TIDESWELL AND WHEELER ON FUSAIN AND ITS OXIDATION. 125 XX1.-On Fusain artd its Oxidation. Studies in the Cornpo&ion of Coal. By FREDERICK VINCENT TIDESWELL and RICIFARD VERNON WHEELER. SPONTANEOUS combustion in a seam of coal in so far as it may be determined by the chemical composition of the materials composing the seam originates with the most readily oxidisable ingredient thereof. Amongst mining men there is a belief the history of which it is unnecessary to trace that a frequent cause of spon-taneous combustion is the presence in the seam of fusain; * that fire actually originates in bands of fusain when such are present, and travels preferentially along them. Data regarding the rate of oxidation of a fusain have been supplied by Winmill (Trans. Inst. Min.Eng. 1913 46 563) who concluded that of all parts of the Barnsley seam which he examined in detail the fusain was the least capable of heating spontaneously. Our own experiments when using coal from the Hamstead Thick seam (J. 1920 117 794) gave quite different results. The vitrain, clarain and durain (the brilliant bright and dull portions of the seam) absorbed oxygen a t rates graded in the direction expected from previous work on the chemical constitution of these ingredients of banded bituminous coal (J. 1919 115 619) but the fusain stood apart. At 15" and 50" its absorptive power for oxygen was several times greater than that of the rest of the coal although at 100" it was of the same order. From this it can be concluded that the fuaain weight fcr weight is the most liable to self-heat (from * Sometimes called " mother of coal," " mineral charcoal," " dant," or " sooty partings.126 TIDESWELL AND WHEELER ON FUSAIN AND ITS OXIDATION. atmospheric temperature) of all the ingredients of the Hamstead coal. It would not however be justifiable to assume that fusains from other coals behave similarly-Winmill’s work indeed suggests that they do not-and further experiments with a number of samples of fusain and of the coals associated with them were therefore undertaken. During the progress of this work which was begun in 1919, determinations of the rates of oxidation of a number of fusains from different coal-fields have been published by Graham (Trans. Inst. Min. Eng. 1923 66 41) who has summarised his results as follows “ This ingredient of coal may vary very considerably in composition but such variaticn does not appear a t low temper-atures to affect materially the absorption of oxygen which in all cases is considerably smaller than that shown by a bituminous coal liable to spontaneous combustion.I n general from the chemical point of view fusain may be exonerated from being considered as the source of the main production of heat during the initial stages of most cases of spontaneous combustion.’, The following results may be quoted from Graham’s work the oxygen absorbed being expressed in C.C. a t N.T.P. per gram of fusain : Oxygen absorbed from air at Fusain description. 30” during 96 hours. C.C. Mossfield seam (North Staffs.) .................................1.93 ( a ) Soft variety ......... 1-19 f ( a ) Soft variety .................................... 1.87 l ( b ) Hard variety ................................. 1-61 Seven Foot seam (North Staffs.) { ( b ) Hard variety ......... 2.04 The absorption of oxygen by the actual coals with which the fusains were associated was not measured but Graham compared his results with some obta,ined by Winmill (ibid. 1916 51 493), under similar conditions of experiment for coals “ liable to spon-taneous combustion,’’ the values for which lay between 3.0 and 6.0 C.C. A closer scrutiny of Winmill’s figures shows however, that coal from.the same fields as those from which Graham’s fusains were obtained did not absorb oxygen any more readily an6Graham’s generalisation does not seem to us justifiable on the evidence.We have measured the absorption of oxygen of a number of coals and of the fusains actually associated with each and we cannot agree that fusains in general absorb oxygen a t slower rates than do coals liable to spontaneous combustion. Seventeen samples of fusain with samples of the adjoining coals, were collected for us by H.M. Inspectors of Mines and from these four were chosen according to their apparent purity for oxidation tests. The samples were as follows : STUDIES IN THE COMPOSITION OF COAL. 127 Lccb. No. A . From Top Mards Barnsley Seam Hucknall No. 2 Pit Notts. Lab. No. B. From Robin’s Seam Cannock Old Coppice Colliery, Walsall Staffs. Lab. No. C. F’rom Deep Softs Seam Mapperley Colliery Notts. Lab. No.D. From Dysart Main Colliery Fife. Analytical data respecting these samples are given in Table I. TABLE I. A. B. C. D. --- Fusain. Coal. Fusain. Coal. Fusain. Coal. Fusain. Coal. Moisture per cent. ... 