142 
DE. WALTER WAHL: PHYSICO-CHEMICAL DETERMINATIONS 
“ melt ” is crystallized either by decreasing temperature or by increasing pressure. 
The crystals both grow very slowly and melt very slowly. The growth of the 
crystals is not much hastened even by increasing the pressure by as much as 
200 atmospheres, but a great many new crystal germs then appear and grow in all 
directions to remarkably evenly-developed small crystals. In spite of the slowness 
with which these crystals grow, the force developed in crystallizing is so great that 
they, even at pressures above 1,000 atmospheres, tend to push the glass plates apart 
in spite of the strong outer pressure acting on these. As a result the glass plates 
are bent, and if the crystals are allowed to grow too large the glass plates are broken 
by the pressure. For these reasons the curve connecting the points where formation 
of crystal growth-structures eventually would occur has not yet been determined. 
In consequence of the slowness with which melting takes place at the equilibrium 
curve crystal—liquid, it is possilde to slightly superheat the crystals by decreasing 
the pressure at constant temperature as described on p. 131. We are able to deter- 
Table V. 
Temperatures, t 
(corrected). 
Pressures, Pi 
(corrected). 
Pressures, Pj 
(corrected). 
° C. 
(64 
1 kg./cm.2) 
— 
66-04 
160 „ 
— 
68-86 
260 „ 
220 kg./cm.- 
73-24 
470 „ 
440 „ 
79-21 
790 „ 
760 „ 
84-73 
1060 „ 
mine a pressure at which the melting of the crystals begins to take place with 
sufficient rapidity to be observed, and on further gradually decreasing the pressure 
the crystals are seen to melt slightly faster, but when a certain pressure, below the 
pressure at which melting is first seen to take place, is reached the melting suddenly 
becomes very rapid. This pressure is, at about 5° C. above the melting-point at 
ordinary temperatures, 40 atmospheres lower than the pressure at which melting 
is seen to take place quite slowly, and at temperatures about 15° C. above the 
melting-point it is 30 atmospheres lower. The extent to which the crystals may 
he superheated therefore diminishes towards higher temperatures on the melting- 
point curve, apparently because the rapidity of melting increases with the temperature 
of the melting-point. The pressure at which melting can be just observed is not so 
easy to determine accurately as the pressure at which crystallization can be just 
observed, and only the latter therefore has been determined. The points of the 
actual equilibrium curve are to be found between these two pressures, which, 
