POLYMORPHIC TRANSFORMATIONS OF SOLIDS. 



107 



to 153° at 2200 kgm., but no transition line was found. Again the 

 question, what had become of the line starting at 127°? Very shortly 

 after this the flaw in the cylinder grew to visible size, a new cylinder 

 was made, the mysterious points found before at high temperatures 

 and pressures disappeared, and the correct explanation of the effects 

 was found. 



In brief, the curious effects are due to a transition curve with a 

 maximum, combined with a region of indifference of unusual shape. 

 This region is indicated by the circles in Figure 24, which mark the 



experimentally determined limits of this region; the transition curve 

 is drawn through the mean points. We see that the region of indiffer- 

 ence is of different shape on the two branches of the curve. If Hgl2 is 

 heated at atmospheric pressure, the red changes to yellow pretty 

 sharply on passing through 127°, but on cooling again, the yellow may 

 persist for several hours, even at room temperature. That is, the red 

 cannot be much superheated, but the yellow can be very considerably 

 subcooled. With increasing pressure and temperature, the shape of 

 the region changes as indicated, until on the descending branch of the 

 transition line, the equilibrium may be overpassed in either direction, 

 but to a very much less extent than at atmospheric pressure. This 



