June 16, 1916. THE COLLIERY GUARDIAN._____ 1137 ________________________ Table IV.—Kates of Oxidation of some South Wales Coals at 30 degs. and 60 degs. Cent. Sample No. 8, steam coal from the Big Vein ; No. 9, Waterloo Red Ash (house coal), No. IO, steam coal from Upper Rhas Las ; No. 11, Admiralty steam coal from the Bute seam; No. 12, Admiralty steam coal from the Yard seam. Sample. 9 at 8 at 10 at 11 at 12 at 8 at Rate after hours 30° C. 30° C. 30° C. 30° C. 30° C. 60°C. 2 . 4’9 .. .. 3-2 . .. 2’1 . .. 2'75 ... 5'1 .. . 8’0 4 . 3-1 . .. 2-2 . .. 1'5 . .. 2’25 . ... 3'8 .. . 5'6 6 . 2’4 . .. 1’7 . .. L2 . .. 1-85 . ... 3'0 .. . 4'3 8 . 2’0 . .. 1-4 . .. 1’1 . .. 1'65 . ... 2-55.. . 3'5 12, . 1’6 .. .. 1’2 . .. 0'95 . .. 1’3 . . . 1'95.. . 2-6 18 . 1’3 .. .. 1-1 . .. 0’85 . .. L2 ... 1-6 .. . 2’05 24 . IT .. . 1’0 . .. 080 . .. IT . ... 1'4 .. . 1'8 48 . V0 .. .. 0'9 . .. 0'70 . .. 3'95 . ... L'l .. . 1'15 72 . 0’8 .. .. 0'8 . .. 0'65 . .. 0'85 , ... 0'85.. . 0'7 96 . 0’65 .. . 0'7 . .. 0'60 . .. 0'75 . ... 0'65.. . 0'3 Total absorption in 96 hours, in c.c.. . 116 .. . 100 . .. 79 . .. 105 . ... 134 .. . 133 No sulphate produced during any of the above oxidations. Analyses of Coals. Sample No. 9. 8. 10. 11. 12. P. cent. P. cent. P. cent. P. cent. P. cent. Moisture ... ... 1-86 . .. 1’60 .. . 1'68 .. . 1-16 .. . 0 89 Ash ... 2'03 . .. 2'88 .. . 2'54 .. . 1'55 .. . 1'55 Carbon ... 83-52 . .. 85'41 .. . 85'34 .. . 88 01 .. . 88'23 Hydrogen... ... 494 . .. 4'52 .. . 4'53 .. . 4'01 .. . 4’09 Nitrogen .. .... 1'34 . .. 1'08 .. . 1'44 .. . 1'30 .. . 1'27 Sulphur ... 1'99 . .. 0’85 .. . 0'88 .. . 0'53 .. . 0'75 Oxygen* ... ... 4'42!,. .. 3'66 .. . 3’59 .. . 3'44 .. . 3’12 * By difference. f Corrected for sulphur content, 4'79. Another district in which gob-fires are very rare is in the Northumberland and Durham coal field. In Table> V. the rates of oxidation and the analyses of some samples taken from this field are given. Of the samples described in Table V., Nos. 3, 5, and 6 have an oxidation much lower than that of the normal oxidisable coal, and the absence of fires is clearly owing to this property. Sample 4 has an oxidation rather less than that of sample D27 (Table I.). Only in rare instances does this latter coal give rise to gob fires, and it would therefore seem that coals having a lower oxida- tion than this will only originate a heating under the most favourable circumstances. In the Low Alain seam (from which sample 4 was taken) the natural conditions are against a gob fire. Little coal is left in the goaf, and there is a good post roof, which does not readily break up, and so gives every chance of an air- tight waste. The coal itself would seem, from other results quoted in this paper, to be just on the limit between a coal liable to fire -and one not liable; and, therefore, so long as the conditions are not made excep- tionally favourable, no fires will occur. Table V.—Rate of Oxidation of Northumberland and Durham Coals at 30 degs. and 60 degs. Cent. Sample No. 1, Main seam; No. 2, waste coal from same place and seam as No. 1; No. 3, Busty seam ; No. 4, Low Main seam; No. 5, Hutton seam; No. 6, Low Main seam (from a different pit from No. 4); No. 7, Yard coal. Rate after Sample No. f hours 1. 2. 3. 4. 5. 6. 7. 5* 6 * 2 .21’6...16'7...6-0 . ..9 2 ...5'1 . ..4'4 ...30'5...9-0 . ..74'0 4 .17'0...12’2...41 . ..6'6 ...3’5 . ..3-0 ...20'6...6'8 . ..41'0 6 .14’6...10’2...3’3 . ..5’3 ...2’5 . ..2-1 ...17'0...5'5 . ..33-6 8 ,12’3... 