  Illustrated Capital I In what form is all matter found? In the form of a solid, a liquid, or a gas. What is true of all solids? All solids must have length, breadth, and thickness. Do solids vary much in length, breadth, and thickness? Yes; they vary so much that we can scarcely find two things exactly alike in shape and size. Can the shape of any substance be changed? Yes; its shape may be changed in many ways. What takes place in india-rubber when it is stretched? Its particles are drawn farther apart, and its shape is altered. When the force is removed, what does the india-rubber do? It springs back into its former shape. What is this property of the india-rubber called? It is called Elasticity. Can air be pressed into a smaller bulk? It can, by means of a weight. When the weight is removed, what does the air do? The air goes back to its former bulk. Is air very elastic? Yes; air is one of the most elastic substances known. Why does a ball rebound when thrown against the floor? Because the substance of the ball is pressed out of shape when it strikes the floor, and, in its effort to spring back to its former shape, it is forced to rebound. Why does the ball rebound from the floor? Because the floor is firm, and will not move from the ball. Does a ball rebound when it strikes a soft substance? No; it does not rebound when it strikes a soft substance, like a heap of wool or feathers. Are solids ever elastic? Yes; many solids are elastic. Name some articles useful from their elastic properties. Watch-springs, wagon-springs, steel pens, and spring seats are very useful. Why does a wooden bow throw an arrow from it? When the force that bends the bow is removed, it springs back to its former shape, and in so doing throws the arrow from it. Can metals be bent? Yes; nearly all metals can be bent. What is this property of being bent called? It is called Flexibility. Do substances usually spring back after being bent? No; they usually remain in the bent form. Can glass be bent? Glass can be bent only a very little without being broken. What is this property of being easily broken called? It is called Brittleness. What may be said of brittle substances? Brittle substances are generally hard, while flexible substances are much softer. What metal may be made either flexible or brittle? Steel, when heated and cooled slowly, becomes flexible, but when cooled quickly, it becomes brittle. For what is brittle steel used? It is used for making knives, razors, axes, and other cutting instruments. What may be done with metals that are flexible? They may be hammered into thin plates. What is this property in metals called? It is called Malleability. Which is the most malleable of all metals? Gold is the most malleable; and it can be made into leaves so thin that three hundred and sixty thousand of them, when placed together, make a bulk only one inch in thickness. Name some other metals that are malleable. Silver, copper, tin, zinc, iron, and lead. Can the particles of a piece of iron easily be separated? No; its particles cannot easily be separated. What is this property of iron called? It is called Tenacity. Can the particles of a brittle substance, like glass, easily be separated? Yes; its particles can easily be separated. Is there much tenacity in brittle substances? No; there is very little tenacity in brittle substances. Is there any tenacity in air? No; because its particles are always trying to separate from each other. Is there any tenacity in water? Only a little, just enough to hold its particles together in the form of drops. Upon what does the strength of substances depend? Their strength depends upon their tenacity. Do the different kinds of wood vary much in strength? Yes; hickory and oak are much stronger than pine or cedar. When is a knowledge of the strength of wood necessary? It is necessary to know the strength of wood used in the construction of stores, bridges, houses, etc. Which is the most tenacious of metals? Iron is the most tenacious of metals. How is this principle in iron made useful? It is useful in the construction of suspension bridges, and in very many other ways. Can iron be drawn into wire? Yes; iron can be drawn into wire. What is this property of being drawn into wire called? It is called Ductility. Which are the most ductile of metals? Platinum, silver, iron, copper, and gold, are the most ductile, in the order named. When is glass ductile? When glass is melted it becomes ductile, and may be drawn into very fine threads. If we take half the air out of a room, what will the remaining half do? Its particles will separate until they fill the whole room. What is said of air when its particles are thus separated? The air is in a state of rarity. What is said of it when the particles are pressed closer together? The air is then said to be in a state of density. Are the particles of water closer together than those of air? Yes; therefore water is denser than air. Upon what does the weight of a substance depend? Its weight depends upon its density. How much heavier is steel than water? Steel is seven times as heavy as water, and is, therefore, seven times as dense. How much denser is mercury than water? Mercury is thirteen times as dense as water, and is, therefore, thirteen times as heavy. Why can a bird move through the air? Because the particles of air can be separated by the bird. Why can a fish swim through the water? Because the particles of water can be separated by the fish. Why can a needle be passed through cloth? Because the fibres of the cloth can be separated by the needle. Why can a nail be driven through a board? Because the fibres of wood can be separated by the nail. What name given to this property in these substances? This property is called Penetrability. What is necessary in order to penetrate a substance? We must use a substance harder than the one which we wish to penetrate. Why will iron penetrate wood? Because iron is harder than wood. Why cannot our bodies penetrate the wood? Because our bodies are softer than the wood. Why can our bodies move more easily through air than through water? Because air is more easily penetrated than water. Why can a nail be driven into a pine board more easily than into an oak board? Because the fibres of pine are more easily separated than the fibres of oak; hence, pine wood is more penetrable than oak wood. Decoration. Decoration.
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