558 THE COLLIERY GUARDIAN. March 24, 1916. bank, and overwinding is prevented. As an additional safety device, a further trip switch is provided in the pit head gear, mechanically-operated by the cages, so that in the event of an overwind, either cage would automatically open this switch and apply the emergency brake. When men are being wound, the speed of the winding motor is, limited by the closing of a switch at the pit head by the banksman, this bringing into play a device which limits the angle through which the winding engineman can move his starting lever. Braking is effected by ordinary post brakes operating on machined brake paths cast on the drum cheeks (fig. 3), the brake blocks being held off the face by the piston of a compressed air cylinder, and applied by counterweights operating through a system of levers when the air pressure is released. In ordinary working, it is seldom found necessary to bring the mechanical brakes into operation, owing to the fact that the cages can be more easily and satisfactorily decked by means of counter-current braking. Compressed air for the brake engine is supplied from a separately driven air com- pressor in conjunction with a suitable reservoir. The emergency brake which automatically cuts current off the winding motor and applies the mechanical brakes on the winding drum is also arranged to come into operation in the event of failure of any of the electrical apparatus, and it can also be operated by hand through a separate lever, mounted on the driver’s platform. CARBON DIOXIDE IN EXTINGUISHING MINE FIRES.* By E. C. Evans, B.Sc., F.LC. (Continued from page 509.) Operation of the CO., Plant. The plant was set in operation on December 10, 1913, the gas being pumped in at the outbye bashing. For some distance in the main intake inside this bashing (in the fire area) very heavy falls had taken place, and in order to find a suitable place for the injection'of the CO2, some of the sandbags were removed from the top of the bashing, and the opening then made tested with a “ smoke box .” for a fissure or cavity into which the C()2 could be pumped. The “ smoke box ” was lent by Dr. W. N. Atkinson, and proved a most efficient little instrument for the detection of leakage. It consisted essentially of two wash bottles connected in series, one containing hydrochloric acid and the other ammonia, and by blowing air through these a dense white cloud of ammonia chloride was produced, by means of which a leakage in the strata surrounding the fire zone could be readily discovered. With the aid of this apparatus a fissure was soon discovered, which could easily take ihe whole of the CO2 generated by the plant, even when that was working at top speed. A pipe was laid con- necting this fissure with the CO2 plant, and the opening around it completely closed up with sandbags to prevent any leakage of air. Throughout the whole of the opera- tions the bashing and strata around it were continually tested for blackdamp, but no trace of this was discovered at the intake side. The plant was set going at 10 a.m. on December 10, 1913, and was charged every 2| hours, producing about 350 cu. ft. of CO2 per hour. The pipes were cleared of air before the plant , was placed in com- munication with the fire area, and the usual precautions were taken to obviate the possibility of any leakage of air. An analysis at the air bridge was made at 1 a.m. on December 10, by means of a portable Orsat apparatus. This analysis (made three hours after the plant had started) gave a C02 content of 12 per. cent., a result practically identical with that of December 6. At 5 p.m. on the same date, a further analysis gave the C02 as 13’5 per cent, (a slight increase) and the oxygen 5’21 per cent. Analyses were also made near the Pretoria bashing, and in the Klondyke return, but no serious effect could be observed on the ventilating current. By 8 a.m. on the following morning the carbon dioxide had increased to 17’8 per cent., while the oxygen had decreased to 3 per cent., a thoroughly satisfactory result for 24 hours’ working. Meanwhile, outbursts of blackdamp had been reported in the return near the air bridge, and also in the Klondyke return, and these outbursts persisted throughout the whole period of the operations. They were, however, purely local, and did not affect the ventilation to a serious extent, but they showed that leakage was taking place in the strata sur- rounding the fire area. Practically no difference had taken place in the temperatures at the air bridge or at the Klondyke bashing. The temperature on the outbye side of the air bridge was 126 degs. Fahr., and on the inbye side 96 degs., while the temperature at the Klondyke bashing fluctuated, with the “ breathing ” of the fire, between 136 degs. Fahr, and 142 degs. Fahr. This temperature of 140 degs., which persisted for nearly the whole period of operations at the Klondyke bashing, was the maximum temperature attained at the air bridge during the period the bashings were in place. It is