Sodium \So"di*um\, n. [NL., fr.E. soda.] (Chem.)
   A common metallic element of the alkali group, in nature
   always occuring combined, as in common salt, in albite, etc.
   It is isolated as a soft, waxy, white, unstable metal, so
   highly reactive that it combines violently with water, and to
   be preserved must be kept under petroleum or some similar
   liquid. Sodium is used combined in many salts, in the free
   state as a reducer, and as a means of obtaining other metals
   (as magnesium and aluminium) is an important commercial
   product. Symbol Na (Natrium). Atomic weight 22.990.
   Specific gravity 0.97.
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   Sodium amalgam, an alloy of sodium and mercury, usually
      produced as a gray metallic crystalline substance, which
      is used as a reducing agent, and otherwise.

   Sodium carbonate, a white crystalline substance,
      Na2CO3.10H2O, having a cooling alkaline taste, found in
      the ashes of many plants, and produced artifically in
      large quantities from common salt. It is used in making
      soap, glass, paper, etc., and as alkaline agent in many
      chemical industries. Called also sal soda, washing
      soda, or soda. Cf. Sodium bicarbonate, and Trona.
      

   Sodium chloride, common, or table, salt, NaCl.

   Sodium hydroxide, a white opaque brittle solid, NaOH,
      having a fibrous structure, produced by the action of
      quicklime, or of calcium hydrate (milk of lime), on sodium
      carbonate. It is a strong alkali, and is used in the
      manufacture of soap, in making wood pulp for paper, etc.
      Called also sodium hydrate, and caustic soda. By
      extension, a solution of sodium hydroxide.
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Ternary \Ter"na*ry\, a. [L. ternarius, fr. terni. See Tern,
   a.]
   1. Proceeding by threes; consisting of three; as, the ternary
      number was anciently esteemed a symbol of perfection, and
      held in great veneration.
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   2. (Chem.) Containing, or consisting of, three different
      parts, as elements, atoms, groups, or radicals, which are
      regarded as having different functions or relations in the
      molecule; thus, sodic hydroxide, NaOH, is a ternary
      compound.
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Caustic \Caus"tic\, Caustical \Caus"tic*al\, a. [L. caustucs,
   Ge. ?, fr. ? to burn. Cf. Calm, Ink.]
   1. Capable of destroying the texture of anything or eating
      away its substance by chemical action; burning; corrosive;
      searing.
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   2. Severe; satirical; sharp; as, a caustic remark.
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   Caustic curve (Optics), a curve to which the ray of light,
      reflected or refracted by another curve, are tangents, the
      reflecting or refracting curve and the luminous point
      being in one plane.

   Caustic lime. See under Lime.

   Caustic potash, Caustic soda (Chem.), the solid
      hydroxides potash, KOH, and soda, NaOH, or solutions
      of the same.

   Caustic silver, nitrate of silver, lunar caustic.

   Caustic surface (Optics), a surface to which rays reflected
      or refracted by another surface are tangents. Caustic
      curves and surfaces are called catacaustic when formed by
      reflection, and diacaustic when formed by refraction.

   Syn: Stinging; cutting; pungent; searching.
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