June 21, 1918.

THE COLLIERY GUARDIAN,

1249

the konimeter: (1) The small quantity of air used
to form the sample. (2) The danger of contamination
in changing the slides. (3) The difficulty of count-
ing, especially when oil and soot are present in the
air. (4) The failure of the konimeter to make a dust
spot on all occasions. (5) The difficulty of making
standard instruments. (6) The labour involved in
counting the dust particles. (7) The personal factor
introduced in counting.

These objections will be dealt with in turn.

1.	The quantity of air used to form a sample is
immaterial, provided that the amount used is repre-
sentative of the air in the immediate neighbourhood.
The nature of the air itself, its continual movement,
etc., allows for the fairly equal distribution of the
injurious dust in a short time, even assuming that
this dust is incapable of producing an equal distri-
bution on its own account. Samples taken at intervals
in air with a more or less constant dust content, such
as upcast air in a shaft, give spots with practically
the same count, proving that a 5 cc. sample is quite
sufficient. In places where a variable amount of dust
is being produced, a variable count is obtained in
different spots as would be expected. An unreliable
result would be obtained if only one spot were taken
under these circumstances, but if a number of spots
be taken spread over an interval of, say, five minutes,
any error would depend not so much upon the amount
of air which formed the samples, but upon how far
the dust sampled during this time was representative
of the dust produced during the shift.

2.	Contamination in changing the slides is rare. If
it is known to have occurred underground, a fresh set
of spots may be taken. Contamination is more likely
to take place in coating the slides with vaseline, but
it can then be detected before the slides are used.
Even if it does occur, the effect may be eliminated
in most cases by determining the average amount
near the spots, and by making the necessary sub-
traction from the count.

3.	Oil has never been noticed even when artificial
pieans were adopted to produce it. Carbon sometimes
occurs in samples from badly ventilated places, and
is shown as large grey granular masses when dark
ground illumination is used, and is easily recognised.*

4.	Failure to make a dust spot. The best answer to
this objection is to analyse the results obtained at
the Ferreira Deep Limited. Since the middle of
September a record has been kept of all the samples,
even if no spots have been counted on a slide. In
the majority of cases the spots have been spoilt in
handling the slides, and in others the spots which
have been found gave so small a count that the dust
in the air may have been insufficient to produce a
spot which could be recognised as such. In all these
cases the fault is not with the konimeter. The failures
may be recorded thus : —

On 3 slides — 0 spots were counted.

On these slides there should have been a total of
112 spots, and only 61 were found. On five of the
slides the average count was 16 particles per cc., so that
it is possible that some of the spots escaped detection
owing to their small dust content. In the three cases
where no spots were found the vaseline was smudged
by handling the slide on the surface. Other spots
were spoilt by placing cover glasses on the slides before
counting. These figures give a rough idea of the loss
to be expected from all sources. In all 1,990 puffs
gave 1,939 spots, a loss of 2-6 per cent.

One case is reported where the loss was over 70 per
cent. There is a serious source of error which may
account for this extraordinary result. If the flat
spring does not cause the glass slide to press evenly
all round the rubber ring, a gap is liable to be formed
on one side, and air then rushes through this opening
instead of up the nozzle. If a very small gap is formed
air might also come up the nozzle and form a spot,
while the air which passes between the ring and the
slide would deposit some of its dust content on "the
vaseline. Under these conditions it is possible to have
spots which are unreliable, as the quantity of air used
is unknown, and contamination which cannot be
accounted for, unless this source of error is detected.
It is therefore always necessary to test the action
of this spring by closing the nozzle and releasing the
piston. If there is no leakage the piston will not
move, or will do so very slowly.

5.	All that is necessary in order to make standard
models of the konimeter is to arrange that the volume
of air drawn in on each stroke of the piston should
be the same and of a known amount, and that the
velocity of the air through the nozzle should be within
certain wide limits, as mentioned before. The first
does not seem difficult to accomplish, while the second
can be adjusted at any time by altering the shape of
the spring which actuates the piston. The nozzle may
vary from 0-5 to 1 mm. in diameter at the small end
without producing discordant results, but a diameter
of 0-6 mm. is preferable.

6.	If six spots have been taken on a slide these can
be found and counted in about ten minutes. If during
a morning underground the dust sampler takes eight
slides of six spots each, or twelve slides of four spots
each, he can have all the results worked out on the
same day, and all the slides cleaned and coated with
vaseline ready for the next day without working over-
time.

If there have been any breaches of the dust regu-
lations which require that a charge should be laid
against any person or persons, his report to the
manager.can contain the results of the dust sampling,
and it can be sent in on the same day that the regu-
lations were broken.

7.	With but little experience it is found that the
counts of the same spots made by two samplers agree
within 10 per cent.

Mr. Selby, manager, Ferreira Deep Limited, has
furnished the results obtained on that mine with the

konimeter (Tables A and B). The sampling was done
in most cases by the dust sampler of the mine.

