Coal inflammation limits

It is a matter of common knowledge that a room may smell quite strongly of coal gas without its being dangerous to strike a match within it. When this observation is pushed to its logical conclusion it is evident that a certain minimum quantity of the coal gas must be present for its inflammation to be self-supporting. This minimum quantity is termed the lower limit of inflammation of the combustible gas, and is influenced by two factors 2... 

Amongst the earliest experiments carried out with a view to the quantitative determination of the limits of inflammability of combustible gases were those of Davy with fire damp, wfliich is mainly methane, CH4. Owing to the importance of this gas m connection with gob fires and explosions in coal mines, several other workers have also investigated it. The value of the results, however, is restricted by the fact that firedamp, like most natural products, is subject to very considerable variation in composition.3 Even Davy recognised that it was not pure methane indeed, perfectly pure methane is not easy to prepare in quantity. The gas, as obtained from sodium acetate, may contain as much as 8 per cent, of hydrogen, as well as ethylene.4 No doubt this variation m composition is one contributory cause of the very varied results listed in the table on p. 93. 

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