352 Prof. W. M. Thornton on Ignition of Gases at 



On the other hand, the ratio may be reduced by lowering 

 the proportion of hydrogen to oxygen as follows : — 



Table II. 



Per cent. Collision 



Mixture. in Air. frequency. 



+ H 2 29-2 1-0 



2 + H 2 17-1 0-58 



3 -fHJ 121 0-41 



4 +H 2 9-35 0-32 



5 4-H 2 . 7 12 0-26 



G + H 2 644 022 



Certain of the numbers in the third column of Table I. are 

 close to those in Table IT., so that in the event of these coin- 

 ciding with the critical stages in ignition it would be difficult 

 to discriminate between them. The curve rises suddenly at 

 TO, 0'6, 0"48, falls through a mean value at about 0*4 and 

 has a minimum at 0*38. The evidence is if anything in 

 favour of Table I., that is, of ignition rising suddenly in 

 difficulty with each added molecule of hydrogen. This 

 is in general agreement with the facts of ignition by con- 

 denser discharge sparks, which passes through critical rising 

 steps when the proportions of hydrogen in air are 29'2, 45*2, 

 55*2, and 70 per cent.* 



And in all kinds of ignition by direct sparks previously 

 examined excess of oxygen is favourable to electrical ignition, 

 though it is not to final combustion, while excess of hydrogen 

 retards it. It is therefore improbable in the above argument 

 that the sudden jumps of difficulty of ignition are due to 

 excess of oxygen, though they maybe to excess of hydrogen. 



7. Methane. 



The curve of fig. 2 has similar points of interest. There 

 are steps at 1*0, 8, 0'6, and 0'45 atmosphere. The mixture 

 for perfect combustion taking air as 4*85 times the con- 

 tained oxygen is 9'35 per cent. Proceeding as in hydrogen 

 we have : — 



Table III. 



Per cent. Observed 



Mixture. in Air. Katios. steps at. 



CH 4 +0 5 764 122 1-25 



CH 4 + 4 935 10 1-0 



CH 4 +0 3 12-0 0-78 0-8 



CH 4 +0 2 171 0-54 0-6 



2CH 4 +0., 216 043 045 



* " The Ignition of Gases by Condenser Discharge Sparks," Proc. Roy. 

 Soc. A, vol. xci. p. 17 (1914). 



