POLYMORPHIC TRANSFORMATIONS OF SOLIDS. 



115 



it. The pressure range of the results given here is considerably greater 

 than that of Tammann, but Tammann's temperature range on the I-II 

 curve is more extensive. Tammann's second paper is almost exclu- 

 sively occupied with the lag phenomena on the I-II curve. He finds 

 that the band of indifference grows rapidly wider at the lower tempera- 

 tures, becoming so wide at liquid air temperatures that II may be 

 realized at atmospheric pressure. In this work, the same qualitative 

 behavior of the band of indifference was found. At 0° the width of 

 the band was 180 kgm.; at 25°, 80 kgm.; at 35°, 50 kgm.; at 50°, 

 20 kgm.; and between 57° and 62° no difference could be detected 

 in the pressures reached from above and below. From one of Tam- 

 mann's diagrams I should estimate the width of his band to be about 

 350 kgm. at -10°, 200 kgm. at 0°, 50 kgm. at 10° and above 30° the 

 scale of his diagram does not allow an estimate. Apparently the width 

 of his band decreases with rising temperature more rapidly than mine. 

 This emphasizes that too little is known at present of the various 

 factors which determine the width of the band to allow us to attach 

 significance to the absolute width of the band when measured under 

 different conditions. 



Tammann's transition line I-II showed one other remarkable 

 feature in that at the upper end it rises 

 much more rapidly than it does at the 

 lower temperatures. Tammann's sub- 

 stance was somewhat impure, as he 

 himself recognized, so that it was ques- 

 tionable how much of the curvature could 

 be laid to the account of the impurity, 

 but Tammann suggested that it might 

 be found that for the pure substance the 

 transition line would pass through a verti- 

 cal position, and consequently the latent 

 heat through a zero value, before reach- 

 ing the triple point. In the effort to 

 settle this question, I made careful meas- 

 urements of the transition coordinates 

 between 50° and the triple point; these 

 are reproduced on a much enlarged scale 

 in Figure 30. It is seen that no point 

 departs from the straight line (this is the 

 same straight line which passes through 

 the low temperature points) by more than 3 kgm., which is the limit 



50 



1900 2100 

 Pressure, kgm. /cm/ 



Phenol 



Figure 30. Phenol. Points 

 on the upper end of the tran- 

 sition line I-II on a very much 

 enlarged scale. There is no 

 curvature appreciable. 



