lONIZATION BY NEGATIVE IONS 17 



charge in attracting a molecule would only last for a 

 short interval, so that for large values of X/p the ions 

 would move with their own proper masses. The 

 transition from one state to the other takes place 

 gradually as the force rises, and it is probable in the 

 case of the negative ions that the corpuscular state 

 prevails even when the force is not large enough to cause 

 new ions to be produced by collisions. One result which 

 points to this conclusion is that when X is small there is 

 no very rapid diminution of a with the force as might 

 be expected if the mass of the negative ion tended to 

 increase. 



Other experiments show also that the mass of the 

 negative ion is much less than that of the positive ion 

 when the forces acting are too small to produce ions by 

 collision. Thus experiments on diffusion 1 of ions in dry 

 air at low pressure show that when X/p^'09, the mass of 

 the negative ion is much less than that of the positive 

 ion, whereas even for X=20 and p=l, the value of 

 a is inappreciable and only attains the value "12 when 



8. Representation of the values of a by a single curve. 



In order to examine the values of a for different 

 forces and pressures, it is convenient to present the 

 experimental results in a special way by means of a curve 

 for each gas. The method leads to great simplification 

 as the value of a corresponding to any force and pressure 

 may be obtained immediately from the curve. If a be 

 determined for a force X and pressure p, and the points 

 whose co-ordinates are a/p and X/p be marked on a 

 diagram, it will be found that they all lie on the same curve, 



1 Proceedings of the Royal Society, 1908, Vol. Ixxxi., p. 470. 

 I.G. C 



