176 



Fig. 4 shows the readings obtained, and the curve which 

 is drawn to find R and /. These are determined to be 4 95 

 and 42'8 respectively, so that 7^7 = 212, the temperature 

 being 30" C, and the pressure being 751 cm. The appara- 

 tus is then exhausted and filled with CS vapour to a pres- 

 sure of about 24 cm. It is known from a separate experi- 

 ment that 1,000 volts per cm. is a saturating potential gra- 

 dient, and a battery of 300 volts is therefore put on to the 

 3 mm. chamber. 



Fig. 5. 



The readings then taken, and the curve drawn are shown 

 in Fig. 5. It appears from these that 7? = 7*74, 7 = 37'3, so 

 that ^7 = 289. The pressure has altered about 1 cm. during 

 the determination of the curve, but was found to be 23'35 at 

 the moment when the corner (7^,7) was passed. The tempera- 

 ture at the same time was 29°. Now, the stopping power of 

 CS2 is 2'20, and the stopping power of the mixture is (com- 

 paring with the previous experiment) — 



495 751 



. = 2-06 



774 233-5 



Hence — 



If X be the percentage of gas, we must have 



ir X 2-2 -F 1 - ^ = 2*06 .*. *■ = 88-5. 



The vapour is then cleared out of the apparatus, and dry 

 air admitted. The value of 7i7 for air is again determined, as 

 shown in Fis^. 6, and found to be 214. 



