240 MOREY art. g 



liters, the entropy must be expressed in liter-atmospheres 

 instead of in calories. The factor for this conversion is 0.0413; 

 inserting the above values in the equation, we get 



dp/dt = (2.180 X 0.0413) /206 = 0.00044 atm. per degree; 



the corresponding experimental value is the same. At 50° the 

 values are 



dp ^ (1.928 - 0.168) (0.0413) ^ 

 dt (12.02 - 0.001) 



Again the experimental value is the same, and the volume of the 

 liquid is still negligible. At 100°, the corresponding quantities 

 are 



dp _ (1.756 - 0.312) (0.0413) _ „' „__ 

 dt (1.209 - 0.001) "•"'^^^' 



agreeing exactly with experiment. At this temperature the 

 volume of the liquid amounts to less than one-tenth of one per 

 cent of the total volume ; the value of dp/dt is increasing with 

 increasing temperature, and the explanation is evident from an 

 inspection of the entropy and volume curves. As the tem- 

 perature is increased the entropy of the vapor diminishes, that 

 of the liquid increases, hence the difference decreases as the 

 temperature increases. The numerator, the entropy of vapori- 

 zation, is therefore diminishing, but its decrease is more than 

 offset by the decrease in the denominator taking place at the 

 same time because the increasing vapor pressure increases 

 the density of the vapor, hence decreasing its specific volume. 

 In the interval from zero to 10° the numerator decreases to 95.6 

 per cent of its value at zero, while the denominator decreases to 

 only 51.5 per cent of its value at zero. The difference does not 

 remain so marked, but for the interval 90-100° the values are 

 96 per cent and 70.9 per cent, respectively, and for the interval 

 190-200°, 96.1 per cent and 81.4 per cent, respectively. Appli- 

 cation of the two equations of the form of (1) [97] to the uni- 

 variant equilibrium, liquid + vapor, in the one-component sys- 

 tem, water, shows us that not only does the pressure increase with 



