1118 ______________________________________________________________________________________________________________ THE COLLIERY GUARDIAN. May 30, 1913. the question, but really there is an opening in many seams for conveyors. Mr. T. Yanagita, a Japanese visitor, said the author had referred in his paper to an example of treatment of a roof over a machine-worked seam in Japan, in which the face was formed in crescent shape. The chief objection to coal conveyors was roof trouble. If the roof fell, the conveyor face was generally demolished- If a conveyor was so designed as to turn curves, there would not be much apprehension as to its adoption. After an accident, a little road should be made round the fall in the goaf to put the conveyor in, and the con- veyor set to work round the fall. Two headings should be immediately started from the ends of the fall; and then after a few days’ working they would get a new straight face. Then the conveyor would be transferred to this face, working in a straight line. Referring to the dis- advantages wh’ch he said were peculiar to the full- length conveyor, the author cited the following—among others—where the coal-cutter holes in dirt, there was difficulty in thin seams of casting holings over the con- veyor into the goaf; and (2) there was difficulty, in seams containing bands, of casting dirt over, the con- veyor to the goaf, especially in thin seams, and where the dirt bands were thick and strong. This dis- advantage could not be laid at the door of a conveyor of the Allardyce type, where the coal moved towards the discharge end along the floor level and the returning chain moved close to the roof. With regard to jigger conveyors, a drawback not mentioned by Mr. Mavor was that if this type was put down in a practically flat seam, a continuous discharge could hardly be expected, and the necessarily varying celerity of travel by various sizes of coal was calculated to lead to obstructions and consequent overflows from the conveyor. Mr. Mavor mentioned that “ in conveyors of the traveller type the discharge is intermittent and periodic, and the road must be at or near the centre of the face.” But if one side of the face from the road was long enough to dis- charge the whole load of coal plus sufficient clearance and space for end pulley, &c., the road might be situated at any place. Coming generally to the mode of opera- tion, the diagrams and tables furnished by the author were undoubtedly valuable references, but the success of coal-conveying operations was the resultant of many factors, not the least important of which was good management. The proper control of wagon supplies was essential to the success of coal conveying, as, indeed, it might be deemed a necessity of mining when the coal was machine cut or hand-wrought. The author had referred to the filling of trams at the face in seams of sufficient height. The idea of using tubs along the face instead of a conveyor was a good one ; but the width of the tub must be in accordance with the depth of under- cut, so that the tubs could easily pass through, with ample clearance, the lines of the sets of props. More- over, the seams should be practically flat, otherwise the runaway tubs would knock down the props. Conveyors are all designed to work in a straight face, with the result that the condition of roof was a prime factor governing their adoption. It should not be beyond the power of inventors to design conveyors so as to turn curves, and thus leave greater support for the roof. Improvements had been made in conveyors in details of working parts, but none in the direction of over- coming the roof difficulty. If the two wheels placed diagonally in the bogie of a traveller conveyor were designed to turn on the axles, he conceived that the conveyor might be got to turn curves easily. The discussion was adjourned. The Yorkshire Boiler. Consideration was next given to the paper of Mr. W. H Casmey describing the features of the Yorkshire boiler. The author replied to the criticisms of Mr. T. Sugden at a previous meeting traversing claims put forward of the alleged superiority of the Yorkshire over the Lancashire boiler. Mr. Casmey quoted further tests and cited the experience of users of the Yorkshire boiler, and once more contended that a 24 ft. Yorkshire boiler will evaporate 15 per cent, more water per hour than a 30 ft. Lancashire, and for equal evaporation will burn about 10 per cent, less fuel, which meant an approximate saving of £50 per boiler per year. Mr. T. Sugden said there were two essential features lacking in the Yorkshire boiler—namely, there was less grate surface and less heating surface than in the Lanca- shire. He complained that Mr. Casmey’s quoted tests were not tests of the Lancashire an$ the Yorkshire boiler