5.6 9.4 5.6 8.9 2-6 9.8 5.7 10.9 matter (Other) 15.7 39.0 17.1 39.8 13.0 40.4 12.3 35.9 than moisture) ... Ash ..................... 10.3 3.3 14.7 8.3 12.5 7.7 11.8 1.3 Carbon per cent. (on Hydrogen ............ 3-0 5-0 3.3 4.8 3.0 4.7 3.2 4.6 Oxygen ............... 7-0 12.8 6-1 15-3 6.4 16.5 10.5 15.1 Nitrogen ............... 0.4 2.2 0.4 1.5 0.7 1.9 0.4 1.3 Sulphur ............... 0.2 0.9 10.4 4.9 2-4 1.3 1.3 0.5 FIG. 1. ash-free dry coal) )89*4 79.1 79.8 73.5 87.5 75.6 84.6 78.5 flME3 MOWRS. The mehhod of experiment was to circulate oxygen in a closed system through the coal or fusain packed in a tube maintained at a constant temperature.* The absorption of oxygen was calculated * Details of the apparatus used and of the method of experiment are given in J.1920 117 795 whilst a diagram of a simi1a.r apparatus is shown in J. 1912 101 831 128 TIDESWELL AND WHEELER ON FUSAIN AND ITS OXIDATION. from the reduction of pressure. Before and after oxidation at a given temperature each sample was heated in a vacuum at 200". The results obtained are shown diagrammatically in Figs. 1 and 2 and are summarised in Tables I1 and 111. These results cannot be directly compared with those of Graham, for he used air in his experiments but Winmill has found (Trans. Inst. Bin. Eng. 1916 51 493) that the absorption of oxygen by coal is nearly proportional to the square root of its concentration, FIG 2.TABLE 11. substance. Oxygen absorbed. C.C. at N.T.P. per gram of ash-free dry Sample. A. B. C. Temp. (hours). Fusam. Coal. Fusain. Coal. Fusam. Coal. 1.3 1-0 1.4 1.2 1.8 1.5 2.3 2.4 2.5 2.6 3-2 3.8 300 3-5 4.3 4.0 5.0 5.1 6.4 196 4.3 5.8 4.8 6-6 6.2 8.1 10.5 19-2 12.2 22.4 11.0 25.0 '*'" { k! 22.0 48.0 24.0 47.0 22.8 61.0 Time & 0 D. Fusain. Coal. 0.8 1.4 1.8 3.8 2.9 6.7 3.5 8.5 7.2 23.8 17.0 59.0 7 STUDIES IN THE COXPOSITION O F COAL. 129 TAELE 111. Ratio Oxygen absorbed by fusniih Osygeil ubsorbed by coul. Temp. (hours). *A. B. C. D. Time Sample. 1.3 1.2 1.2 0.6 0.95 0.96 0-84 0.47 30" !;k 0.83 0.81 0.80 0.43 0.74 0.73 0.76 0 4 1 0.55 0.55 0.44 0.30 0.46 0.48 0.38 0.25 \ 96 100" 150 10 so that a rough comparison can be made if Graham's figures are doubled.It then appears that the fusains he used were decidedly less readily oxidised a t 30" than most of those we have investigated. We suggest that this is due in part t o the different experimental methods used (Graham for example does not appear to have allowed for the oxidation of his samples a t atmospheric temperature previous to their introduction into his apparatus) but mainly to differences in the nature of the fusains themselves. The abnormally low rate of oxidat'ion of the Barnsley fusain recorded by Winmill would appear to be due to weathering of the sample previous to his tests. It will be seen froin Tables 11 and I11 that with three of the pairs of samples examined the initial absorption of oxygen by the fusain a t 30" was greater than that by the coal but on comparing the results obtained a t 30" and loo" the oxidisabilit'y of fusain is found to increase less rapidly with temperature than bhat of the coal.The temperature coefficients of the amounts of oxygen absorbed during the early stages (up io 10 hours) are : A. B. C. D. Hamstead. Fusain ...... 1.24 1-27 1-12 1.29 1.20 Coal ......... 1.34 1.34 1.39 1.37 1-35 In each instance the coefficient is less than 2 and probably is the resultant of two coefficients. The reaction between oxygen and coal is not simple it may be expressed as follows : Coal and oxygen + coal-oxygen (adsorbed) + coal-oxygen (com-plex) + oxidised coal + oxides of carbon + water.The last phase of the reaction is incomplete at low temperatures, but can be completed by raising t'he temperature (it is nearly complete a t 200") ; a t such low temperatures absorption of oxygen is determined by the formation of the coal-oxygen complex. Com-pared with the rate of formation of this complex the first action of adsorption may be regarded as instantaneous. The rate of complex Iormaiion will therefore depend on the concentration of oxygen on the surface of the coal. The temperature coefficient of the con-VOL. CXXVII. 