1138

THE COLLIERY GUARDIAN.

June 16, 1916.

vertical partings, which appear to contain a high propor-
tion of pyrites, and along which breaks often develop.
A sample of this pyritic material has been examined.
It consists of a soft bright yellow mass, apparently com-
posed of flaky crystals, and showed very little oxidation
in situ. The measured rate of absorption of oxygen is
set forth in Table VII. Sample No. 42 contained about
54 per cent, of pyrites, which absorbed 131 c.c. of
oxygen in 96 hours; at the same rate 100 grammes of
pure pyrites would have absorbed 25(Jc.c., or only about
a quarter of the quantity absorbed by other specimens
of pure finely-ground pyrites. This must indicate that
sample No. 42 contains the pyrites in very small
crystals, which are about small enough to pass a 60-mesh
sieve, and that the surfaces of these crystals, like those
of the largei* ones, are not readily attacked by oxygen.

In a break formed along one of these veins of pyrites
a great deal of the heat production may come from the
pyrites. Supposing that the dust in the break had the
composition of sample No. 42, it would account for
rather more than half the heat produced :—

Calories.

Heat produced by coal = 225 x 2'1 ..... =472

,,	,, pyrites = 131 x 4‘3........ - 563

Total.......................... 1,035

But even with this high percentage of pyrites, more
heat would be produced if the break were filled with
coal dust :—

The average from samples Nos. 38, 39, and 40 = 510
X 2-1 = 1,071 calories—especially when the reduction
of the oxygen percentage in the break is considered, as
in the case of sample No. 2 (Table V.). Whilst, there-
fore, the origination of some heatings in this mine may
be assisted by pyrites, the bulk of the coal would
appear to fire equally readily in its absence.

The lignite described in Table VIII. is about three
times, as oxidisable as any other coal examined, but in
the particular mine from which the sample was taken it
does not fire spontaneously. As the pit is very wet,
often being flooded, and the roadways are normally
knee-deep in water, this is not remarkable. In drier
lignite mines, especially in Germany, fires occur very
readily, as would be expected. The very high propor-
tion of water naturally contained by lignite reduces the
liability to spontaneous combustion, otherwise it would
be difficult to see how the coal could be worked at all.
For lignite containing 25 per cent, of moisture to reach
100 degs. Cent, and evaporate off its water requires an
expenditure of about 17,000 calories of heat, which
would correspond to an oxygen absorption of about 8*5
litres per 100 grammes. This large expenditure of
energy brings the possible spontaneous rate of increase
in temperature down to that of a normal oxidisable coal.

Table VIII.—Rate of Oxidation of Lignite.
Sample obtained from Portrush.

Sample. No.

Rate after	37 at 30	37 at 60^
hours	degs. Cent.	degs. Cent.
2	88’0	—
4	60’0	200’0
6	44’5	125’0
8	34’5	85’0
12	23’5	60’0
18	18’0	42’0
24	15’0	34’5
30	12’9	300
36	11’3	28’0
48	9’2	23’5
60	7’6	19’2
72	6’5	16’1
96	5’2	12’1
Total oxygen absorbed		
in 96 hours, in c.c....	1,476	3,8'0

Analysis of Sample No. 37.

Per cent.

Moisture .................... 24’87

Ash ....................... 18’31

Carbon ...................... 36’52

Hydrogen ..................  3’48

Nitrogen ................... 0’41

Sulphur ................... 1 00

Oxygen (by difference) ...... 15’41

Table IX.—Rates of Oxidation of Ayrshire Coals at
30 Degs. and 60 Degs. Cent.

Sample No. 33, Bottom coal; No. 34, Middle coal or No. 2
seam ; No. 35, Top coal or No. 3 seam; No. 36, (i Smithy ”
coal.

Sample No.

