POLYMORPHIC TRANSFORMATIONS OF SOLIDS. 91 



in analogy with CCI4, that a new modification would be found on 

 increasing pressure at room temperature. None was found, however, 

 up to 12000 kgm. Temperature was then raised to 127°, and pressure 

 relieved from 12000. Two transitions were found, at 2800 and 2310. 

 These transitions both ran sharply, with no rounding of the corners, 

 and were entirely reversible. The change of volume at the lower 

 transition was considerably^ less than that of the higher. Even the 

 approximate location of the melting curve was not known at the time 

 of this run, so that the low pressure transition might have been melting, 

 although this seemed unlikely in view of the complete absence of 

 rounding of the corners. Temperature was then raised to 152°, 

 and the transitions found with decreasing pressure. Two transitions 

 were found, but separated by a much wider interval than before, and 

 there was some preliminary rounding of the corner at the lower point. 

 This lower point might have been melting this time, therefore, but 

 there seemed no connection with the low point at 127°. Temperature 

 was now raised to 176°. The regular transition was found at high 

 pressures, on a line with the other two points, and a lower point was 

 also found. This lower point was too high to fall with either of the 

 other two lower points, and the transition was partly reversible and 

 partly irreversible; that is, on increasing pressure the return of ^'olume 

 to the original value was not complete. At 176°, pressure was now 

 raised to 6000, and the temperature raised to 200°. Pressure was 

 now increased to 12000 kgm. Two notable decreases of volume were 

 found on the way to 12000, at approximately 6800 and 7500. But on 

 decreasing pressure, no transition of any kind could be found down to 

 4000 kgm., that is, considerably beyond the higher of the two transition 

 lines. The apparatus was now cooled and taken apart; the CBr4 

 was found completely decomposed into carbon and bromine. The 

 products of the decomposition reached all parts of the apparatus, 

 and there was considerable trouble in cleaning it. In view of this 

 decomposition and of the fact that the higher of the transition points 

 lie on a line which extrapolates with little curvature to the known 

 transition point at atmospheric pressure, this first run was supposed 

 to indicate only one modification, the lower transition points being 

 ascribed to some obscure effect of the decomposition. 



With this conclusion, the subject was dropped for over a month, 

 when the rest of the first lot of material was used in the low pressure 

 apparatus to fix the transition data at atmospheric pressure. Two 

 runs were made with this; one with increasing temperature at con- 

 stant pressure, and the other with decreasing pressure at constant 