130 TIDESWELL AND WHEELER ON FUSAIN AND ITS OXIDATION. centration of adsorbed oxygen on the surface of the coal is less than unity and is probably about 0.80 (see Graham Trans. Inst. M i n . Eng.1916 52 338; Tideswell and Wheeler J. 1919 115 895). Assuming that the rate a t which the coal-oxygen complex is formed is directly proportional to the concentration of the oxygen main-tained on the surface of the coal and that its temperature coefficient is 2 the expected coefficient for the series of reactioiis would be 1.6. An explanation of this is that the surface of the coal becomes clogged by the products of decom-position of the complex an effect which would be greater the higher the temperature of reaction and more noticeable with fusain than with coal because of the more open texture of its surface. A study of the gases evolved during the oxidations (see Table IV) suggests that the mode of oxidation of fusain and of coal is similar. At 30" the amount of carbon monoxide was too small to admit of exact determination but a t 100" the volumes were both larger and more regular in amount and it was found that the ratio between the carbon dioxide and carbon monoxide produced at this tem-perature lay within the same range (2.4 to 3-4) with the fusains as with the coals.TABLE IV. The observed values are less. Oxides of carbon evolved. Per cent. of oxygen absorbed. Sample. Temp. A. B. C. D. 4.0 0.8 1.6 0-8 1.5 3.2 6.6 0.7 30" Carbon dioxide { g::rh 100 Carbon dioxide (Ezp 12.8 11.7 10.8 14.5 10.6 12.1 14.5 . 17.6 4.0 4.0 4.4 6.2 6-2 100 Carbon monoxide { gzp 4*7 4.0 4-9 {El?? 2.7 2.9 2.7 3.3 Ratio 2 2-65 2.5 2.4 3.4 With none of the fusains examined was the rate of absorption of oxygen a t low temperatures so rapid as with the Hamstead fusain, which may be regarded as exceptional.Fusain does not form an important part by weight (rarely more than 5%) of the mass of a coal but it occurs frequently in patches or in layers of considerable extent generally adjacent to or embedded in bright coal and its porous nature allows of ready access of oxygen. Both its chemical properties and its physical state therefore enable it to produce the first local rise in temperature that may result in self-heating of the adjacent coal. Once the temperature has risen the continuance of the heating is no doubt mainly due to oxidation of the coal. It is not to be expected that all fusains no matter from what seams of coal they are procured should have similar chemical and physical properties any more than that all coals should be similar STUDIES IN THE COMPOSITION OF COAL.131 We have in fact evidence from the work of Sinnatt (Trans. Inst. Min. Eng. 1921 62 156) that in the Lancashire coal-fields there are a t least two types a dense and a pulverulent variety whilst, as already mentioned the Hamstead fusain with which we made our previous experiments seems to be of a particularly reactive character. We concluded from our work on banded bituminous coal (Zoc. cit. p. 634) that the three principal ingredients of Hamstead coal vitrain clarain and durain are each composed of a " reactive " group of compounds together with a relatively " inert " material, and differ from one another mainly in the proportions of these constituents contained in them.Although the fact was not empha-sised a t the time the chemical examinatiun of the Hamstead fusain showed that it also must be regarded as containing a certain pro-portion of " reactive " constituents of similar type to those in the coal which is responsible for many of its properties. Similarly it would appear from Sinnatt's work and from our own observations that many if not all fusains consist of an intimate mixture of coaly material with an " inert," or true fusain constituent. The occurrence of fusaiii in coal seams is usually attributed to rapid aerial decay of the plants at or near the water surface of the swamps in which most of the dibris was submerged and the process most often appears to have taken effect on the woody parts of the plants.There is no reason why such aerial decomposition should always have been completed before the plants became submerged and anaerobic decomposition began; indeed it is more probable that in the majority of instances the aerial decay was not