ON AEGON AND ITS COMPANIONS. (^7 
Volume of bulb . . . 7‘152 cub. ceiitims. 
Weight of gas . . . 0'01224 oTamme. 
Pressure. 245‘4 millims. 
Temperature . . . . 21’6° C. 
The density calculated from these numbers is 64'0. 
Unfortunately, after this experiment, a small quantity of air became mixed 
accidentally with the gas, and lowered the density to 62’96 ; but after refractionation 
its density was redetermined with the following results :— 
V olume of bulb . 
Weight of gas 
Pressure 
Temperature . 
Density of xenon. 
7’152 cub. centims, 
0'01114 gramme. 
225'3 millims. 
22-45° C. 
G3-64 
The Vapour-pressures of Argon, Krypton, and Xenon. 
We have not found it possilde to contrive an arrangement whereby the temperature 
of liquid argon, krypton, and xenon should be gradually altered, as is generally done 
in measuring the vapour-pressures of substances liquid at the ordinary temperature, 
l)y means of a bath of some liquid, the temperature of winch can be raised at will, or by 
jacketing the vapour-pressure tube with vapour from some pure liquid, boiling under 
different pressures. All substances liquid a.t the ordinary temperature freeze at the 
lower temperatures required for these gases. But it is possible to employ liquid 
ethylene, cooled either by external apjdication of liquid air, or by causing it to boil 
under reduced pressure ; both these means of obtaining a known low temperature 
have been used, l)ut only a small range of temperature is thus covered. The results, 
moreover, were not so trustworthy as those obtained when a liquid of known boiling- 
point, boiling under atmospheric pressure, was used as a refrigerant. 
The plan adopted, therefore, was to determine the pressure corresponding to certain 
known temperatures, and then by means of the formula suggested by Bamsay and 
Young,"^ the accuracy of which has been demonstrated in a great number of instances, 
to ascertain the vapour-pressures at intermediate temperatures. This method 
depends on the fact that the ratios of the absolute temperatures of two liquids 
corresponding to a series of pressures are a linear function for one of them corre¬ 
sponding to the same pressures. It therefore becomes possible to calculate a whole 
series of vapour-pressures of any substance, if the pressures are corresponding to two 
or more temperatures accurately known ; the application is briefly as follows :—- 
The vapour-pressures of the substances are determined at absolute temperatures 
Phil. Mag.,’ vol. 21, p. 33, 1886 ; vol. 22, p. 37, 1886. 
K 2 
* { 
