FLU 



FOC 



assume a pulverulent form by sublima- 

 tion or crystallization : thus we have 

 flowers of zinc, or the oxide ; flowers of 

 benjamin, or benzoic acid ; flowers of 

 sulphur, or sublimed sulphur, &c. 



FLU'CERINE. The native deutoxide 

 of cerium, occurring near Falun, in 

 Sweden. 



FLU'ELLITE. A rare mineral, con- 

 sisting of hydrofluoric acid and alumina, 

 occurring at Stenna-gwyn, in Cornwall. 



FLUENT or FLOWING QUANTITY. 

 This term denotes, in analysis, the vari- 

 able quantity, considered as increasing 

 or diminishing. The term is now super- 

 seded by that of integral, and the methods 

 of fluxions and fluents have been laid 

 aside for the difierential and integral 

 calculus. 



FLUID. A fluid is a collection of 

 material particles, which are held to- 

 gether by so slight a degree of cohesion, 

 as to be easily moved among themselves. 

 1. Elastic fluids are those which are ca- 

 pable of being compressed into a smaller 

 bulk, and of recovering their dimensions 

 when the compressing force is removed ; 

 of this kind are atmospheric air and all 

 the gases. 2. Inelastic fluids are those 

 formerly supposed to be incompressible, 

 and among these were ranged water, 

 mercury, alcohol, and liquids generally. 

 But the term is incorrect: the phenome- 

 non of the transmission of sound through 

 water and other liquids had long ago 

 indicated that they were capable of being 

 compressed. 



FLUI'DITY {fluo, to flow). The state 

 of bodies when their parts are very readily 

 moveable in all directions with respect to 

 each other. There is a partial fluidity, 

 in which the particles are condensed or 

 thickened into a coherent though tremu- 

 lous mass. Jellies are of this kind, and 

 may be considered as holding a middle 

 place between liquids and solids. 



FLUOBO'RIC ACID. Fluoride of 

 boron. A gas produced by the decompo- 

 sition of fluor spar, by means of vitrified 

 boracic acid. 



FLUOR SPAR. The technical name 

 for the fluoride of calcium, a salt found 

 crystallized in cubes of various colours. 

 A compact variety occurs in Derbyshire, 

 which is cut into ornamental vases. 



FLU'ORIDES. Compounds of fluorine 

 with the electro-positive elements, ob- 

 tained by treating the fluate of mercury 

 or of lead with bodies more positive than 

 these metals. 



FLU'ORINE. An elementary body 

 139 



generally found in the mineral kingdom 

 in combination with calcium, or as fluor- 

 ide of calcium, which constitutes the 

 mineral fluor spar. 



FLUOSI'LICIC ACID. Fluoride of 

 silicon. A colourless gas, produced by 

 the action of hydrofluoric acid on glass. 



FLUX {fluo, to flow). A substance 

 used in Chemistry and Metallurgy, to 

 reduce ores or metallic compounds to the 

 metallic state, by promoting their fusion. 

 Alkaline fluxes are generally employed, 

 which render the earthy mixtures fusible 

 by converting them into glass. Black 

 flux is a mixture of nitre and bitartrate 

 of potash ; white flux is a carbonate of 

 potash. Other fluxes consist of argol, 

 charcoal, and some kinds of glass. 



FLU'XIONS ifluxio, a flowing). In 

 the Newtonian analysis, fluxions are the 

 " velocities of motions." More particu- 

 larly defined, a fluxion is the magnitude 

 by which any flowing quantity would be 

 uniformly increased in a given portion of 

 time, with the generating celerity at any 

 proposed position, or instant, supposing 

 it thence to continue invariable. Hence 

 it appears that the fluxions of quantities 

 are always as the celerities by which the 

 quantities themselves increase in magni- 

 tude. The method of fluxions, derived 

 from that of prime and ultimate ratiott 

 has been entirely superseded by that of 

 the differential calculus. 



FLY POWDER. An oxide of arsenic, 

 formed by the exposure of native arsenic 

 to the air, and employed, when mixed 

 with sugar and water, for destroying 

 flies. 



FLY-WHEEL. A large heavy wheel 

 applied to steam engines and other ma- 

 chines, for the purpose of equalizing the 

 effect of the moving power. If the 

 moving power slackens, the fly-wheel 

 impels the machine forward; if the power 

 tends to impel the machine too fast, the 

 fly-wheel slackens it. Its object is, 

 therefore, to absorb, as it were, the sur- 

 plus force at one part of the action of the 

 machine, and to give it out when the 

 action of the machine is deficient. At 

 one time it is an impelling, at another a 

 retarding power. 



FOCUS. The Latin term for a hearth 

 or fire-place ; hence it denotes any point 

 in which light, or heat, is concentrated. 

 In Optics, it is the point where several 

 rays are collected, in consequence of re- 

 fraction or of reflexion. In Geometry 

 and Conic Sections, it is applied to cer- 

 tain points in the ellipse, the parabola, 



