PRESIDENTIAL ADDRESS. 



375 



of the atmosphere is reduced, the limits of inflammability are narrowed until 

 they coincide when the oxygen content falls below 13'3 per cent., which means 

 .that an atmosphere containing 13'3 or less per cent, of oxygen is truly extinctive 

 for a methane flame at ordinary pressures. 



My review of this part of the subject would be incomplete without a refer- 

 ence to some interesting observations which have been made by Dr. H. F. 

 Coward and co-workers at the Manchester School of Technology upon the 

 behaviour of weak mixtures of various inflammable gases and air at or just 

 below the lower limit of inflammability in each case.' Their principal experiments 

 were carried out in a rectangular box of 30 cm. square section and 18 metres 

 length, with two opposite sides of wood, and the other two of plate glass. The 

 box was placed in an upright position, the bottom being water-sealed and the 



120 



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 7o METHANE 



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Burgess and 'Wheeler _^^_^^_^__ 

 Mallard and Le Chatelier 



Fig. 3. 



top closed, with a suitable igniting device near the bottom. They have shown 

 that caps or vortex rings of flame may be projected for some distance upwards 

 from the source of ignition, sometimes apparently for an indefinite distance, 

 without igniting the whole of the combustible mixture. In such mixtures 



' Trans. Chem. Sor. 1914, 105, p. 1859. 



