434 THE COLLIERY GUARDIAN. February 28, 1913. performed in which a small f in. spark from an induc- tion coil was used as the source of ignition. A mixture having the following composition exploded :— Per cent. Carbon dioxide.............. 3 92 Oxygen .................... 16 25 Methane....................... 9’43 Nitrogen .................... 70 37 In using the flame as a source of ignition, it was brought close to a small aperture in the flask and a glass plate covering same quickly removed. It was found that unleakage of air by this slight exposure of the gas mixture was not appreciable. Under the same conditions a mixture having the following composition, in which the oxygen was slightly diminished, did not inflame at all:— Per cent. Carbon dioxide............. 3*99 Oxygen .................... 15’90 Methane................... 9 25 Nitrogen .................. 7086 It was observed in conducting these explosibility -experiments that both the electric flash and flame produced inflammation under more severe conditions than the small spark, also a flame when applied from below will produce inflammation, under more severe conditions, than when applied from above. These are only a few of many experiments which have been made on the explosibility of gaseous mixtures at the Bureau’s laboratory. Some experiments have been made in which black powder has been fired into mixtures of gas and air, in a gallery having a capacity of 600 cubic feet. Much interest and criticism has followed Dr. John Harger’s (England) proposal that the oxygen be decreased and carbon dioxide be increased in mines to prevent explosions. Briefly, Dr. Harger’s proposition is this:—A small reduction in the oxygen percentage, and a small increase in the carbon dioxide percentage in mine air, will suffice to produce an atmosphere incapable' of supporting combustion, and, consequently, an atmo- sphere in which explosions and gob fires cannot occur. For average mines it is suggested to start the experi- mental work on a large scale—that the oxygen should be reduced to 20 per cent, {i.e., 1 per cent, below normal), and | per cent. CO2 added to it. Where the conditions were more dangerous the oxygen should be further reduced, say, to 19 per cent., and the CO2 increased to i per cent. Time will not be devoted now to a discussion of the many points involved in Dr. Harger’s suggestion, unless it is the wish of the institute. Experiments which have been performed by the Bureau, some of which are here presented, indicate that the oxygen percentage will have to be reduced much below the figures mentioned by Dr. Harger to prevent all explosions. Of course, as the •oxygen percentage is decreased the mixture explodes less violently and less completely. As regards carbon dioxide, so much would have to be added to prevent firedamp explosions, that it appears that its use for that purpose would be entirely precluded. Mine-gas Mixtures Containing Explosive and other Proportions of Methane. Below are given some analyses of mine-gas samples, some of which contain explosive proportions of methane. 'The accompanying carbon dioxide and oxygen content are of interest in connection with foregoing experiments. The samples were collected in mines wherein ventilation had been interrupted for some time. Explosions had occurred in these mines. Sample number. co2 o2 CH. 1 ... 8’28 ... 10’50 .. .. 4’49 ... 76 73 2 ... 0’48 ... 17 49 .. .. 920 ... 72 83 3 ... 581 ... 13’95 .. .. 5'07 ... 7517 4 ... 1’75 ... 17 63 ., .. 7'60 ... 73’02 5 ... 034 ... 19’46 .. .. 5-79 ... 74-41 6 ... 0’35 ... 18’81 .. .. 7’25 ... 73'59 7 ... 200 ... 15’64 .. .. 7’37 ... 74-99 Samples 2, 4, 5 and 6 are explosive. There could be but very slight inflammation in mixtures represented by samples 1 and 3. Knowledge of the explosibility of mixtures as they occur in mines has been especially useful to the Bureau in that such atmospheres are frequently encountered in exploration work following mine explosions and fires. Extinction of Acetylene Flame. The Bureau has already called attention to the tenacity to existence of the acetylene flame, in that it will exist in atmospheres in which the ordinary wick-fed flame is extinguished. It was found that a residual atmosphere in which an acetylene flame had been extinguished contained 11’70 per cent, oxygen and 6’30 per cent, carbon dioxide. More recent experiments have confirmed this finding. It was also found that when about one-half of the carbon dioxide was removed as it was formed, the acetylene flame burned in a slightly greater oxygen deficiency. For these experiments, the flame was placed in a gastight cabinet having a capacity of 25 cubic feet. The residual atmospere after the flame had been extinguished had the following com- position :— Sample from Sample from middle bottom of chamber. of chamber. CO2 .............. 