Ignition of Gases by Hot Wires. 



627 



Methyl and Ethyl alcohol, fig. 7, take the same mean 

 ■current, 1*2 amperes, but the former is more difficult to 



ignite in the weaker mixtures, the curve rising from 12*0 per 

 -cent., the mixture for perfect combustion.. The base of 

 methyl alcohol is flat, resembling methane, that of ethyl 

 alcohol slopes rather more than the curves of fig. 5. 



Ethyl ether is slightly more inflammable, with sharp limits 

 and a flat base. Benzene compares with ethane in magnitude 

 of igniting current and has a practically flat base. 



There is therefore strong evidence that ignition oE most 

 gases by hot wires is within a small range of current inde- 

 pendent of the proportion of combustible gas present. This 

 had been observed by Oouriot and Meunier in the case of 

 methane, and is characteristic of certain forms of spark 

 ignition, for example of hydrogen and carbon monoxide 

 by break sparks *, methane by impulsive discharge f. 

 All cases of stepped ignition by sparks are examples <ff 

 the same phenomenon +, the difficulty of ignition changing 

 suddenly at each step, where the proportion of oxygen to 

 combustible gas passes through integral values, or as in 

 Paterson and Campbell's work at critical electrical con- 

 ditions. 



Since oxygen is the only active gas common to all 

 mixtures and since the igniting current is the same in so 



* Roy. Soc. Proc. A. vol. xc. pp. 284 285 (1914). 

 f R)y. Soc. Proc. A. vol. xcii. pp. 381 401 ^1916). 

 X Hoy. Soc. Proc. A. vol. xci. pp. 17-22 (1914). 



