Filter, charcoal, 57.

    Filtering water, 77.

    Fire, 9.
      and oxygen, 45, 47.
      and tinder box, 47.
      making of, 51.
      primitive production of, 47.
      produced by friction, 47.
      spontaneous combustion, 52.
      sores and burns, 52-53.
      extinguisher, 55, 56.

    Fireless cooker, 25, 26.

    Fireplaces, 17, 18.

    Fixing, in photography, 128.

    Flame, hydrogen, 80.

    Flood, Johnstown, 214, 215.
      relation to forests, 217.

    Flour, self-raising, 231.

    Flume, 177.

    Flute, 297.

    Focal length, 118.

    Focus, of lens, 118.

    Fog, 37.

    Food, 60-69.
      carbohydrates, 64, 65.
      economy in buying, 66-69.
      fats, 65.
      fuel value of, 60-62.
      need of, 63, 64.
      preservatives, 252.
      proteids, 66.
      value, 67.
      waste, 60.
      water in, 75.

    Foot pound, 172.

    Force and motion, 156, 157.
      and work, 156, 157.
      magnetic lines of, 329-331, 334.
      muscular, 155, 160.

    Force pumps, 192, 193.

    Forests and water supply, 216-217.

    Forging of iron, 40, 41.

    Formaldehyde, 253.

    Freezing, effect of salt, 44.
      effect on ground and rocks, 42.
      expansion of water on, 41.
      ice cream freezer, 44.

    Frequency in music, 273, 275.

    Fresh air, 22-24, 49.
      amount consumed by gas burner, 22.
      and health, 49, 50.
      in underground work, 202.
      in work under water, 203-205.

    Friction, 173, 174.
      losses by, 174, 210.
      source of heat and fire, 47.

    Frost, 36, 37.

    Fruit, canned, bleached with sulphurous acid, 242.
      colored with coal tar dyes, 253.

    Fuel value of foods, 60-62.
      table of fuel values, 67.

    Fulcrum, 159, 160.

    Fumigation, 251.

    Fundamental tone, 290, 291, 292.

    Furnace, hot air, 19.

    Fuse, 340.

    Fusion, heat of, 40.

    Galvanometer, 341.

    Gas, acetylene, 152, 153.
      and unburned carbon, 151.
      coal, 151, 152.
      effect of heat on volume, 96, 97.
      effect of pressure on volume, 95-96.
      engine, 185-186.
      for cooking, 151, 152.
      illuminating, 92, 93, 150, 151.
      liquefaction, 97, 98.
      meter, 93, 94.
      natural, 152.

    Gasolene, 149, 150.
      as cleaning agent, 227, 243.
      in gas engine, 185, 186.

    Gauge, pressure, 92-94.

    Gelatin, plate and film, 129.

    Glass, kinds of, 119.
      molding of, 40.
      non-conductor, 321.