The Collaborative International Dictionary of English v.0.48:

Persulphocyanic \Per*sul`pho*cy*an"ic\, a. (Chem.)
   Pertaining to, or designating, a yellow crystalline substance
   (called also perthiocyanic acid), analogous to sulphocyanic
   acid, but containing more sulphur.
   [1913 Webster]