FLU 



FLU 



tional to the depth, and equal in every 

 horizontal line of fluid ; consequently, the 

 pressure on the bottom of vessels is equal 

 in every part. The pressure of fluids up- 

 wards is equal to the pressure down- 

 wards, at any given depth. For, suppose 

 a column of water to consist of any given 

 number of particles acting upon each 

 other in a perpendicular direction, the 

 first particle acts upon the second with 

 its own weight only ; and, as the second 

 is stationary, or fixed by the surrounding 

 particle, according to the third law of 

 motion, that action and reaction are 

 equal, it is evident that the action, or 

 gravity, in the first is repelled in an equal 

 degree by the reaction of the second; and 

 in like manner the second acts on the 

 third, with its own gravity added to that 

 of the first; but still the reaction increases 

 in an equivalent degree, and so on 

 throughout the whole depth of the fluid. 



The particles of a fluid, at the same 

 depth, press each other equally in all di- 

 rections. This appears to rise out of the 

 very nature of fluids ; for as the particles 

 give way to every impressive force, if the 

 pressure amongst themselves should be 

 unequal, the fluid could never be at rest, 

 which is contrary to experience ; there- 

 fore, we conclude that the particles press 

 each other equally, which keeps them in 

 their own places. This principle applies 

 to the whole of a fluid as well as a part. 

 For if four or five glass tubes, of differ- 

 ent forms, be immersed in water, when 

 the corks in the ends are taken out, the 

 water will flow through the various wind- 

 ings of the different tubes, and rise in all 

 of them to the same height as it stands 

 in the straight tube : therefore the drops 

 of fluids must be equally pressed in all di- 

 rections during their ascent through the 

 various angles of the tube, otherwise the 

 fluid could not rise to the same height in 

 them all. 



From the mutual pressure and equal, 

 action of the particles of fluids, the sur- 

 face will be perfectly smooth and parallel 

 to the horizon. If from any exterior cause 

 the surface of water has some parts high- 

 er than the rest, these will sink down by 

 the natural force of their own gravitation, 

 and diffuse themselves into an even sur- 

 face. See HYDROSTATICS. 



FLUIDS, motion of. The motion of fluids, 

 viz. their descent or rise below or 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 re- 

 servoir, when it is at the same time either 

 taken off or diminished on some part in 

 aqueducts or pipes of conduit. 3. By 

 the spring or elastic power of compress- 

 ed or condensed air, as in the common 

 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. 



FLUIDITY. The state of bodies when 

 their parts are very readily moveable in 

 all directions with respect to each other. 

 Many useful and curious properties arise 

 out of this modification of matter, which 

 form the basis of the mechanical sciejice 

 called hydrostatics, and are of considera- 

 ble importance in chemistry. But the 

 attention of the chemist is chiefly direct- 

 ed to the state of fluidity, as it may affect 

 the component parts of bodies. 



A solid body may be converted into a 

 fluid by heat. The less the temperature 

 at which this is effected, the more fusible 

 the body is said to be. 



All fluids, not excepting the fixed me- 

 tals, appear, from various facts, to be dis- 

 posed to assume the elastic form, and this 

 the more readily the higher the tempera- 

 ture. When a fluid is heated to such a 

 degree as that its elasticity is equal to the 

 pressure of the air, its interior parts arise 

 up with ebullition. 



The capacity of a dense fluid for caloric 

 is greater than that of the same body 

 when solid, but less than when in the elas- 

 tic state. If this were not the case, the 

 assumption of the fluid and elastic state 

 would be scarcely at all progressive, but 

 effected in most cases instantly as to 

 sense. See CALORIC. 



The state of dense fluidity appears to 

 be more favourable to chemical combi- 

 nation than either the solid or elastic 

 state. In the solid state, the cohesive 

 attraction prevents the parts from obey- 

 ing 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 nisi fluida. 



FLUOR spar, the native fluate of lime. 

 See the next article. 



FLUORIC add, in chemistry, is obtain- 

 ed from fluor spar, or, as it is technically 

 called, fluate of lime. It has not yet been 

 decomposed, unless it be among the 

 grand discoveries of Mr. Davy, not yet 

 announced to the world. We have at- 



