AIR
Air is made up principally of two elements, nitrogen and oxygen. It also always contains vapor of water and carbonic acid. Its average composition is as follows:
| Nitrogen | 78.49% | Aqueous Vapor | .84% |
| Oxygen | 20.63% | Carbonic Acid | .04% |
These are mixed together, not chemically united. Oxygen and nitrogen do unite chemically, but not in the proportions in which they exist in the air. Nitrous Oxid (N2O), sometimes called "Laughing Gas," is one of the compounds of nitrogen and oxygen.