Fluorene

A white crystalline compound (C13H10), a product of coal-tar. When impure it of the Gei ler or Crookes tube. If portions of thes tubes are made of the fluorescent "canary gla ," or are surrounded with jackets of gla holding fluorescent liquids, interesting effects appear, the colored light of the discharge being varied by luminous colors of different shades, due to the action of the fluorescent material. The principle of F. was first announced by Prof. G. G. Stokes in 1852, to the effect that the wavelength of the light emitted by a fluorescent body is always greater than that of the incident light. For this reason, light waves which are too short to affect the eye may be lengthened and become visible through the action of a fluorescent body. In this way rays far beyond the ordinary limit of visibility may be seen and the lines of their spectrum mapped out, Stokes having obtained by this means spectra five times as long as the ordinary solar spectrum. In addition to fluorescent liquids, there are certain solids which po e this property, including fluor-spar (from which Stokes derived the name of the property), platino-cyanide of barium (which has striking fluorescent powers), thalline (a petroleum product of brilliant powers), and canary gla . The latter is a gla colored yellow with oxide of uranium, which fluoresces with a brilliant green tint. The salts of uranium yield fluorescent spectra of great variety and many of them very beautiful. In fluorescent liquids, and some solids, the effect IMG:content-0282.jpg:[graphic][merged small] the machinery of a flour-mill is automatic, and only requires careful supervision to have the work done rapidly and accurately. The great flour center of the U. S. is Minneapolis, the production of that city alone in one year being about 10,000,000 barrels. The value of the total annual flour product of the U. S. is estimated at about $600,000,000.