complete. Fusains may therefore be expected to differ from one another not only occasionally by reason of differences in the plant remains fusainised but also frequently because the material has suffered in differing degree an in part aerobic and in part anaerobic decom-position the latter resulting in ulmification. Lomax has indeed, observed complete stems of plants that have been fusainised on the outside and consist of true coal within (Trans. Inst. Nin. Eng., 1921 62 171) but we suggest that each individual fusain fibre may often consist of an inner core of coaly material with an outer layer of true fusain with no doubt intermediate zones merging the one into the other ; and there may also be only partial fusainis-ation of some of the cell-walls composing the fibre.The " true fusain " material appears to be quite insoluble in organic solvents; it yields mainly oxides of carbon and methane on distillation with little or no liquid products and consists usually of thickened and " carbonised " cell-walls. We consider that the intimate admixture of different proportions of oxidisable coaly material with this chemically " inert " but very porous true fusain F 132 POIV'VELL AND WHITTAKER THE CHEMISTRY OF LIGNIN. material mainly determines the different degrees of oxidisability of fusains as they exist in coal the fusain in the Hamstead coal for example containing a high proportion of coaly material throughout its fibres Support is lent to this view by analyses of a number of fusains made for us by Mr.A. E. Beet. These samples of fusain had been collected with great care and before they were subjected to analysis were examined closely for fragments of adhering coal. Yet it was found that each could be separated into two distinct classes of material by sieving through a 40's mesh. The fraction which remained on the sieve was associated with much coaly material to judge by the results of analysis (more particularly distillation tests at 900") though it could not be recognised as coal; whilst that which passed through was on the same evidence, mainly what we have termed " true fusain " material.DEPARTNENT OF FUEL TECHNOLOGY, SREFFIELD UNIVERSITY. [Received October llth 1924. TIDESWELL AND WHEELER ON FUSAIN AND ITS OXIDATION. 125 XX1.-On Fusain artd its Oxidation. Studies in the Cornpo&ion of Coal. By FREDERICK VINCENT TIDESWELL and RICIFARD VERNON WHEELER. SPONTANEOUS combustion in a seam of coal in so far as it may be determined by the chemical composition of the materials composing the seam originates with the most readily oxidisable ingredient thereof. Amongst mining men there is a belief the history of which it is unnecessary to trace that a frequent cause of spon-taneous combustion is the presence in the seam of fusain; * that fire actually originates in bands of fusain when such are present, and travels preferentially along them.Data regarding the rate of oxidation of a fusain have been supplied by Winmill (Trans. Inst. Min. Eng. 1913 46 563) who concluded that of all parts of the Barnsley seam which he examined in detail the fusain was the least capable of heating spontaneously. Our own experiments when using coal from the Hamstead Thick seam (J. 1920 117 794) gave quite different results. The vitrain, clarain and durain (the brilliant bright and dull portions of the seam) absorbed oxygen a t rates graded in the direction expected from previous work on the chemical constitution of these ingredients of banded bituminous coal (J. 1919 115 619) but the fusain stood apart. At 15" and 50" its absorptive power for oxygen was several times greater than that of the rest of the coal although at 100" it was of the same order.From this it can be concluded that the fuaain weight fcr weight is the most liable to self-heat (from * Sometimes called " mother of coal," " mineral charcoal," " dant," or " sooty partings. 