129-131] 



Numerical Values of Velocities 



113 



From these values in the standard case of oxygen at C., we can 

 calculate the quantities C and Rjm for other temperatures and substances. 

 The following table is calculated from recent observations. 



Certain other quantities which are tabulated here will be found useful in 

 later parts of the book. 



The value of the constant R can be found, although of course with less 

 accuracy than the values of R/m, by assuming the value 4 x 10 19 for the 

 number of molecules per cubic centimetre under normal conditions ( 8). 

 The weight of a cubic centimetre of hydrogen being '000090 grammes, and 

 the number of molecules in this cubic centimetre being 4 x 10 19 , we find that 

 for hydrogen, m = 2'25 x 10" 24 . Since R/m for hydrogen is 413 x 10 5 , this 

 leads to the value A yio 



131. The quantity C which has been tabulated, must be carefully dis- 

 tinguished from the mean velocity in the gas, of which the value is 



c = 



7T 3 



r 00 

 Jo 



J^ 



V 37T 



J. 



,.(273) 



.(274). 

 8 



