Air—The air consists chiefly of two substances, only one of which can keep up the process of burning. This substance is known as oxygen. The other, in which nothing can burn, is known as nitrogen. Besides these the air contains smaller quantities of other substances, particularly water vapor, carbonic acid (carbon dioxid), ammonia, and carburetted hydrogen.
Distribution of oxygen
Oxygen—Oxygen is the most common element in nature. It forms between forty and fifty per cent of the solid crust of the earth, eight-ninths of all the water on the globe, and one-fifth of all the air around the globe.
We have oxygen around us in great abundance, but it is mixed with nitrogen, and it is difficult to separate the two so as to secure the oxygen for any practical or commercial use.
MANUFACTURE OF OXYGEN
There are three methods of obtaining oxygen:
1 From potassium chlorate, or, as it is commonly called, chlorate of potash.
When potassium chlorate (KCLO3) is heated in a closed vessel (closed vessel means "closed at one end"), it breaks up into potassium chlorid and oxygen; that is, KCLO3 + heat = KCL + O3.
Potassium chlorate is used in fireworks because it gives up its oxygen readily. Potassium nitrate serves the same purpose in gunpowder, which is a mixture of sulfur (S), charcoal (C), and salt-peter or potassium nitrate (KNO3). The explosion of gunpowder, after a certain temperature has been reached, is due to the formation of oxygen, which, combined with the potassium nitrate, is set free by the very rapid burning of the charcoal and the sulfur. Other gases formed by the explosion are nitrogen, and probably sulfur dioxid (SO2), and oxids of nitrogen, N2O, NO2, etc. Carbon monoxid and carbon dioxid are sometimes formed. Potassium nitrate, however, is the most active agent in gunpowder.
2 By the electrolysis of water.
By this method the oxygen and the hydrogen are separated by electricity.
3 By the liquefaction of air, which is a very recent and a very scientific method.
By this method the air is cooled down until it liquefies. At normal atmospheric pressure it liquefies at a temperature of —312.6°F., but under pressure of about 585 pounds it liquefies at a temperature of —220°F. After the air has been liquefied, it is allowed to go back to vapor by exposing it to the surrounding heat of the atmosphere, and this vaporization separates the nitrogen from the oxygen, as the nitrogen boils at a temperature of —318°F., while the oxygen boils at a temperature of —294°F. There is a difference of about 24° in the boiling points of these two gases, which at this low point amounts to more than the difference between the boiling points of alcohol and water, and this difference is sufficient to separate the oxygen from the nitrogen.
Production of oxygen by the liquefaction of air is the latest, cheapest, and most approved method, and is now becoming extensively used in obtaining both oxygen and nitrogen for commercial use.
Properties of oxygen
Oxygen is tasteless and odorless. It is slightly heavier than air. When subjected to an extremely high pressure and low temperature it becomes liquid.