TRANSACTIONS OF SECTION B. 337 
WEDNESDAY, AUGUST 19. 
The following Papers were read :— 
1. A New Method for the Determination of Vapour Pressures and an 
Examination of a Source of Error in certain Dynamical Methods. 
By F. H. Campseuy, M.Sc. 
Since none of the accepted methods is suitable for the determination of the 
vapour pressure of a binary mixture of a volatile with a non-volatile liquid a 
new method has been devised for the purpose. 
The principle used is that of allowing a liquid saturated with a suitable gas, 
usually hydrogen, to evaporate into an enclosed space filled with the same gas at 
the same temperature and pressure, the latter being approximately atmospheric. 
The extra pressure exerted by the vapour is measured by means of an open 
mercury manometer after the volume has been restored to its original value by 
means of a levelling vessel. ‘The method can be applied to volatile organic liquids 
of many kinds, since they come into contact with glass and mercury only. The 
liquid is enclosed in a glass tube projecting through a rubber stopper, which 
closes an opening at the bottom of the vessel, the stopper being protected from 
the action of the liquid by a layer of mercury. When the apparatus has reached 
the temperature of the constant temperature bath in which it is immersed, the 
tube, previously deeply scratched, is broken by gentle sideways pressure on the 
projecting end. Saturation of the gas by the vapour is hastened by gently 
shaking the apparatus. ; 
Experiments have been made with the following liquids and gases: Methyl 
alcohol, ethyi alcohol, diethyl ether, carbon disulphide, chloroform and water, 
evaporating into carbon dioxide, air, hydrogen, and, in the case of chloroform, 
nitrogen in addition. In every case the values obtained, though very con- 
cordant, are lower than the most reliable results obtained by the ordinary static 
method. The magnitude of the error evidently depends on the solubility of the 
particular gas in the particular liquid as it diminishes in each case, except that 
of water, in the order carbon dioxide, air, hydrogen. With water at 60° CG. 
the results obtained with air and hydrogen are practically identical. The 
error when hydrogen is used is generally less than 1 per cent., and it is con- 
sidered that the agreement is sufficient, as with mixtures the ratio between the 
observed pressure of the solution and that of the pure volatile solvent is to be 
considered. With air the errors are from 2 to 6 per cent., and it is concluded 
_ that methods depending on the saturation of a current of a gas passing through 
or over solution and pure solvent must therefore involve more or less error from 
this cause, a fact which does not seem to have been appreciated in the past. 
Perman (‘Proc. Roy. Soc.’ 1903, 72, 72) and Krauskopf (‘J. Phys. Chem.’ 
1910, 14, 489) obtained satisfactory results with water, although those of 
Regnault (‘ Ann. Chim. Phys.’ 1845 (3),15, 129) and Tammann (‘ Wied. Ann.’ 
1888, 28, 322), which are lower than those obtained by the static method, are 
brought into satisfactory agreement with these upon the author’s assumption, 
which indicates that the errors introduced by the presence of a dissolved gas 
are negligible under certain conditions. 
2. A New Method for determining the Specific Heals of Liquids. 
By Ernst Jowannes Hartuna, B.Sc. 
The method described, which was suggested by Professor Orme Masson, is 
a modification of the mixture method for determining specific heats. The 
principle consists in measuring the lowering in temperature of a known amount 
of the particular liquid on the introduction of a definite weight of dry ice 
contained in a thin glass bulb. The calorimeter is a thin glass vessel of about 
one hundred cubic centimétres capacity, and is supported inside a silvered Dewar 
tube. A well-fitting rubber stopper closes the mouth of this tube, making the 
apparatus airtight. Through the stopper is fitted a Beckmann thermometer 
and also a thin glass stirring rod, the lower end of which is suitably shaped to 
receive the small ice-bulb. A third hole, lined with glass and closed with a 
1914. Zz 
