c4h4o5

from The Collaborative International Dictionary of English v.0.48

Tartrelic \Tar*trel"ic\, a. [From {Tartar} the chemical
   compound.] (Chem.)
   Of, pertaining to, or designating, an anhydride, {C4H4O5}, of
   tartaric acid, obtained as a white crystalline deliquescent
   substance.
   [1913 Webster]