544 



Mr. Richard Threlfall 



[Marcli 19, 



called a melting-point curve, and this divides the field into two parts, 

 so that on one side of the curve the temperature and pressure at each 

 point have such values that the substance is solid, while on the 

 other side their values are such that the substance is liquid. It is 

 instructive, therefore, to regard the melting-point curve as the line 

 separating the region of solid from the region of liquid. Along the 

 line, and along it only, i.e. at the pressures and temperatures indi- 

 cated by points on the line, the solid and liquid phases can exist in 

 equilibrium together. Such a diagram is called a " Diagram of Con- 

 dition." 



5000 



3000 



2000 



-1000^ 



4000 



3000 



2000 



1000 



80 



100 

 cc 



40 



120 

 cc 



42 



14-0 

 CC 



44 



Fig. 1. 



46" 48 



ISO" 

 cc 



200° 



50" 



52 



240 



54" 



Full lines indicate party field actually explored. 

 Dotted lines indicate extrapolations. 



By far the greater part of our information as to the quantita- 

 tive relations of bodies at high pressures we owe to Prof. Gustave 

 Tammann, who has collected his results in a book entitled " Kristal- 

 lisieren und Schmelzen," whose advent (1908) must lie regarded as 

 an important event in the history of the subject. 



The complete thermodynamic specification of a body involves a 

 knowledge of its mass, volume, pressure, temperature, energy, entropy, 

 surface tension, and nature — whether Hquid, solid, glassy, crystalHne 

 or amorphous. 



Prof. Tammann has simultaneously measured the pressure, tem- 

 perature, volume and mass of many substances under high pressure, 

 and at temperatures extending from 80° to 200° C. — taking cognizance 



