B A1UIS. J 
CALIBRATION OF ELECTRICAL PYROMETERS. 
89 
of tube shown in Fig. 11 is convenient. This differs from the other 
forms only inasmuch as the outer tube a a is closed upon the central 
tube d d both above and below. A special lateral tubulure, h, commu- 
nicating with a manometric arrangement subserves the purpose of vary- 
ing the pressure by any amount compatible with the strength of the 
tubes. It is also through h that the substance to be boiled is intro- 
duced. It is by means of this arrangement, that I purpose to study the 
relation between boiling point and pressure over long ranges, and 
for mercury, sulphur, and divers other substances. The thermo-ele 
ment for such purpose must be calibrated with the re-entrant glass air 
thermometer described in Chapter IV. 
Tubes of this kind I obtained from M. Emil Greiner, of Nassau street 
New York. Glass of a specially hard quality is made by Appert freres 
Olichy, France. Inasmuch as M. Troost was able to boil selenium in 
this material with impunity, the upper thermal limit of the glass boil 
ing tube may be considered given by the boiling point of selenium 
Tubes of the kind here described for investigating the boiling-point 
pressure functionality are the simplest and at the same time the most 
Fig. 12. Ring-burner. Scale, £. 
(743) 
