42 Mr. E. M. Wellisch on the Motion of 



would ultimately remove the nuclei from the gas ; however, 

 the current measurements failed to indicate any tendency 

 to restore the original condition of the gas under which 

 permanently free electrons were in evidence. 



The same gas was subsequently passed several times through 

 P 2 5 by means of a mercury-reservoir attachment in order to 

 remove any trace of water vapour which might have arisen 

 from the metal walls ; the free electrons, however, did not 

 reappear, and the possibility of the existence of nuclei con- 

 sisting of molecules of water vapour was thus excluded. 



A few experiments were made to ascertain whether free 

 electrons are present in carbon monoxide. This gas was 

 liberated by the action of concentrated sulphuric acid on 

 potassium ferrocyanide and was passed through solid caustic 

 potash, calcium chloride, and phosphorus pentoxide before 

 admission into the measuring vessel. A typical EI curve 

 was obtained for CO at a pressure of 13 mm., demonstrating 

 thus the existence of free electrons ; these were, however, 

 not nearly so numerous as in air at the same pressure, and, 

 as the manipulation with this gas presented difficulties, it was 

 not considered expedient to extend the investigation. 



It seems fitting to refer here to an apparent difficulty in 

 connexion with the existence of free electrons in gases. The 

 electrons were shown to appear in measurable amount in dry 

 air at pressures as high as 8 cm., and yet it has been mentioned 

 in this section that a trace of oxygen is sufficient to cause 

 them to disappear from C0 2 or H 2 at relatively high 

 pressures. Reference is made later (sec. 5) to this apparent 

 discrepancy; the difficulty is in large measure removed by a 

 consideration of the experimental fact that the sensitivity to 

 oxygen decreases rapidly as the pressure of the original gas 

 is reduced. To take actual figures, it was found that a trace 

 of air would rob H 2 at 1 atmosphere of its free electrons, and 

 yet in a mixture of H 2 at 82^ mm. and air at 2\ mm. the 

 electrons appeared in considerable numbers. 



(B) Motion of Free Electrons. 



A number of experiments were undertaken to determine 

 the velocity with which the free electrons moved in an 

 electric field through C0 2 and H 2 . Mobility values have 

 already been assigned by Franck * for the electrons in argon, 

 helium, and nitrogen at atmospheric pressure ; the values 

 given were respectively 209, ca. 500, and 120 cm. per sec. 

 per volt per cm. The mobility values were found to be 



* Franck, Verh. Deutsch. Phys. Ges. xii. pp. 291, 613 (1910). 