Table A.

Description.

bi)
.2 a
<D j CQ m
ft
to : .2 »

Upcast air		9 ...	49 ..	.. 96	... 1*5 ..	. 33
Downcast air 	  Drives (axial water-feed	11 ...	26 ..	. 94	... 3 2 ..	. 8
machines)	  Drives (reciprocating	7 ..	. 328 .	.. 99	... 4-9 ..	.. 67
machines) 	  Raises (axial water-feed	3 ..	. 230 ..	.. 98	... 4’0 ..	.. 58
machines)	  Winzes ’ (reciprocating	11 ..	. 313 .	.. 99	3 5 .	.. 89
machines)		5 ...	. 484 ..	. 96	... 15*0 ..	. 32
Ore bins	  Stopes (axial water-feed	37 ..	.	70 .	.. 93	... 4*2 ..	.. 17
machines) 	  Stopes (reciprocating	7 ..	. 129 .	.. 97	... 3’6 .	.. 36
machines) 	  Stopes (hammers and	78 ..	. 102 .	.. 96	... 4’1 .	.. 25
reclamations) 		32 ..	49 .	.. 93	... 3 0 .	.. 16

Table B.			
		Number of	Per cent.
""X"'		particles under  5 microns	of under  5 microns to total
		per cc.	dust.
Upcast air 		31	....	61	...	...	96
Downcast air 	  Drives (axial water-feed	23	....	39	...	...	91
machines)	  Drives (reciprocating	13	....	..	353	...	...	98
machines)	  Raises (axial water-feed	5	....	307	...	...	98
machines)		32	....	..	315	...	.. ‘98
Winzes (reciprocating			
machines)		8	....	..	484	...	...	97
Ore bins	  Stopes (axial water-feed	48	....	86	...	...	95
machines)	  Stopes (reciprocating	11 ....	178	...	...	98
machines)	  Stopes (hammers and	118			127	..	... 97
reclamations) 		35	....	46	...	...	93
Blowing-out holes		5	....	..	170	...	95
Blasting dust 			5	....	..	320	...	...	88

A number of samples were taken at the same time
as the sugar-tube sample—not for the purpose of estab-
lishing a relationship between the two methods, but
to show that the gravimetric results depend on the
character of the dust and not on the number of in-
jurious particles present. On an average six spots
form one sample.

Table A shows these comparisons, while Table B
shows the average of the total number of konimeter
samples for different classes of work.

THE AMERICAN COAL TRADE.

Coal production in the United States is now nearer
its maximum (says the Coal Age, May 25), but even if
this rate of production is continued to the end of the
year the country will still be faced with a fuel shortage
unless immediate steps are taken to conserve every
single ton. It is becoming more and more apparent
that plants other than those directly at work on sup-
plies to aid in winning the war will receive little
consideration so far as fuel is concerned.

The question of labour is one of paramount impor-
tance. Sadly depleted by the military draft and the
return of many of its workers to the farms, the coal-
mining ranks are being still further demoralised by
the enticing appeals of war industries. Working on
a cost-plus basis, munitions plants and shipyards offer
almost any wage in order to get enough men.

The railroad fuel question remains unsettled.
Another month will see the termination of nearly all
contracts for railroad coal, and both railroad pur-
chasing agents and operators are in a quandary over
what course to pursue.

Market conditions are strong and active in every
way, with the demand for coal for storage purposes'
sufficiently large to take care of all the available fuel.
While early in the season it was proposed to ship no
domestic sizes of anthracite to manufacturing plants,
it has already become necessary to make exceptions
to this to the extent of over 2,000,000 tons for war
work.

Supplies of anthracite to New York are far below
i requirements, yet dealers are optimistic. Bituminous
is scarce. In Philadelphia the prices per gross ton
f.o.b. cars for line shipments are as follows : Broken,
4’90 dols.; egg, 4'50 dols.; stove, 4'75 dols.; nut,*
4*85 dols.; pea, 3-45 dols.; buckwheat, 3’15 dols.; rice,
2'65 dols.; boiler, 2’45 dols.; barley, 2’15 dols. Ship-
ments are below expectations. On the other hand,
Pittsburg district is easily shipping more fuel than
evei’ before, and a large supply of free coal is offered
openly.

It has become fairly clear that Connellsville coke
production is unlikely to increase materially over the
rate of the past few weeks, say, 325,000 to 350,000
tons a week, but there will be increases in the coal
shipped to by-product operations. The production of
coke in the United States in the ten weeks ended
May 11 was at the rate of 10 per cent, above the rate
in 1916, while the present blast furnace capacity is
only between 10 and 15 per cent, in excess of the
actual pig-iron production in 1916.

The Black Diamond calls for the exemption of coal-
miners from military service, and the appointment of
a Production Committee to deal with the growing
deficiency. It speaks of a growing tendency to let
coal affairs drift into another national smash, and
observes : “ The awful fact is that even in summer
we are falling behind the coal production schedule
by 7J million tons a month. By the First of November
we will be behind schedule f?om 40 to 50 million
tons. And, on the First of November we will come
into a period when current consumption will exceed
current production by at least 250,000 tons a day.”

