Positive Ionization fr om Hot Salts. 693 



number of experiments were therefore made in this gas. 

 Although the results obtained are very complicated they are 

 quite clear as to the point that heating in an atmosphere of 

 hydrogen greatly increases the emission. In the following- 

 descriptions the currents are in terms of scale divisions 

 one division being equal to l'25x 10" 9 amp. 



At the commencement of the experiment the air was 

 pumped down to a pressure of *003 mm. and the emission 

 was then 22 divisions. The temperature was 800° C. 

 Hydrogen was then let in to a pressure of 11 mm. and the 

 emission rose almost immediately to 110 divisions and then 

 more slowly, so that at the end of 40 minutes it had become 

 268 divisions. The hydrogen was then pumped out, the 

 current and pressure being observed from time to time. 

 There was an increase with diminish ng pressure to 5 mm. 

 when the emission was 390 divisions. Jt then fell gradually 

 to 114 divisions at 0'003 mm. JMore hydrogen was then 

 admitted when it increased to a temporary maximum of 350 

 divisions at 7 mm. pressure. The decrease was very slight, 

 however, and on admitting more hydrogen the emission 

 began to increase again more rapidly than the pressure. At 

 224 mm. it had reached 3100 divisions. The temperature 

 only varied 3° from 800° during these experiments. The 

 pressure slowly fell a little after each admission of gas, 

 showing that the hydrogen was being converted into water 

 which was being absorbed by the phosphorus pentoxide bulb. 

 After admitting hydrogen to a pressure of 348 mm. the 

 apparatus was left for two hours. On returning, the tempe- 

 rature had fallen from 798° to 768°, the pressure was reduced 

 to 323 mm., and the emission had increased to 6000 divisions. 

 The hydrogen was then pumped out, when the emission fell 

 to a minimum of 2100 divisions at 1500 mm. followed by a 

 maximum of 5300 divisions at 20 mm. and a rapid drop 

 thence to 145 divisions at 0*005 mm. Air was then let in to 

 atmospheric pressure when the emission fell to 20 divisions. 

 The temperature had dropped to about 730° by this time. 

 On pumping out the air the emission rose slowly to a 

 maximum of 53 divisions at 30 mm. from which it fell, 

 slowly at first and then more quickly, to 15 divisions at 

 0-006 mm. 



When the apparatus was taken down the cold electrode 

 had been blackened by the sulphuretted hydrogen. The 

 lower end was covered with a saline deposit, much dis- 

 coloured, which smelt strongly of hydrogen sulphide. An 

 examination of the substance left in the tube indicated that 

 it was principally barium sulphide with some barium sulphate 



