The Collaborative International Dictionary of English v.0.48:

Persulphide \Per*sul"phide\, n. (Chem.)
   A sulphide containing more sulphur than some other compound
   of the same elements; as, iron pyrites is a persulphide; --
   formerly called persulphuret.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Persulphuret \Per*sul"phu*ret\, n. (Chem.)
   A persulphide. [Obs.]
   [1913 Webster]