490 



Dr. J. E. Mills on the 



two exceptions greater than the calculated. The difference 

 was insignificant when compared with the total vapour- 

 pressure, but occurred rather suddenly, thereby altering the 

 trend of the vapour-pressure curve and causing very serious 



dV 

 errors in the -^ calculated from the Biot curve. This fact 

 ai 



was discussed at length in my fourth paper *, and it was 



clearly revealed later that no possible recalculation of the 



Biot formulae constants could possibly make the calculated 



values of the vapour-pressure fit the observed values in the 



immediate neighbourhood of the critical temperature. 



Young has recognized this point and called attention to it f. 



Second. — I noted J that the values of k for the critical 



isochors which Young and his co-workers had obtained for 



isopentane, normal pentane, and ether, must be identical 



with the -7™- of the saturated vapour at the critical temperature. 



Young acknowledged this fact and has called public attention 

 to it § . The discovery was extremely fortunate, for it gave 



fairly accurate values for the -^ at the critical point for 

 three substances. The limit of the equation 

 L-E e 

 rfi/a-Dva = constant 



at the critical temperature as d approaches D in value is, 



3V c 4/3 x 0-0 4 31833^T-P \ = constant, . 



(3) 



and the values of the constants for the three substances men- 

 tioned then come out as follows : — 





Using 



frT r from ±>iot 

 d£ 



formula. 



Using 



dP 



-PT, from k. 



d± 



Using 

 dP 2R 



Average of 



values at lower 



temperatures. 



Isopeu tane. . 



95-5 

 f)7'3 



90-5 



107-2 

 111-1 

 1004 



107 05 



109-4 



102-0 



105-46 

 109-94 

 103 76 



Normal pentane . . 

 Ethyl oxide 



* Journ. Phys. Ohem. vol. ix. p. 402 (1905). 

 t ' Stoichiometry,' pp. 129-130. 



X Journ. Phys. Chem. viii. p. 594 (1904). k is in that paper called b, 

 following Ramsay and Young's original nomenclature. 

 § ' Stoichiometry,' p. 213. 



