Physics. “Observations of the Temperature during Solidification’. By 
Dr. H. C. Burger. (Communicated by Prof. H. A. Lorentz). 
(Communicated at the meeting of June 26, 1920). 
1. When in a supercooled liquid in a cylindrical tube, a seed 
of the solid substance is inserted, the boundary plane of the solid 
substance moves with uniform velocity. This velocity (linear velocity 
of crystallisation) has been measured by many investigators as func- 
tion of the temperature of the surroundings (thermostat), in which 
the tube is placed. They have, however, not measured the temperature 
prevailing during the solidification in the two phases and at their 
boundary plane, though it is the measurement of this temperature 
that is of great importance for the true insight into the process of 
solidification. More than once the opinion has been expressed that 
at the boundary plane solid-liquid the meltingpoint-temperature would 
prevail *), but no grounds were adduced in support of this statement. 
As, however, appears from my observations this is not the case, at 
least not for the substance examined by me. | 
The small quantity of substance. hence the small quantity of heat 
which is generated, renders it necessary that the instrument with which 
the temperature is measured, should have a very small heat capacity. 
If this is not the case, the distribution of the temperature in the 
substance is disturbed by the insertion of the instrument to such a 
degree that the temperature that is observed, is by no means equal 
to the temperature that would prevail at the same place, when this 
was absent. Besides the measurement of the temperature must take 
place with an instrument that possesses slight inertia, because the 
temperature that is measured at a fixed point of the tube, rapidly 
changes with the time. The temperature further shonld be registered, 
because reading is impossible on account of the rapid variation. 
Consequently a temperature measurement must be chosen which 
is made by the aid of a thermo-element, which must have as small 
a mass as possible. The current supplied by this thermo-element in 
consequence of the rise of temperature in the tube, must be observed 
with a galvanometer, which is sufficiently rapid to follow the process 
1) W. HerGESELL, Ann. d. Phys. u. Chem, 15, 1882. p. 19. 
G. Tammany, Kristallisieren und Schmelzen, 1903, p. 135. 
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Proceedings Royal Acad. Amsterdam. Vol. XXIII. 
