Influence of Oxygen

In a series of experiments carried out with a Bunte burette (19 mm. in diameter and 115 to 120 c.c. capacity), top ignition being adopted, Terres has found that whilst the lower limit of a combustible gas in air is but slightly different from that in oxygen, the upper limit is considerably higher in pure oxygen.

Lower Limit of methane

Parker, using a glass globe with central ignition similar to that figured, determined the lower limits of inflammation of methane with mixtures of oxygen and nitrogen, the oxygen ranging from 100 to 13.25 per cent, by volume. His results are shown diagrammatically in fig.

"The lower limit of methane reaches a minimum of 5.70 in a mixture containing 25 per cent, of oxygen and 75 per cent, of nitrogen. Increase in the oxygen content causes a gradual rise in the lower limit, whilst decrease effects a rapid rise. This latter rise may be explained by the decreased rate of combustion and the consequent greater loss of heat to the surroundings." For air the lower limit is found as 5.77 per cent, methane.

The fact that the lower limit of methane is greater in the case of pure oxygen than with air is probably connected with the fact that the specific heat of oxygen is higher than that of air.