INSTITUTION OF MINING ENGINEERS.

(Continued from page 1206.)

Terrestrial Magnetism and Mine Surveying.

The following additions to the discussion were read
by the Secretary : —

Mr. G. W. Walker (Portsmouth) stated that the
question of terrestrial magnetism in relation to mine
surveying had been repeatedly brought to his notice
by engineers in connection with the revision of the
magnetic survey of Britain which he had recently
carried out for the Royal Society. Little was known
about the relation between the magnetic forces at the
surface and those which obtained down in a mine. It
was very unlikely that they would be the same. The
differences might arise from (1) the effects of the rock,
(2) the presence of iron railways or electric currents
in the mine, or (3) secular or daily variation of the
normal magnetic forces at the surface. All those made
the use of surface values even near the mine quite
inadmissible underground. Moreover, the values
varied greatly in different parts of these islands. It
would be most valuable to have investigation of under-
ground magnetism made; but if the mining engineer’s
immediate need was to get his true direction down
below, the proper solution was to transfer the geo-
graphical meridian down to the bottom by optical
means, and then carry out the normal theodolite
survey from that direction. That was a matter which
could easily be done by the Ordnance Survey Depart-
ment.

•	Defective Instruments.

Mr. H. J. Crofts (Whitfield Colliery) stated that
the first object of the paper was certainly achieved,
as it gave information of the utmost value to mine
surveyors. It would form a notable addition to the
Transactions. It was to be hoped that the second
object would be as fully realised, and that advantage
would be taken of the opportunity which Dr. Chree
indicated, by many practical surveyors who doubtless
were puzzled and anxious about the conflicting results
which were frequently experienced in the course of
their use of the magnetic needle. Of recent years
the number of men was rapidly growing who were so
sceptical of the possibility of accurate work being
done by the compass that they were now discarding
its use in underground surveys. It should be said
at once that in many mines in this country the nature
of the ground was such that it was practically hope-
less to attempt to fix permanent base lines, and in
such case the discontinuance of the use of the mag-
netic needle might easily lead to serious error. The
uneasiness in the minds of surveyors regarding the
use of the compass was due principally to two causes—
(1) unreliable instruments, and (2) ignorance of such
information as it was the first object of the paper
to supply. Regarding the latter cause, a glance at
the Kew observations now being published weekly
showed clearly the great necessity which had always
existed for that information to be available. The
makers of surveying appliances did not appear to
regard it as a matter of importance that the mag-
netic needles of their different instruments should
be adjusted to give light readings. In the case of
two modern dials of identical pattern, and made by
a first-class firm, readings on the same base line,
checked time after time, showed a difference of no
less than 20 minutes. That was due to inaccurate
centring of the needle. As the dials were perfect
in all other respects, it would appear a relatively
small matter to give more attention to that very
important detail. After repairs it had been, until
recently, a common experience to find, on careful
checks being made, compasses giving readings three
to nine minutes different from those obtained before.
It was therefore necessary in important work that
the same compass should be used throughout the
survey for all magnetic observations, and the bases
connected by the theodolite. It might be noted that,
speaking generally, the needles as supplied with theo-
dolites were of no value for accurate work. There
was no doubt that with a mining dial in which the
needle point had been properly shaped and the needle
carefully suspended, when quietness, magnetically
and atmospherically, prevailed, the dial could be set
five times out of six to give readings varying not
more than one minute. With regard to the connec-
tion of surface and underground surveys, at many
collieries it was not practicable, for various reasons,
to use two wires in the shaft, or even a single wire in
two shafts, and in those instances the magnetic needle
must be relied on. To secure a reasonable degree
of accuracy some method such as the following case
described might be adopted. At a large North of
England colliery, in which the main roads extended
north, south, east and west for about a mile in each
direction and joined at a point near the shaft, surveys
were made with the theodolite from magnetic bases
at the inbye end of each main road, established at
the same hour on successive nights by three or four
observations at the same point. The readings from
the four surveys on to the common base near the shaft
varied less than one minute. At the surface a true
north line three miles long had been laid down from
observation of the pole star, and careful magnetic
readings were taken at the same hour as the under-
ground work, but, of course, on different nights. It
was a simple matter to make the connection from those
bases by means of a single wire in one shaft. All
the magnetic observations were made with the same
5 in. dial. A remarkable example of accurate work
done with the needle was the driving of the Ladysmith
drift at the Whitehaven Collieries by Mr. John
Shanks. It went without saying, however, that
wherever it was possible to obtain a direct connection
by wires in one or, better still, two shafts, the use of
the theodolite only was permissible except where the
needle was used as a check. One would be glad to
know whether magnetic storms, particularly those
which only caused small fluctuations of the needle,
were general throughout the country, or whether they