12 



Proceedings of the Royal Irish Academy. 



any essential change of appai-atus, for the measurement of widely different 

 mobilities. 



General Results. 



An example of the sort of curve obtained is given (fig. 2). This curve as 

 drawn is made up of a number of straight lines, showing that ious of different 

 mobilities are present. Satui-ation of the slowest class is effected at 266 volts, 

 and two other classes of ions are saturated at 78 volts and 20 volts. Under 

 the conditions of this experiment these voltages correspond to ions of 

 mobUities -OOOoi, -00116, and -004:5 respectively. 



It is clear that while the bend at 20 volts and to a less degree that at 

 266 volts are well marked in this cuive, considerable hesitation might be felt 

 at marking a bend exactly .at 78 volts. The position of this bend wUl to a 



Sdthratian. Ti^jbt^es 



Kohildles 



266 



0003^ 



78 



00//6 



20 



oots 



tuts 

 Fie. 2. 



great extent be determined by the position of one point of the cui-%-e. In 

 fact, it might be said that a smooth curve might be drawn with almost equal 

 exactness, showing that, instead of an abrupt step in mobilities, there was a 

 gradual shading off from one to another, with ions of aU intermediate 

 mobilities present. "With the object of eliminating this sort of uncertainty, 

 and of obtaining as accurate values as possible for the mobilities of the 

 different ions, the current- voltage curve was worked over ru detail many 

 times, each section being investigated under conditions specially chosen to 

 bring out it-s features. 



Yvf. 3 gives two examples of the curves drawn to determine the mobility 

 of the slowest ion, and two referring to the ion next in order of mobility. 

 These curves are plotted in arbitrary and different units. The values of 

 mobility deduced from the points of bending of the curves are given. 



Fig. 4 gives an example of each of the next three bends of the curve and 

 the corresponding values of the mobilities. These have been plotted to 

 different axes and in different units for convenience, and are not to be con- 



