Insoluble phosphoric acid

Phosphoric \Phos*phor"ic\, a. [Cf. F. phosphorique.]
   1. (Chem.) Of or pertaining to phosphorus; resembling, or
      containing, phosporus; specifically, designating those
      compounds in which phosphorus has a higher valence as
      contrasted with the {phosphorous} compounds.
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   2. Phosphorescent. "A phosphoric sea." --Byron.
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   {Glacial phosphoric acid}. (Chem.)
      (a) Metaphosphoric acid in the form of glassy
          semitransparent masses or sticks.
      (b) Pure normal phosphoric acid.

   {Phosphoric acid} (Chem.), a white crystalline substance,
      {H3PO4}, which is the most highly oxidized acid of
      phosphorus, and forms an important and extensive series of
      compounds, viz., the phosphates.

   {Soluble phosphoric acid}, {Insoluble phosphoric acid}
      (Agric. Chem.), phosphoric acid combined in acid salts, or
      in neutral or basic salts, which are respectively soluble
      and insoluble in water or in plant juices.

   {Reverted phosphoric acid} (Agric. Chem.), phosphoric acid
      changed from acid (soluble) salts back to neutral or basic
      (insoluble) salts.
      [1913 Webster]