3 22 ..... 3 17 Oo ............. 10’99 ..... 1112 The Bureau has observed that in coalmines where the oxygen has decreased to 11 per cent., about 6 per cent- of carbon dioxide on the average will be present. An objection has been raised to the use of the acetylene flame in that it becomes extinguished only when there may be grave danger to men because of the presence of much blackdamp. The acetylene flame, as is the case with other flames, burns less brightly as the proportion of oxygen in mine air diminishes. It was observed at the Bureau’s laboratory that when the oxygen content of air decreased to about 16 or 16’5 per cent., the flame resembled the ordinary wick-fed flame when the latter burns in pure air—i.e., air containing 21 per cent, oxygen. This indication can be used as a guide against men venturing into blackdamp workings. containing less oxygen than this proportion. Effect of Carbon Dioxide on the Extinguishment of the Flames of Miners’ Lamps. The ordinary miner’s lamp is extinguished when the oxygen falls to about 16’5 or 17 per cent. This extinguishment is almost entirely due to the oxygen deficiency, and not to the carbon dioxide, since this constituent is rarely ever present in sufficient quantity when the oxygen in mine air drops to 16 or 17 per cent, to exert any appreciable effect. When a lighted candle was placed in a bell jar filled with ordinary air, it went out when the oxygen percentage fell to 16'34 per cent. The carbon dioxide produced by the burning amounted to 2’95 per cent. When 3’22 per cent, of carbon dioxide was originally in the air, the atmosphere after the extinguishment of the flame contained 16’68 percent. When the atmosphere originally contained 13’52 per cent, carbon dioxide, the flame went out when the atmosphere contained 17’39 per cent, oxygen. These analyses are tabulated below:— Composition of atmosphere at beginning of experiment. ---------------------- O2 21-00 2113 20’67 Composition of atmosphere in which flame went out. CO2 0’04 3’22 13’52 CO2 2 95 6’51 1600 O2 16 34 16’68 17’39 It will be observed that the initial presence of a large amount of carbon dioxide had little effect on the flame extinguishment. In all of these laboratory experi- ments the flame probably existed a trifle longer than would be the case in actual mining practice, because in mines a slight gust of air or sharp thrust of a lamp would puff out a diminishing flame. Effect of Vitiated Air on the Luminosity of Miners’ Lamps. Dr. J. S. Haldane* recently made an important contribution to mining literature when he determined the effect on the light of a safety lamp when burned in atmospheres deficient in oxygen. Mine air is always deficient in oxygen to some extent as compared with outside air. This deficiency may amount to from OTO or 0’20 per cent, to 2 or more per cent, under ordinary working conditions. A table which Dr. J. S. Haldane prepared is of exceptional interest and is here presented:— Observed Percentage Diminution of Light with Observed Percentage Diminution of Oxygen. Light given. Oxygen percentage. Light percentage diminished. Oxygen percentage diminished. 100 .... .. 20’93 0 ... .... 0’00 90 .... .. 20’66 . 10 ... .... 027 77 .... .. 20 34 . 23 ... .... 0’59 66 .... .. 19 88 . 34 ... .... 1’05 41 .... .. 19 34 . 59 ... .... 1'89 27 .... .. 18’92 . 73 ... .... 201 11 .... .. 18’28 . 89 ... .... 265 0 .... .. 18’01 .. 100 ... .... 