Physical Properties of Oxygen

Gaseous oxygen is without colour, odour, or taste. The weight of 1 litre of the gas under standard conditions has been repeatedly determined, the more important results being given in the following table. The same result is reached irrespective of whether the gas is obtained chemically or from the atmosphere. As the result of a critical consideration of modern data Moles concludes that the most probable value is 1.42891 ± 0.00003 grams.

It may be mentioned that 1000 cubic feet of oxygen at 15° C. weigh 84.56 lb. (avoir.), whilst 1 lb. of the gas occupies 11.83 cubic feet.

The very important Physical Properties of Oxygen is the weight of the oxygen at normal conditions. Assuming the mean weight of a litre of air at Paris to be 1.2930 grams and of oxygen 1.42891 grams, the relative density of the latter is 1.1051. Since the air is a mixture, and its composition subject to slight variation, its density is not perfectly constant, so that the above figure for the relative density of oxygen is merely a close approximation.

With reference to hydrogen as unity, the density of oxygen is 15.87.

With reference to water at 4° C., the density of oxygen at N.T.P. is 0.00142952.

Despite its greater density, oxygen transfuses through a caoutchouc membrane some 2½ times as rapidly as nitrogen and a rough separation of the gases from ordinary air can be effected in this manner.

A very interesting physical property of Oxygen - when subjected to increase of pressure, does not strictly obey Boyle's Law. At first the gas is slightly more compressible than the law demands, owing to the attraction between the gaseous molecules. Above 300 atmospheres, however, the product PV increases steadily as the influence of the dimensions of the molecules themselves begins to make itself felt. The gas thus becomes increasingly less compressible than the law requires.

Considerable care must be exercised in compressing oxygen, for unless proper precautions are taken there is considerable danger of explosion. Thus the gauges must be particularly clean and free from oil and other organic matter, the only permissible lubricant being water. Cylinders containing compressed oxygen are painted black; those with hydrogen, red; whilst nitrogen and air are stored in grey cylinders. This device tends to avoid confusion and explosions due to mixing the gases.

The diameter of a molecule of oxygen is given as 0.265 μμ.