"A solid is a body whose molecules are held strongly together. It is a solid simply because the force of cohesion is very strong in it. Even when we break a soft solid, like a piece of chalk, it does not fall to powder. It breaks into pieces, and these pieces still hold together.""It was so easy, sir," said Will, "to compare the cohesiveforce in a liquid and a solid, when you set me to take the water out of the basin, a spoonful at a time. It was no trouble to separate the molecules of water from one another with the spoon, because they are not held together firmly, as the molecules of a solid are.""Quite right, boys," said Mr. Wilson. "Now what have you to say about the gases?""The molecules of a gas soon spread themselves out till they seem to fill the room," said Fred. "This proves that gases are quite different from either solids or liquids. Their molecules have no cohesion at all; they actually repel each other. They are always trying to get as far away from each other as possible.""Now I want you to try and tell me how the force of cohesion acts," said Mr. Wilson.
"The force of cohesion can act only when the particles are in close contact," said Fred.
