DAVIS. — CERTAIN THERMAL PROPERTIES OF STEAM. 309 



The third published value of the critical volume, 

 v c = 4.025 cm. 3 /gr. (Diet.), 



was computed by Dieterici 55 in 1904, from the empirical law of 

 Young 56 that, for " normal " substances, the ratio of the actual t© the 

 gas-law density at the critical pressure and density is 3.8. Dieterici's 

 belief that water becomes a " normal " substance at high temperatures, 

 even though it is known to be very abnormal at ordinary temperatures, 

 is based on the fact that the ratio of the change of internal energy dur- 



Figure 17. The polymerization factor for liquid water as a function of 

 the temperature. The small circles below 150° are Ramsay's earlier values; 

 the large circles below 150° are his revised values; the circle at 365° is the 

 value indicated by the critical volume. 



ing evaporation to the whole heat of evaporation, L, seemed to ap- 

 proach a value which he had predicted for " normal " substances. The 

 present determination of v c shows that water is, as one would have ex- 

 pected, still abnormal at the critical point. If interpreted in the usual 

 way, it would indicate a polymerization factor of 1.3. Figure 17 shows 

 how well this number fits a smooth curve through Ramsay's earlier 

 large values of the polymerization factor at ordinary temperatures ; 57 



" Wied. Ann., 1904, 15, 864. 



»• Phil. Mag., 1892, 34, 507, and Jour. Chem. Soc, Papers, 1893, 63, 1251. 



" Phil. Trans., 1893, 184A, 647;' translated in Zeitsch. Phys. Chem., 1893, 

 12, 433; second paper in Jour. Chem. Soc, 1893, 63, 1089; translated in 

 Zeitsch. Phys. Chem., 1893, 12, 458. 



