558 
CHEMISTRY: A. W. C. MENZIES 
NEW MEASUREMENTS OF THE VAPOR PRESSURE OP 
MERCURY 
By Alan W. C. Menzies 
Department of Chemistry, Princeton University 
Communicated by W. A. Noyes, October 14, 1919 
Writing in 1908, Laby^ retnarked "The vapor pressure of mercury is 
intrinsically important; it has been determined for a wider range of 
temperatures than that of any other substance. . . . Yet the 
greatest — and, it should be added, unnecessary — disagreement is to be 
found in the current values for this vapor pressure, nor is there any table 
combining all the existing observations. " Laby thereupon proceeded 
to collate the best observations available at that time and published 
a weighted average table. 
In 1910 Smith and I pubHshed^ the results of 43 direct observations 
of the vapor pressure of mercury by a static method over the tempera- 
ture range 250° to 435°. The pressure measurement was immensely 
facihtated by the use of the newly-devised 'static isoteniscope;'^ and a 
good form of platinum resistance thermometry was available. The 
average divergence in temperature of an individual observation from 
the smooth curve given by the equation 
log p = 9.9073436 - 3276.628/^ - 0.6519904 log B, (R) 
whose constants were chosen to fit our results, was 0.050°. Because of 
the rather high degree of consistency thus attained, we were encouraged 
to exterpolate the curve in both directions and found that the values so 
obtained agreed remarkably well with the average experimental findings 
of those who had worked either above or below our temperature region.* 
A critical discussion of our own and of the older work on this subject, 
with tabular comparisons, may be found in the paper referred to.^ 
In 1909, Knudsen developed a relationship^ connecting the weight of 
gas passing through tubes containing pierced diaphragms with the 
difference of gas pressure at the ends, the density of the gas, the resist- 
ance of the tube and diaphragm and the time of flow. He appHed this 
to measure the vapor pressure of mercury^ from 0° to 50°, above which 
temperature his relationship failed to hold. From the lower to the upper 
end of this range, his results run from 10.9 to 6.2% respectively in 
pressure lower than the values given by extrapolation of our 1910 results 