8'9...2'8 . ..4’7 ...2-0 . ..1'7 ...14-5...4-5 . ..29'2 12 . 9'9... 7’5...2’2 . ..4'0 ...1'5 . ..1-65...11'5...3'3 . ..24'0 18 . 7'9... 6'2...2-1 . ..3-6 ...1'3 . ..1'3 ... 8'5...2'5 . ..17-1 24 . 6 9... 5'5...1-95. ..3'2 ...1'2 . ...1-2 ... 6-6...2-3 . ..13'9 30 . 6’2... 5'0...1'85. ..2'95...1'15. .1’15... 5’5...2-1 . ..11'6 36 ... , 5-7... 4'7...1’8 . .2'80...IT . ..1-1 ... 4’9... — . .. 9'9 48 . 4'8... 4-4...1'6 . ..2'60...1'0 . ..1-0 ... 4-2 ..1-9 . .. 7'9 60 . 4T... 4'0...1’4 . ..2'30...0-9 . ..0'9 ... 3'6... — . .. 6-9 ■72 . 3'7... 3'7...1'2 . ..2-10...0'85. ..0-85... 3'1...1'6 . .. 6'4 96 . 31... 3'1...1'0 . ..1'60...0'7 . ..0'7 ... 2-3.. 1'25. .. 5'6 A ... 608... 511... 176... 290... 122... 118... 623 . 220..1-305 B ... 81... 226... 0 ... 0 ... 0 ... 0 ... 0 ... 0 ... 0 C ... 527 285... 176... 290... 122... 118... 623... 220..1'305 A = Total absorption in 96 hours, in cubic centimetres. B = Absorption due to pyrites, in cubic centimetres. C = Absorption due to coal, in cubic centimetres. * At 60 degs. Cent. Analyses of Coals. Sample No. Moisture. Ash ____ Carbon.... Hydrogen Nitrogen . Sulphur . Oxygen* . Oxygen! . _______ L 2. 3. 4. 5. 6. 7. Per Per Per Per Per Per Per cent. cent. cent. cent. cent. cent. cent. 9-31... 6-76... 2-75... 5’00... 1-75... 1’40...11*15 3’63...36-46.. 7-78... 4-02... 1-71... 2*19... 1’27 69-16...40-19...75-47...76-94...82-29...82-66...71-70 4-17... 2-72... 4-50... 4*56... 4-86... 4’96... 4’85 1-13... 0-62... 1’23... 1’29 .. 1’48... 1’40... 1’35 1-42...13-02... 2-22... 1’02... 1’83... 1-38... 0*77 11-18... 0-23... 6-05... 7’17... 6-08... 6-01... 8’91 11-43.:. 4-73... 6’50... — ... 6-39... 6-15... — * By difference. ! Corrected for sulphur content. Sample No. 7 is somewhat different : it shows high oxidation, which increases both in magnitude -and in rate with increase of temperature, and it should there- fore be liable to fire. In Dre pit no- fires occur, and an inspection of the workings makes the reason of this clear. The seam is about 3 ft. thick, with a hard roof and a good floor. The coal is very clean, so that practi- cally none is left behind in the wastes. The absence of fires underground is therefore -due to the absence of coal from goaves which might fire. When the coal is taken out of the pit and stacked on the surface, or loaded as cargo, different conditions obtain, which are more favourable to spontaneous heating, and fires in both cargoes and stacks do occur. Samples Nos. 1 and 2 were taken from one of the few pits in which gob-fires have broken out in this field. In the normal workings fires are rare, but at exceptional places where the coal thickens, or near a “ wash-out ” or “ overlap,” extensive breaks are set up in the roof and the coal. The coal becomes poorer, and is associated with bands of fine pyrites, so that a considerable quantity is thrown back into the goaf. Such places have been the scene of several fires in this pit. Stacks and cargoes of the coal have also been known to fire. At the place from which samples Nos. 1 and 2 were taken, a fire had already occurred. Owing to- the nature of the coal, a great deal was being left in the waste, and it was impossible to remove all -the timber. The roof was very, badly broken, some of the breaks extending through into neighbouring roadways, so that the place had every chance of heating spontaneously, and, in fact, another fire occurred shortly afterwards. In view of the oxidisable