FLUX. A general term used to denote any substance or mixture added to assist the fission of minerals. In the large way, limestone and fusible spar are used as fluxes. The fluxes made use of in philosophical experiments consist usually of alkalies, which render earthy mixtures fusible by converting them into glass, or else glass itself into powder. Alkaline fluxes are either the crude flux, the white flux, or the black flux. Crude flux is a mixture of nitre and tartar, which is put into the crucible along with the metal intended to be fused. White flux is formed by projecting equal parts of a mixture of nitre and tartar, by moderate proportions at a time, into a red hot crucible. In the detonation which ensues, the nitric acid is decomposed and flies off with the tartaric acid, and the remainder consists of the potash in a state of considerable purity. Black flux consists of two parts of tartar to one of nitre, on which account the combustion is incomplete, and a considerable portion of the tartaric acid is decomposed by mere heat, and leaves behind a quantity of charcoal, on which the colour depends. It is used in the reduction of metallic ores, which it effects by combining with the oxygen of the oxide. Mowean's reducing flux is made of eight parts of pulverised glass, one of calcined borax, and half a part of charcoal. Care must be taken to use a glass which contains no lead.
PLY, in Mechanics, a wheel with a heavy rim, placed on the shaft of any machinery put in motion by any irregular or intermitting force, for the of rendering the motion equable and regular by means of its effect results from a law of nature, that all bodies have a tendency to continue in their state either of motion or of rest, until acted upon by some extraneous force. Thus the rim of a fly-wheel, after a few revolutions, acquires a momentum sufficient to cause it to revolve with a velocity depending upon the resistance of the machinery ; and the augmentations and diminutions of the impelling power succeeding each other rapidly, neither cause acts sufficiently long to either augment or diminish the velocity acquired in any considerable degree, so that it remains equable, or newly so. Thus in the case of a man
working at a winch, the power which he exerts in pulling upwards from the lower part considerably exceeds his power in thrusting forwards in the upper quarter ; but before the extra force thus exerted has acted sufficiently long to clear the velocity of the wheel, the winch arrives at the point where his force is the least, by which time the excessive force previously exerted having taken effect, the equable motion of the fly is maintained; and the resistance of the work being equalized, a man is enabled to raise throughout a whole day a weight of forty pounds with more ease than he could raise thirty pounds without a fly. In all cases where a rotatory motion is to be obtained from a reciprocating one, by means of a crank, a flywheel is necessary to continue the motion at those two points of the revolution in which the crank lies in the direction in which the moving force acts; for in this case the crank affords no leverage to the power either on one or other side of the fulcrum, and consequently no motion could be produced in either direction ; but the momentum acquired by the fly urges the crank forward in the direction in which it was previously moving, and con tinues the rotation until the crank is brought into such a position as to offer sufficient leverage to the power to maintain the impetus of the fly.