Glenn Gregory, age 11, of Rockford, Ill

What is gas?

Early on a spring morning, the puddles may be covered with thin sheets of ice. As the dawn pokes its fingers through the eastern trees, the ice begins to turn into liquid water and by noon the puddles may dry up and disappear. In a few hours the ice passed through three states of matter ‑ solid ice, liquid water and gaseous vapor. Only the warmth of the sun was needed to make these changes.

Water freezes solid at 0 degrees Centigrade and boils into a gaseous vapor at 100 degrees Centigrade, In everyday life, iron and tin, zinc and copper are frozen solid at ordinary temperatures. But with enough heat, they reach their melting points and turn into liquids. With more heat they reach their boiling points and turn into gases. Iron begins to melt around 1535 degrees Centigrade and at 3000 degrees it turns into gas.

With enough heat, an Iron poker will change from a solid to a liquid to a gaseous state of matter. But the basic atoms from which the iron is made do not change. They are merely rearranged, Heat is energy and the iron atoms turn this energy into speed and free themselves. In a solid poker, the individual atoms do not have enough energy to pull apart from each other. Their natural attraction for each other pulls them together and they are locked in a rigid state,

In the gaseous state, each speeding atom flies off into the air and seems to disappear. The word gas is thought to have come from a word for ghost, for most gases are invisible. When we trap and analyze them, however, we find that they are far from ghostly, Gases have substance. They are made from the self‑same atoms and molecules from which all matter is made. However, gases obey different laws from those governing liquids and solids.

A pail of water weighs about 800 times more than a pail of air. Gases are light, but they do have weight and, like solid substances, each gas has its own weight. Ordinary air is 10 times heavier than hydrogen gas. The separate atoms and molecules of a gas spread out to fill all the available space around them, but we can estimate their numbers. The number of atoms in a flask holding a litre of neon gas is about 26, followed by 21 zeroes. The same flask full of oxygen contains twice that many atoms. In the gaseous, as also in the liquid and solid states, the particles of neon tend to be single atoms. The particles of oxygen and many other gases tend to be made from two atoms.

The particles of gas are widely separated and moving at great speeds. When heat is added, the gas expands at a definite ratio. When heat is removed, it contracts. We can squeeze the particles in a container of gas closer together under pressure and this also follows a definite ratio. When the pressure on a litre of gas is doubled, we have just a half litre of gas.