23. What is said of the amount of space in gases and vapors? Give the statement in regard to steam. What is said of solutions of solids in fluids? What of evaporation? What of the diffusion of odors in the air? 24. What is the relation of heat to space in matter? Upon what do density and rarity depend? Explain tenacity. What is said of this property in gases and liquids? 25. How is the comparative tenacity of substances ascertained? Give the comparative tenacity of various substances. What animal substances have great tenacity? What is said of the value of tenacious substances? 26. What is said of hardness? What of flexibility and brittleness? 27. Give examples of flexible and brittle steel. Explain the actual difference between them. Explain the tempering of steel. 28. What is said of the annealing of glass? What of Prince Rupert's drops? What metals are the most malleable? What the most ductile? 29. What is said of the ductility of melted glass? What of the change of position of particles in making plates and wires of metals? What of welding? What is said of compressibility? What of the incompressiblity of liquids? 30. What influence has heat on the bulk of liquids? Illustrate by the thermometer. What is said of the compressibility of gases? How does elasticity operate in the case of the India-rubber ball? 31. Give the illustration in regard to jumping. State the experiment with the ivory ball. What is said of the movements of particles on each other in elastic substances? What of the degrees of elasticity in different substances? 32. What is the definition of elasticity? What is said of the usefulness of the variety of properties in matter? CHAPTER III. 33. What is meant by extension as a property of matter? Illustrate the fact that it is an _essential_ quality. What is said of it in reference to air? 34. Does matter ever penetrate matter? Give the illustration represented in Fig. 6. Give that represented in Fig. 7. 35. State the arrangement of the diving-bell. Give the comparison between bullets and needles in relation to penetration. What is said of solution? What of odors? 36. What is the property of matter called inertia? Give illustrations of it. Illustrate the fact that matter has no power to stop its own motion. What is the reason that the popular notion is that matter is more inclined to rest than to motion? 37. What is said of perpetual motion? Why is it not true of divisibility that it is an essential property of matter? What is said of weight? CHAPTER IV. 38. What is said of the nature of attraction? What was Newton's idea of it? 39. What is said of attraction in solids? What of its different modes of action? What is the difference in attraction in the case of steel and of water? What is said of the freeness with which particles of a fluid move among each other? 40. Explain Fig. 9. Explain Fig. 10.