lUUS. ] 
CALIBRATION OF ELECTRICAL PYROMETERS. 
109 
milar observations relative to the constancy of temperature along the 
sis of a zinc crucible. The form with open tube, Fig. 15, is used, so 
lat the variation of temperature along as much as 14 cra of the axis can 
e measured. During measurement the central tube is closed above 
ith a loose plug of asbestos wicking. Experiments are made with two 
irnaces, placed side by side and heated simultaneously. It is difficult 
) define the surface of ebullition with reference to tbe crucible, for the 
inc is apt to be porous and of great bulk, and it is sure to be spattered 
gainst the top of the crucible and to solidify there. T in Table 15 is 
pproximate, since the variation of T is alone of interest here. It was 
ecessary to finish the observations for the first crucible before com- 
mencing those of tbe second. 
able 15. — Constancy of temperature along the axis of the zinc crucible. Form, cf. Fig. 15 
FURNACE No. 1. 
Height above 
bottom 
of crucible. 
t. 
C20. 
T. 
Time. 
Remarks. 
Cm. 
4 
8 
10 
12 
8 
4 
21.6 
21.6 
21.6 
21.6 
21.6 
21.6 
Microvolts. 
11060 
11060 
10950 
10670 
11090 
11090 
° C. 
Hours. 
3.18 
3.25 
3.30 
3.33 
3.38 
3. 43 
1 
i Liquid surface about 8 rm 
i above bottom. 
1 
1 
FURNACE No. 2. 
4 
8 
' 10 
12 
14 
10 
8 
4 
21.6 
21.6 
21.6 
21.6 
21. G 
21.9 
21.9 
21.9 
11040 
11060 
11010 
10970 
10830 
11090 
HObO 
11080 

3. 55 
3.58 
3.67 
3.70 
3.85 
3.92 
4.00 
i 
1 
1 Liquid surface about 8 cm 
[ above bottom. 
1 
i 
To obtain a full understanding of the purport of these data it is neces- 
ary to turn to Fig. 15, p. 94, where tbe positions of the present points 
I observation have been marked with little circles. Tbe data, there- 
)re, show most remarkable and unexpected constancy, particularly so 
'ben compared with tbe results for mercury and sulphur. This is due 
i tbe fact that tbe distilled zinc condenses on the sides of tbe upper 
nd colder parts of the crucible and then runs down on the walls — a 
let well demonstrated by breakage of the crucible after the exped- 
ient. Hence the interior is practically encased in an envelope of boil- 
ig zinc, although the exterior of the crucible by actual measurement 
bows 1,400° and more. A significant result of these explorations is 
lis, that the passage from t\n> region of boiling liquid into the region 
f vaporized zinc is not discernible in the data. Temperature is prac- 
.cally constant until the upper cold parts of the crucible are reached. 
(703) 
