626

THE COLLIERY GUARDIAN

March 30, 1917.

for a period of over 24 hours under ordinary operating
conditions. Each bin is filled through three separate
gates with spouts in the bottom of the conveyor, so that
the supply to any bin can be controlled as desired.

Air Blast for Feeding the Coal.

Underneath and between the sides of the inverted
“ V ” formed by the two hoppers of the bin is placed a
direct-coupled motor-driven fan with a down-blast
discharge which is divided into two 7-in. blast pipes.
These two pipes diverge at an angle of 60 degs. with
each other and descend in a plane parallel to the front
of the boilers, about 8 ft. from the front wall of the
firebox or combustion chamber, making an easy sweep-
ing bend and discharging into the burner nozzle in
front of each boiler 3 ft. from the floor. The fan
supplies the requisite air for feeding the coal (4.200 cu. ft.
per minute) at 3 oz. static pressure, to a burning nozzle
in front of each boiler.

At the bottom of each hopper for each bin is a 4 in.
screw feeder enclosed in a circular cast iron casing.
Above each feeder, between the hopper and the screw
proper, is a slide, so that if the feeder should become
jammed or broken, it could be readily removed without
drawing the coal from the bin. Each feeder is chain
and sprocket driven by a two-horse power variable-speed
back-geared motor, the controlling resistance of which
is in a convenient position in front of the boilers.

The Burners.

Each feeder discharges into a 3 in. pipe, 8.ft. long,
which drops the coal straight down and into a funnel-
shaped opening in the top of the burner nozzle. This
burner, which is both simple and highly efficient,
consists of an outside 14 in. cylindrical pipe, one end
of which projects into the furnace ; the 7 in. blast pipe
being inserted into the other end and extending inwardly
from 12 in. to 18 in. A metal cone is fitted over the
blast pipe so that it can be moved back and forth any
desired distance, thus forming a valve to regulate the
amount of air that is induced in the burner or to close
the opening entirely if desired. Directly over the
inserted end of the blast pipe a small funnel-shaped
cone is placed in the outside pipe, into which the cone
is fed and drawn in by the suction formed, by the blast.
The funnel opening into which the coal is fed is directly
over the discharge end or nozzle of the blast pipe, so that
the.coal will be drawn in and thoroughly mixed with the
blast and induced air before reaching the combustion
chamber of the furnace.

A large quantity of air can be induced in this burner,
which, together with that blown in by the fan, will
supply all the air required for combustion. The blast
pipe is provided with a 2 in. screw-capped opening just
back of the sliding cone, so that the pressure and
velocity of the air can be determined when desired.
The outside burner pipe is also provided with two
similar openings, one between the coal opening and the
open end, and the other about 1 ft. from the furnace
wall.

At normal rating on a basis of 70 per cent, efficiency
and with feed water at 208 degs. Fahr., these boilers
will each consume 958 lb. of coal per hour, or 16 lb. per
minute, and will therefore require about 3,200 cu. ft. of
air per minute for combustion. Half of the capacity
of the fan (or 2,100 cu. ft.) will be supplied through the
7 in. blast pipe to each boiler, the remainder being
induced by the action of the blast in the intake end of
the burner.

The Furnaces.

The furnace or combustion chamber of these boilers
is well adapted for firing with pulverised coal, having a
cubical content of 583 cu. ft., or, at normal rating,
364 cu. ft. per pound of coal fired per minute. The
bridge wall is 7 ft. from the front wTall of the setting
and from the end of the burner. The baffle wall is
of brick, with a U-shaped opening in one side to fit the
tubes, and protect them from the direct action of the
flame. By this means the top, bottom and sides of the
combustion chamber present to the entering coal dust
a surface entirely lined with refractory firebrick, the
top or roof being protected by the tubes. From the
base of the arch wall, on a level with the floor of the
boiler-room, the bottom of the combustion chamber
slopes down forward at an angle of 45 degs. till it
reaches a point directly under the front setting, where
a shelf 2 ft. wide projects straight out to a door, in the
ash tunnel, through which steel cars are operated and
into which the ash and slag precipitated on to this
shelf are raked. The bottoms of these ash doors are 7 ft.
below the floor of the boiler room, and the tops of the
cars come to within 3 in. of this level, so that all that is
necessary is to move the car in front of the ash door.
The sides of this sub-combustion chamber extend
vertically downward from the floor level for a distance
of 3 ft. 6 in. and then converge toward the centre at an
angle of 53 degs. until they meet the bottom shelf, so
that the bottom of the furnace or combustion chamber
forms a firebrick-lined hopper with a bottom 2 ft.
square. The remaining front wall of the furnace is
extended straight down to 3 ft. 6 in. below the floor
level and cut under in a sloping arch parallel to the rear
side so that it will form a sloping roof to the top of the
ash door.

