The Collaborative International Dictionary of English v.0.48:

Orthocarbonic \Or`tho*car*bon"ic\, a. [Ortho- + carbonic.]
   (Chem.)
   Designating a complex ether, C.(OC2H5)4, which is obtained
   as a liquid of a pleasant ethereal odor by means of
   chlorpicrin, and is believed to be a derivative of the
   hypothetical normal carbonic acid, C.(OH)4.
   [1913 Webster]