiff was detained
for 20 minutes in the colliery. The defence was that the
defendants were under no obligation to take the plaintiff
up in the cage until his work was done, viz., the completion
of the shift. They contended that his detention or the
delay in taking the plaintiff to the surface could not be
construed to be false imprisonment.—Lord Justice Vaughan
Williams, in delivering judgment, said the appeal, in his
judgment, should be dismissed. Lord Justice Buckley and
Lord Justice Hamilton were of a different opinion, and by a
majority of the Court the appeal was allowed, with costs.

New Railway in Notts.—Mansfield’s new railway has
been pushed forward so swiftly since the first sod was
turned about 18 months ago that business men in the
district were able, on Monday, to celebrate the opening for
traffic of half of the 10 miles of route. The scheme puts
Mansfield and its new coalfield on the Great Central main
line from Grimsby to London. It runs into the existing
main line at Kirkby on the one side, and at Clipstone on
the other, and the enormous volume of coal traffic will have
direct access to the ports of Immingham and Grimsby.
When the line is completed, as it will be in about
12 months’ time, Mansfield people will have far better
facilities for getting to distant parts of the country. The
line will reduce the journey from Grimsby to London by
about 5 miles. It will be worked by the Great Central
Company, and the brains responsible for the enterprise are
those of Mr. J. P. Houfton, the managing director of the
Bolsover Colliery Company. The total cost, including some
miles of concentration sidings which the Great Central
Company deem necessary, will be about .£400,000, the bulk
of which has been subscribed locally. The sidings will be
placed between Mansfield Colliery and Clipstone, somewhere
near the site of the new Clipstone Colliery. They will
afford accommodation not only for the Mansfield, Clipstone
and Rufford collieries of the Bolsover Company, but also for
the Welbeck Colliery of the new Hucknall Company, which
is being sunk near Warsop. The Bolsover Company have
guaranteed a minimum of 500,000 tons of coal annually for
shipment at Immingham from the Mansfield and Rufford
collieries. Coalowners, railway officials, engineers and local
traders, on Monday, made a tour of inspection on the com-
pleted portion of the new line from Mansfield to Clipstone.
At the opening, Mr. J. P. Houfton said the Bolsover Com-
pany had developed their Mansfield Colliery. They were
now sinking another at Rufford, and proposed to sink
another in the near future at Clipstone.

THE MEASUREMENT OF AIR IN MINES.

By Prof. Henby Louis, of the Armstrong College,
Newcastle.

At a meeting of the members of the Northumberland
and Durham Association of Collery Under-managers,
held in the Lecture Theatre of the Wood Memorial
Hall, Newcastle, on Saturday, the 7th inst., Prof. Louis,
of the Armstrong College, read a paper on the above
subject. He said that dne of the few advantages that
could be set down to the credit of the Coal Mines Act,
1911, was that it had directed close attention to the
important problem of the measurement of the ventilating
current in mines. At the same time he was afraid that
they must admit that of the many absurdities of that
Act, there were few more grotesque than the provision
that a deputy must be able to measure the quantity of
air in an air-current, seeing that it could be asserted
with every confidence that the accurate measurement of
the quantity of air flowing in an airway was a problem
presenting such exceptional difficulties as to be practi-
cally impossible of solution by even the most eminent
of modern scientists. Nevertheless, it was a matter of
great importance that the quantity of air in a ventilating
current should be determined within reasonable limits
of correctness. In this country we appeared to have
accepted one method of air measurement—namely, that
by the anemometer, as the only one possible—whilst
other, and possibly better, methods were wholly over-
looked, though these might, nevertheless, be in regular
use in other countries.

After briefly discussing the laws that govern the flow
of air in the mines, the lecturer said that if the
position of a point of mean velocity in an airway be
determined once for all, all future measurements might
be made at that one point, instead of making a number
of observations to determine the average rate of flow
every time. Unfortunately, there appeared to be no
means of determining beforehand where the point of
mean velocity would be. A number of experiments had
been made upon the flow of water, and it had been
found that in the case of water flowing in a cylindrical
pipe, the position of the film of mean velocity was about
one-fourth of the radius of the pipe away from the
walls of the pipe. There was less information available
with regard to air, though most authorities agreed that
air would probably obey a somewhat similar law.

Mr. Murgue, in his well-known paper, had plotted
lines of equal flow in a number of airways, and these
lines were very irregular except in case of a straight
symmetrical piece of road; from his figures he (Prof.
Louis) deduced that if two points be selected halfway
between the roof and flow, and one-sixth of the width of
the airway from either side, the mean of the velocities at
these two points would give a figure not differing
greatly from the true mean velocities of the air in the
passage; if the velocities obtained at opposite sides of
the drift did not differ greatly from each other this
might be accepted as evidence that the mean of the two
would be very near the true mean velocity. Mr. Murgue,
in his paper (Trans. Fed. Inst. Min. Eng., vol. 6, 1893,
p. 135) gave diagrams of the curves of equal velocities
obtained in a number of underground airways, and the
average velocity of flow in each; by selecting those
cases where the airways were fairly straight and there-
fore suitable for measuring the velocities of the air, it
was possible to compare the true mean velocities as
calculated by Murgue, with the approximations obtained,
by reading off the diagrams the velocities of the air at
one-sixth of the width from each side; the following
were the results thus obtained:—

No. of	Readings 1/6		Mean	True	Error.
experi-	off each side.		of	mean	Per
ment. t		A		>	both.	velocity.	cent.
1. ...	445	400 .	..	422’5	...	427 ..	. -16
2. ...	515	505 .	...	510	...	468 ..	. + 8’2
3. ...	1,005	1,110 .	.. 1,057'5	... 1,050 ..	. +0’7
6. ...	380	405 .	...	392 5	...	391 ..	. +0'3
10. ...	800	600 .	...	700	...	744 ..	. -6'3
11. ...	310	510 .	...	410	...	423 ..	. - 3'1

It will be noted that, although the places selected for
the measurements in question were not well suited for
the determination of mean velocities (this not having
been the object of Murgue’s work), the errors were not
excessive—in fact, not much greater than would be
obtained in the ordinary way, thus suggesting that the
figures obtained by his (Professor Louis’s) method
would probably be quite sufficiently correct for most
purposes, especially if an instrument no more accurate
than the ordinary anemometer was considered sufficiently
exact.

It might be said that the correct method of measuring
the velocity of air in the airway of a mine, would be, as
recommended by the German Commission, to prepare a
suitable place in each airway, by planking, or otherwise
smoothly lining a section of an airway, at which spot
the measurements should always be made. If, instead