126 TIDESWELL AND WHEELER ON FUSAIN AND ITS OXIDATION. atmospheric temperature) of all the ingredients of the Hamstead coal. It would not however be justifiable to assume that fusains from other coals behave similarly-Winmill’s work indeed suggests that they do not-and further experiments with a number of samples of fusain and of the coals associated with them were therefore undertaken. During the progress of this work which was begun in 1919, determinations of the rates of oxidation of a number of fusains from different coal-fields have been published by Graham (Trans.Inst. Min. Eng. 1923 66 41) who has summarised his results as follows “ This ingredient of coal may vary very considerably in composition but such variaticn does not appear a t low temper-atures to affect materially the absorption of oxygen which in all cases is considerably smaller than that shown by a bituminous coal liable to spontaneous combustion. I n general from the chemical point of view fusain may be exonerated from being considered as the source of the main production of heat during the initial stages of most cases of spontaneous combustion.’, The following results may be quoted from Graham’s work the oxygen absorbed being expressed in C.C. a t N.T.P.per gram of fusain : Oxygen absorbed from air at Fusain description. 30” during 96 hours. C.C. Mossfield seam (North Staffs.) ................................. 1.93 ( a ) Soft variety ......... 1-19 f ( a ) Soft variety .................................... 1.87 l ( b ) Hard variety ................................. 1-61 Seven Foot seam (North Staffs.) { ( b ) Hard variety ......... 2.04 The absorption of oxygen by the actual coals with which the fusains were associated was not measured but Graham compared his results with some obta,ined by Winmill (ibid. 1916 51 493), under similar conditions of experiment for coals “ liable to spon-taneous combustion,’’ the values for which lay between 3.0 and 6.0 C.C. A closer scrutiny of Winmill’s figures shows however, that coal from.the same fields as those from which Graham’s fusains were obtained did not absorb oxygen any more readily an6Graham’s generalisation does not seem to us justifiable on the evidence.We have measured the absorption of oxygen of a number of coals and of the fusains actually associated with each and we cannot agree that fusains in general absorb oxygen a t slower rates than do coals liable to spontaneous combustion. Seventeen samples of fusain with samples of the adjoining coals, were collected for us by H.M. Inspectors of Mines and from these four were chosen according to their apparent purity for oxidation tests. The samples were as follows : STUDIES IN THE COMPOSITION OF COAL. 127 Lccb. No. A . From Top Mards Barnsley Seam Hucknall No.2 Pit Notts. Lab. No. B. From Robin’s Seam Cannock Old Coppice Colliery, Walsall Staffs. Lab. No. C. F’rom Deep Softs Seam Mapperley Colliery Notts. Lab. No. D. From Dysart Main Colliery Fife. Analytical data respecting these samples are given in Table I. TABLE I. A. B. C. D. --- Fusain. Coal. Fusain. Coal. Fusain. Coal. Fusain. Coal. Moisture per cent. ... 5.6 9.4 5.6 8.9 2-6 9.8 5.7 10.9 matter (Other) 15.7 39.0 17.1 39.8 13.0 40.4 12.3 35.9 than moisture) ... Ash ..................... 10.3 3.3 14.7 8.3 12.5 7.7 11.8 1.3 Carbon per cent. (on Hydrogen ............ 3-0 5-0 3.3 4.8 3.0 4.7 3.2 4.6 Oxygen ............... 7-0 12.8 6-1 15-3 6.4 16.5 10.5 15.1 Nitrogen ............... 0.4 2.2 0.4 1.5 0.7 1.9 0.4 1.3 Sulphur ............... 0.2 0.9 10.4 4.9 2-4 1.3 1.3 0.5 FIG.1. ash-free dry coal) )89*4 79.1 79.8 73.5 87.5 75.6 84.6 78.5 flME3 MOWRS. The mehhod of experiment was to circulate oxygen in a closed system through the coal or fusain packed in a tube maintained at a constant temperature.* The absorption of oxygen was calculated * Details of the apparatus used and of the method of experiment are given in J. 1920 117 795 whilst a diagram of a simi1a.r apparatus is shown in J. 1912 101 831 128 TIDESWELL AND WHEELER ON FUSAIN AND ITS OXIDATION. from the reduction of pressure. Before and after oxidation at a given temperature each sample was heated in a vacuum at 200". The results obtained are shown diagrammatically in Figs. 1 and 2 and are summarised in Tables I1 and 111. These results cannot be directly compared with those of Graham, for he used air in his experiments but Winmill has found (Trans.Inst. Bin. Eng. 1916 51 493) that the absorption of oxygen by coal is nearly proportional to the square root of its concentration, FIG 2. TABLE 11. substance. Oxygen absorbed. C.C. at N.T.P. per gram of ash-free dry Sample. A. B. C. Temp. (hours). Fusam. Coal. Fusain. Coal. Fusam. Coal. 1.3 1-0 1.4 1.2 1.8 1.5 2.3 2.4 2.5 2.6 3-2 3.8 300 3-5 4.3 4.0 5.0 5.1 6.4 196 4.3 5.8 4.8 6-6 6.2 8.1 10.5 19-2 12.2 22.4 11.0 25.0 '*'" { k! 22.0 48.0 24.0 47.0 22.8 61.0 Time & 0 D. Fusain. Coal. 0.8 1.4 1.8 3.8 2.9 6.7 3.5 8.5 7.2 23.8 17.0 59.0 7 STUDIES IN THE COXPOSITION O F COAL. 129 TAELE 111. Ratio Oxygen absorbed by fusniih Osygeil ubsorbed by coul.Temp. (hours). *A. B. C. D. Time Sample. 