Physical Properties of Xenon

Xenon is a colourless gas. Whether it has any taste or odour is not known .

The early determinations of its density were made by Ramsay and Travers, but their result was necessarily of a provisional nature as they had only 3 c.c. of the gas. A subsequent determination is that of Moore, who, during an investigation of the residues from the evaporation of 120 tons of liquid air, obtained xenon in quantity sufficient for its thorough fractionation and exact weighing. These residues were freed from krypton and other gases at the temperature of liquid air (vide supra), and the impure xenon thus obtained was fractionated at -130° C. The mean of two determinations made on the purest fraction gave for the density the value 65.35 (O = 16), i.e. a normal litre of xenon weighs 5.851 grams.

The compressibility of xenon was investigated by Ham say and Travers (loc. cit.), who found that the value of p v decreased very markedly as the pressure increased. This behaviour is, of course, quite in accordance with the fact that the critical temperature of xenon is about the ordinary temperature, at which the experiments were conducted. Calculating according to Guye's method of critical constants, we have for the molecular weight of xenon the value 130.22. From this result it can be calculated indirectly that at 0° and between 0 and 1 atmosphere the compressibility coefficient is equal to +0.00690.

Xenon is relatively very soluble in water, its absorption coefficient being 0.2189 at 0° C. and 0.0878 at 50° C. a point of minimum solubility occurring at about 40° C.

The viscosity of xenon at 0° C. is η₀ = 2.107×10^-4, and if its variation with temperature is given by the linear equation -

η_θ = η₀(1+βθ),

then β = 3.39×10^-3.

The refractivity of the gas for white light was originally found to be 2.364 times that of air. Later determinations have given the value μ - 1 = 705.49×10^-6 for the green mercury line (λ = 5461). The dispersion at N.T.P. is given by the equations -

μ – 1 = ,

or μ – 1 = ,

where C×10^-27 = 12.2418, n₀²×10^-27 = 8977.87, and n is the frequency of the light.

The passage of an uncondensed discharge through a vacuum tube containing xenon causes the emission of light of a sky-blue colour; if a spark-gap and Leyden jar be interposed in the circuit the colour of the light changes to green. This change is similar in character to that seen under similar conditions in helium and krypton; and xenon, like these gases, has two spectra. A list of the more prominent lines of xenon is given below -

First Xenon spectrum (Uncondensed Discharge.)

Wave-Length	Intensity	Wave-Length	Intensity	Wave-Length	Intensity
4923.28	6	4624.46	15	4116.25	7
4916.63	6	4582.89	5	4109.84	5
4807.19	6	4524.83	6	4078.94	10
4734.30	8	4501.13	10	3967.74	10
4697.17	7	4193.70	8	3951.16	10
4671.42	10

Second Xenon spectrum (Condensed Discharge.)

Wave-Length	Intensity	Wave-Length	Intensity	Wave-Length	Intensity
6097.80	7	4921.68	6	4415.00	7
6051.36	7	4890.24	5	4406.99	5
6036.40	6	4887.47	5	4395.91	10
5976.67	7	4883.68	6	4393.34	10
5751.28	5	4876.68	7	4330.63	15
5727.15	5	4862.69	8	4296.52	5
5719.83	6	4844.50	10	4245.54	10
5667.85	6	4823.47	6	4238.37	10
5659.67	5	4698.20	5	4223.14	5
5616.99	6	4683.76	5	4215.77	5
5531.33	7	4652.15	6	4214.17	5
5472.90	7	4615.72	5	4213.80	5
5460.63	6	4603.21	10	4208.61	6
5450.71	5	4592.22	6	4193.25	8
5439.19	8	4585.65	10	4180.20	10
5419.40	10	4577.36	6	4158.14	5
5372.62	8	4545.34	8	4145.85	5
5339.56	9	4541.03	8	4109.20	6
5314.15	8	4532.67	5	4057.55	5
5292.40	10	4524.38	5	4050.19	6
5262.16	5	4481.01	7	3992.98	5
5260.65	5	4462.38	20	3950.70	8
5191.60	5	4448.28	10	3922.67	10
5080.88	7	4434.35	6	3908.00	7

The Zeeman effect in xenon has been studied by Lohmann. The ratio of the specific heats of xenon has been determined by Ramsay according to Kundt's method. The following data were obtained -

	Temperature.	Half Wave-length.	Density
Air	19°	27.92	14.48
Xenon.	19°	14.32	65.11

Hence the ratio Cp/Cv = 1.666.

The critical temperature of xenon is +16.6° C., and the gas may be liquefied at this temperature by a pressure of 58.2 atmospheres. The liquid is colourless and boils at -109.1° C. under atmospheric pressure; its density at the boiling-point is 3.06, whence the molecular volume = 42.7. Its vapour-pressure ratio, is 0.0675. Xenon is easily solidified at the temperature of liquid air; its melting-point is about -140° C.

The "rectilinear diameter" for xenon is given by the equation Dt = 1.205 – 0.003055t (Dt = mean density of liquid and saturated vapour at t° C.) and the value of the coefficient of t, i.e. the slope of the diameter is greater than for any other gas. The density of the liquid varies from 1.468 at 16° to 1.987 at 0° and 2.694 at -59.3°.

No compounds of the element are known, and it is therefore impossible to apply to xenon any of the ordinary methods for the determination of atomic weight. It is, however, believed, for reasons exactly similar to those given under Krypton, that the molecule of the gas is monatomic, and its atomic weight is taken as 130.2 (O = 16).