1909-10.] Method for Determining Vapour Pressures. 
437 
XXVIII. — A Simple Dynamic Method for determining Vapour 
Pressures. By Alexander Smith and Alan W. C. Menzies. 
(MS. received April 13, 1910. Read May 16, 1910.) 
(Abstract.) 
Vapour Pressures . — The submerged bulblet apparatus described in a 
preceding paper may readily be adapted to determining vapour pressures. 
Die apparatus is unchanged, excepting that the lower part of the thermo- 
meter is enclosed in a test-tube containing a portion of the bath-liquid 
(fig. 1). The interior of the test-tube communicates, through the L-tube, 
with a gauge, with a pump, and with the atmosphere. The bath is 
brought to constancy at the required temperature with the pressure in the 
apparatus above the vapour pressure of the substance. The pressure is next 
lowered gradually until a continuous stream of bubbles issues from the 
capillary. Then the pressure is allowed to rise until the stream ceases. 
The details of manipulation and correction may be understood from the 
former paper without special description. 
To illustrate the adaptability of this method to securing rapidly a series 
of measurements of considerable accuracy, the following results with water 
are given. The bath-liquid was a heavy paraffin oil. The gauge consisted 
simply of a tube tied to a meter-rule and dipping into a vessel of mercury. 
Corrections for capillarity in the gauge and for immersed depth were made, 
and mercury heights were reduced to 0°. The thermometer showed no 
errors over 005°, and its thread was completely immersed. 
Temp. 
V. P. 
S. & M. 
V. P. 
H. & H. 
Diff. 
mm. 
Temp. 
V. P. 
S. & M. 
V. P. 
H. & H. 
Diff. 
mm. 
49-0 
88-0 
87*8 
+ 0-2 
80-0 
355-4 
355-1 
+ 0-3 
60*7 
155-3 
154-1 
+ P2 
85-5 
441-5 
442-2 
-0-7 
67-8 
213-8 
212-2 
+ 1-6 
90-0 
526-5 - 
525-8 
+ 0-7 
736 
2735 
272-5 
+ 1*0 
95-3 
640-5 
641-1 
-0-6 
The column H. & H. contains the values found by Holborn and Henning,* 
and in the fourth column appear the differences. The average divergence 
from our values is 046 mm., corresponding to an average temperature error 
* Ann. d. Physik, [4], 26, 882 (1908). 
