yyyyhhThe temperature changes of the sample during the specific-heat
measurements will be given in some detail', since it is possible that the
results of this investigation may depend somewhat on the thermal
history of the material. The first'run was made after the sample had
cooled quickly from room temperature to that of liquid air, about 85°
K. Seven individual heatings in this run brought the temperature to
136° K. The sample was then cdQ,led quickly again to 85° K and the
second run was made, ending at 221 ° K. Next the sample was cooled
by carbon dioxide snow to about 195° K. In the third run the temperature
was raised to 273° K. At about 251 0 K (mean temperature
of heating 247.26° K), the end of the sixth heating of this run, the
temperature drifted downward at an initial rate of about a thousandth
of a degree per minute under the usual adiabatic conditions. The
drift continued for about 2 hours before it became inappreciable. At
temperatures more than about 10 degrees above or below the second- order transition, the temperature became constant within a period of
about 8 minutes after the completion of a heating.
Overnight the temperature was allowed to rise to 2870 K. From
this temperature the specimen was cooled to 2570 K, and during the
fourth run the temperature was raised to 307° K. The specimen was
cooled quickly again to 1960 K for the fifth run. At about 246° K,
the temperature at the end of the fourth heating of the run, a downward
drift of temperature again took place. Before the temperature
became constant, more heat was added until the temperature was
250° K.
The temperature was then allowed to decrease slowly by discontinuing
the heating of the thermal shields around the sample container.
The temperature fall was at the average rate of about 2.40
per hour. At 209° K the sL'{th run was started. Downward drifts of
temperature were again observed at the ends of the fifth, sixth, and
seventh heatings of this run, although only the normal time was required
for equilibrium in all the other heatings. The approximate
times required for a constant temperature to be reached after each of
the three heatings just mentioned were 0.5 hour at 2430 K, 1.5 hours
at 2480 K, and 1 hour at 252° K. From 260° K where the run ended,
the temperature was reduced slowly, reaching about 241 0 K in 16
hours. When subjected to adiabatic conditions after this treatment,
the sample was found to drift upward slowly in temperature. The
initial upward drift was about the same as the previous downward
drifts, about a thousandth of a degree per minute. After about 2
hours no further change in temperature could be observed. The
specimen was next heated to 2540 K, and a downward drift of temperature
was again observed.
The specimen was then allowed to come to room temperature and
remained at that temperature for several days. The temperature
was next quickly lowered to 12.50 K, and the seventh run brought it
up to 1020 K. An immediate cooling brought the temperature to
21 0 K in preparation for the eighth run. After this run the specimen
was warmed to 217.5° K and a 50-minute heating, to be discussed in
more detail later, raised the temperature to 270.20 K. After the
sample had remained at room temperature overnight, the ninth run