during the combination of hydrogen and chlorine ? 91 
that the first effect of exposing the mixed gases to light is a 
considerable increase in volume without any production of HC1, 
then after an interval which depends on the intensity of the 
light the formation of HCl begins, and when once started 
persists. 
The conductivity of the mixed gases was tested in both these 
stages, the gases being exposed to diffuse and not very bright 
daylight ; many experiments were made but in no case was any 
increase observed in that small rate of leak which exists in these 
as well as in other gases, even when not exposed to light. It 
thus appears that both during the combination of hydrogen and 
chlorine as well as in the preliminary stage marked by an increase 
iu volume there are no free charged ions. 
In the next place an experiment was tried to see whether the 
artificial production of free charged ions in the mixed gases would 
affect their rate of combination. In this experiment the mixed 
gases were exposed to Rontgen rays which produced free ions in 
such numbers that the leaves of the electroscope collapsed in 
a few seconds, but no effect could be detected either in promoting 
combination when the gases w r ere kept in the dark or in altering 
the rate of leak when the gases were exposed to diffuse daylight. 
The radiation from thorium was also tried, but it was without 
effect. 