	33. 34.	35.	36. d	34 at 60
Rate after hours.				.egs. Cent.
2	... 36’0 ...	17’5	.. 5’5	... 52’0
4	... 15’4 ...	11’9 .	...40	... 32’0
6	... 11’9 ...	8’9	...3’2	... 25’4
8	... 10’0 ...	. 6’9	..2’7	... 21’2
12	...	7’4 ...	50	...2T5	... 166
18	...	6’8 ...	4’3 .	...1’7	... 12’8
24	...	50 ...	3 9 .	...1’35	... 11’0
30	4’4 ...	3’7 .	..IT	... 10’0
36	...	4’0 ...	3’4 .	..1’0	...	9’2
48	...	3’4 ...	3’0 .	...0’85	...	8’0
60	...	2’9 ...	2’7 .	—	...	7’2
72	...	2’4 ...	2’45 .	”0’7	...	6’5.
96	...	1*9 ...	2’45 .	..0’6	...	5’8

Total oxygen absorbed in 96
hours, in cubic centimetres 502 ...

392 ... 124 ... 1,100

Analyses of Coal.

		Sample No.		
	33.	34.	35.	... ... ...  36.
	P. cent.	P. cent.	P. cent.	P. cent.
Moisture . 		8’05 :.	.. 6’94 ..	.. 5’74 ..	. 9’72
Ash 		4’62 .	.. 4’81 .	.. 8’03 .	.. 3’47
Carbon		72’44 .	.. 73’05 .	.. 71’06 .	.. 70’44
Hydrogen 		4’59 .	.. 4’69 ..	.. 4’53 ..	.. 4’69
Nitrogen 		0’98 ..	.. 0’80 ..	.1’02 .	. 1’23
Sulphur		0’76 ..	. 0 69 ..	. 0’77 ..	. 0’73
Oxygen (by difference)	8’56 ..	. 9’02 ..	. 8’85 ..	. 9’72

Lignite produces far more carbon dioxide per volume
of oxygen absorbed than any other coal. After 120 hours
at 30 degs. Cent., about a quarter of the volume of
oxygen absorbed reappears as carbon dioxide, and at
60 degs. Cent, about half; this is between four and five
times as much as is produced by a true coal.

In Table IX. the rates of oxidation of some samples of
Ayrshire coals are recorded. The mine from which these
samples were taken had had two fires, and the heated
areas were sealed off. It was not known which coal
caused the fires, but the smithy coal was suspected.
The three main seams all have a rate of oxidation which
would render them liable to fire, whilst that of the
smithy coal shows that it cannot be the cause of a
spontaneous heating. No evidence of any oxidation of
pyrites was found.

Of the forty coals examined, 22 airo from pits in which
fires have occurred, 12 from pits in which fires are not
known, and 6 from pits in which fires do occur, but are
not attributable to the coal. Tire time-absorption cuives
of all the coals are of the same type, but vary con-
siderably in magnitude. A convenient way of classifying
the oxidation of the samples its by the quantity of
oxygen absorbed during the first 96 hours. Three main
divisions are then apparent, namely :—

(1)	Those like anthracite and the Welsh .steam coals,
which have a small definite, capacity for oxygen, which
is not'altered by increase of temperature (at any rate
up to 60 degs. Cent.), and cannot therefore fire
spontaneously.

(2)	Those which have a low rate of oxidation, the
capacity for which does increase with temperature, but
are not liable to- spontaneous combustion unless mixed
with pvrites (see Table V., samples Nos. 3, 5, and 6,
and Table VI.).

(3)	Those coals which have a sufficiently large rate of
oxidation to give rise to fires without the intervention
of any other (substance (see Tables I. and II.).

There does not seem to be a gradual transition
between classes 2 and 3 in the quantity of oxygen
absorbed. Those coals that are not liable to fire usually
absorb less than 200 c.c; of oxygen in 96 hours at 30 degs.
Cent., and those liable to fire well over 300 c.c. in the
same time. The measurement of the oxidation of a coal
by the methods described should therefore be a ready
means of distinguishing between these classes, especially
if measurements are made both at 30 degs. and at
60 degs. Cent. If a sample shows a very low oxidation,
it cannot be said definitely that it is not liable to fire
unless the quantity and kind of pyrites found in the
seam is also known (see the samples in Table VI.). So
long as the pyrites is all in the form of “ brass,” or as
bright thin veins, it plays no part in causing a heating.
If, however, it is found in high proportion as an intimate
mixture with the coal, it may become the deciding
factor, causing a coal which is not of itself liable, to- fire
to become liable.

