Page:The American Cyclopædia (1879) Volume VII.djvu/299

FLUORINE FLUOR SPAR 291 in the dark, placed over sensitized or photo- graphic paper, with a partially translucent drawing or printed sheet interposed, and left so for many hours, gives a very good negative picture on the sensitized paper, the latter being darkened through the lights and pro- tected by the shades of the interposed figure. But it is still a question whether this effect is due to preserved light, or rather actinism, or to the effect of hydrogen gas set free from compounds in the prepared card, and acting chemically on the photographic paper. Invis- ible drawings in fluorescent substances, exposed to the sun and immediately or soon after ap- plied in the dark, acted more powerfully ; but interposed fluorescent bodies, as well as glass, arrested the action. At a session of the Ameri- can academy of sciences held at the Stevens institute, Hoboken, Oct. 30, 1873, President Morton of that institution related some investi- gations recently made upon a new body which he has discovered by means of spectrum analy- sis, associated with anthracene. This new body, which he has succeeded in isolating and subjecting to the action of the solar spectrum, possesses remarkable fluorescent properties. It is isomeric with anthracene, but differs from it in its chemical reactions, particularly with chlorine, bromine,, and sulphuric and pic- ric acids, requiring twice as many equivalents of the latter bodies to form a compound as an- thracene does. Its action upon actinic light is unlike that of all other fluorescent bodies yet experimented upon. Its continuous spec- trum is banded, and if a strong solution is placed in a bright sunlight and kept hot to maintain the solution, it undergoes a definite change and has all its bands moved upward to higher positions in the spectrum. In its first or normal condition its fluorescence produces a green light, but in its second condition it is blue. To the substance in the first condition President Morton has given the name thallene, and to the modified form the name petrolucene in reference to its origin and its brightness. FLUORINE, a gaseous body, regarded as an elementary substance, the chemical equivalent of which, calculated from the combination of calcium and fluorine in fluor spar, is 19. It is found in the teeth and bones of animals, in sea and some mineral waters, and in many phosphates and other minerals. On account of the great difficulty of preventing fluorine, when driven from its combination with one substance, from immediately combining- with any other with which it comes in contact, it has been impossible to investigate its qualities in its isolated state, and hence the slight un- iiity as to its elementary nature. Louyet obtained it by decomposing dry fluoride of sil- ver by means of chlorine gas in vessels of fluor spar. He found the dry gas possessed affinities analogous to those of oxygen and sulphur ; it arU-<l upon almost all metals, but attacked glass feebly or not at all. Prat prepared it from fluoride of lead, and says that it decomposes water with intensity. Combined with hydro- gen in the form of hydrofluoric acid, however, its most remarkable property is its rapidly cor- roding glass ; and for this reason it is employed for etching. Its presence is detected in any body that contains it, by submitting this in a vessel of platinum or lead, which are but slightr ly affected by the acid, to the action of con- centrated sulphuric acid, and placing a plate of glass across the mouth of the vessel to re- ceive the vapors evolved on the application of a gentle heat. This is the process by which hydrofluoric or fluohydric acid is obtained from fluor spar, the metallic vessel being a retort, furnished with a crooked neck of lead, in which the vapor condenses in the water placed in the bend to receive it, and which is kept cool by being surrounded with ice. It may also be ob- tained by condensing the vapors without the use of water in the lead tube ; in this state it is called anhydrous fluohydric acid. The h.y- drated acid is a colorless fluid, of specific gravity 1'06, boils at 86, and cannot be made to con- geal at any temperature. It has a strong af- finity for water, its vapor rising and forming thick white fumes as it combines with the moisture in the air, until by dilution this action at last ceases. Dropped into water, a sound is produced with the fall of each drop, as if it had been red-hot iron. When diluted with water it is highly corrosive, and according to its strength may produce injury by touching the skin. A single drop of the anhydrous acid may produce acute inflammation accompanied with fever. The marks made by the gaseous acid when used for etching are fine and visible on account of their opacity, while those produced by the liquid are transparent, and must be deeply etched. The product of this action of the hydrofluoric acid upon silicious substances is the gaseous compound known as fluosilicic acid or fluoride of silicium ; and thus is a means afforded of volatilizing silica and removing it from some of its combinations, by which their analysis is facilitated. FLUOR SPAR, fluoride of calcium, a mineral species consisting of fluorine 48*7 and calcium 51*3 per cent., named from the Latin fluere, in reference to its property of flowing when used as a flux. It is met with in cubical crystals, which easily cleave into octahedrons and te- trahedrons by removal of the solid angles. These crystals, collected in groups, their faces presenting a fine splendent lustre, and some brilliant shade of red, blue, green, or purple, constitute some of the most beautiful minera- logical specimens. They are sometimes trans- parent, but commonly translucent, and are brittle, breaking into splintery and conchoidal fragments. The hardness of the mineral is 4 ; its specific gravity 3'14 to 3'19. Coarsely pul- verized and heated, it emits phosphorescent light of various colors. Before the blowpipe it decrepitates and fuses to an enamel. It is met with in veins in the metamorphic rocks, and in the limestones of formations as recent as the