barus.] CALIBRATION OF ELECTRICAL PYROMETERS. 121 
Table 22.— Available substances for boiling point experiments— Continued. 
Elem. 
No. 
Substance. 
e 20 . 
T. 
Time. 
2 25 
30 
37 
Remarks. 
36 
Benzoic acid 
Micro- 
volts. 
1731 
2071 
2071 
° C. 
209 
254 
251 
Boils quietly; perhaps more so than naphtha- 
line. 
2071 
254 
45 
2071 
254 
3 
2077 
255 
25 
2077 
255 
35 
36 
Camphor 
1632 
1638 
1638 
209 
210 
210 
4 
45 
20 
Boils quietly. Preferable to benzoic acid. 
Scarcely changes color. Inodorous. 
1645 
211 
45 
1649 
211 
5 15 
1642 
211 
35 
1640 
211 
6 
Distance Between planes of demarcation = 
12 c:n . Asbestos jacket evon red hot at one 
1634 
1644 
210 
211 
C 
6 
point. 
— > just below upper plane of demarkation. 
— > just above lower plane of demarkation. 
Data for the variation of boiling point with pressure with a special 
view to thermometric application have been investigated for naphthaline 
(218°) and benzophenol (306°) by Crafts. 1 The possibility of using selen- 
ium in glass boiling tubes has been demonstrated by Troost. 2 V. Meyer 3 
has made use of amylbenzoate, diphenylamin, and phosphorous penta- 
sulphide. 
Volatilizing points. — In addition to the experiments on boiling points, 
I made an attempt to utilize the above apparatus for measuring points 
of volatilization. Professor F. W. Clarke suggested the arsenic point as 
a desirable and insufficiently known datum and Mr. G. F. Becker made 
a special request for the point of volatilization of cinnabar. With both 
of these substances as well as with sal ammouiac I made large numbers of 
experiments, but failed in getting satisfactorily constant and reliable re- 
sults. The effect of applying the ring burner around the sublimable solid 
in the tube is to form a very perfect hyperboloid of one nap, as it were ; 
a figure, in other words, which resembles in form a united stalactite and 
stalagmite. The effect of heating is to volatilize the solid around the 
plane of the ring burner, and condensation takes place above and below 
the plane, forming the figure specified. A priori, it might be argued 
that so long as the hyperboloid remains intact and completely envelops 
the thermo-element, so long will the temperature of the junction not 
increase above the point of sublimation of the substance. Except in 
« Crafts, Chem. Ber., vol. 20, 1887. p. 709. 
2 Troost, C. R., vol. 95, 1882, p. 30. 
Goldschmidt u. Meyer; Chem. Ber., 1882, vol. 10, p. 137. 
(775) 
