[ 613 ] 



1. 



Introduction. 



9. 



2. 



Experimental Method. 





3. 



Influence of Metal and Diameter 

 of Wire. 



10. 



4. 



Methane. 



11. 



5. 



Heat of Combustion of Gas. 



12. 



6. 



Heat generated by Current. 



13. 



7. 



Convection. 



14. 



8. 



Surface Combustion. 





LX. The Ignition of Gases by Hot Wives. By W. M. 

 Thornton, D.Sc, D.Eng., Professor of Electrical En- 

 gineering in Armstrong College, Neiccastle-upon-Tyne* . 



Temperature of Wires at which 

 Ignition begins. 



Nature and Proportion of Com- 

 bustible Gas in Mixtures. 



Gas Pressure. 



Electric and Magnetic Fields. 



Application of Results. 



Summary. 



1. Introduction. 



A RED-HOT metal in contact with a gas loses energy as 

 heat and by the discharge of ions or electrons. Radia- 

 tion has little if any effect on gaseous combination except in 

 well-known mixtures that are sensitive to light. 



When the source is a hot wire conduction and convection 

 effects are inseparable; the effect of ionic discharge has 

 not hitherto been examined. Paterson and Campbell have 

 recently given evidence f in support of the view that ioniza- 

 tion is the chief agent in ignition by spark discharge, and 

 have confirmed the existence of stepped ignition, essentially 

 a selective phenomenon. All such singular time effects are 

 necessarily absent from hot-wire ignition. By their elimina- 

 tion the problem of ignition is simplified to the question of 

 how far gaseous combination can be started by a hot wire 

 at temperatures below those at which gases combine when 

 heated by external action, such as passage through hot tubes 

 or sudden compression, and whether it is a purely thermal 

 effect. 



Previous work on hot-wire ignition, done to determine 

 safe limits to the use of electricity in coal mining, deals only 

 with methane. Wiillner and Lehmann's investigation for 

 the Prussian Fire Damp Commission of 1881 was the first 

 systematic work on the subject +; § 57 deals with ignition 



* Communicated by the Author. 



f " Some Characteristics of the Spark Discharge, and its Effect in 

 Igniting' Explosive Mixtures," by Clifford C. Paterson, M.I.C.E., 

 M.I.E.E., and Norman Campbell, Sc.D. Proo. Physical Soc. London, 

 vol. xxxi. Part IV. June loth, 1919, pp. 168-228. 



X Report of the Prussian Fire-Damp Commission (1884}. Trans, for 

 the Institution of Mining Engineers, by Prof. P. 1'. Bedson. 



Phil. Mao. S. 6. Vol. 38. No. 227. Nov. 1919. 2 U 



