132 



BRIDGMAN. 



investigation of a substance showing a new phase at 200° and not 

 at 20°. 



The transition is singular in that there is a region 150 to 250 kgm. 

 wide within which the transition velocity is very slow, whereas outside 

 of this band the velocity increases with unusual rapidity. At any 

 given temperature the equilibrium point was found by artificially 

 changing pressure until a point was found at which the pressure did 

 not change by as much as 0.5 kgm. in 5 minutes. These stationary 

 points are the equilibrium points shown in the diagram. Points were 



TABLE X. 

 Cuprous Iodide. 



also found on each side of the equilibrium points at which the transi- 

 tion was perceptibly running in opposite du'ections. These points 

 are also indicated in the diagram. 



Within the limits of error the transition line is straight. It would 

 extrapolate to a transition point at atmospheric pressure at 690°. 

 The melting point of this substance is listed at 638°. Gossner ^^ 

 makes the statement that, on heating, the ordinary cubic form of 

 CU2I2 changes to a doubly refracting form. He does not state the 

 temperature of transition, except to say that it is very high, but it 

 must probably be considerably lower than 638° if the optical observa- 



26 B. Gossner, ZS. Kryst., 38, 110 (1903). 



