9;
hydrochloric acid test for, 373.

Silver chlorid, formation of, 327.

Sinking and floating, 23-28*.

Siphon, 18*.

Sky, reason why blue, 169;
why red at sunset, 170.

Smoke, consistency of, 318-319.

Snow, 275;
formation of, 285-286.

Snowflakes, 97, 286*.

Soap, how made, 357-358.

Soda water, how made, 365-366.

Sodium, experiment with, 304.

Softening due to oil or water, 290-292.

Soil, litmus test of, 359.

Solution, defined, 261;
difference between emulsion and, 263;
a mixture and not a compound, 309;
chemical change helped by, 349.

Sound, cause of, 174;
rate of speed, 181-182;
action of, in echoes, 183-185*;
pitch of, 185-188.

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 o