The ultimate analysis of a coal -seems to give little
definite information as to- its liability to spontaneous
heating. A coal which contains both a high percentage
of moisture and a high percentage of oxygen is usually
more oxidisable than one with low oxygen and low
moisture. The oxygen percentage by itself is no guide
to- the capacity of the coal for absorbing oxygen. For
example, sample No. 7 contains 8’93 per cent, of oxygen
and absorbs 623 c.c.; whilst sample No. 18 contains
almost the same percentage of oxygen within the limits
of experimental error and only absorbs 133 c.c. The
latter sample contains more oxygen than sample No. 25,
of which the absorption is 34 times as great. A number
of other instances of the same sort can be found in the
tables given in this paper. A high natural moisture
content is on the whole a more reliable indication, but
no one constituent in the coal can be said to vary
regularly with the oxygen absorption. The quantities of
oxygen and moisture already in the coal do not them-
selves influence the absorption of oxygen, but are
indications of the presence of othe-r compounds or
classes of compounds in the coal substance which are
easily oxidised. If water had any direct influence on
the absorption, then addition of water to coals of low
moisture content should increase their power of
absorption. In every sample of which the oxidation has
been measured the natural moisture present was enough
for the coal to exert its full capacity. Complete removal
of the last traces of water does reduce the rate of
absorption -considerably,* but the re-addition of 1 per
cent, of moisture is amply sufficient in most cases for
the coal to regain its activity.

A suggestion has been made I that it is the oxygen
normally present in coal which causes spontaneous
heating, the theory being that the coal may be con-
sidered to consist of two parts, one containing much
oxygen and the other little oxygen. The part containing
little oxygen is supposed to react with the other part and
abstract -some of its oxygen, the reaction being accom-
panied by evolution of heat. No experimental evidence
in favour of this view has been adduced. There is,
however, definite evidence against it, so far as it refers
to the origin of gob-fires. During a study of the thermal
changes which take place when coal is heated in vacuo,
Cobb has shown that no- distinct exothermic change
takes place until the temperature reaches 600 degs.
Cent.J—that is to say, until the coal is red hot. Before
this point such thermal -changes as do occur are mainly
accompanied, by an absorption of heat. It is difficult to
see how a change which does not take place until the
coal is red hot can be the cause of its arriving at a red
heat.

On the other hand, there i-s abundant evidence to
support the commonly-accepted view that spontaneous

* See Trans. Inst. M.E., 1915, vol. xlix., p. 39.

t R. V. Wheeler, Minutes of Evidence, Departmental
Committee on Spontaneous Combustion in Coal Mines,
April 18, 1913.

1 “ Thermal Phenomena in Carbonisation,” by Harold
Hollings and John ‘W. Cobb, Journal of Gas Lighting,
1914, vol. exxvi., p. 917.

heating is due to the heat evolved during the absorption
of oxygen from, the air by coal or pyrites. The quantity
of heat produced by the reaction has been measured, and
it has been shown that the observed rate of heating of a
sample of coal agrees. with the rate calculated from the
heat of reaction and the rate of absorption of oxygen.

MINING INSTITUTE OF SCOTLAND.

A meeting of the Mining Institute of Scotland was
held in the Heriot-Watt College, Edinburgh, on
Saturday, the 10th inst. Mr. D. M. Mowat, Coat-
bridge, the president of the institute, occupied the chair,
and there was a representative attendance of members.

