452 Mr. S. Ratner on the 



pressure. In this figure the mobilities at different pressures 

 are given in different units in order to avoid using too small 

 a scale. In the curves I. and II. the mobility at any point 

 may be given in terms of the normal mobility represented 

 as straight lines in the beginning of the curves, while in the 

 curves III. and IV. it may be calculated from the mobility 

 of the positive ion at the same pressures. The curves show 

 that the velocity of the ions always increases with increasing 

 forces, even in the case when their mobility diminishes. 



By their maximum points the curves are divided into two 

 parts, the first part corresponding to the gradual dissociation 

 of the ion and the second to the pure electronic state of an 



ion. The value of — corresponding to the maximum 



mobility is constant at pressures up to 200 mm. and is equal 

 to 6*2, which is very large compared with 0*2 — the value 

 given by J. S. Townsend in case of carefully dried air. 



The rate of decrease of the mobility, as seen from the 

 curves, diminishes with the increase of the force, and at 



sufficiently large values of — the mobility tends to reach a 



minimum value. At low pressures this bend in the curve is 

 well marked, as shown by curve IV. Experiments with 



still larger values of — are made impossible by the luminous 



discharge which takes place under these conditions between 

 the heated strip and the grating. It is possible that the 

 luminous discharge is preceded by a feeble ionization by 

 collision, which might be responsible for this bend of the 

 curves. Further experiments in this direction are now in 

 progress. 



With regard to positive ions, the experiments show that 

 at pressures down to 5 mm. and with very large forces the 

 mobility remains constant. 



3. Experiments in hydrogen. — The same experiments were 

 carried out in hydrogen — a gas in which the negative ion 

 is known to exist in the electronic state under ordinary 

 conditions. The hydrogen was generated in a Kipp appar- 

 atus from hydrochloric acid and zinc and purified by passing 

 slowly through JSTaOH, KMn0 4 , and H 2 S0 4 . It was always 

 contaminated with small quantities of impurities, since the 

 brass-plate and the bell-jar enclosing the apparatus contained 

 a great number of different joints which allowed a constant 

 small leakage of air. The mobility curves in hydrogen show 

 the same characteristic features as in the case of air. The 



