Great Salt Lake, reason for salt in, 104-105. Greeks, early knowledge of electricity possessed by, 196. Green color of water, reason for, 169-171*. Grounded circuits, 225-229*. Gun, shooting of, caused by explosion, 345-346. Gunpowder, action of, in shooting of a gun, 345-346; how made, 347. Hail, explanation of, 286. Heat, a result of friction, 53; is the motion of molecules, 90; not caused by expansion, 94-95; cold is absence of, 95, 120; required to evaporate liquids, 102-103; conduction of, 116-118; carried by air, by convection, 118-119; radiation of, 122-128; of incandescent lamp, 125-126; brought to focus by convex lens, 149; chemical change caused by, 323-325. Heaters, hot-water, 120*; electric, 230, 232; gas, 319, 321*, 322*. Heat waves, cause of, 141. Hydrochloric acid, getting hydrogen from, 301-304; testing for silver with, 373. Hydrofluoric acid, 351. Hydrogen, an element, 294, 299; in water, 295-296; experiments with, 301-304*; one of chief elements in fuel, 315-316; part taken by, in burning, 312-319. Ice, slight friction of, 52*; action of molecules in, on freezing and melting, 96-97; reason for floating of, 98-99. Incandescence, defined, 125. Incandescent lamps, 125-126; number of electrons in, 197; working of, 229-232. Inertia, 66-71; definition of, 70. Insulators, of heat, 118; of electricity, 213; substances used as, 215. Iodine, an element, 299; testing with, for starch, 373-374. Iron, a good conductor of heat, 118; an element, 299. Irons, electric, 229*, 230, 232. Iron salt, formed by lemon juice on steel, 353. Iron ships, reason for floating, 24*-26. Kerosene, boiling of, 112; distilled from petroleum, 114; carbon and hydrogen in, 315. Laughing gas, 309. Lava in volcanoes, 110. Lead, an element, 299. Lead pencils, arc light from, 233*-234*. Leaning Tower of Pisa, 29*-30. Lemon juice, action of, on silver and on steel, 353; litmus test of, 359. Lens, of eye, 142, 151*-153; of camera, 143, 149*, 328; convex, 148-149; concave, 149*; in telescope, 157. Levers, 57-65*. Light, radiation of, 122, 123*-128; reflection of, 129-135*; refraction of, 136*-141; focus of, 142-149*; brought to focus by convex lens, 149; diffusion of, 158-161*; color a kind of, 162; speed of, 182; chemical change caused by, 326-335; and manufacture of food in plants, 332-333. Lightning, cause of, 200-201. Limewater test for carbon dioxid, 375*-376. Liquid air, 97, 112. Liquids, absorption of, 36-40; diffusion in, 272. Litmus paper, experiments with, 358-359. Litmus test, the, 358-359. Lye, a common base, 356; experiment with, 356; soap made from, 357; used for clearing out drainpipe, 358; neutralization of, by acids, 363.