nature of the coal, and the simultaneous oxidation of the pyrites associated with it, samples Nos. 1 and 2 -are peculiarly liable to fire. In the second sample nearly half the total oxygen absorbed was taken by pyrites, and since pyrites produces about double the quantity of heat per volume of oxygen absorbed that coal does, nearly two-thirds of the total heat production will come from the admixed pyrites of the sample. The condition of this pyrites seems very similar to that in the .Bullhurst coal. The sample contained little visible pyrites, and no heavy lumps of “ brass.” The quantity -of oxygen absorbed corresponds very nearly with that of the finely-divided Bullhurst sample. From the sulphur content about 24 per cent, of pyrites may be present, which absorbs 226 c.c. of oxygon—that is, 100 grammes would absorb 950 c.c. The pyrites evidently may be a very serious factor in causing spontaneous heating in this particular place, if all the waste coal left in the goaf contains as high a proportion of pyrites as sample 2. This sample was, however, a picked one, and contained an unusually high percentage; the average of the waste coal would contain perhaps only half as much. It should be noticed, too, that the heat production from sample 1, which contains very little pyrites, is nearly equal to that of sample 2, which contains a high proportion :— Sample No. 1. TT J __ Calories. Heat produced by coal ....... 527 x 2’1 = 1,107 Heat produced by pyrites ... 81 x 4‘3 = 348 Total heat production ... —1,155 Sample No. 2. Heat produced by coal ....... 285 x 2’1 = 598 Heat produced by pyrites ... 226 x 4’3 = 972 Total heat production ... = 1,570 Further, the effect of the conditions which obtain in the goaf may modify the relative heat productions a good deal. At a short distance- in from the road into a closed waste the oxygen percentage in the -air may fall very considerably. If, for example, it were to fall to 10 per cent., the rate of heat production from the pyrites would bo just less than half, whilst that from -the coal would be .a little less than three-quarters of the rate in normal air. The heat production in 96 hours would then be as follows :—- Sample Sample No. 1. No. 2. Calories. Calories. From coal 786 . .. 425 From pyrites 166 . .. 463 — ■ Totals 952 . .. 888 The heat produced by the pyrites in sample No. 2 is, therefore, little more than that produced by the coal in the sample, and much less than that from the coal in sample No. 1. Very possibly, therefore, in the goaf samples Nos. 1 and 2 would be about -equally liable to fire, and it would be difficult to say which was the responsible agent, the coal or the pyrites. In one place where the percentage of pyrites was very low (sample No. 1), undoubtedly the origin of the heating would be in the coal. In another place where the percentage of pyrites was rather higher than that in sample No. 2 (24 per cent.), the larger proportion of the heat would come from the pyrites, but the two places would be almost equally liable to fire. • A very different proportion between the heat produc- tion by coal and by pyrites is found in the Bullhurst seam in North Staffordshire. The oxidation of the pyrites associated with this coal has already been discussed. The oxidations of the coals are recorded in Table VI. It is quite clear that the coals from this particular section of the Bullhurst seam cannot be responsible for the fires which occur, even if the percentages of