BRIDGMAN. — WATER UNDER PRESSURE. 487 



even though the V-L curve has to be slightly raised to pass through 

 the point. 



The Curve I-II. 



We return now to the curve meeting the I-III curve at the lower 

 temperatures, the I-II curve. The points on this curve were found 

 with the low temperature piece of apparatus. 



The data, shown in Table XIV., were obtained on five separate occa- 

 sions with three different manganin resistance coils. The first three 

 sets, on March 24, 29, and April 5, were obtained before the points on 

 the I-III curve were obtained at the low temperatures. 



The whole investigation at the low temperatures was approached 

 with the prejudice that Tammann must have been wrong. In particu- 

 lar, the existence of two separate modifications of ice, II and III, with 

 only slightly different properties, was thought to be explicable by some 

 instrumental error. This prejudice was strengthened by Tammann's 

 failure to find the triple point I-II-III, or any points on the melting 

 curve of II, although he must have passed over this curve if there were 

 such a one. His failure to find the II-L curve was difficult to explain 

 because the reaction from solid to liquid always runs, and in this case 

 the accompanjdng change of volume is fairly high. The work of the 

 first three days still further strengthened the impression of error in 

 Tammann's work. It showed conclusively that there was a modifica- 

 tion of ice different from III in equilibrium with I at low temperatures, 

 but seemed to show that this was not the variety supposed by Tam- 

 mann. The points of the three days all lay on the same curve, which 

 was headed exactly for the intersection of the I-L and the V-L curves 

 both prolonged into the region of stability of III. It seemed probable, 

 therefore, that Tammann's II was nothing but our V in the unstable 

 region. 



The determinations of these two days were made with two different 

 coils, one a well seasoned one that had been maltreated in many ex- 

 plosions, and the other a brand new one. After several days' work 

 suspicion was drawn to these coils and they were checked by measuring 

 with them the equilibrium pressure on other already well established 

 curves. Both on the I-III curve and the III-V curve they gave 

 results consistent with each other but about 100 kgm. higher than the 

 previous values. There seems no reason to doubt, therefore, that these 

 coils were both in error and, by a stroke of luck, by the same amount. 

 This disposed definitely of the idea that the new ice was V subcooled. 

 The values tabulated are corrected by this quantity 100 kgm. There 

 seems no reason why these readings should be entirely discarded ; they 



