MINING 389 



a platinum wire increases in the presence of methane. (5) The safety lamp. (6) Chemi- 

 cal analysis. The feeling at present is that the only reliable indicators are the safety 

 lamp for routine observations, and chemical analysis for the more elaborate calcu- 

 lations. Numerous ingenious appliances however have been devised of late to provide 

 an efficient substitute. 



The apparatus invented by Philip and Steele (Journ. Society of Chemical Industry, 

 Vol. 30, p. 867, 1911) depends on the sensitiveness of a relay containing iron, and as the 

 hysteresis lag in the iron tends to reduce the sensitiveness of the instrument, this lag is re- 

 moved or reduced either by mechanically vibrating the relay, or by passing intermittent 

 pulsating currents through it, superimposed on its normal currents. Somewhat similar 

 apparatus have been devised in the Holmes- Alderson gas-detecting apparatus and the 

 Holmes-Ralph portable electric lamp (G. J. Ralph, Trans. Inst. Min. Eng., Vol. 40, p. 282, 

 and vol. 42, p. 201). In actual practice however it has been found that such apparatus, 

 which depend upon the conductivity of platinum, have given less satisfactory results in a 

 normal firedamp mixture than in coal gas or "petroleum vapour. The "interferometer," 

 devised by Professor Haber of Karlsruhe, and Dr Lowe of the firm of Carl Zeiss, of Jena, 

 depends upon the refraction of light in firedamp and other media. The apparatus is in 

 daily use at Gelsenkirchen for the examination of gases passing out of .the upcast. 



Several devices have been introduced with the view of increasing the sensitiveness of the 

 ordinary safety lamp. Of these mention may be made of the Cunynghame and Cadman 

 device by which the cap on a safety lamp is converted from an indistinct blue to a distinct 

 orange yellow by introducing a little asbestos paper soaked in carbonate of soda into the 

 flame (Trans. Inst. Min. Eng., vol. 39, p. 13). Briggs has also proposed the use of a copper 

 loop (Trans. Inst. Min. Eng., vol. 43, p. 64). 



Turning now to the more accurate determinations obtained from chemical analysis, 

 it may be observed that J. S. Haldane has recently designed an apparatus for estimating 

 percentages of firedamp, in which the potash solution is dispensed with, the percentage 

 of firedamp being given simply by the contraction on combustion (Colliery Guardian, 

 Sept. 27, 1912). In the United States a modified Orsat apparatus has been employed 

 by Burrell and Seibert (U.S. Bureau of Mines, Technical Paper 13, 1911) for use in con- 

 nection with mine fires, with which, it is stated, COz, CO and CHi can be determined 

 within about 0.2 per cent. 



New views have quite recently been advanced by physiologists as to the influence of 

 oxygen and CCk upon human life, and it has been urged by Leonard Hill and Harger 

 amongst others that the existing standards might be varied without dangerously affect- 

 ing health, even when due consideration has been given to alterations in barometric 

 pressure. The object is to produce an atmosphere in which the liability to firedamp 

 explosions and fires would be reduced, owing to the incompatibility of the media. Ob- 

 jections raised, apart from the suspected dangers to health, are, the effect upon lighting, 

 and the difficulty of obtaining CO2 free from dangerous quantities of CO, if introduced 

 in the form of flue gas as proposed. Harger claims to have obviated the latter difficulty 

 by the use of small gas engines. The former difficulty may be overcome in specific cases 

 by the use of acetylene lamps or portable electric lamps. The value of inert gas as a 

 means of combatting fires has been recognised, and it was used in the recovery operations 

 following the Cadeby explosion (1912), which was due to the existence of gob fires. In 

 the United States the influence of carbon dioxide on the explosibility of mine gases has 

 been investigated, primarily for the purpose of determining the practicability of intro- 

 ducing carbon dioxide into mine workings to extinguish fires and prevent explosions. 

 The results have led to the following conclusions, (i) Carbon dioxide, owing to its 

 higher specific heat, is more effective than nitrogen in preventing explosions.- (2) The 

 addition of 25 parts (by volume) of CO2 to 75 parts of the most explosive mixture of 

 methane and air renders the mixture nonrexplosive. (3) When carbon monoxide is 

 introduced in place of oxygen, 7 per cent of CO2 is sufficient to prevent explosion. 



The rapidity with which coal absorbs oxygen has been shown by Porter and Ovitz 

 (U.S. Bureau of Mines, Technical Paper 2, 1911). Ten kilograms (22 lbs.)-of coal from 

 Connellsville absorbed during first day after mining nearly one-half the oxygen in 10 

 litres of air. Slightly more than one-tenth as much carbon dioxide was produced as 

 would have been produced had all the oxygen absorbed combined with carbon to form 



