BARUS.] 
CALIBRATION OF ELECTRICAL PYROMETERS. 
105 
heights above the surface of ebullition. In the following tables, there- 
fore, the absolute values of the high temperature T is of less importance 
and of smaller accuracy, while the variations of T are represented with 
nicety. In the table the temperature t of the cold junction is constant; 
e (microvolts) is the measured electromotive force of a new element, 
Pt hard-Pt Ir 20 per cent., from which the temperature T is computed. 
Table 12. — Constancy of temperature along the axis of boiling tube. Steam. T=100°. 
Height of junc- 
tion above 
bottom. 
t. 
e. ■ 
T. 
• 
Remarks. 
Cm. 
°<7. 
Micro- 
volts. 
°a 
5 
20.0 
660.7 
98.9 
Surrounded by liquid. 
10 
20.0 
673.0 
100.1 
Surrounded by vapor. 
15 
20.0 
672. 2 
100.0 
Do. 
20 
20.0 
672.0 
100.0 
Do. 
25 
20.0 
672. 
100.0 
Do. 
30 
20.0 
672.0 
100.0 
Do. 
34 
20.0 
666.0 
99.4 
Surrounded by cork. 
5 
20.0 
683.7 
101.2 
Surrounded by liquid ; burner lowered. 
This table is cited as an example of many similar observations made 
with like results. The adjustment of heat was nearly perfect, so that 
no steam escaped. The ebullition was quiet and the water was left in 
the tube in almost undiminished amount at the close of the experiment. 
The first observation 5 cm above bottom of tube is taken at about tbe 
middle of the boiling liquid and the temperature here depends upon 
whether the ring burner encircles the tube above or below this point. 
The next observation, 10 cm from the bottom, is about 2 cm above the 
surface of ebullition, and from here to the upper cork the temperature 
is absolutely constant. To make these explorations it is necessary that 
the thermo-couple be new or perfectly homogeneous and annealed; other- 
wise the error of homogeneity will be falsely attributed to an error of 
the constancy of the boiliug tube. Exploration with a mercury ther- 
mometer is less satisfactory than the thermo-couple test because the 
stem of the thermometer usually projects. 
Similarly constant results may be obtained with aniline at 187°, 
which it is therefore not necessary to cite. They show that with the 
junction about l cm above the zone of ebullition, quiet boiling presup- 
posed, its temperature may be regarded identical with that of a mer- 
cury thermometer placed contiguously with the mentioned junction 
and i user ted from above. 
Exploration for constancy of temperature ; mercury. — In the case of mer- 
cury the zone of constant temperature is of course much less in height, 
and special investigations with respect to it are therefore essential. 
The data in the table are given on a plan identical with the foregoing. 
Eesults are also appended for mercury impure with oxide, in which 
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