164 BRIDGMAN. 



Elements: Hg, cubic; K, tetragonal; Na, tetragonal; Sn*, rhom- 

 bic, tetragonal; Bi, trigonal; Tl*; S*, rhombic, nionoclinic; P*, cubic; 

 I*, rhombic, monoclinic; As*, cubic, trigonal; Sb*, trigonal; Se*, mono- 

 clinic (2), trigonal. 



The investigation of mercury was concerned primarily with the 

 melting curve. Its freezing behavior is known to be abnormal, but 

 since the freezing temperature is a much smaller fraction of the critical 

 temperature than it is for most other substances, one would not 

 perhaps expect the abnormality to result in polymorphism. Sodium 

 and Potassium show nothing unusual. Perhaps, from the rather rapid 

 approach of Av toward zero, Potassium might be regarded as a candi- 

 date for polymorphism at some pressure beyond the range of this 

 work. Bismuth would be expected to have another form because its 

 melting is of the ice type ; it is a great surprise that it does not. Thal- 

 lium has another known form; the change of volume is so small that 

 I could not make accurate measurements. 



The reason for trying Tin was that it is known to have a transition, 

 point at 20°, with a large change of volume, the low temperature 

 phase (gray tin) being the less dense. A phase diagram like that of 

 Agl might be expected. The transition from white to gray tin is- 

 known to be enormously viscous, so that one could not expect to 

 observe this, but there was a possibility that the reaction to Tin III, 

 if there is such, might run more readily. No such transition was 

 found. It would be of interest to start with pure gray tin, and subject 

 this to pressure at a low temperature. 



Werner ^^ has recently given a provisional location for a transition 

 line between two varieties of white tin. The transition point at 

 atmospheric pressure is at about 160°, and at 200°, it is 500 kgm. The 

 change of volume is extraordinarily small, so small that I could hardly 

 expect to detect it with my apparatus at a pressure so low as 500 kgm.,, 

 where it is most insensitive. 



The other elements have been described in a previous section. 



Miscellaneous Substances. — H2O*, trigonal; CO2; KNO2*; 

 K4P2O7; K4S2O7; K2CO3; KHCO3, monoclinic; Potassium Acid 

 Tartrate, rhombic; Methyl Oxalate, monoclinic; Ure thane*; Naph- 

 thaline, monoclinic; Cane Sugar, monoclinic. 



H2O has a phase diagram exceeded in number of phases only by 

 NH4NO3, and possibly by camphor. CO2 was at first thought by 

 Tammann, to have a triple point with the liquid near 4000, but he 



38 M. Werner, ZS. Anorg. Chem., 83, 275 (1913). 