The President made sympathetic reference to the
death of Lieut. J. M. Dunnachie, one of their members,
who was killed in action on April 15.—It was agreed to
record in the minutes a reference to the appreciation
which the members of the institute entertained for the
supreme sacrifice he had made.

New Members.

The following gentlemen were admitted to the mem-
bership of the institute :—Messrs. J. H. Bennet, mine
manager, Appleby, Westmorland; W. G. Gallaher,
colliery manager, Baillieston; Thomas Graham, colliery
manager, Wankie, Rhodesia, South Africa; Alex.
McCall, colliery manager, Whitburn-; W. A. M‘Ilvena,
colliery manager, Shettle-ston; L. W. Macer, colliery
manager, -Pilgrim’s Rest, Transvaal, South Africa;
W. C. Parker, colliery manager, Kirkintilloch; J. M.
Ritchie, colliery manager, Upper Assam, India; and
A. W. N. Laing, mining engineer, Summerlee Iron
Works, Coatbridge.

The Council of the Institution.

The- following gentlemen were elected to represent the
institute on the council of the Institution of Mining
Engineers :—Messrs. D. M. Mowat, Coatbridge; C. A.
Carlow, Leven; Wallace Thorneycroft, Bannockburn;
R. W. Dron, Glasgow; J. Balfour Sneddon, Mid-Calder;
William Williamson, Hamilton; Thomas Arnot,
Glasgow; Douglas Jackson, Newmains; William
Smith, Dalmellington; James Barrowman, Hamilton;
James Hamilton, Glasgow; Harry W. Lewin, Glasgow;
Charles Latham, Glasgow; and James Black,
She ttl.es ton.

The President said the members of the institute
would be interested to hear that Mr. Wallace Thorney-
croft, East Plean House, Bannockburn, had been nomi-
nated for the post of president of the Institution of
Mining Engineers. The General Purposes Committee
of the institution had unanimously recommended him
for the office, and the likelihood was that when the
institution met in Glasgow in the month of September
Mr. Thorneycroft would be duly appointed president.

Rapid Estimation of Oxygen and Blackdamp.

The discussion was thereafter resumed on the paper
contributed at a recent meeting by Mr. Henry Briggs,
Heriot-WTatt College, Edinburgh, on “ A Device for the
Rapid Estimation of Oxygen and Blackdamp in Mines.”
(Colliery Guardian, Feb. 25, 1916, p. 359.)

Mr. Robert McLaren, H.M. inspector of mines, said
it was quite apparent that this paper had gone a long
way afield. Only the other day he had a communica-
tion from a gentleman in Canada, who had evidently
seen the paper, and desired to be furnished with addi-
tional information in regard to it. They would have
noticed that Mr. Briggs had that day submitted for
their inspection a lamp with an improved attachment.
When explaining the features of the new attachment,
Mr. Briggs might mention whether he considered it -an
improvement on the old arrangement, and, particularly,
if it enabled the fireman to get a complete reading from
the lamp at one glance.

Mr. Briggs at this stage exhibited a lamp fitted with
the newer type of attachment. He explained that no
change had been effected on the principle of the attach-
ment; it had merely been rendered much simpler and
neater. He had been notified by the Government
authorities that it might be possible for them to approve
of the newer type of attachment as a modification.

Mr. McLaren asked if it would not be possible to
adapt the attachment to other popular types of lamps,
in addition to the Gray lamp; and the author replied
that there was a difficulty in regard to that. For
instance, there required to be a definite partition, or
separation, between the inlet and outlet currents.
Could the attachment be adapted to a Cremer lamp?

Mr. Briggs admitted that it would be difficult to
do so.

Mr. Hugh Waddell (Tranent) wrote that he had
gained some practical experience in the use of this
device in the course of the tests made at St. Germains
Collieries, and he was surprised at the moderate claim
put forth by Mr. Briggs for his apparatus. Although
Mr. Briggs had introduced the device as one for the
estimation of oxygen and blackdamp in the air of
safety lamp mines, it was, however, also capable of
fulfilling these functions in naked light mines. It