116 MEASUREMENT OF HIGH TEMPERATURES. [bull. 54. 
standpoint of the present investigation, is not the purpose of the 
present chapter and will be touched upon later. 
Time variations of thermo-electric data. — In this place a consideration 
of the degree of coincidence between present and former zinc data is per- 
tinent. In the results given in Table 6, Chaper I (p. 78, June 11), the 
values for the boiling point of zinc if expressed in (reduced) units ol 
elctromotive force were : 
Microvolts. 
No. 17 ^20 = 9220 
No. 18 2O = 918O (188; 
No. 22 2 o = 924O 
These values are available for comparison with the data of Table 16 
Chapter II, from which the corresponding mean values are found to be : 
Microvolts. 
No. 17 2 o = 919O 
No. 18. 0,o = 914O (188; 
No. 22 2 o = 92OO 
This slight difference of iess than J per cent, in the values of 2O , and! 
which amounts to only about 3° of temperature, is quite negligible and! 
easily referable to the incidental errors of experiment. In the large 
furnaces of Chapter I such an error is possible, even at the cold junction,! 
Duration of continued ebullition, constant high temperatures. — This> 
brings me finally to a consideration of the constancy of the boiling point 
as observed with the crucibles described, when this constancy is con- 
sidered with reference to the time during which ebullition has beem 
going on. A series of such results are given in Table 16, and if neces- 
sary others may be supplied during the course of the discussion. Turn 
ing first to the results, 2O , for zinc, it appears that after the value of 1 
has become constant at about 3 o'clock, the variation in 2O from this 
time until 5 o'clock (9180 microvolts to 9230 microvolts) are only a little 
more than J per cent, of 2O , corresponding to about 4° centigrade for 
the two hours of ebullition. This variation is an almost regular in- 
crease of T. This strikingly perfect degree of constancy of the tem- 
perature of this crucible is additionally attested by the values of ei 
for the elements Nos. 18, 22, 35, 36, to which I might adel many other 
results, were it at all necessary to supply further corroboration. By 
way of illustration, merely, I will give a few data obtained when the 
contents of the crucibles are antimony or bismuth instead of zinc. J 
will also add some results derived from commercial caelmium. In the 
case of bismuth the walls of the cold crucible, after boiling, were lined 
above the surface of the metal with a fine granular coating of bismuth, and 
very near the surface a narrow zone of little bismuth beads was appa 
rent. Nevertheless, ebullition can only have commenced, as is proved 
by the thermo-electric data, and the incrustation is due to volatilizatioE 
(770) 