pyrites normally associated with them (to the extent shown by the -oxidations and analyses in Table VI.) be taken into account. In some places, however, there is a very high percentage of pyrites in a very finely-divided condition mixed with the coal, and it must be at these points that the initial rise in temperature required to cause the coal to fire is produced. At low temperatures the rates of oxidation of the samples described in Table VI. are very similar to those off the -South Wales coals described in Table IV.; but, as the temperature rises, the quantity of oxygen that the coal is capable of absorbing also -seems to increase, which was not the case with the Welsh coals. The rate of increase is very small, but it seems to be real. When the pyrites has produced a sufficiently large rise in -temperature, the coal will begin to produce a more considerable quantity of heat by its own oxidation. There is no doubt at all that the initial rise in tempera- ture is due to’ the oxidation of the pyrites, and that in its absence the coal could not produce sufficient heat at ordinary temperatures ’ to cause any noticeable increase in temperature. Details of the outbreak of fire in the Bullhurst seam confirm the conclusion that pyrites must be the origin. It is said that heaps of coal and “ dirt ” left at the face have fired in from 24 to 48 hours. No coal yet examined is capable of generating heat spon- taneously at this rate, but if the heap contained in one part a very high percentage of pyrites in that state in which it is found in the Bullhurst seam, then it has been shown that a fire may easily break out in this time. Table VI.—Rates of Oxidation of Various Parts of the Bullhurst Seam, North Staffordshire. Sample No. 15, bottoms or wall coal; No. 16, hard part of bottoms; No. 17,'‘middles; No. 18, hustle; No. 19, little tops ; No. 20, big tops Sample No. Rate after (---------------------*---------------------- hours 15. 16. 17. 18. 19. 20. 16.* 17.* 19.* 2 ...5'4 ...3'0 ...5'4 ...42 .. .3’1 ...2'8 .. ..8’3 . ..9'7 .. .8'0 4 ...3'7 ...2'6 ...3'7 .. 2'6 . ..2'0 ...1'9 .. ..6'2 . ..7-2 .. .4'9 6 ...2'85...2'3 ...2'85...1'9 . ..1'55...1-3 . ..5'8 . ..5’9 .. .3'4 8 .. 2-50...2'05...2'5 ...1'6 . ..1’35 . IT . ..5'2 . ..5T .. .2'6 12 ...2’1 ...1'75...2T ...1'45. ..1-20...0'9 . ..4'4 . ..4-4 .. .2'05 18 ...1-85...1'6 ...1’85...1’40.. ..1'15...0'85. ..3'6 . ..3-9 .. .1'9 24 ...1'65...1'45...1'65,.1'35. ..IT ...0'8 . .3'25. ..3-45.. .1'8 30 ...1'50...1'3 ...1'5 ...1'30. ..1'05...0-75. ..3-0 . ..3'1 .. .1'65 48 ...1'30...IT .. 1'3 ...1'25.. .1'0 ...0'70., ..2'25. ..2'4 .. .1'4 72 ...1'20...1'0 ...1'2 ...IT .. .0'9 ...0'6 .. .1’85. ..2'0 .. .1-05 96 ...1-10. .0'9 ...1'1 ...0-95.. .0'75...0'5 .. ,.1’5 . ..1'7 .. .0'7 A ... 167... 132... 167... 133., .. 107... 81.. . 273. .. 292.. . 164 B ... 35... 35... 20..Not determined.. 130... 70... 30 C ... 132... 97... 147... — ... — ... — ... 143... 222... 134 A = Total oxygen absorbed in 96 hours, in cubic centimetres. B = Total oxygen absorbed by pyrites, in cubic centimetres. C = Total oxygen absorbed by coal, in cubic centimetres. * At 60 degs. Cent. Analyses of Coals. Sample No. ___________________ __________________ 15. 16. 17. 18. 19. 20. Per Per Per Per Per Per cent. cent. cent. cent. cent. cent. Moisture ... 2*12 ... 3*50 ... 2’25 ... 2’37 ... 1’80 ... 1’94 Ash ......... 3’60 ...39-82 ... 2*73 ... 2’39 ... 2’68 ... 4’86 Carbon........... 77’93 ...44-29 ...79-31 ...78’87 ...78-56 ...76-80 Hydrogen ... 