FLUORINE 



2230 



FLUX 



experiments with light. He admitted a beam 

 of sunlight through a lens into a solution of 

 chlorophyll, which is the green coloring matter 

 of plants, and discovered that the path of the 

 rays within the solution was marked by a 

 bright red light, though blue, yellow and orange 

 were absorbed. Similarly, he found if a beam 

 of sunlight falls upon a solution of sulphate 

 of quinine the portions of the surface where 

 the light strikes show a bright blue color. 

 Canary glass, which is glass colored with oxide 

 of uranium, also possesses this property, and 

 when illuminated its surface exhibits a beauti- 

 ful yellowish-green. In each case the fluorescent 

 light corresponds to a wave-length longer than 

 that of the colors absorbed by the substance. 

 Nearly all kinds of paraffin oil and solutions 

 made from the bark of the horse chestnut are 

 highly fluorescent. 



When the source of illumination is removed, 

 most fluorescent substances cease to give off 

 light. There are some, however, such as dia- 

 monds, calcium tungstate and the sulphides of 

 barium, calcium and strontium, which glow for 

 some time in darkness. Such bodies are called 

 phosphorescent. 



Related Subjects. The reader is referred to 

 the following articles in these volumes : 

 Color Light 



Fluor Spar Phosphorescence 



FLUORINE, floo'orin, an element which 

 enters into the composition of the very abun- 

 dant mineral known as fluor spar, which is a 

 combination of fluorine with calcium. Small 

 quantities of combined fluorine are also found 

 in bones, in the enamel of the teeth and in 

 the blood. Fluorine is never found in a free 

 state in nature, because it is the most active 

 element chemically and enters easily into com- 

 bination with other elements. Fluorine was 

 isolated for the first time in 1886 by the French 

 chemist Henry Moissan (1852-1907), who de- 

 composed hydrofluoric acid by electricity. 



Fluorine belongs to the group known as the 

 halogens (which see). It is a greenish-yellow 

 gas, with a sharp odor, and it is just a little 

 heavier than air. It can be liquefied when 

 subjected to high pressure and low tempera- 

 ture. Fluorine does not burn in air, which 

 means that it does not combine with oxygen, 

 but most metals burn in it, forming fluorides. 

 Hydrogen, sulphur, phosphorus and carbon take 

 fire when put into a vessel containing fluorine. 

 Water is decomposed by fluorine at ordinary 

 temperatures, on account of the great attrac- 

 tion it has for hydrogen, with which it forms 



hydrofluoric acid (which see). The chemical 

 symbol for fluorine is F. See CHEMISTRY. 



FLUOR SPAR, floo' or spahr, the mineral 

 used for etching glass. It is a compound of 

 oxygen, fluorine and calcium, and occurs in 

 beautiful cubelike crystals, which may be blue, 

 yellow, green or red, but the blue are the 

 most common. 



To write your name on glass with fluor spar, 

 place some powdered fluor spar and sulphuric 

 acid in a lead dish. Coat a piece of glass with 

 wax, then write your name in the wax with 

 some sharp-pointed instrument, such as a brad- 

 awl. Place the glass wax side down on the 

 dish and slightly warm the mixture. In a 

 few minutes the acid set free will etch the name 

 in the glass. See FLUORESCENCE. 



FLUTE, in music, a term applied to a wind 

 instrument, usually made of wood and con- 

 sisting of a pipe pierced with holes. In the 

 same class are the fife, flageolet and piccolo, 

 all described in these volumes. Sound is pro- 



FLUTE 



duced by a current of air entering the tube. 

 The ancient Hebrew and Greek forms were 

 held away from the player, who blew through 

 a mouthpiece at the end. The modern flute 

 is played by blowing through a mouthpiece 

 in the side. The tube is about twenty-seven 

 inches long, and may be made of boxwood, 

 ivory, ebony or silver, with mountings to suit 

 individual taste. In a modern orchestra the 

 flutes have an important and most effective 

 part. Usually there are two, and when, in loud 

 and strong passages, a third is required, it is 

 generally the piccolo that is used. This is a 

 small flute, with a high, shrill tone, a little 

 unpleasant to some people. 



FLUX, fluks, a word derived from the Latin 

 fluere, meaning to flow, and now applied scien- 

 tifically to any substance added to ore before 

 melting, as an aid in separating impurities 

 from the metal. In iron smelting, the flux 

 generally used is limestone, which readily com- 

 bines with the undesirable properties in the 

 ore and forms a slag which may be easily 

 removed from the molten iron. Fluxes consist- 

 ing of mixtures of borax, soda and potash are 

 used to separate base metals from gold and 

 silver. In assaying silver, litharge and red 

 lead are used, as they quickly dissolve metallic 

 oxides. The proportion of flux required can 

 only be decided by experiment, as ores vary 

 considerably. 



