BRIDGMAN. — WATER UNDER PRESSURE. 



483 



ture above the II-III curve, the reaction ran back to III, so that at 

 C the phase present was III, as it should be. The line 6 A was per- 

 fectly straight ; it was assumed, therefore, that the line CB would also 

 have been perfectly straight if it had been possible to trace it out for 

 its entire length. 



TABLE XI. 

 Latent Heat, etc., on Equilibrium Curve Ice I-Ice III. 



The upper ends of the lines of equal volume for the phase I, that is, 

 the lines ED and FG above the triple point at — 35°, bear less and less 

 to the right, and at their extreme upper ends are actually bearing to the 

 left. This would mean a negative thermal dilatation for ice I at these 

 temperatures. The effect deserves to be investigated for its own sake. 

 The effect is so slight as to make very little difference for the purposes 

 of this paper, however, and it was not investigated further. That 

 there may be such an effect is borne out by the rather sharp change in 

 the curvature of the A V curve at the triple point —35°, while the 

 accuracy of the A V curve is made very probable by the closeness with 

 which it checks at the two triple points. Pettersson ^ claims to have 

 found that ordinary ice at atmospheric pressure shows a negative dila- 

 tation between — 35° and — 25°. 



Table XI. gives the values taken from the equilibrium and the 

 change of volume curves for the various quantities involved in the 

 determination of the latent heat and the change of energy. The 

 values of ^E and A// are shown graphically in Figure 11. The in- 

 ternal energy of III is greater than that of I, and practically all this 

 change of energy comes from the mechanical work absorbed when I 



' Pettersson, Vega Expedition, vol. 2 (1883). 



