180 EQUILIBRIUM OF HETEROGENEOUS SUBSTANCES. 



reciprocal of the latter quantity is given for each experiment of 

 this series. It seemed best, however, to make a trifling sacrifice of 

 accuracy for the sake of simplicity. 



It might be thought that the experiments under discussion would 

 be better represented by a formula in which the term containing log t 

 (see equation (333)) was retained. But an examination of the figures 

 in the table will show that nothing important can be gained in this 

 respect, and there is hardly sufficient motive for adding another term 

 to the formula of calculation. Any attempt to determine the real 

 values of A, H and C in equation (333) (assuming the absolute 

 validity of such an equation for peroxide of nitrogen), from the 

 experiments under discussion would be entirely misleading, as the 

 reader may easily convince himself. 



From equation (336), however, the following conclusions may be 

 deduced. By comparison with (334) we obtain 



,', C Q ,,- n , r 3118-6 



A + log 10 *-T = 9-47056 -- - , 



1*2 v v 



which must hold true approximately between the temperatures 11 

 and 90 C . (At higher temperatures the relative densities vary too 

 slowly with the temperatures to afford a critical test of the accuracy 

 of this relation.) By differentiation we obtain 



MB' C_ 3118-6 



a 2 t + t*~ t z 



where M denotes the modulus of the common system of logarithms. 

 Now by comparing equations (333) and (334) we see that 



Hence 



which may be regarded as a close approximation at 40 or 50, and 

 a tolerable approximation between the limits of temperature above 

 mentioned. Now B't-\-C represents the heat evolved by the con- 

 version of a unit of N0 2 into N 2 O 4 under constant pressure. Such 

 conversion cannot take place at constant pressure without change of 

 temperature, which renders the experimental verification of the last 

 equation less simple. But since by equations (322) 



we shall have for the temperature of 40 C 



Now Bt + C represents the decrease of energy when a unit of N0 2 is 

 transformed into N 2 4 without change of temperature. It therefore 



