8 



A quantity of the gas is now drawn over into an ex- 

 hausted bulb, whose temperature (that of the oven) is 311 

 (absolute) ; the pressure is observed to be 34"5. The weight 

 of this gas is •2536 gr. It is then calculated from a know- 

 ledge of the capacity of the bulb that the mixture weighs 

 2*22 times as much as air. From this it is found that to 

 every molecule of pentane there are '23 molecules of air, 

 assuming the pentane molecule to weigh 2 '5 times as much as 

 the average air molecule. If •§ = stopping power of pentane, 

 we have, therefore — 



On the same day and under the same conditions RI for 

 air = 231. The leakage correction is found to be the same for 

 both, and need not be applied. Now, as far as consumption 

 of energy is concerned, '23 molecules of air are equivalent to 

 •23/3"59 molecules of pentane = '065. Hence, if all the 

 energy had been spent on pentane molecules, the value for 

 RI would have been — 



1-065x321 --06.5x231 

 = 342-15 

 = 327. 

 Finally — 



Total ionisation in pentane 327 , . , 



Total ionisation in air 231 



Determination of Stopping Power and RI in 

 Acetylene (CoH.,). 



Same conditions as previous experiment. Apparatus 

 charged to atmospheric pressure with gas ; when tested gas 

 was found to contain less than 2% of impurities. Tempera- 

 ture of apparatus = 37"5° C. Barometer = 763 mm. 



