ON GASEOUS COMBUSTION. 501 



Discussion. 1 



Sir J. J. Thomson called attention to the fact that combustion was 

 concerned not only with atoms and molecules but also with electrons 

 — i.e., bodies of much smaller dimensions and moving with very high 

 velocities. These may precede the explosion-wave and prepare the 

 way for it by ionising the gas. But the motion of the ions can be 

 stopped at once by means of a transverse magnetic field, in which they 

 curl up and are caused to revolve in small circles. It would be of 

 very great interest if Professor Dixon's experiments on the photography 

 of the explosion-wave could be repeated under such conditions as to 

 determine whether the form of the wave could be modified by such a 

 magnetic field. The positive and negative electrons were of very 

 different dimensions, and when first projected travelled with widely 

 different velocities ; but in an ordinary gas these velocities soon become 

 almost identical. It had, however, been shown by the work of 

 Townsend at Oxford and of certain workers on the Continent that in 

 carefully-dried gases the velocity of the negative electrons might be 

 100 times as great as the velocity of the positive electrons. The 

 amount of moisture required to reduce this velocity to its ordinary 

 lower value was exceedingly small comparable with that required to 

 initiate chemical change. It was not unlikely that the two phenomena 

 were very closely related. 



In reference to the influence of hot surfaces in promoting combustion 

 to which Professor Bone had drawn attention, it was not improbable 

 that the emission of charged particles from the surface was a factor of 

 primary importance. Hot lime gave out an enormous stream of nega- 

 tive electrons travelling with a high velocity, whilst hot metals emitted 

 an excess of positive electrons, as indeed Professor Bone had found by 

 the development of a negative charge on the silver foil which he had 

 used as a contact surface. These electrons might produce very impor- 

 tant effects by uniting (perhaps selectively) with moisture, with the 

 oxygen, and with the inflammable constituent of the gaseous mixture. 

 The mode of action of the oxides was specially worthy of investigation. 

 Chemists recognised two stages of oxidation in baryta, and perhaps in 

 lime. It might be that the problem of the source of the energy of the 

 torrent of electrons might be found in the oxidation and reduction of the 

 contact substance. He suggested that the action of surfaces might 

 ultimately be found to depend on the fact that they formed a support 

 for layers of electrified gas in which chemical changes proceeded with 

 high velocity. 



Sir Oliver Lodge strongly supported the proposal that experiments 

 should be carried out on the velocity of propagation of explosion-waves 

 in a magnetic field. The high velocity of the detonation-wave seemed 

 to point to the initiation of some new type of chemical change, such as 

 a burning of carbon following the burning of sulphur in the combustion 

 of carbon bisulphide, or the initiation of a change involving the collision 

 of three instead of two "molecules. The velocity of sound which had 



1 Compiled by the Sectional Secretaries. 



