Sour milk, litmus test of, 359; neutralization of, by baking soda, 362. Sourness, taste of, caused by acids, 353, 354-355. Spectroscope, use of the, 172. Spectrum, the, 172. Spring water, carbon dioxid in, 366. Stability, 29-34. Starch, iodine test for, 373-374. Stars, twinkling of, 141; how to tell of what made, 171-172. Static electricity, 196-202*. Steam, reason for force exerted by, 110; geysers and volcanoes caused by, 110; real, not visible, 112 n. Steel, generally an alloy, 310. Stereopticons, lenses of, 148. Storage battery, 206, 207*; action of electricity in, 339. Stoves, electric, 230, 232. Street car, electric motor of, 255-257. Suction pump, 19*. Sugar, making of, by plants, 332-333; litmus test of, 359. Sulfur, an element, 300. Sulfuric acid, action of, on cloth, 354; litmus test of, 359. Sun, radiation of heat and light from the, 122-128; how to tell of what made, 171-172. Sunbeams, explanation of, 131. Sweat glands, function of, 291. Tanning, process of, 327. Telegraph apparatus, 247-252*, 380-381*. Telegraph code, 253. Telephone, working of, 253-255. Telescopes, 156*, 157; how made, 157; reflecting, 157. Temperature, finding the, by reading a thermometer, 90-91. Thermometer, the, 89*-91*. Thermos bottle, how made, 126-127*. Thunder, cause of, 200-201. Tin, an element, 300. Tin salt, poisonous, 353. Toasters, electric, 230, 232. Tomatoes, use of soda to neutralize acid of, 362-363. Tungsten, in incandescent lamps, 231. Tuning-fork experiments, 181*, 186-187*. Twinkling of stars, cause of, 141. "Up," meaning of word, 4. Vacuum, defined, 11; reason for, in electric lamp, 12*, 317; use of, in manufacture of thermos bottles, 126-127*; impossibility of producing sound in, 176-177. Valves, safety, on boilers, 347. Vaseline, production of, 114. Vibrations, of air, 174-181*; pitch due to rapidity of, 186. Vinegar, litmus test of, 359; neutralization of lye by, 363. Violin, tuning of, 187. Volcanoes, cause of, 110; explosions and, 346*. Volume, elasticity of, 86-87. Washing soda, a common base, 356; litmus test of, 359.