FLUIDS FLUORIC ACID. 



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but effected, in most cases, instantly as to sense. 

 (See Caloric.) The state of dense fluidity appears 

 to be more favourable to chemical combination than 

 either the solid or elastic state. In the solid state 

 the cohesive attraction prevents the parts from 

 obeying their chemical tendencies ; and, in the 

 elastic state, the repulsion between the parts has, in 

 a great measure, the same effects. Hence it has 

 been considered, though too hastily, as a chemical 

 axiom, that corpora non. agunt nisifiuida. 



FLUIDS, MOTION OF. The motion of fluids, 

 viz., their descent below or rise above the common 

 surface or level of the source or fountain, is caused 

 either, 1. by the natural gravity or pressure of the 

 fluid contained in the reservoir or fountain ; or, 2. 

 by the pressure or weight of the air on the surface of 

 the fluid in the reservoir, when it is, at the same time, 

 either taken off or diminished, on some part, in aque- 

 ducts or pipes of conduit ; 3. by the spring or elastic 

 power of compressed or condensed air, as in the com- 

 mon water engine ; 4. by the force of pistons, as in 

 all kinds of forcing pumps, &c. ; 5. by the power of 

 attraction, as in the case of tides, &c. 



FLUOR, or FLUOR-SPAR. The crystals and 

 crystalline masses of this mineral, when so cleaved 

 as to improve all its cleavages in an equal degree, 

 result in regular octahedrons, which figure is there- 

 fore assumed as the primitive form of the species. 

 It presents an extensive variety of crystals, of which 

 the cube and the cubo-octahedron are the most fre- 

 quent, the primitive form being comparatively rare. 

 They vary, in size, from very minute to several inches 

 in diameter. Lustre, vitreous ; colour, white, though 

 not very common, and seldom pure ; more generally 

 wine-yellow or violet-blue. Among its brightest 

 colours are emerald and pistachio-green, sky-blue, 

 rose-red and crimson-red. Very dark blue colours, 

 bordering on black, and probably owing to foreign 

 admixtures, sometimes occur. Sometimes different 

 shades of colours are disposed in coats parallel to the 

 faces of the cube, or symmetrically distributed along 

 the edges or solid angles of crystals. Translucent 

 as well as transparent ; brittle ; hardness, between 

 apatite and arragonite, and capable of being scratch- 

 ed with ease by the knife; specific gravity, 3.14. 

 Besides occurring in well-defined crystals, it often 

 appears massive, in which case the composition is 

 columnar, the particles being of considerable size, 

 sometimes diverging, but more often forming a 

 curved, lamellar composition. The composition is 

 also granular, the individuals being of various sizes. 

 It is likewise, though more rarely, impalpable, the 

 frecture becoming flat, conchoidal and splintery, and 

 the surface of fracture being scarcely glimmering. 

 Fluor is composed of 72.14 of lime, and 27.86 of 

 fluoric acid. Before the blow-pipe, it decrepitates, 

 and becomes phosphorescent, but loses its colour, and 

 melts, at last, into an opaque globule. It phosphoresces 

 likewise, if thrown upon ignited charcoal or heated 

 iron. The light emitted is generally purple, though 

 some varieties afford bright green colours. In conse- 

 quence, they have received the name of chlorophane, 

 or pyrosmaragdus. A variety of this latter kind , from 

 Ecaterineburg, in Russia, phosphoresces simply from 

 the warmth of the hand. If fluor be exposed to too 

 high a temperature, is loses the property of again 

 showing this phenomenon. Sulphuric acid decom- 

 poses the powder of -the mineral ; fluoric acid is dis- 

 engaged in a gaseous state, and corrodes glass. 

