BRIDGMAN. — WATER UNDER PRESSURE. 555 



ends in a critical point. From the point of view of Tammann's theory, 

 it is unfortunate that the form I gives place to III at higher pressures, 

 for in the ideal diagram the behavior of I is the normal behavior at 

 high pressure and that of III at low pressures, while here we have a 

 form which should be adapted for the high pressures giving place at 

 high pressure to one apparently appropriate to low pressures. 



The change of volume curves next concern us. These also all show 

 the general behavior demanded by Tammann's theory, the change of 

 volume solid-liquid becoming algebraically less at high pressures. On 

 the I-L curve this means that the change becomes numerically greater. 

 The approximate reason of this has already appeared from the discus- 

 sion of the compressibility of the solid to be merely that the solid is 

 more incompressible than the liquid, whether it has the greater or 

 smaller volume. The curvature of these change of volume curves is 

 also everywhere, except for the curve VI-L, such as to suggest that 

 the change of volume becomes zero at some finite temperature not very 

 far removed firom the temperatures actually reached. 



The latent heat curves also bear out Tammann's point of view, for 

 they all rise at the higher temperatures on the equilibrium curves. 

 The direction of curvature of these latent heat curves appears to be 

 governed by no such general rule as the change of volume curves, since 

 the curve may be either concave or convex toward the temperature 

 axis. 



So far, for the forms of ice I, III, and V, which are stable at low 

 pressures, everything seems as indicated by Tammann's theory. It 

 should be remarked that the pressure range of existence of these forms 

 is twice that reached before. It is on the VI-L curve, however, which 

 reaches to much higher pressures, that we find the significant sugges- 

 tion as to what to expect at still higher pressures. This suggestion 

 comes from the change of volume curve, which shows a pronounced 

 point of inflection in the neighborhood of 30".^^ Below 2.0°, the curva- 

 ture is like that for the other modifications at low pressures, indicating 

 the vanishing of the change of volume at perhaps 50° or 60°, but 

 beyond 30° the change of volume decreases less and less rapidly 

 with rising temperature, with the possibility of becoming asymptotic. 



2° With regard to the effect of probable experimental error at the high 

 pressure it is to be said that the effect of this would be to make the inflec- 

 tion shown in the diagram appear less pronounced than it really is. The 

 change of volume at high pressures is too low if anything, because in making 

 the correction for the change in the bore of the cylinder under pressure it was 

 assumed that the increase of bore is linear with pressure, whereas, if anything, 

 it increases more rapidly at high pressures. 



