16 Miss Martin, Expansion, etc. [Nov. 11, 1895. 



luminosity and movement of the gauge which after the air had 

 assumed a steady volume were too weak to have any effect. 

 Working with the same strength of charge it was found that 

 coal-gas underwent practically no diminution — in comparison with 

 air and C0 2 , that is to say, there was actually a small diminution 

 most likely due to the presence of a small quantity of air in the 

 tube — and the discharging of the condenser thus filled was at- 

 tended with no greater effects than observed at the close of the 

 observations with air. With C0 2 the first movements of the 

 gauge were enormously greater than those obtained with coal 

 gas and appreciably greater than those noticed with air ; and the 

 time taken by this gas to assume a steady volume was at least 

 twice as long as that required by air. This steady volume how- 

 ever having once been reached, the effects of any subsequent dis- 

 charge were the same as with coal gas or air. 



It would therefore seem that any sudden and temporary 

 splitting up of the molecules of the gas which may take place 

 under the influence of the induction discharge is more easily and 

 thoroughly accomplished while any definite chemical change is in 

 progress. When nothing of this nature is taking place, all gases 

 seem to behave more or less alike and to require equal forces to 

 cause any disintegration. It is quite easy to understand how this 

 may have escaped observation ; for if a vessel of the dimensions 

 used has been filled with air whilst free from any electric dis- 

 turbance, it requires about 600 discharges to reduce the air to its 

 permanent volume when it gives the least movement for a given 

 fall of potential ; and to similarly reduce an equal volume of 

 carbon dioxide at least 1 1000 discharges are necessary. 



It would seem that the chemical change which produces this 

 diminution of volume takes place more easily and quickly at low 

 pressures; for though, as was before remarked, the gas to be 

 observed was let in slowly, the rate was not nearly so slow as the 

 above figures would require ; nevertheless the volume was constant 

 whenever the condenser had been exhausted and refilled whilst 

 still connected to the Wimshurst. 



I should remark that the above phenomena were also ob- 

 served whenever the apparatus was suddenly charged, but the 

 great majority of observations were made on the sudden discharge 

 through the spark at the Wimshurst as this method was found to 

 be rather more convenient. 