 Several varieties, particularly the sky-blue and rose- 

 coloured ones, lose their colour on exposure to the 

 light. Fluor is not unfrequently found in beds, as at 

 Alston Moor and Castleton, in England : more gener- 

 ally, however, it occurs in veins in argillaceous schist 

 and secondary limestone, accompanied by galena- 



blende, calcarious and pearl spars, heavy spar, 

 quartz, bitumen and clay, as at several places in 

 Cumberland and Durham, of the same country. It 

 also frequents primitive rocks, accompanying tin ore, 

 mica, apatite and quartz, as at Zinwald, in Bohemia. 

 The most remarkable deposit of fluor in America, 

 hitherto discovered, is along the country south-west 

 from Cave rock, on the Ohio, for thirty miles, in 

 Gallatin county, Illinois, where it exists in an alluvial 

 situation, or in veins traversing a compact limestone. 

 Its crystals are often large, and various in their 

 colours ; the prevailing tint, however, is a dark 

 purple, approaching black, which is owing to the 

 interfusion of bituminous matter, as is apparent from 

 the odour when the crystals are broken. The chloro- 

 phane variety exists very plentifully at New Strat- 

 ford, Connecticut. The uses of fluor are numerous 

 and important. It is employed as a flux in the reduc- 

 tion of various ores, from which circumstance the 

 name fluor has been derived. The fluoric acid, dis- 

 engaged from it by means of sulphuric acid, is used 

 for corroding and etching upon glass. Formerly the 

 finest specimens were cut and worn as gems ; but 

 their inferiority in point of hardness, being considera- 

 bly below that of the artificial gems, has brought 

 them into disuse. It still continues, however, when 

 obtainable in masses of sufficient dimensions, to be 

 wrought into various extremely ornamental objects, 

 such as vases, basins, obelisks, &c. This manufac- 

 ture is confined to Derbyshire, no other part of the 

 world affording fluor sufficiently firm and tenacious 

 for the purpose, and which is, at the same time, 

 possessed of fine colours. The work is performed 

 on a lathe turned by water, the foot-lathe being much 

 more liable to produce fractures in the piece worked, 

 by its want of steadiness. The tool employed, at 

 first, is a piece of the best steel ; after which a coarse 

 stone is applied, with water, so long as the smooth- 

 ness is Improved by these means : then the finer grit- 

 stone, pumice, &c. ; till, finally, the article becomes 

 sufficiently smooth to receive emery, with which the 

 operation is completed. The crevices which frequent- 

 ly occur in the masses of fluor, are sometimes con- 

 cealed by the introduction of galena ; and, as this 

 substance is often naturally found with the fluor, it 

 becomes difficult to detect the fraud. In selling the 

 articles, also, it is a frequent practice to moisten them 

 with water, under the pretence of removing dust, 

 which is clone to bring out the colours otherwise 

 invisible, and which, of course, disappear as soon as 

 the objects become thoroughly dry. 



FLUORIC ACID is prepared by mixing pure 

 fluor-spar, in coarse powder, with twice its weight of 

 sulphuric acid, in a leaden or silver retort, and apply- 

 ing heat. The acid distils over in vapour, and must 

 be collected in a receiver of the same metal, surround- 

 ed by ice. At the temperature of 32 Fahrenheit, 

 fluoric acid is a colourless fluid, and remains in that 

 state at 59, if preserved in well stopped bottles; but 

 when exposed to the air, it flies off in dense white 

 fumes, which consist of the acid in combination with 

 the moisture of the atmosphere. Its specific gravity 

 is 1 .0609 ; but its density may be increased, by 

 gradual additions of water, to 1.25. Its affinity for 

 water is far greater than that of the strongest 

 sulphuric acid. When a drop of it falls into water, a 

 hissing noise is heard, similar to what is occasioned 

 by plunging a red-hot iron into that liquid. Its odour 

 is extremely penetrating, and its vapour dangerous to 

 inspire. When applied to the skin, it instantly dis- 

 organizes it, and produces the most painful wounds. 

 It acts energetically on glass ; the transparency of 

 the glass is instantly destroyed, caloric is evolved, 

 and the acid boils, and, in a short time, disappears 

 entirely, a colourless gas being the sole product. 



