„699 
Impurities diminish the maximum velocity of crystallisation. Therefore 
the substance has been recrystallized before it was used, till the 
velocity of crystallisation no longer varied. *) 
2. The determination of the specific heat took place in the usual 
way in a calorimeter filled with water. The liquid salol had been 
fused into a glass tube to prevent crystallisation of the supercooled 
substance. 
The values found were for solid substances and liquids resp. 
é; = 0:35 
Cs = Cain 
3. In order to measure the heat of fusion, a tube filled with 
melted supercooled salol was put in the calorimeter, and then left 
till the temperature had become constant. By placing a particle of 
the solid substance into the supercooled salol, crystallisation was 
started. The heat of fusion followed from the rise of temperature 
found. The former depends on the temperature, in this way. that 
the increase per degree is equal to the difference c, — c, = 0.02 of 
the specific heats of the Jiquid and the solid phase. For the end in 
view determination of the value of the heat of fusion at a tem- 
perature not lying too far under the melting-point e.g. 16°, will 
suffice. 
As this temperature the heat of fusion is found to be: 
Q = 18.2 cal. 
4. The density of the liquid was determined in the supercooled state 
by means of a pycnometer, and amounted at room-temperature to: 
vla 
_ The ratio of the densities of solid and liquid phase was found 
from the contraction on solidification in a cylindrical tube. 
The density of the solid substance appeared to be: 
0, = 1:289: : 
5. The conductivity was measured in comparison with that of 
glycerine. These relative measurements were carried out in the 
following way. 
1) Great care should be taken not to heat the substance tov much above its 
melting-point, because a change takes place at higher temperature, which greatly 
diminishes the velocity of crystallisation. This phenomenon can possibly explain 
why Tammann has found a smaller value (3.46 m.m. per minute) forthe maximum 
velocity of crystallisation. When the substance which has been changed by too 
great heating, is recrystallized several times with avoidance of temperatures 
above 100°, the rate of crystallisation decreases. For the sufficiently purified sub- 
stance the value of 3.68 m.m. a minute is always again found for the maximum 
velocity of crystallisation. 
