528 PROCEEDINGS OF THE AMERICAN ACADEMY. 



to —7°. The fact that there is a different modification is shown by- 

 placing the ice so formed in a dilatometer, and warming slowly. At 

 —2° there is a sudden increase of volume of about 1/10 per cent, fol- 

 lowed by regular increase of volume and melting at 0°. The ice IV 

 appears, therefore, to have a slightly less volume than ice I. In this 

 experiment, sufficient attention does not seem to have been paid to the 

 possibility of there being internal strains in the ice. It seems plausible 

 that the water, freezing suddenly as it must at —7°, might so freeze as 

 to produce a slight volume compression. On increasing temperature, 

 this strain is relieved by the softening of the ice in the neighborhood 

 of the melting point. This weakening of the ice near the melting 

 point has been established by experiment. At high pressures it is un- 

 doubtedly true that internal strains may produce anomalous effects, as 

 was found on at. least two occasions. 



Entirely apart from.Tammann, however, there is independent experi- 

 mental evidence of the possibility of two forms of ice, differing in den- 

 sity by 1/10 per cent, the amount found by Tammann.. Two modern 

 experimenters, Nichols ^^ and. Vincent, ^^ as well as several previous 

 observers, have each found that the density of ice may have either one 

 of two distinct values. The* difference seems to be connected with the 

 manner of formation of the ice, whether natural or artificial. The nat- 

 ural ice, when kept for some time, tends to assume the value for the 

 artificial ice. Barnes, i* however, failed to verify the work of Nichols, 

 and the most recent work of Leduc suggests that the discrepancies may 

 possibly be due to dissolved air. 



The question is as yet unsettled, with the probability, however, that 

 the ice does not exist. In order to leave open the possibility of the 

 establishment of its existence, however, the numeral IV has been re- 

 served for this according to Tammann, and the first of the two new 

 varieties found in this paper has been called V. 



Besides this, there have appeared from time to time spasmodic 

 notices concerning ice existing in crystalline forms other than the hex- 

 agonal. This is usually natural ice, which has been subjected to in- 

 tense cold in the far north. None of these statements seem to have 

 been subsequently verified, however. 



In the course of the present work evidence was obtained as to the 

 possibility of the existence of another form at high pressures. It seems 



" Nichols, Phys. Rev., 8 (Jan., 1899). 

 ^3 Vincent, loc. cit. 



" Barnes, Trans. Roy. Soc. Canada, 3, Sect. Ill, 3-27 (1909), and Phys. 

 Rev. (July, 1901). 



