1910-11.] Isopiestic Expansibility of Water. 475 
mined. These critical constants, as tabulated in Winkelmann’s Handbuch 
der Physik, are for water as follows 
Critical Temperature. 
Critical Pressure. 
Critical Volume. 
Observer. 
358T 
2-3 
Nadejdine. 
364-3 
194-61 
4-8 
Battelli. 
365-0 
200-5 
Cailletet and Colardeau. 
3590 
Knipp. 
374-0 
Traube and Teichner. 
The temperatures are here expressed in degrees centigrade, the pressures 
in atmospheres, and the volume is that of 1 gramme of the substance in the 
critical state expressed in c.c. Approximately, then, these units are the 
same as we have been dealing with, except that our unit of volume is a 
hundred times greater. The values for the critical temperature and the 
critical pressure show very little deviation from one another as compared 
with the two values for the critical volume, one of which is more than 
twice as great as the other. Of the four isopiestics drawn in fig. 4 we 
see, therefore, that the value of the pressure for the lowest is well over the 
critical. Attempts to obtain values at much lower pressures than 400 were 
attended by the risk of serious damage to the apparatus through the 
possibility of the mercury being suddenly expelled from the dilatometer 
and coming in contact with the metal work, such as the cooling spiral. 
Two such attempts, one to gradually lower the pressure when the 
temperatures were about the critical temperature, and another to gradually 
raise the temperature while the pressure was below the critical pressure, 
gave so unsatisfactory results that I decided to devote the time at my 
disposal to the investigation of the higher isopiestics. Besides, at these 
lower temperatures and pressures the method employed is not sufficiently 
accurate, as may be seen from the following results. The same change of 
volume * was obtained for the quoted values of T and P : — 
P= 50 
100 
250 
500 
750 
1000 kgs. /cm. 2 
T 1 = 225 
232 
242 
260 
280 
290° C. 
T 2 = 150 
145 
155 
172 
185 
196° C. 
* In the Table, T x gives the temperatures at which the liquid has a definite volume Y 1 
(say), and T 2 gives the corresponding temperatures at which the volume is V 2 (say), where 
V 2 is different from Y v 
