Vol. 7, 1921 
CHEMISTRY: A.W.C. MENZIES 
83 
lower bulb. With regard to (7), it is indeed most necessary to employ 
a factor, different for each temperature, to convert observed readings to 
temperature; and this factor may be criticized as inconvenient to use, 
inaccurate in value and laborious of computation. But the use of a 
similar factor is likewise necessary, albeit frequently neglected, in the case 
of the Beckmann thermometer, whose degree, if true at 0°, is, for example, 
about 3% in error at 80°. 5 The accuracy of the conversion factor for the 
newer type is dependent in part on the accuracy with which the vapor 
pressure of the filling liquid is known. For such liquids as would be em- 
ployed, and within the ranges of temperature that come here in question, 
this quantity, the vapor pressure, can now be measured to better than 
one part in one thousand. 6 The table that will be published for the filling 
liquid water, in a more comprehensive article elsewhere, was derived by 
differentiation from the highly satisfactory, if cumbrous, equation con- 
necting temperature and vapor pressure of water given in the 1918 edi- 
tion of the Smithsonian Meteorological Tables, and has an accuracy of 
just this order. The process of computing factors for, perhaps, each tenth 
part of a degree over a considerable range of temperature may indeed be 
laborious; but, once published, the factor table may be used by everyone. 
This inconvenience, therefore, is shifted from the shoulders of the user of 
the thermometer to those of him who first computed the table. It may be 
added that the Beckmann type is considerably more cumbrous as well as 
very much more fragile than the type here described, which one constructs 
from stout-walled Pyrex tubing. 
In certain respects, therefore, it would appear that this type of differ- 
ential thermometer has advantages over the Walferdin metastatic type 
as elaborated by Beckmann; and the question arises as to whether such 
other factors as are peculiar to a given application are favorable to its 
use. In studying its application in ebullioscopy, for example, as outlined 
in the article following, one finds that the important disturbing factor, 
peculiar to ebullioscopy in its incidence, of barometric fluctuation does 
not measurably affect the readings of the newer type, while such pressure 
fluctuations are one of the chief outstanding sources of error when the 
metastatic type is used. Another application in a different field may be 
described in the near future. 
1 Menzies, A. W. C, Easton, Pa., J. Amer. Chem. Soc, 42, 1920 (1951-1956). 
2 Cavendish, London, Phil. Trans. Roy. Soc, 50, 1757 (300); Walferdin, M., Bull. 
Soc. geol. de France, 13, 1841-2 (113). 
3 Beckmann, Leipzig, Zeit. physik. Chem., 2, 1888 (644); 51, 1905 (329). 
4 Cf. Staehler, A., Leipzig, Arbeitsmethoden in der Anorg. Chemie, 3, i, 1913 (106). 
5 Staehler, A., Ibid., p. 108. 
6 Cf. Smith, A., and Menzies, A. W. C, Easton, Pa., J. Amer. Chem. Soc, 32, 1910 
(1412-1434). 