5’35 ... 3-42 ... 5 48 ... 5’20 ... 5'35 ... 4’85 Nitrogen ... 0’80 ... 0 86 ... 0‘69 ... 0’60 ... 0 92 ... 1’21 Sulphur ..... 3’50 ... 3’11 ... 2’27 ... 2’51 ... 2’96 ... 3’85 Oxygen* ..... 6’70 ... 5’00 ... 7'27 ... 8'06 ... 7’73 ... 6’49 Oxygen! ..... 7’63 ... 5’80 ... 7’75 ... 8’63 ... 8’46 ... 7’55 * By difference. ! Corrected for sulphur content. The analyses recorded in Table VI. are interesting, since they show that not all the sulphur can be present as pyrites. Every part of sulphur in the form of pyrites leaves 1-25 parts of ferric oxide ash when the coal is burnt, so that, calculating from the -sulphur content, and allowing no- ash to the coal, the weights of ash in samples Nos. 15, 17, 18, and 19 -would be 4-37, 3-14, 3-70, and 4-81 per cent, respectively. In each case, except the last, the ferric oxide would w-eigh more than the actual -weight of ash from the sample. Obviously, therefore, part of the sulphur must be present as organic compounds, and since the coal itself will give some ash, ■a fair allowance for the organic sulphur seems to be about 1 per cent. Table VII.—Rates of Oxidation of Samples of Thick Coal at 30 degs. Cent. Sample No. 38, white coal; No. 39, Rooves coal; No. 40, top stone coal; No. 41, bottom stone coal; No. 42, pyritic material from partings in coal; No. 42u, same sample as No. 42, but passes a 10-mesh and is left on a 30-mesh sieve. Sample No. Rate after hours. 38. 39. 40. 41. 42. . . ..... 42u. 2 22'0 . ..25'2 . ..19'0 ...15'6 .. .13-7 .. . 3'4 4 16-2 . ..17’6 . ..15-0 ...110 .. . 9'8 .. . 2'9 6 13'5 . ..14-0 . ..11-6 ... 8'4 .. .78.. . 2'5 8 11'3 ...11’9 . .. 9'6 ... 7'0 .. .. 6'7 .. .. 2-2 12 8’5 . .. 8'7 . .. 7-2 ... 5'6 .. .. 5’4 . .. 1'7 18 6'5 . .. 6'5 . .. 6'3 ... 4'55. .. 4'4 . .. 1'2 24 5'6 . .. 5’6 . .. 5'6 ... 4'0 .. .. 4’0 . .. IT 30 5'0 . ... 5’0 . .. 5'1 ... 3'6 .. . 37 .. . 1'0 36 4'4 . ... 4'4 . .. 4'6 ... 3'2 .. .. 3-4 .. — 48 3'6 . .. 3'6 . .. 3-8 ... 2'6 .. . 2-9 .. 0-9 bb 72 2’6 ‘ 2 6 .’ 2’8 1'8 " 2'7 — 96 2'1 . .. 2’1 . .. 2'3 ... IT .. . 1'7 .. .' 0'65 Total oxygen absorbed in 96 hours, in c.c. ... 512 . .. 532 . .. 489 ... 344 .. . 356 .. . 110 Oxygen absorbed by pyrites, in c.c — . .. — . .. 90 ... 50 .. . 131 .. & Oxygen absorbed by coal, in c.c 512 . .. 532 . .. 399 ... 294 .. . 225 .. — * Not determined. Analyses of Coals. Sample No. ______________ _____ ________ 38. 39. 40. 41. P. cent. P. cent. P. cent. P. cent. Moisture 15-05 .. ,. 15'51 .. .. 14'09 . .. 11'38 Ash 3'64 . .. 3'61 . .. 7'44 . .. 12'78 Carbon 64'63 . .. 64'73 . .. 61'62 . .. 57'51 Hydrogen 4'27 .. . 4'30 .. . 4'10 . .. 4'11 Nitrogen 0'96 .. .. 0'97 .. .. 0'75 . .. 0’98 Sulphur 1'01 .. .. 1'01 .. .. 3'29 . .. 2'53 Oxygen* 10'44 . .. 9-87 .. .. 8'71 . .. 10'71 Oxygen! — — .. 9-57 . .. 11-28 * By difference. ! Corrected for sulphur content. Sample No. 42. Per cent. Moisture __........................... 6’3 Ash (other than ferric oxide) ....... 5’6 Coal (ash free, dry) ................ 34’0 Pyrites ............................ 54’1 Although pyrites is the main cause of heating in the Bullhurst seam in North Staffordshire, it has little to do with spontaneous combustion in the Thick coal in South Staffordshire. The rates of oxidation of some samples from the Thick coal are recorded in Table VII. The pit from which these coals are taken is very liable to fire, as might be expected from the oxidisable nature of the coals. The seam is often divided by thin