Hydrogen and Nitrogen by Electron Impacts. 793 



No measurable amount of dissociation could be obtained 

 when electrons of energy 8*9 volts were used. One might 

 expect some dissociation at, or above, 3*6 volts, since this 

 corresponds to the measured work of dissociating the 

 hydrogen molecule. Either no dissocation at all occurs, or 

 else it is produced in so small an amount as not to be 

 detected in these experiments. The latter would demand 

 very special circumstances, either in the momentary state of 

 the hydrogen molecule, or in its orientation at impact, to 

 give dissocation at these low values. The alternative view- 

 is that dissociation cannot occur until radiation of the proper 

 type (the 13*5 volt effect, corresponding to dissociation and 

 radiation from one atom) or ionization (the 17'0 volt effect 

 corresponding to dissociation and ionization of one atom) 

 takes place, i. e. dissociation by electron impacts must ac- 

 company some other effect. 



The " clean up " of hydrogen by say an electric dis- 

 charge in the presence of sodium or potassium, is probably 

 due to combination between the metal and the atomic 

 hydrogen produced. It is possible that lining the experi- 

 mental tube with sodium would show a more rapid clean up 

 than in the experiment if the chemical forces were stronger 

 than the forces controlling temperature condensation. 



Nitrogen. 



Preparation. — Nitrogen was prepared by warming a solu- 

 tion of ammonium chloride and sodium nitrite. Ten litres 

 were collected over water. This was passed slowly through 

 calcium chloride, soda lime, red-hot copper turnings, and 

 phosphorus pentoxide, into a reservoir R of one litre capacity 

 permanently attached to the apparatus (fig. 1). Several 

 litres of the nitrogen were used to wash out the apparatus 

 before finally filling the reservoir. Small quantities of 

 nitrogen could be admitted into the apparatus by manipu- 

 lating the stopcocks S x and S 2 . 



Method of Experiment. — Experiments were conducted in 

 the same way as those on hydrogen. 



Results. 



The clean up of nitrogen for different accelerating 

 potentials is shown in Table V. The experiments on nitrogen 

 were not as extensive as those on hydrogen. No experi- 

 ments have, up to the present, been carried out on the effect 

 of varying the initial pressure. 



