BRIDGMAN. — WATER UNDER PRESSURE. 489 



The last set of determinations on April 6 and 18 were \vitli still 

 another coil, a comparatively new one, but one which had been suffi- 

 ciently seasoned. This coil gave readings consistent with the previous 

 values on the l-III and II-V curves, and gave the same shape for the 

 curve as that found with the two previous coils. There seems to be 

 no question but that these are the correct values. 



This variety of ice was obtained by increasing the pressure on I at 

 low temperatures. The temperatures used here ranged from —65° to 

 —80°. At —80° it is possible to run as much as 1000 kgm. beyond 

 the transition curve before the reaction begins to run. Even so far 

 removed from equilibrium as this, the reaction runs slowly and never 

 seems to run to completion. The table shows the discrepancies in the 

 stationary pressures when approached from above and below. The 

 other points on the curve were obtained with regularly increasing tem- 

 perature after the lowest. The temperature was raised as high as 

 —23° to get the last point. The succession of points found in this 

 way lie on a curve running nearly linearly with increasing temperature 

 and pressure up to about — 35°, where it turns and proceeds upwards 

 nearly vertically. This verifies the form found for the curve by 

 Tammann. This curve as found by Tammann crossed his I-III curve. 

 Tammann advances as an argument against there being a true triple 

 point at the point of intersection the experimental fact that it was 

 possible to start with II at low temperatures, to proceed along the 

 equilibrium curve with increasing temperature across the I-III curve 

 into the supposed region of stability of III, and then to retrace one's 

 steps, following down the original curve into the region of II where the 

 two curves I-III and II-III are unmistakably different. This possi- 

 bility, surprising as it seems, was verified also by direct experiment. 

 The points of April 6 at —40° and —53° on the I-II curve were 

 separated by points at — 32°.5 and —26°. 5, which are in the supposed 

 region of stability of III. 



The whole mystery is cleared up by the discovery of the II-III equi- 

 librium curve. It may be permitted to anticipate the results as they 

 were found on this curve in so far as they are needed to explain the 

 curious facts found on the I-II curve. In the first place, the existence 

 of the II-III curve puts beyond question the fact that there are two 

 varieties of ice, II and III. The point of intersection of the II-III 

 curve with the I-II and the II-III curves is at —35°, the triple point. 

 This point is also the point at which the change in direction of the 

 supposed I-II curve was found. Above this point the modification II 

 passes into the modification III. The absolute regularity with which 

 this turning point was found, both here and by Tammann, is to be ex- 



