122 
MEASUREMENT OF HIGH TEMPERATURES. 
[BULL. & 
the case of TJ 4 K01, in which sublimation is very rapid, I was not abl 
by using the tubes to obtain very distinct points of sublimation, sho\s 
ing an unmistakable tendency of these substances to superheat, o 
at least to contain superheated vapor in the interstices of the rnas* 
Arsenic, for instance, forms a distinct mirror on the tube before an; 
constancy of temperature is reached, and, moreover, the temperatur 
may be increased above this point almost to the limits of heatin; 
capacity of the burner. In the case of cinnabar the conditions are stil 
further complicated by the tendency of this substance to decompose ii 
air at high temperatures. It is necessary, therefore, to pass thrOugl 
the tube a current of carbonic acid. By doing so, however, the tend 
ency to irregularities of thermal constancy are much increased. Fo 
the reasons stated I think it preferable to withhold my data from thi, 
chapter altogether, and to publish them in connection with certain ex 
periments on the relation between boiling point and pressure which 
have in view. For such experiments the above apparatus, Fig. 11, ii 
eminently fie. Possibly if the given substances be under sufficien 
pressure to liquefy them at the subliming point, a true value for the tern 
perature of ebullition may be found. 
Subsidiary data. — In conclusion I desire to insert here a number o 
subsequent results, the electro-motive force of which is given on a dif 
erent scale from that heretofore adopted. These data are not to be pu 
in relation with the results given above, but are subsidiary as regards 
the matter discussed in Chapter IV, on which they have an importam 
bearing. In each case the apparatus used to obtain them has been tin 
perfected form, and the results are therefore as trustworthy as mj 
methods can make them. Allowing for the difference in the assumec 
value of the standards used, they agree with such results as have al 
ready been given, with all desirable nicety. 
Table 23. — Calibration in zinc vapor, December 10, 1886. 
[Charge of crucible, 9 ounces.] 
No. 
t. 
e. 
e-2o. 
Time. 
Mean 620, 
37, 38, 39, 40. 
o a 
Micro- 
volts. 
Micro- 
volts. 
h. m. 
Microvolts. 
22 
20 
9830 
9830 
2 15 
11033 
35 
21 
11070 
11078 
20 
36 
22 
10980 
10997 
25 
37 
23 
, 11010 
11036 
30 
22 
24 
9780 
9814 
35 
38 
25 
10980 
11023 
37 
39 
26 
10980 
11031 
40 
40 
27 
10980 
11040 
45 
22 
28 
9735 
9803 
55 
22 
28 
9780 
9848 
3 00 
The following results were obtained at a later date. The thermo- 
couples are tested in three different furnaces, placed side by side and 
(776) 
