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GENERAL SCIENCE 285 Per cent «„„, Question Right r ~ *? m Initial Gam (2) the pneumatic cups on the tread of an automobile tire, (3) the oil pump on an automobile engine, (4) the differential on an automobile. 20. Our bodies are prevented from being crushed by the X 47.8 15.6 enormous pressure of the atmosphere by (1) the C 57.8 15.2 bones of our bodies, (2) the resistance of the skin, which envelops the body, to pressure, (3) the balance of internal and external pressure, (4) high blood pres- sure. 21. Compressed air is especially valuable in mining be- X 48.1 —5.5 cause (1) it is more powerful than electricity, (2) it is C 58.6 —. 7 cleaner, (3) there is no danger from sparks or fire, (4) air power is more cheaply transmitted. 22. The air brakes used on trains were invented by (1) X 38.3 13.0 Holley, (2) Westinghouse, (3) Galileo, (4) Firestone. C 50.6 14.0 23. A riveting machine is driven by (1) steam, (2) elec- X 51.6 40.0 tricity, (3) compressed air, (4) a steel spring. C 62.2 36.3 24. Compressed air is essential in the manufacture of X 50.3 15.4 (1) bricks, (2) Bessemer steel, (3) pottery, (4) con- C 58.8 21.0 crete. 25. The main difference between free air and compressed X 42.8 11.6 air is that compressed air (1) has a greater num- C 53.6 9.4 ber of gas particles per unit volume, (2) is colder than free air, (3) is more easily stored than free air, (4) is lighter than an equal volume of free air. 26. A basketball bounces when dropped to the floor X 31.3 21.9 because of (1) air elasticity, (2) the rubber bladder, C 43.2 26.4 (3) gravity, (4) atmospheric pressure. 27. The engineer applies the brakes on a train (1) by X 20.8 43.9 starting the air pump on the engine, (2) by cutting off C 24.0 22.0 the ah* to the cars, (3) by turning steam into the pressure tank, (4) by turning on the air to the cars. 28. The air pressure maintained by a locomotive is ap- X 20.3 —7.6 proximately (1) 10 pounds per square inch, (2) 40 C 22.1 —8.6 pounds per square inch, (3) 80 pounds per square inch, (4) 100 pounds per square inch. 29. A sand blast is used to (1) polish marble, (2) drive a X 35.4 42.0 ventilating fan, (3) clean the walls of a building, C 35.1 16.5 (4) carve stone. 30. Air is pumped into an automobile tire to (1) stretch X 60.6 19.6 the inner tube, (2) furnish an elastic cushion, (3) pre- C 73.8 19.2 vent skidding, (4) prevent punctures. 31. Low, heavy rain clouds are called (1) cirrus, (2) X 33.2 19.2 cumulus, (3) nimbus, (4) cirro-cumulus. C 34.9 12.1