The area between the top of the bridge wall and the
bottom row of brick-protected tubes is 19 sq. ft., and
with a temperature in the furnace of 2,800 degs. the
velocity of the gases over the bridge wall at normal
rating will be about 16 ft. per second. With such a
low velocity it can be readily seen that the greater part
of the process of combustion should be completed before
the gases pass over the wall, and also that a large
percentage of the ash or slag will be deposited in the
hopper bottom. There is also a settling chamber back
of the bridge wall, and any ash that settles in this
chamber can be raked out of a door at the side.

PORTABLE MINERS’ LAMPS.*

By E. M. Chance.

During the past 10 years the safe and efficient light-
ing of the coal mines of the United States has received
an ever-increasing amount of attention. Several
States have passed laws attempting to regulate the
type of lamp to be used and the nature of the fuel to
be burned, and the mining departments of coal mining
States have generally shown a keen and intelligent
interest in this subject. The passage of the recent
Employers’ Liability Act in Pennsylvania has made it
necessary for many coal mining companies to take out
liability insurance, and the companies underwriting
such insurance have made it desirable for the insured
to permit the use of none but illuminants of estab-
lished worth. While these conditions have not
obtained for a sufficient length of time to permit the
statement that the illumination of coal mines by
portable lamps has been standardised, still, consider-
able progress has been made, and the direction of
future practice in this branch of coal mining tech-
nology is very evident. Under these conditions, it
seemed that a review of the methods now used in coal
mine illumination, together with a brief consideration
of the principles underlying these methods, might be
of some interest.

Miners’ lamps may be divided into three classes:
the open light, the electric cap lamp, and the flame
safety lamp. It will be desirable to consider each of
these classes separately, as each has properties peculiar
to itself, and one class is hardly comparable with
another.

In the United States, without question, the open
light is the most generally used of all miners’ lamps.
This fact is explained by the relative freedom of a
large proportion of the mines from gaseous conditions,
and by the admirable systems of ventilation installed
in those that show a tendency toward such conditions.
In the metal mines, the miner’s candle has had, and
still has, considerable vogue. Because of the small
amount of ventilation usually supplied in metal mines,
the freedom of the candle from any tendency to pro-
duce noxious gases or offensive odours, and the small
amount of air it consumes, are valuable assets, while,
because of the light colour of the rocks in which work-
ings are driven, the meagre light is not a serious
handicap.

In coal mines, however, conditions are very different.
Because of the considerable volume of air passed
through the workings, the small air consumption of
the candle is of little moment, and its feeble rays are
so completely absorbed by the dusky background, that
its light is entirely inadequate. Moreover, the cost of
the candle is relatively high. For these and other
less obvious reasons the metal miner’s candle is prac-
tically unknown to the coal miner.

Up to a few years ago the open oil lamp had no rival
in non-gaseous mines, and it is still very largely used,
though its use is becoming limited, as will be shown
later. The oil lamp has many disadvantages, and the
Legislatures of a number of States have endeavoured
from time to time to remedy these defects by law. As
the service given by an oil lamp varies largely accord-
ing to the character of the oil, efforts have been made
to fix by law the quality of the oil that may be sold to
miners for use in these lamps. These efforts, unfortu-
nately, have proven rather ineffectual, as the result
has generally been to increase the cost of oil to the
miner without increasing its quality in anything like
the same proportion. These laws, therefore, may well
be considered one of the most potent of the forces that
have driven the oil lamp out of its once strong
position.

An example of the manner in which a law, that was
honestly intended to be beneficial to the miner, failed
of its purpose is found in the Bituminous Mining Law
of 1911 of the State of Pennsylvania. This law stipu-
lated that oils sold for use in miners’ lamps should not
yield more than 0-11 per cent, of soot when burned in
a miner’s lamp under standard conditions. One of
these conditions was that the flame of the lamp should
be 1J in. long. Now, low-grade oils, when burned
under these conditions, yield as much as 1 per cent,
of soot, while high-grade oils will give as little as 0 03
per cent. Thus it would seem, at first glance, that
this law would considerably better conditions in the
mines.

Such is not the case, however. Oils to pass this test
must be very largely composed of costly fatty oils, and
this so greatly increased the cost to the miner that he
was obliged to look for some cheaper illuminant. More-
over, instead of a flame lj in. long, the miner burns
one of a maximum length, because he wants as much
light as he can get. The writer has found that while
costly oils, containing high percentages of fatty ingre-
dients, will produce much less soot than oils of medium
price, and less fatty material, when burned under
legal test conditions, these differences very largely dis-
appear when these oils are burned under the condi-
tions that obtain in the mines. With very long flames,
the high-priced oils still show a superiority to the
medium grade, but the differential is so slight as to be
of little real moment.

Indeed, the soot-forming propensities of both these
oils under the conditions of use are so great that it is
idle to attempt to classify one as better than the other.
They are both very bad. Thus, with a legal require-
ment of 0T1 per cent, soot or lower, we find the oil
passing this test will give about 8 per cent, of soot
when burned as it would be in the mines—-that is, with
a flame 5 to 6 in. long—while the oil that will not pass
the legal requirement, giving under test conditions,

* Paper read before the American Institute of Mining
Engineers.

let us assume, 0*5 per cent, soot, will make under
actual working conditions about 9 to 10 per cent. soot.
Thus we may say that, despite the greatly increased
cost of the legal test oil, it is practically no better than
many oils that may be secured at half or one-third the
price. It is to be understood that many oils are of so
low a grade as to be entirely unsuited for use in
miners’ lamps, and, of course, these remarks do not
apply to them. The point is that the tendency of
many of the State laws is to increase the cost of oil
very considerably to the miner and mine operator
without proportionately improving its quality.

