Paper making, 219.

    Paraffin, 150, 321.

    Pasteurized milk, 250.

    Patent medicines, 257-260.

    Peas, sources of nitrogen, 263.

    Pelton wheel, 177.

    Percussion instruments, 299.

    Period of a body, 273.

    Peroxide of hydrogen, 53, 252

    Petrolatum, 150.

    Petroleum, 149, 150.

    Phonograph, 303-305.

    Phosphorus, in fertilizer, 263, 264.
      in making nitrogen, 261.
      in matches, 47, 48.
      poisoning by, 47.

    Photography, 127-131.

    Photometer, 107.

    Pianos, 284-292.

    Pin wheel, 181.

    Pitch of sound, 280, 281.
      cause of, 282.
      in wind instruments, 296-299.

    Plane, inclined, 162-166.

    Plants, and atmosphere, 55.
      and light, 131-132.
      and nitrogen, 261.

    Plate developing, photographic, 128.

    Pneumatic dispatch tube, 205.

    Poles, magnetic, 330-332.
      of cell, 308.

    Positive electrode, 308.

    Potash, in fertilizer, 263-265.

    Potassium chlorate and oxygen, 46.
      permanganate, 100.
      tartrate and Rochelle salt, 227.

    Power, candle, 105-107.
      electric, 351.
      horse, 173, 351.
      sources of, 174, 175, 185.
      transmission by belts, 171.
      water, 176-180.

    Precipitation, 72, 73.

    Preservatives, food, 252.
      wood and metal, 253-254.

    Pressure, atmospheric, 82-86.
      calculation of atmospheric, 83, 84.
      calculation of gas, 92, 93.
      calculation of water, 94.
      gauge, 92-94.
      of illuminating gas, 93.
      relation of pressure of gas to volume, 95, 96.
      water pressure, 208-211, 214-216.
      within the body, 86.

    Primary colors, 135.

    Print, photographic, 131.

    Printing, color designs in cloth, 248, 249.
      electrotype, 317.

    Prisms, 135.
      refraction through, 117.

    Proteids, 66.

    Pulleys, 166-169.
      applications of, 169.

    Pump, 187-205.
      air, 201-205.
      force, 192, 193.
      lifting, 189-192.

    Pupil of the eye, 122.

    Pure food laws, bleaching, 242.
      preservatives, 252.

    Purification of water, 77, 196.

    Push button, 321.

    Radiator, 19-21.

    Railroads, grading of, 165-166.

    Rain, 36, 37.

    Rainbow, 134.

    Rain water, 225.

    Reflection, angle of, 110.
      of light, 109-112.
      of sound, 278, 279.

    Refraction, angle of, 114.
      by atmosphere, 114.
      of light, 113.
      uses of, 115-116.