due to Heating Aluminium Phosphate. 



587 



of 65G volts there was a current of 8 or 9 arbitrary units. 

 The total current on the back electrode when the front tube 

 was earthed was found to be 118 units. Thus about 8 per cent, 

 of the total current here appears to be due to ions which are 

 too slow moving to be extracted even with the very high 

 voltage used, or which have been formed after passing the 

 front electrode. 



It may be mentioned that it was necessary to raise the 

 back tube to a high potential before any indication of these 

 extra ions was forthcoming. Thus with 432 volts on the 

 front tube a current could be just detected when 190 volts 

 was put on the back tube. 



If the current of 8 units on the back electrode is due to 

 ions which are too slow to be stopped by the field on the 

 front electrode, then some indication of these would be 

 expected on the saturation current curve, i. e. after passing 

 314 volts the curve should still gradually ascend. 



Nothing of the kind, however, takes place, and, as is seen 

 from the table of observations given, a small increase could 

 easily have been detected. 



If we assume that neutral doublets are present which 

 break up into ions after passing the first electrode, then the 

 results are readily explained. 



Should the extra ions be in reality due to the splitting up 

 of neutral doublets rather than to the presence of ions o£ 

 extremely low velocity, one would expect to find an equal 

 number of negative and positive ions formed after passing 

 the first electrode, and this should occur although the satu- 

 ration currents on the front electrode due to positive and 

 negative ions may differ widely. For aluminium phosphate 

 these saturation currents on the front electrode are in fact 

 very different. It was found that a negative voltage of 220 

 on the front tube was sufficient to obtain a saturation current 

 with negative ions. When both tubes were brought to a 

 negative potential of 650 volts, the front electrode being 

 earthed, and the back electrode connected with the electro- 

 meter, there was a current of 8 units — i. <?., precisely the 

 same as that obtained with positive ions under exactly similar 

 conditions. 



This appears strong evidence in favour of the view that 

 the extra ions are due to the splitting up of neutral doublets 

 and not to ions of very low velocity. 



When a current voltage curve for the positive ions is 

 plotted using the values given above, it is seen that the 

 curve formed by joining the points obtained is not of the 

 usual type. 