1.3 1.2 1.2 0.6 0.95 0.96 0-84 0.47 30" !;k 0.83 0.81 0.80 0.43 0.74 0.73 0.76 0 4 1 0.55 0.55 0.44 0.30 0.46 0.48 0.38 0.25 \ 96 100" 150 10 so that a rough comparison can be made if Graham's figures are doubled. It then appears that the fusains he used were decidedly less readily oxidised a t 30" than most of those we have investigated. We suggest that this is due in part t o the different experimental methods used (Graham for example does not appear to have allowed for the oxidation of his samples a t atmospheric temperature previous to their introduction into his apparatus) but mainly to differences in the nature of the fusains themselves. The abnormally low rate of oxidat'ion of the Barnsley fusain recorded by Winmill would appear to be due to weathering of the sample previous to his tests.It will be seen froin Tables 11 and I11 that with three of the pairs of samples examined the initial absorption of oxygen by the fusain a t 30" was greater than that by the coal but on comparing the results obtained a t 30" and loo" the oxidisabilit'y of fusain is found to increase less rapidly with temperature than bhat of the coal. The temperature coefficients of the amounts of oxygen absorbed during the early stages (up io 10 hours) are : A. B. C. D. Hamstead. Fusain ...... 1.24 1-27 1-12 1.29 1.20 Coal ......... 1.34 1.34 1.39 1.37 1-35 In each instance the coefficient is less than 2 and probably is the resultant of two coefficients.The reaction between oxygen and coal is not simple it may be expressed as follows : Coal and oxygen + coal-oxygen (adsorbed) + coal-oxygen (com-plex) + oxidised coal + oxides of carbon + water. The last phase of the reaction is incomplete at low temperatures, but can be completed by raising t'he temperature (it is nearly complete a t 200") ; a t such low temperatures absorption of oxygen is determined by the formation of the coal-oxygen complex. Com-pared with the rate of formation of this complex the first action of adsorption may be regarded as instantaneous. The rate of complex Iormaiion will therefore depend on the concentration of oxygen on the surface of the coal. The temperature coefficient of the con-VOL. CXXVII. 130 TIDESWELL AND WHEELER ON FUSAIN AND ITS OXIDATION.centration of adsorbed oxygen on the surface of the coal is less than unity and is probably about 0.80 (see Graham Trans. Inst. M i n . Eng. 1916 52 338; Tideswell and Wheeler J. 1919 115 895). Assuming that the rate a t which the coal-oxygen complex is formed is directly proportional to the concentration of the oxygen main-tained on the surface of the coal and that its temperature coefficient is 2 the expected coefficient for the series of reactioiis would be 1.6. An explanation of this is that the surface of the coal becomes clogged by the products of decom-position of the complex an effect which would be greater the higher the temperature of reaction and more noticeable with fusain than with coal because of the more open texture of its surface.A study of the gases evolved during the oxidations (see Table IV) suggests that the mode of oxidation of fusain and of coal is similar. At 30" the amount of carbon monoxide was too small to admit of exact determination but a t 100" the volumes were both larger and more regular in amount and it was found that the ratio between the carbon dioxide and carbon monoxide produced at this tem-perature lay within the same range (2.4 to 3-4) with the fusains as with the coals. TABLE IV. The observed values are less. Oxides of carbon evolved. Per cent. of oxygen absorbed. Sample. Temp. A. B. C. D. 4.0 0.8 1.6 0-8 1.5 3.2 6.6 0.7 30" Carbon dioxide { g::rh 100 Carbon dioxide (Ezp 12.8 11.7 10.8 14.5 10.6 12.1 14.5 . 