G28 



Prof. W. M. Thornton on the 



many and varied cases, the suggestion is again strong that 

 io-nition begins bv some action from the hot wire that is 

 dominated by oxygen. The probability is rather against the 

 emission of positive oxygen ions at low temperatures since 

 oxygen is electronegative. Hydrogen is so intimately re- 

 lated to platinum by the phenomena of absorption that its 

 sensitiveness to ignition by platinum wires can be readily 

 understood on the assumption that the low temperature 

 emission is of hydrogen ions. 



The action of methane on hot wires is unknown, except 

 that in certain gas-aetectors in which a heated platinum 

 wire forms one arm of a resistance bridge, a cooling effect is 

 observed when the wire is placed in weak mixtures of methane 

 and air. This requires further investigation, but in t he- 

 present work it has been observed frequently that wires of 

 all metals glow more briohtlv at the same current in air than 

 in an inflammable mixture. It is highly probable that any 

 double layer or surface charge would be removed by the 

 flame. 



11. Influence of Gas Pressure. 



(1) Below Atmospheric. 



A further illustration of the indifference of ignition to 

 external physical conditions is given by reducing the pres- 

 sure of the mixture. The curves of fig. 8 are practically 



1-6A 



METHANE . JOP.C.TUNG5TENV/IRE.-0 

 OR 01*4 attest© BE . ooUBUEO 



S IO 15 20 2S 30 35 40 45 50 55 60 65 70 75 30 r 



p\Q Q PRESSURE.. CM. SYXE-FlCUFTr. 



identical ; the pressure at which ignition begins to fail is 

 between 12'5 and 20 centimetres of mercury, and below 

 10 cm. it was impossible. From this point to atmospheric 

 pressure there is no variation of igniting current. 



