308 PROCEEDINGS OF THE AMERICAN ACADEMY. 



very small relative errors in the mean of the densities. Thus in the 

 most unfavorable case, at 320°, if an error in either dpjdt or in the 

 extrapolated value of L made the computed change of volume wrong 

 by five per cent, the resulting error in the mean of the densities would 

 be less than half of one per cent. 



The substitution of Cailletet and Colardeau's value for the critical 

 temperature of water, t c = 365°C, in the equation of the diameter gives 



s c = \/v c = 0.329 gr./cm. 8 , 



from which it follows that the critical volume is 



% = 3.04 cm. 8 /gr. 



There are three previous determinations with which this can be com- 

 pared, two of which are direct measurements. These are 



v c = 2.33 cm 8 /gr. (Nad.), 



found by Nadejdine 53 in 1885, and 



v c = 4.812 cm.Vgr. (Batt.), 



found by Battelli 54 in 1890. In both cases a known weight of water 

 was enclosed in a steel tube and heated at constant volume until the 

 contents became homogeneous. If there was too little liquid, this oc- 

 curred when it was all evaporated ; if too much, when it had so ex- 

 panded as to fill the tube ; if just enough, at the critical point. The 

 last case they hoped to recognize because of its corresponding to a 

 higher temperature than either of the others. Such a method gives an 

 excellent determination of the critical temperature, but it can hardly 

 be expected to give an accurate determination of the critical volume. 

 It amounts to trying to find the highest point of the steam dome by 

 selecting experimentally its longest ordinate on the v t plane. The ex- 

 tremely flat top of the steam dome makes this almost impossible, and 

 it is interesting to notice that both Nadejdine and Battelli fell within 

 the nearly flat region, one at one end and one at the other. The present 

 determination lies between theirs and should be much more accurate 

 than either. 



53 Universitatakija Investia Kiew., 1885, 6, 32; Mel. Phys. et Chim. tir6s 

 du Bull, de l'Ac. de St. Petersb., 1885, 12, 299; Chem. CB1., 1885, 17, 401. 

 64 Mem. dell. Ac. di Torino, 1891, 41, 76; Physikal. Rev., 1892, 2, 1. 



