92 BRIDGMAN. 



temperature. The corners of the cur^'es were rounded, an effect not 

 found before at high pressures. Evidently the CBr4 had become 

 impure on standing. This same lot of CBr4 was then used again in 

 the high pressure apparatus to give two points on the transition line 

 below 127°, the lowest temperature previously used. The data were 

 apparently all in; but on working them up, it appeared almost unmis- 

 takable that the two low pressure transition points first found were 

 genuine, really belonging to a new modification, and were not the effect 

 of decomposition. The evidence which made this almost inescapable 

 was the values of AT, which had not been computed before. There 

 was a discontinuity in the values for AV along the transition line, 

 the amount of discontinuity corresponding very closely with the AV 

 found for the questionable points. Furthermore, the points on the 

 lower end of the transition line, below 127°, did not lie smoothly with 

 those above 127°, but there was a pronounced change of direction at 

 about 110°. The perfect reversibility of the two suspected transitions 

 strengthened the probability. The reason why it took me so long to 

 admit that this was a new form, was because thus is a new type of 

 transition, in which a new form appears at high pressures and tempera- 

 tures with a volume intermediate between the two low pressure forms; 

 there seems to be no excuse for the existence of such a form. In order 

 to make certain that there was really a new form, a fresh lot of CBr4 

 was ordered from Hoffmann and Kropff, with the request that they 

 take special precautions in purifying it. This lot was triply distilled 

 in steam. The new material was first used in the high pressure 

 apparatus. The first point was obtained at 108°, below the sup- 

 posed triple point, and the second at 123°, above the supposed point 

 and as near to it as was convenient to work. Only one transition 

 was found at 108°, but two at 123°. The lower of these two, which 

 is the questioned one, was found to be reversible exactly as before. 

 There could be no doubt of the genuineness of the transition. It is 

 unfortunate that this second lot decomposed at a lower temperature 

 than the first lot; the decomposition was barely perceptible as low 

 as 108°, and at 145° was proceeding so rapidly that even p-t values 

 for the higher pressure could not be obtained. The AT' values at 108° 

 and 123° with this second lot are both too high because of decomposi- 

 tion. The rest of this second lot was used for a determination of the 

 transition point at low pressures by the method of changing pressure 

 at constant temperature: The value found by extrapolation for the 

 transition temperature was 46.2°. This is somewhat higher than the 

 A'alue given by the first lot, and as there was less roimding of the cor- 