of the same size and working under precisely the same conditions in every respect. The discussion was closed, and the President moved a vote of thanks to Mr. Casmey. Discussion on the paper by Mr. S. Haslam on “ Recording Instruments ” was deferred. (THE CADEBY MAIM COLLIERY EXPLOSION. Home Office Report. (Concluded from page 1060.) Experiments with the Cadeby Dust. Reporting on his analysis of samples of dust from the south district of the Cadeby Colliery, Dr. R. V. Wheeler says four samples were received on July 31, 1912, the legends on the envelopes containing the samples (which were in tin boxes) being as follow:—No. 1: “ From 164’s X gate, South Drift below fault, where Mr. Herbert Smith took sample.” No. 2: “ Taken in South Plane opposite 33’s level, from floor.” No. 3: “ Taken in South Plane off girder at roof, 100 yards above 33’s level.” No. 4 : “ Taken from side of road 50 yards down plane, apparently plenty of coaldust in it.” Sample No. 1 contained much straw and large pieces of dirt and coal of size varying up to | in. square. Sample No. 2 contained but little straw, and, though coarse, did not contain so many large pieces of'dirt and coal as No. 1. Sample No. 3 was very fine. It was dark grey in colour, and apparently contained much dirt dust. Sample No. 4 was very fine and of a dull black colour. Each sample was sieved through a 100-mesh sieve and the propor- tion passing through determined, with the following results:— Sample Sample Sample Sample No. 1. No. 2. No. 3. No. 4. Percentage passing through 100-mesh sieve ....... 15*6 ... 27*0 ... 90 0 ... 95*0 A proximate analysis was then made of the sieved dusts—i.e., that portion of each sample that passed through a-100-mesh sieve:— Sample Sample Sample Sample No. 1. No. 2. No. 3. No. 4. Moisture ................ 3'25 ... 2 77 ... 2 51 ... 3*05 Volatile matter .... 26 04 ... 25 37 ... 23 75 ... 25 60 Fixed carbon ...... 42 61 ... 40 61 ... 3128 ... 49*13 Ash........................ 28*10 ... 31’25 ... 42’46 ... 22*22 It is to be noted that in no case does the sample contain such a proportion of incombustible dust as would render it incapable of propagating an explosion or even of originating an explosion — granted a sufficiently violent source of ignition. The Altofts experiments showed that a mixture of coaldust and stonedust containing 40 per cent, of the latter could be ignited by a blown-out shot of 24 oz. of blasting powder* and would propagate flame; whilst the Lievin experi- ments have shown that a mixture of coaldust and shale- dust containing 75 per cent, of the latter will propagate the flame arising from the ignition of 250 ft. (in length) of pure coaldust. Of the four samples, No. 4 is obviously the most dangerous, being very fine and fairly pure. No. 3, on the score of fineness, comes next in order of dangerousness. The large percentage of coarse lumps present in Nos. 1 and 2 might render them inert and incapable of propagating any explosions, except those initiated by very violent means. An experiment was carried out as to the liability of Barnsley Thick Seam, Cadeby Main coal to spontaneous combustion. The principle upon which this experiment was based was gradually to heat a speciment of the coal in dry air and to raise the surrounding temperature. This, of course, would promote spontaneous combustion in those materials which were liable to it. By observing the temperature of the coal, and observing how much it exceeds the surrounding temperature, an estimate may be formed of its self-heating capacity. The method of experimenting is as follows :—Twenty grammes of the sieved coaldust (through a 150 and on a 240 mesh sieve) is loosely packed in a glass tube. The top of the tube is closed by a rubber stopper carrying a thermometer, the bulb of which reaches to the middle of the column of coaldust. The bottom of the tube is drawn out to a smaller diameter and passes, through a rubber stopper, into a small glass vessel with a side tube, which makes connection (through a bubble- counter) with an exhaust pump. The tube containing the dust is passed vertically through an electrically- heated sand bath, and a current of dry air drawn at a given speed through the dust, the entrance being at the top. Simultaneous readings are taken (1) of the “ external ” temperature—that is to say, of the sand bath, which is gradually raised in temperature ; and (2) of the “ internal ” temperature : that is to say, of the coaldust. At the beginning of the experiment the external tempera- ture is higher than the internal, owing to the time taken for the heat to pass through the glass to the thermometer embedded in the coaldust. The point at which the difference between the external and internal tempera- tures begins to grow less marks the beginning of self-heating of the coaldust (due to oxidation by the air current). The record obtained with the Cadeby coal is given below. The dust used was obtained from a collector at the screens at the Denaby and Cadeby Main Collieries:— Time. 11.0 a.m. . 