560 
CHEMISTRY: A. W. C. MENZIES 
temperature of the hot gauge could be computed in an obvious manner, 
if Dalton's law were assumed. 
For details of the experiments and mode of reduction of the results, 
as well as for tabular comparison with the heretofore existing data, a 
paper may be consulted that will appear elsewhere.^^ It should, however, 
perhaps be stated here that, at the pressures and compressions used, the 
neglect of the known divergence of hydrogen from the simple gas laws 
would cause an error very much smaller than other errors of the experi- 
ment. Equlibrium in the hot gauge was, apparently, always established 
sooner than a measurement could be made. A small correction was 
applied to correct for the vapor pressure of mercury in the cold gauge. 
A possible systematic error may arise from the fact that the apparent 
vapor pressure of a liquid in contact with a gas is not in all cases identical 
with the vapor pressure at the same temperature of the same liquid in 
a vacuum. Although this fact was observed by Regnault,^^ it has 
apparently escaped the notice of many users of the gas-current method 
for determining small vapor pressures. The error is the greater the more 
soluble the gas in the liquid, although it is not conditioned solely by this 
solubility as such. With hydrogen gas at atmospheric pressure, the 
order of this error, in the case of liquids in which hydrogen shows 
marked solubility such as ether, carbon disulphide and acetone, is about 
1% at 30°; with mercury, in which no evidence of solution was found, 
and at the temperatures here in question, the order of the error might 
be expected to be much smaller, were it not that low gas pressures may 
be especially prejudicial. Further study of this possible error is planned, 
and one can only say, with T. W. Richards, that these results are of but 
a preliminary character. 
The brief table belov/ summarizes the results obtained. The ' calculated' 
values in the third column are those derived from the Kirchoff-Rankine- 
Dupre equation (R), whose constants were given above; the values in 
the fifth column are likewise derived from this equation. In the last 
column, P stands for the pressure, in millimeters of mercury, of hydrogen 
in the reservoir. 
Vapor pressures of mercury 
TEMPERATURE 
VAPOR PRESSURE IN MILLIMETERS OF 
MERCURY AT 0° 
xioo 
CALCULATED 
PERCENTAGE 
CHANGE OF 
PRESSURE PER 
0.1° 
P 
Found 
Calc. 
191.5° 
13.02 
13.02 
100.00 
0.34 
14.28 
150.0° 
•2.802 
2.811 
99.67 
0.39 
3.564 
121.8° 
0.829 
0.823 
100.75 
0.47 
1 . 73-S 
