J. W. (rlhbs — I'JquUlbrluiii of Heterogeneous Substances. 24.3 



perimeiit of this series. It seemed best, however, to make a triHiiio; 

 sacrifice of accxiracy 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 sufticient motive for adding another term 

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

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

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

 periments under discussion would be entirely misleading, as the 

 reader may easily convince himself. 



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

 deduced. By comparison with (334) we obtain 



. , ^' C ^ 311S.6 

 A + — log.o « - 7 = 9-47056 ^, 



which must hold true approximately between the temperatures 11*^ 

 and 90'\ (At higher temperatures the relative densities vary too 

 slowly Avith the temperatures to afibrd a critical test of the accuracy 

 of this relation.) By diiFerentiation we obtain 



Jlf_S'C_ 3118.6 



a^t *" ¥~ W~' 



where 31 denotes the modulus of the common system of logarithms. 



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



MC C 



C = = .43429 — . 



Hence 



B'i-^ C= 7181 «2 = 3590 «j, 



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 NOg into NgO^ 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) 

 B' = B+a^ - rt2 = ^ + i«i, 

 we shall have for the temperature of 40*^' 



Bt-\- C;=3434a,. 

 Now B t -\- (J reiH-esents the decrease of energy when a unit of NOg is 

 transformed into NgO^ without change of temperature. It therefore 



