701 



LTC 

 It will be clear that the values of -— — ^ represent the values for 



A 2' 



log M calculated from equation (9). Therefore the value of M 



becomes lO-^"^ according to Tetrode, 10 -^^.os according to Sackur, 



10-3"-6 according to Van der Waals for ; — 0, lO-^^'J for ;. = 20f<. 



It is clear from the calculation that the variation of X from zero 

 to 20 ft does not cause a change in the order of magnitude of J/, 

 that therefore the fact that the frequency is unknown jet renders 

 the rough calculation of M possible, and that reversely the frequency 

 cannot be calculated but from exceedingly accurate observations. 

 With the measurements available at present this is not yet possible, 

 as appears from table 2. 



If the iodine molecule is represented by two spheres, the masses 

 of which are thought concentrated in the centres, and if the distance 

 from the centres is d, the moment of inertia with respect to an axis 

 through the centre of gravity and normal to the molecule axis is 



fd\ 

 2 7??J ~ . From this follows for the limits of (/ 



127 dr 

 10-37.6, resp. 10-38.3 z= 2 --orc/^1.6.1Q-8, resp. 7 10 -o no) 



boo 10'^'^ 4 i \ / 



a value which as far as the order of magnitude is concerned is in 

 satisfactory concordance with the diameter calculations according to 

 other methods. 



6. Sackur and Tetrode's entropy expressions which were used in 

 the pi'eceding paragraph are founded on the assumption that the 

 specific heats of the gases are independent of the temperature; the 

 test of these formulae can therefore only be a rough one. ') In the 

 expression proposed by Van der Waals, the variability of the specific 

 heats is, however, taken into account. 



According to this expression the transformation energy for the 

 iodine dissociation is represented by : 



Nvh 



2nE = 2nET^s) -r'Ui^T .... (11) 



ekf-l 

 Hence the algebraic sum of the specific heats becomes : 



Av 



d:SnE 1 HivY e^ 



— -- = ~R- R\~] . 



dT 2 \kTJ 



\e^T_i) 



^) A number of calculations of chemical equilibria carried out by the aid of 

 his formula are found in Sackur. Ann. d. Phys. (4) 40. 87 (1913). 



