220 Mr. E. Jacot on a Relation between Ionization by 



The gauge used was a McLeod gauge with a bulb o£ large 

 capacity. The gauge had been carefully calibrated before 

 setting up, observations being made directly in mm. In 

 the course of the work the readings were of course com- 

 parative, and were accepted as correct to two parts in ten 

 thousand. 



The gas used throughout the work was specially prepared 

 and carefully dried nitrogen. In practice the preparation of 

 the pure gas involves considerable difficulty, chiefly in the 

 removal of the nitric oxide, which is produced in small 

 quantities by most of the reactions in which nitrogen is the 

 chief product. Nitric oxide is an extremely stable compound, 

 and can only be eliminated with great difficulty. Hempel 

 first showed that copper gauze in contact with a solution 

 containing equal parts of ammonia solution ('880) and water 

 saturated with ammonium carbonate absorbs oxygen abso- 

 lutely and with great rapidity. This was made the basis of a 

 method for preparing nitrogen. The gauze was packed in 

 rolls into a gas pipette G, which was then filled with the 

 solution. Air, duly freed of C0 2 , was forced into the pipette, 

 and total absorption of oxygen followed. The residual 

 nitrogen, with possible traces of argon and free ammonia, 

 was admitted into the apparatus through the drying-chamber 

 D, where it was left for some time in contact with P 2 5 . 

 Here the gas was thoroughly dried and any traces of 

 ammonia eliminated *. 



Sir J. J. Thomson has also made use of this method of 

 preparing nitrogen in his more recent work on positive 

 rays f. 



The method of experiment was as follows : 



Let Vi = volume of the apparatus included by the bulb and 

 the solenoid. 

 V 2 = volume of the ionization-chamber I. 

 V 3 = volume of the apparatus contributed by P, Ui, U 2 , 

 the gauge, and any connecting tubes. 



V 2; then, was separated from Y ± at o ; and V 3 from V 2 

 by the tap T^ A large flask Y of known volume could be 

 very thoroughly exhausted by the use of the coconut-char- 

 coal tube G] maintained at the temperature of liquid air. It 



* Ammonium metaphosphate, in the presence of moisture, being 

 formed at once : 



2NII 3 + H 2 0+P A = (NII 4 ) 2 P 2 O c . 



t E. ff., Phil. Mag. vol. xxi. no. 122, Feb. 1911. 



