Physical Properties of Ethylene

Ethylene is a colourless gas with an ethereal smell. It was first liquefied by Faraday in 1845 at - 1° C. under 42 atmospheres pressure. Thus the boiling-point of ethylene at atmospheric pressure is about -104° C. Cardoso and Ami give B.P. - 104.3° C.

The vapour pressures of ethylene at temperatures below its normal boiling-point may be calculated from the equation

logP = -767.8/t + 7.433.

The following critical data for ethylene have been determined by different observers:

	Critical Temperature	Critical Pressure
Van der Waals	9.2° C	58.0 atm.
Dewar	10.1° C.	51.0 atm
Olszewski	10.0° C	51.7 atm
Cardoso and Ami	9.50° ± 0.10° C	50.65 ± 0.10 atm.

The constants a and b in van der Waals' equation are for ethylene 0.00889 and 0.00254 (Dewar) or 0.00877 and 0.00251 (Olszewski) respectively.

The density of gaseous ethylene is 0.9852 (air = 1), whilst the density of a perfect gas of molecular weight 28.03 would be 0.9684.

Liquid ethylene solidifies at -169° C.; the density of the liquid at its boiling-point is 0.6095, and at the melting-point 0.6585. According to Cailletet and Mathias, however, liquid ethylene has a density of 0.306 at 6.1° C. The cryoscopic constant of dry ethylene is 125, that of the moist compound 118. The specific heat of ethylene between 10° C. and 220° C. is 0.4040; its heat of combustion is 341,100 calories (Berthelot and Matignon) or 333,300 calories (Thomsen).

Ethylene is slightly soluble in water, but much more soluble in alcohol; Henrich expresses its solubility in these two solvents by the following equations:

Solubility of ethylene in water at t° C.:
c = 0.25487 – 0.0088312t + 0.00017417t²
Solubility of ethylene in alcohol at t° C.:
c = 3.5876 – 0.0561532t + 0.00062369t².

Ethylene under pressure forms with water the hydrate C₂H₄.6H₂O.