17.6 4.0 4.0 4.4 6.2 6-2 100 Carbon monoxide { gzp 4*7 4.0 4-9 {El?? 2.7 2.9 2.7 3.3 Ratio 2 2-65 2.5 2.4 3.4 With none of the fusains examined was the rate of absorption of oxygen a t low temperatures so rapid as with the Hamstead fusain, which may be regarded as exceptional.Fusain does not form an important part by weight (rarely more than 5%) of the mass of a coal but it occurs frequently in patches or in layers of considerable extent generally adjacent to or embedded in bright coal and its porous nature allows of ready access of oxygen. Both its chemical properties and its physical state therefore enable it to produce the first local rise in temperature that may result in self-heating of the adjacent coal. Once the temperature has risen the continuance of the heating is no doubt mainly due to oxidation of the coal.It is not to be expected that all fusains no matter from what seams of coal they are procured should have similar chemical and physical properties any more than that all coals should be similar STUDIES IN THE COMPOSITION OF COAL. 131 We have in fact evidence from the work of Sinnatt (Trans. Inst. Min. Eng. 1921 62 156) that in the Lancashire coal-fields there are a t least two types a dense and a pulverulent variety whilst, as already mentioned the Hamstead fusain with which we made our previous experiments seems to be of a particularly reactive character. We concluded from our work on banded bituminous coal (Zoc. cit. p. 634) that the three principal ingredients of Hamstead coal vitrain clarain and durain are each composed of a " reactive " group of compounds together with a relatively " inert " material, and differ from one another mainly in the proportions of these constituents contained in them.Although the fact was not empha-sised a t the time the chemical examinatiun of the Hamstead fusain showed that it also must be regarded as containing a certain pro-portion of " reactive " constituents of similar type to those in the coal which is responsible for many of its properties. Similarly it would appear from Sinnatt's work and from our own observations that many if not all fusains consist of an intimate mixture of coaly material with an " inert," or true fusain constituent. The occurrence of fusaiii in coal seams is usually attributed to rapid aerial decay of the plants at or near the water surface of the swamps in which most of the dibris was submerged and the process most often appears to have taken effect on the woody parts of the plants.There is no reason why such aerial decomposition should always have been completed before the plants became submerged and anaerobic decomposition began; indeed it is more probable that in the majority of instances the aerial decay was not complete. Fusains may therefore be expected to differ from one another not only occasionally by reason of differences in the plant remains fusainised but also frequently because the material has suffered in differing degree an in part aerobic and in part anaerobic decom-position the latter resulting in ulmification. Lomax has indeed, observed complete stems of plants that have been fusainised on the outside and consist of true coal within (Trans.Inst. Nin. Eng., 1921 62 171) but we suggest that each individual fusain fibre may often consist of an inner core of coaly material with an outer layer of true fusain with no doubt intermediate zones merging the one into the other ; and there may also be only partial fusainis-ation of some of the cell-walls composing the fibre. The " true fusain " material appears to be quite insoluble in organic solvents; it yields mainly oxides of carbon and methane on distillation with little or no liquid products and consists usually of thickened and " carbonised " cell-walls. We consider that the intimate admixture of different proportions of oxidisable coaly material with this chemically " inert " but very porous true fusain F 132 POIV'VELL AND WHITTAKER THE CHEMISTRY OF LIGNIN. material mainly determines the different degrees of oxidisability of fusains as they exist in coal the fusain in the Hamstead coal for example containing a high proportion of coaly material throughout its fibres Support is lent to this view by analyses of a number of fusains made for us by Mr. A. E. Beet. These samples of fusain had been collected with great care and before they were subjected to analysis were examined closely for fragments of adhering coal. Yet it was found that each could be separated into two distinct classes of material by sieving through a 40's mesh. The fraction which remained on the sieve was associated with much coaly material to judge by the results of analysis (more particularly distillation tests at 900") though it could not be recognised as coal; whilst that which passed through was on the same evidence, mainly what we have termed " true fusain " material. DEPARTNENT OF FUEL TECHNOLOGY, SREFFIELD UNIVERSITY. [Received October llth 1924.