2‘92 Dr. Haldane observed, roughly speaking, that every diminution of 0’1 per cent, in the oxygen caused a diminution of 3’5 per cent, of the value of the light in the pure air. High Velocity of Air Currents in Mines. As against many good reasons put forth for keeping miners plentifully supplied with fresh air, there has arisen the protest that with high velocities of air currents in mines and high oxygen content of mine air, explosions have increased in number. Low oxygen content as a preventive of explosions has been discussed in part in this paper; the question of high velocities is more completely wrapped up with the question of dust explosions, and will not be discussed here. * Colliery Guardian, October 25, 1912. Afterdamp. Two samples of afterdamp atmospheres are here presented. They are of interest as showing the large amount of carbon monoxide present shortly after an explosion. Sample No. 1 was collected 30 minutes after an explosion had occurred at the experimental mine of the Bureau at Bruceton, Pa. It was taken in the main entry at the junction with the first right butt entry after ventilation had been restored in the main entry. Sample No. 2 was collected at the face of the first right butt entry 100 ft. from where Sample No. 1 had been collected. Ventilation had not been restored in this entry. Sample No. 1. Sample No. 2. Carbon dioxide 0 26 .. .... 1’54 Oxygen 20’26 .. .... 17-79 Carbon monoxide .... 016 .. .... 189 Methane 012 .. .... 065 Nitrogen 7920 .... 7813 These analyses are instructive as showing that very dangerous atmospheres may exist after an explosion in a mine in close proximity to atmospheres wherein men would not soon feel distress. The Bureau found that in 0 16 per cent, carbon monoxide a mouse shows only slight signs of weakness at the end of one hour’s time. In the same atmosphere a bird showed signs of distress in three minutes’ time and fell from its perch in 18 minutes. In exploring a mine containing afterdamp a person could, by disregarding the warning of a sensitive animal like a canary, travel in a very short time from an atmosphere that would not distress him rapidly into one where collapse would quickly follow. Automatic Gas Sampler. The Bureau has lately developed an automatic mine gas sampler to a stage of completion where it is believed samples of after gases can be trapped at the time an explosive wave goes by and at prearranged intervals thereafter in order that the chemistry of the explosions in the experimental mine may be better studied. An analysis of a sample collected at the Altofts experimental station (England) one-twentieth of a second after the explosion had passed, contained the following constituents— Percentage. Carbon dioxide........... 11’25 Oxygen ................... 1’15 Carbon monoxide............ 815 Hydrogen.................... 2 75 Methane..................... 2 95 Nitrogen .................. 73 75 The high percentage of carbon monoxide will be noticed. The British report calls attention to the presence of oxygen as showing the inrush of air even so short a time after the explosion wave had passed. They state that at the instant of passage of the flame the oxygen should have been entirely consumed. The gallery at Altofts is above ground, however, and inrush of pure air would be quicker than in a mine. Distribution of Afterdamp. It is well known to mining men that after an explosion parts of a mine may be quite unaffected by the explo- sion, and that in some places the products of the explosion (whitedamp, &c.) may not penetrate. Men have lived for days in some mines after explosions until rescued. On the other hand, men rushing into the track of the explosion in the dash for safety have frequently been overcome. As is generally recognised, the heaviest toll of life is almost invariably due to the whitedamp and not to explosive violence. Use of Birds for Continued’Exploration Work. The Bureau has made experiments, having to do with the use of canaries for continued exploration work, having in mind the fact that the same animal might be used and overcome several times in the same day. It was found that even after repeated exposures to carbon monoxide, these animals, upon subsequent exposures, show distress, collapse and revive in about the same period of time as on the first exposure. Consequently, these animals can be used again and again for all practical purposes, with the knowledge that they will not be less efficient for exploration work even after repeated exposures. No parallel can be drawn regarding the effects on men of carbon monoxide from these experiments. Men have been months recovering from severe cases of slow poisoning, and the after effects have been very formidable. To show how differently carbon monoxide affects men and animals, the following experi- ments performed by the Bureau are here tabulated:— Quantity of CO Used = 0 25 Per Cent. Effects on Canaries. Time exposed. Distress. Collapse. Recovery. 3 minutes ... 2 minutes ... 3 minutes ... 7 minutes Effects on Mice. Time exposed. Distress. Collapse. Recovery. 12 minutes ... 6 minutes ... 12 minutes ... 25 minutes