One of the drawbacks to the use of the open oil
lamp is the greatly increased fire risk where such lamps
are used in dry workings. It is necessary for the user
of such a lamp to renew its wick or lamp cotton at
frequent intervals, and it is customary to pull out the
old cotton and insert the new while the old lies blazing
on the ground. When the new cotton is in place and
alight the miner places his heel on the blazing remains
of the old, and perhaps extinguishes it; at any rate,
he goes away and leaves it, to burn or not as may be.
Another source of fire is the shower of sparks that is
blown from the wick when the wearer of the open oil
lamp is travelling against a strong ventilating current.
Together, these are the possible causes of mine fires
that have disposed thoughtful mine operators to look
with disfavour upon this source of illumination.

Of recent years a substitute for miner’s oil, called
“ miner’s wax ” and a host of proprietary and brand
names, has been placed upon the market. It is a
paraffin wax obtained in the refining of petroleum,
and possesses the property of burning with a whiter
flame than miner’s oil, and giving somewhat less soot.
It must be used in a special lamp, however, as means
must be provided for keeping it in a molten condition
in the lamp fount. This is accomplished by conduct-
ing heat from the flame to the fount. Its use, though
considerable, is decreasing, because the fire hazard
with this illuminant is as great as with miner’s oil,
and it is troublesome to handle.

Undoubtedly the greatest advance made in the
illumination of non-gaseous mines is the acetylene or
“carbide” miner’s lamp. This lamp has come into
general use during the past seven years, and is now
probably the most widely used of miners’ lights. The
reasons for its popularity are not far to seek; in brief,
it gives far more light than any other portable miner’s
lamp, and costs less to operate. It gives a clear,
white light, in which objects have very much the same
colour value as in daylight. It makes no smoke or
soot, and its demands on the oxygen of the mine air
are moderate. It gives more reliable indications of
the presence of dangerous proportions of blackdamp
than the oil-fed lamp. It gives off no sparks, and
hence decreases the fire hazard very considerably. It
may thus be seen that this type of miner’s lamp has
benefits for the mine operator and the worker, and is
liked by both. The author understands that insur-
ance companies underwriting the insurance of many
coal mining companies under the new Pennsylvania
Compensation Act, have recognised the safety features
of the acetylene miner’s lamp by giving credits on the
insurance rate where such lamps are used in non-
gaseous mines.

Some years ago considerable uneasiness was felt
among mining men because it was thought that the
acetylene lamp failed to give adequate warning of the
presence of blackdamp. In the past, blackdamp had
been believed by many to be an atmosphere in which
a lamp would not burn, the reasoning being along
these lines: If an oil lamp goes out, it is because there
is not enough air (meaning oxygen). Now, it is a fact
that the acetylene lamp will burn where an oil lamp
will not. Hence, if the oil lamp will not burn, there
is no air, and as the acetylene lamp continues to burn,
this indicates that the acetylene lamp will burn with-
out air. Therefore, a man may carry an acetylene
lamp into an atmosphere containing so little air that
he may be rendered unconscious, and still his lamp will
give no indication of the dangerous condition of the
atmosphere.

The facts of the matter are these: The oil-fed flame
requires a minimum of about 17| per cent, of oxygen
for its maintenance; the acetylene flame requires about
12J per cent.; and a man’s life is endangered should
the oxygen content fall much below 10 per cent. At
about 14 per cent, of oxygen, however, the colour of
the acetylene flame changes markedly. It loses its
brilliance and illuminating power, and becomes greatly
elongated and unstable. From these data it will be
seen that the miner is given obvious and adequate
warning of the vitiation of the atmosphere through
deficiency in oxygen. While this warning is not so
peremptory as that given by the oil lamp, still it is
of ample distinctness for men to appreciate and value,
and, above all, it is essentially a real danger warning.

On the other hand, the warning of the oil-fed flame
is given with so high an oxygen content that miners
have learned to disregard it, and will frequently go
into workings containing air in which their oil lamps
will not burn. They know that they can live in an
atmosphere in which these lamps will not burn, but do
not realise that, once in the dark, they have no further
guide to the quality of the atmosphere, and that in a
few feet it may become lethal. Such is not the case
with the acetylene lamp; its warnings are given so
near to the danger point that men will have a whole-
some respect for them, to the great increase of their
own safety.

While the author has heard of cases in which men
after working with acetylene lamps in sections in
which oil lamps would not burn became sick when
brought into fresh air, these always proved to be based
upon a fallacy. Upon investigation, the fact has
always developed that the disability of the men was