Physical Properties of Methane

Methane is a colourless gas without taste or smell, and is not poisonous. Its density at 0° C. is 0.5576 (air = 1), whilst that corresponding to the molecular weight (16.03) would be 0.5539. Consequently methane is slightly more compressible than an ideal gas, and its constants for van der Waals' equation are: a = 0.00376, b = 0.001557 (Olszewski), or a = 0.00357, b = 0.001625 (Dewar). The mean specific heat between 18° and 208° C. is 0.5930, and the ratio of the two specific heats is 1.313. Its heat of combustion is, according to Thomsen, 211,900 calories, and according to Berthelot and Matignon, 213,500 calories.

Methane is slightly soluble in water, but much more soluble in alcohol. Measurements of solubility have been made by Bunsen, Henrich, Winkler, and Christoff. The following equations are given by Henrich:

For water. C = 0.05473 – 0.0012265t + 0.000011959t²

For alcohol. C = 0.522745 – 0.00295882t + 0-0000177t².

Methane was first liquefied by Cailletet in 1877, and its boiling- points at different pressures have been estimated by Wroblewski and Olszewski. The following figures are selected from those given by Olszewski:

Pressure.	B.P. ° C.
40 atm.	-93.3
11 atm	-126.8
2.24 atm	-153.8
1.00 atm	-164.0
80 mm. Hg.	-185.8
5 mm. Hg.	-201.5

According, however, to Ladenburg and Krugel methane boils at -152.5° under 749 mm. The critical temperature and pressure are -81.8° C. and 54.9 atm. (Olszewski), or -95.5° C. and 50.0 atm. (Dewar). According to Cardoso, however, the critical constants are: critical temperature, 82.85° C.; critical pressure, 45.60 atm.; critical density, 0.1623.

The density of liquid methane at -164° C. is 0.415; solid methane is snow-like and melts at -184° C. The temperature and pressure at which solid, liquid, and gaseous methane co-exist (i.e. the triple point) have been found by Crommelin to be -183.15° C. and 70 mm. of mercury. A previous determination by Olszewski gave -185.8° C. and 80 mm.

On account of the large proportion of hydrogen in methane the flame of this hydrocarbon is but slightly luminous. Wright found that the gas, when burnt in an Argand burner at the rate of 1 cubic foot per hour, gave a flame of 5.2 candle-power, whilst that of coal-gas examined at the same time was equal to 14-20 candle-power.