96 Journal of the Mitchell Society. [Jun e 



curve of observed vapor pressures cuts the curve of calculated 

 vapor pressures in the neighborhood of the critical tempera- 

 ture, the observed vapor pressure curve having, of course, the 

 steeper trend. This is at once evident by the change from 

 positive to negative values of the differences between the 

 calculated and observed vapor pressures. 



We would here point out the great accuracy of these meas- 

 urements made by Drs. Ramsay and Young and by Dr. Young 

 and his co-workers. The conclusion that the calculated 

 minus the observed vapor pressure should be negative near 

 the critical temperature was wholly theoretical on our part. 

 That we should be able at once to verify this conclusion from 

 the measurements when the differences were so small as to 

 have been laid by the observers themselves on the errors of 

 measurement (the regularity of the differences having escaped 

 observation) speaks for itself as to their accuracy and skill. 

 The observed and calculated vapor pressure lines are almost 

 indistinguishable even at the critical temperature and when 

 drawn to a large scale. 



In order to show that equation 4, or the more general form 

 equation 3, does g'ive results in accord with Biot's formula at 

 points considerably below the critical temperature we have 

 published in Table 2, Jour. Phys. Chem. 9, p. 408 (1905), 



SP 

 the values of the ^7=- calculated from both formulas at inter- 

 6 1 



vals for some 50° C below the critical temperature. We have 

 already pointed out that equation 3 itself becomes inaccurate 

 at yet lower temperatures. 



CORRECT VALUES FOR p NEAR THE CRITICAL TEMPERATURE. 



Since equation 3 enables us to obtain in the neighborhood 

 of the critical temperature more nearly correct values for the 



SP 



^7p than we had been able to obtain in previous papers when 



