Why Can’t We See Air?
We cannot see air because it has no color and is perfectly transparent. If at times it appears that there is color in the air it is not the air you see, but some little particles of various substances in it. Sometimes you think when you look off toward a range of mountains or hills, for instance, that the air is blue. You know the grass and trees on the mountains are green, so it cannot be they that have turned blue, and so you think the air is blue. But it is only the sunlight reflected to your eyes from the little particles of dirt and other substances which fill the air at all times which makes the blue that you see, and not the air.
Pure air is a mixture of gases without any color and is perfectly transparent. Air is nearly entirely composed of a gas called nitrogen—the remainder being oxygen with a little water and carbonic acid gas, which latter is thrown off in breathing. This is, however, but a very small percentage.
Air has been and still can be reduced to a liquid state, and with the use of it in this form many seemingly wonderful things can be done, which are interesting to look at, but have not as yet become commercially practical.