Re·ac·tion n.
 1. Any action in resisting other action or force; counter tendency; movement in a contrary direction; reverse action.
 2. Chem. The mutual or reciprocal action of chemical agents upon each other, or the action upon such chemical agents of some form of energy, as heat, light, or electricity, resulting in a chemical change in one or more of these agents, with the production of new compounds or the manifestation of distinctive characters. See Blowpipe reaction, Flame reaction, under Blowpipe, and Flame.
 3. Med. An action induced by vital resistance to some other action; depression or exhaustion of vital force consequent on overexertion or overstimulation; heightened activity and overaction succeeding depression or shock.
 4. Mech. The force which a body subjected to the action of a force from another body exerts upon the latter body in the opposite direction.
    Reaction is always equal and opposite to action, that is to say, the actions of two bodies upon each other are always equal and in opposite directions.   --Sir I. Newton (3d Law of Motion).
 5. Politics Backward tendency or movement after revolution, reform, or great progress in any direction.
    The new king had, at the very moment at which his fame and fortune reached the highest point, predicted the coming reaction.   --Macaulay.
 6. Psycophysics A regular or characteristic response to a stimulation of the nerves.
 Reaction time Physiol., in nerve physiology, the interval between the application of a stimulus to an end organ of sense and the reaction or resulting movement; -- called also physiological time.
 Reaction wheel Mech., a water wheel driven by the reaction of water, usually one in which the water, entering it centrally, escapes at its periphery in a direction opposed to that of its motion by orifices at right angles, or inclined, to its radii.

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 Blow·pipe n.
 1. A tube for directing a jet of air into a fire or into the flame of a lamp or candle, so as to concentrate the heat on some object.
 Note: ☞ It is called a mouth blowpipe when used with the mouth; but for both chemical and industrial purposes, it is often worked by a bellows or other contrivance. The common mouth blowpipe is a tapering tube with a very small orifice at the end to be inserted in the flame. The oxyhydrogen blowpipe, invented by Dr. Hare in 1801, is an instrument in which oxygen and hydrogen, taken from separate reservoirs, in the proportions of two volumes of hydrogen to one of oxygen, are burned in a jet, under pressure. It gives a heat that will consume the diamond, fuse platinum, and dissipate in vapor, or in gaseous forms, most known substances.
 2. A blowgun; a blowtube.
 Blowpipe analysis Chem., analysis by means of the blowpipe.
 Blowpipe reaction Chem., the characteristic behavior of a substance subjected to a test by means of the blowpipe.

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