614 Prof. W. M. Thornton on the 



of firedamp by heated wires. The researches of Hauser * in 

 Spain, and and of Couriot and Meunier f in France, deal 

 with the possibility. of igniting methane by hot wires, 

 platinum in particular. Mallard and Le Ohatelier examined 

 ignition of firedamp by the heated gauze o£ safety-lamps. 

 More recently the properties of hot tungsten filaments liave 

 been investigated at the Bureau of Mines in Washington, by 

 breaking lamps in an inflammable mixture. 



The influence of hot surfaces on combustion is fully dis- 

 cussed in § VI. of Prof. W. A. Bone's Report on Gaseous 

 Combustion to the Sheffield meeting of the British 

 Association (1910). The present paper deals with the 

 special problem of ignition by hot wires such as may occur 

 in coal mines, battery rooms of submarines, or in manu- 

 facturing processes where combustible gas is set free, but, 

 the bearing of the results on the more general question of 

 surface combustion lias been considered throuohout. 



2. Experimental Metliod. 



In work of this kind it is desirable to use as large a 

 volume as possible to ensure that the explosion wave is fully 

 established. On the other hand, convection currents are so 

 marked at high temperatures that the use of too large a 

 vessel is equivalent to enclosing the wire in a tube and 

 passing a steady current of gas over it. It is known that a 

 current of gas is favourable to ignition by hot platinum wires 

 in tubes. 



When many trials are to be made in quick succession it is 

 found convenient to use a cylindrical glass vessel of 50 cubic 

 centimetres volume, having short opposite branches. Through 

 a stopper in one of these pass two copper rods 2 mm. diameter, 

 to the ends of which the wires to be tested are soldered, eiiher 

 straight as at b, fig. 1, or forming an arch as at a. Through 

 the opposite branch plates or tubes were led by which any 

 desired electrostatic field could be maintained on the wire. 

 When these are fixed in position the vessel is exhausted, 

 a current from a low voltage battery passed for a fev^ seconds 

 to drive off organic contamination, and the inflammable 

 mixture admitted, the wire then being cold. The electric 



* Collected in Lemons sur le Grisou, E. Hauser, Madrid, 1908. See 

 Abs. by L. Denoe 1 , Annates des Mines de Belgiqup, t. xii. p. 1088 (1907). 



t Couriot et J. Meunier, " Sur l'inflarnmaiion du Grisou par les Con- 

 ducteurs electriques incandescents." Ann. d. Min. d. Belgiquc, 1908, 



p. 87. 



