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XXXVIII. Ionic Mobilities in Hydrogen.— -II. By W. B. 

 Haines, B.Sc, D.I.C., Beit Scientific Research Fellow*. 



IN a recent paper f the author gave the preliminary 

 results o£ experiments showing the presence of several 

 kinds of negative carriers in pure hydrogen ionized by a-rays. 

 Experiments have now been made at different pressures, so 

 that a revised and extended series of measurements can be 

 given. 



Experimental. 



As described in the former paper, the apparatus is so 

 arranged that the ions move under the influence of a simple 

 harmonic alternating field between two metal plates. From 

 readings of the current carried by the ions for different 

 values of the amplitude of the field, the critical value of the 

 amplitude can be found at which the ions just travel the 

 distance between the plates and back in one cycle of the field. 

 A mercury manometer tube was attached to indicate the 

 pressure of the gas in the experimental chamber. Measure- 

 ments could be conveniently taken between atmospheric 

 pressure and about 8 cm., so that a filter-pump sufficed for 

 lowering the pressure. In order to ensure that the hydrogen 

 should retain a high state of purity at lowered pressures the 

 chamber had to be rendered thoroughly air-tight, which is 

 not an easy matter with different parts of glass, ebonite, and 

 brass held together with sealing-wax. After one or two 

 attempts this was satisfactorily accomplished by covering all 

 the joints, when caref ally made with sealing-wax, with a 

 soft wax requiring only a moderate degree of heat to render 

 it quite fluid, so effectively filling all minute cracks and 

 pores. 



The method adopted as giving the most consistent results 

 was first to fill the chamber at the pressure desired with 

 pure hydrogen as it comes from the cooled charcoal bulb. 

 The gas was then left standing and at intervals a complete 

 series of readings of current against voltage was taken, so 

 that the changes in the ions which go on as the contamination 

 increases could be observed. In most cases the hydrogen 

 was freshly prepared from zinc and dilute sulphuric acid, 

 but the same results are noticed when the gas has stood for 

 some days in a holder, provided that it is freshly purified 



* Communicated Iw the Author. 

 t Phil. Mag. October 1915. 



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