11.15 a.m.. External Temperature. Degs C. 108 Internal Temperature. Degs. C. 69 Difference. Degs. C. .. - 39 120 .... 78 .. - 42 11.20 am,- 126 83 .. - 43 11.25 a m.. 11.30 a.m.. 11.35 a.m.. 11 40 a m.. 11.45 a.m.. 11.50 a m.. 11.55 a.m.. 12 noon.... 12.1 p.m. . 12.2 p.m. . 12.3 p.m. . 12.4 pm. . 132 89 .. - 43 138 95 .. - 43 145 .... 101 .. — 44 151 .... 107 .. - 44 157 .... 112 .. - 45 162 .... 117 .. - 45 172 .... 127 .. - 45 195 .... 203 .. + 8 200 .... 256 .. + 56 203 .... 307 .. +104 206 .... 348 .. +142 208 .... 370 .. +162 One coal differs from another in several respects when treated in this way. The chief points of difference are . (1) The temperature at which self-heating begins. (2.) The rapidity with which the degree of self-heating increases. (3.) The degree of temperature attained. On all these counts the coal from the Cadeby mine has shown itself in the laboratory to be of a character very liable to spontaneous combustion—as shown by the self-heating that takes place in a stream of air—of any tested. The figures given above are, of course, only comparative. They do not indicate the lowest tempera- ture at which self-heating can take place. Analyses of four samples of dust collected by Mr. T H. Mottram, H.M. inspector of mines, at Cadeby Colliery, Yorkshire, on September 21, 1912, are also given as follows:—A, from South Plane, just below 33’s ; B, from South Plane, 14 yards top side of 14’s level ; C, from upper side of 14’s level, at foot of 19’s crossgate; D, from 19’s crossgate below 19 landing. Fineness. Sample. A. B. C. A D. Per Per Per Per cent. cent. cent. cent. Percentage passing through a 100-mesh sieve 28 75... . 29 60... 69*00... 1052 Proximate Analysis. Moisture 172... 2’85... 4 53... 1*79 Volatile matter 24 73... . 2316... 14’95... 8’61 Fixed carbon 3815... , 27’48... 32 21... 8’79 Ash 35 40... . 46 51... 48’31... 80 81 Mr. Chambers’ Evidence with Reference to Spontaneous Combustion and its Treatment. Mr. W. H. Chambers said he had had 30 years’ experience of underground fires at Denaby and Cadeby, during which period he had dealt with 56 cases, some at the coal face and others in the goaf. A very large proportion of the face fires had occurred in the neigh- bourhood of faults, a fact which he accounted for by the presence in the fissures of pulverised coal, which offers a considerable area for the absorption of oxygen from air which may percolate through the fissures. There is often sufficient air to start such chemical action, but insufficient to carry off the resultant heat, and hence the fine coal gets hotter and hotter until it reaches the point at which combustion commences. A number of fires, however, had occurred in the goaf, or, rather, they generally originated in the fissures above the goaf, the oxygen necessary for combustion finding its way along these fissures. He said there was a “ rotten ” roof, and that was the reason why they could not work the whole of the seam. They had to leave the top coal to support the roof. It had been found that fires were prolific if the workings were allowed to stand even for a few days, also when progress was slow, as when impeded by faults, and therefore he found it necessary to keep the face continually advancing irrespective of the state of the coal market. Fires had been known in the solid coal when the face had been left standing for a short time. Mr. Chambers defended his present system of 7 yard wastes with 7 ft. 6 in. gate packs and intermediate packs principally on the ground that the latter were necessary to keep the face open. Regarding the hydraulic method of stowing the waste, he said he had doubts as to its alleged efficiency in preventing the formation of fissures, and he foresaw insuperable difficulty in the way of its adoption at Cadeby Colliery, owing to the fact that water was necessary to this system. He had experi- mented with water as a means of laying the dust upon roadways, but he had found that even the small quantity required for this purpose had such an injurious effect upon the strata as to close the roads. Since the explosion at Cadeby Colliery he had, how- ever, devised a method of dealing with gob fires by excluding the oxygen altogether, which had proved successful in the recovery of the south district after the recent explosion. If a sign of heating in the gob is detected by an analysis of air or otherwise, the ordinary ventilation of the pit is excluded from that particular area, and there is forced into it a gas deficient or entirely wanting in oxygen, so that, instead of the fire