signi- ficant that Fayol repeatedly obtained the same figure in his researches on the spontaneous combustion of coal. Very little difference was shown either in the tempera- tures or in the analyses during the two following days, and thence forward the CO2 increased only slightly, but never exceeded 19’2 per cent. Considerable leakage was evidently taking place, and could not be overcome. In the Klondyke return especially, the task proved of enormous difficulty. The heated strata often gave way, falls occurred repeatedly, leaving cavities of considerable size, out of which came large volumes of steam and blackdamp. To cope with these, the work of arching the roadway and facing it with concrete was commenced,. * From a paper read before the Manchester Geological and Mining Society, on March 14. t>ut this proved a most difficult task. Immediately a section of the roadway was completed, the weakened strata adjacent to it gave way, and ultimately it was found necessary to extend the arching for quite a con- siderable length. This leakage in the Klondyke return played a very important part in keeping combustion going. The evolution of blackdamp and steam caused a considerable reduction of pressure in the fire area, and this was only partly counterbalanced by the compara- tively small quantity of carbon dioxide that was con- tinually being pumped in. There was considerable excess pressure on the intake side and, in consequence, considerable leakage of air inwards took place, especially for about 30 yds. on either side of the outbye bashing, through the numerous fissures and crevices. The cumulative effect, therefore, was a short-circuiting of air through the strata from the intake to the return, and this slow current of air was sufficient to keep combustion proceeding for an indefinite period. Further, this shon- circuiting was increased by any meteorological changes or changes in ventilation that increased the difference in pressure between the intake and return. To some extent the continuous current of CO2 pumped in assisted in eoumerbalancing these factors, in three ways :— (1) By reducing the oxygen content of the air passing through the fire area; (2) assisting in maintaining the pressure in the fire area, and thus reducing the leakage; (3) by damping fluctuations of pressure in the fire area. That this process was to some extern taking place is shown by the analyses already given, but after the first 24 hours working a condition of equilibrium had been produced in which the amount of CO2 pumped in and the amount of blackdamp leaking outwards were practically equal. Samples analysed by fractional combustion gave the following results :—• Dec. 12. Dec. 13. Per cent. Per cent. Methane 0’8 0’75 Carbon dioxide 16’90 .. 17’26 Carbon monoxide 0’17 .. 0’37 Hydrogen 0’04 0’03 Ethane 9’22 ... 0’19 Oxygen 3’0 2’61 Nitrogen 78’87 .. 78’79 The reduced percentage of carbon monoxide shows that the combustion was decreasing, whilst the percen- tage of ethane present indicates that distillation had begun to predominate over combustion. Unfortunately, a serious alteration in the condition of things took place on the 13th. The work of clearing and exploring the various districts on the west side of the colliery was still proceeding, whilst one or two of the districts were full of firedamp, which could not be cleared by the modified system of ventilation then in use. An official inspection of the Ladysmith district was to take place on December 16, and in order to clear this district of gas, the doors in the main intake were opened. The air pressure against the outbye bashing, and the follow- ing series of determinations, show clearly the changes produced :— Temperature at air bridge. Time. r Outbye Inbye. Water gauge. Dec. 13. Degs. F. Degs. F. In. 7.15 a.m 126 104 0’90 8.15 „ 126 100 0’95 9.45 „ 127 100 0’90 10.45 „ 124 100 1’0 12.0 noon ... 126 9b 1’0 1.15 p.m 126 100 0’95 3.15 „ 130 100 0’95 4.30 „ 134 110 1T0 5.40 „ 137 126 IT 6.45 „ ... 139 130 1’2 8.10 ,, 139 130 1’2 9 45 ,. ... 140 133 IT 11.0 „ 139 131 1’2 12.0 139 134 1’20 Rem^rks. —The ventilation was changed at 3.40 p.m. The water gauge immediately jumped to 1’2, dropped to 1 in., and afterwards rose at 4.30 p.m. to IT in. The sudden jump in the water gauge readings was due to the sudden increase of pressure, and the subsequent fall probably to the cooling action of the air current (air temperature at surface about 36 degs. Fahr.) on the strata. This was transmitted to the fire zone by con- duction, producing condensation of some of the water vapour, and causing a reduction in pressure. It is evident from the increase of temperature on the inbye side of the air bridge that a current of air had been produced, probably from the outbye bashing to the Pretoria bashing, and this caused an increase of combus- tion, and therefore of temperature, which ultimately raised the air pressure to 1-2 in. water gauge. The analyses for the next few days are rather interesting. Analyses of Gas from Fire,Zone. rl ^3 . i—I “ to r-l1^ .