DETERMINATION OF MELTING POINTS 
221 
butyrorefractometer may be ‘ employed. By regulating the 
heating flame and the rate of flow of hot water, very gradual or 
very rapid rises of temperature may be obtained or the temper¬ 
ature may be maintained almost constant. Jacketing the cell 
with asbestos simplifies the regulation of temperature. Heaters 
functioning on the principle of the thermo-siphon, Fig. 133, may 
also be employed for temperatures up 
to 85 to 90° C.; but above 90 de¬ 
grees the regulation of the height of 
the heating flame becomes rather diffi¬ 
cult and the sudden formation of 
steam usually results in a blow-off 
through the safety tube, in which the 
thermometer is only very closely in¬ 
serted. 
Substituting brine or oil for water, 
the temperatures can be raised to 
125-150 degrees if the heating coil be 
used, but the author has never found 
hot oil to give satisfactory results in 
any thermo-siphon system, since the 
viscosity of the oil in the glass cell 
is too great to permit an even and sufficiently rapid rate of flow 
unless large conducting pipes be employed, necessitating a cell 
far too thick for use. 
The temperatures may be conveniently measured by means 
of a set of Anschutz thermometers. Thermometers of this 
type are sufficiently small, so as not to project too far, and their 
graduations are such as to permit readings to be taken to o.i 
degree. 
A convenient arrangement for reading the thermometer and 
observing the melting point of the substance under observation 
is given below. 
With hot stages of the sort just described it is always a wise 
precaution to place the cell in a glass tray or shallow crystallizing 
dish to guard .against damage to the microscope should the hot 
stage break. 
Fig. 133. Heater for Melting 
Point Apparatus. 
