BRIDGMAN. — WATER UNDER PRESSURE. 513 



The missing triple point, mentioned at the beginning, is evidently 

 given by the intersection of this line, V-VI, with the line II-V. This 

 point is apparently situated at about —65° and 6300 kgm. Evidently 

 the reaction velocity will be so slow at these temperatures and pres- 

 sures that it would be hopeless to try to reach it. The missing equi- 

 librium curve starting from this point is evidently II- VI. There is 

 even less chance of realizing this than of getting down to the triple 

 point, always assuming of course that some new variety of ice does not 

 appear. 



The values of the latent heat and the change of energy calculated 

 in the usual way from the data are given in Table XXV. and Figure 

 30. The latent heat, owing to the approximate perpendicularity of the 

 equilibrium curve, is almost vanishiugly small. V gives out heat on 

 passing to VI, but absorbs work. The heat is almost negligible com- 

 pared with the work, so that the internal energy of VI is greater than 

 that of V by nearly the amount of this work. 



The Cur\^ VI-L. 



This modification of ice was the first one discovered in the present 

 work, and has engaged more attention than any of the other forms. 

 It has been studied over a pressure range of more than 16,000 kgm., 

 nearly three times the pressure range of all the other modifications 

 put together. So far as can be judged, this is the final form of the 

 solid. This ice shows characteristics in its behavior different from any 

 of the others, characteristics which are particularly significant for the 

 theory of the solid-liquid states. In fact, this is the only modification 

 stable over a pressure range wide enough to indicate what may be ex- 

 pected at still higher pressures, as yet unreached. 



The manner in which this variety of ice was first found in the course 

 of the measurements of compressibility has been already described in 

 the introduction. The appearence of this ice resulted simply in an 

 irregular disturbance at the upper end of the compressibility curve. 

 It was evidently impossible to make any accurate measurements by 

 this method of the freezing pressure or of the change of volume. All 

 that could be stated about the freezing pressure was that it was less 

 than a certain value, the maximum pressure reached during a run 

 when there was a disturbance, and all that was known about the change 

 of volume was that it was higher than a certain value, tlie discontinuity 

 in the compressibility curve. The lower and upper limits so set on 

 these quantities were found to be consistent with the more accurate 

 values found later. 



VOL. XLVII. — 33 



