The Collaborative International Dictionary of English v.0.48:

Supercarbonate \Su`per*car"bon*ate\, n. (Chem.)
   A bicarbonate. [Obsoles.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Bicarbonate \Bi*car"bon*ate\, n. [Pref. bi- + carbonate.]
   (Chem.)
   A carbonate in which but half the hydrogen of the acid is
   replaced by a positive element or radical, thus making the
   proportion of the acid to the positive or basic portion twice
   what it is in the normal carbonates; an acid carbonate; --
   sometimes called supercarbonate.
   [1913 Webster] Bicarbureted