Sona Hicks, age l3, of Muncie, Ind., for her question:
What gases are in the air?
Our luxurious planet is blessed with abundant supplies of sir and water but samples of pure air and water are not to be found in nature. The seas and streams teem with dissolved chemicals and floating fragments. Tons of surprising substances float in the atmosphere.
We can list the standard gases in a sample of air, but this gives us only part of the true story. The air above a smoky factory is choked with fumes. Desert air holds less water vapor than ocean air and the air of a mountain forest is fresh with extra Oxygen. Volcanoes add carbon dioxide and sulphur gases to the air. In various places countless other substances boil up and add their gaseous molecules to the atmosphere.
Traces of hundreds of different substances are mingled with the gases of the air. Nevertheless, it is possible to name the standard gases in any sample of the air around us and also give their amounts. For the breezy air is a great mixer. The proportions of standard gases remain more or less the same in samples of hot or cool air, moist or dry air and even in light or heavy air. A few of the impurities change or replace the standard gases, but the majority merely add themselves to the mixture.
The most important gas to us is Oxygen. All plants and animals need it to carry on their respiration. Fires cannot burn without oxygen. Yet this vital gas makes up only 2l% of the air. Nitrogen, the most plentiful gas, makes up 78% or more than three quarters of our standard sample. The usefulness of this inert, inactive gas is its laziness. It slows up the activity of busy oxygen in fires and in the combustion processes of life.
Nitrogen and oxygen make up 99% of pure air. Most of the remaining l% is argon. The last fraction of our standard sample contains traces of five gases. Neon and xenon, krypton and helium are lazy gases, present in traces almost too small to detect. The last of these smidgen gases in the air happens to be as vital to life on earth as oxygen.
It is carbon dioxide, the waste gas We breathe out from our lungs. Its usefulness lle8 fn the fact that plants need it to carry on photosynthesis, the process that feeds the plant world and indirectly feeds all the plants and animals. Yet carbon dioxide makes up only 0.03% of the air.
The gases in our samples of vapor less, purified air are measured by volume. Suppose the volume of the sample is one cubic foot, which is l,728 cubic inches. The nitrogen and oxygen account for more than l,7l2 and argon for almost, but not quite, l6 of these cubic inches. The five rare gases, including vital carbon.. dioxide, account for the final fraction of the volume.