794 Prof. A. LI. Hughes on Dissociation of 



Table V. 



Electron Current 650 microarnps. 

 Initial Pressures approx. const. 

 Unit of pressure= 10- 5 mm. 



Exp. tube E in liquid air. 



Time 

 interval M >T P Q 



mins.l. 



291 145 72 j 29 23"8 

 volts, volts, volts, volts. ; volts. 



596 

 364 

 288 

 244 

 212 

 181 

 144 

 118 

 101 

 94 

 88 



566 

 376 

 304 

 264 

 224 

 204 

 176 

 162 

 141 

 122 

 112 



520 

 376 

 294 

 264 

 234 

 208 

 192 

 166 

 144 

 132 

 128 



520 

 456 

 416 



392 

 382 

 348 

 316 

 282 

 274 

 260 

 255 



552 

 520 

 494 

 464 

 444 

 420 

 404 

 388 

 370 

 348 

 344 



Exp. tube at 

 20° C. 



E 



S 



T 



17-8 



72 



72 



volts. 



volts. 



volts. 

 890 



650 



900 



650 



662* 



724 



630 



580 



642 



630 



532 



578 



612 



480 



532 



612 



444 



506 



600 



3 ( ,)2 



450 



586 



; 354 



404 



580 



i 318 



376 



580 



392 



344 



572 



260* 



328 



* The first and last time intervals iu S were 4 mins. The other 

 intervals were as shown in the first column. 



Runs S and T were taken under different conditions from 

 the rest. In run S the whole apparatus was at room temper- 

 ature so that mercury vapour had access to the experimental 

 tube. In run T the U-tube was surrounded by liquid air to 

 freeze out mercury from the experimental tube. The initial 

 pressures were chosen so as to give the electrons much the 

 same mean free path as in the runs M, N, . . . . R. 



77 R a ' Number- of Nitrogen Molecules cleaned up 



Number of Collisions between Electrons and Molecules' 



The value of " b " given in Table VI. was calculated for 

 nitrogen in exactly the same way as for hydrogen. The 

 calculations of various mean free paths were based on the 

 value given by Jeans in his ' Dynamical Theory of Gases/ 

 viz. 5'7 x 10~ 6 cm. at 760 mm. pressure and 0° C. 



It was rather surprising that the clean up without liquid 

 air around the experimental tube (runs S and T) were as 

 great as they were. 



