in Hydrogen and Nitrogen, 507 



A few substances have such an immediate effect that, after 

 the first traces have been added, no electronic carriers at all 

 can be detected. Among these are iodine, chlorine, sulphur 

 dioxide, nitrous oxide, carbon bisulphide, and chloroform- 

 When once they have been admitted to the apparatus it is 

 extremely difficult to remove their influence. The method 

 used was to pump dry air through for hours in succession. 



With the other substances tested the influence was not 

 so great, and quantitative estimates could be made. The 

 following are the figures for oxygen: — 



Initial mobility (nitrogen not intentionally 



contaminated) 158 cm./sec. 



•05 per cent, oxygen 88 



•2 „ „ 30 



•7 „ , 11 



With carbon dioxide the addition of 2 per cent, reduced 

 u to 100, and with 5 per cent, a mobility a little higher 

 than the normal ion could be detected. The accompanying 

 list of substances follows the one given above in approximate 

 order of activity : oxygen, sulphuretted hydrogen, ammonia, 

 acetylene, methane, ether, carbon dioxide. The vapour of 

 naphthalene and of camphor had only a small effect, it being 

 not greater than the contamination from unavoidable sources. 

 But it must be remembered that the saturated vapour pres- 

 sure of these substances is very small. There is every reason 

 to suppose that they would considerably reduce the value 

 of u } if present in larger quantity. When the nitrogen was 

 saturated with phosphorus vapour, the value of u was 90. 



The following figures were obtained on adding hydrogen, 

 showing that it* effect is at most very small : — 



Initial value ?f = 254 



5 per cent, hvdrogen 218 



10 „ „ ' 183 



14 „ „ 148 



Further results showed that this small effect varied according 

 to the care taken to first purify the hydrogen used. This 

 indicated that the hydrogen itself might be neutral, and led 

 to the following experiments with pure hydrogen. Franck 

 records a negative result from an attempt at finding free 

 electrons in hydrogen. 



Hydrogen. — The gas was generated as required from dilute 

 sulphuric acid and zinc in an improvised Kipp's apparatus. 

 After being dried it was thoroughly purified by passage 



