thiosulphate

from The Collaborative International Dictionary of English v.0.48

Thiosulphate \Thi`o*sul"phate\, n. (Chem.)
   A salt of thiosulphuric acid; -- formerly called
   {hyposulphite}.
   [1913 Webster]

   Note: The sodium salt called in photography by the name
         sodium hyposulphite, being used as a solvent for the
         excess of unchanged silver chloride, bromide, and
         iodide on the sensitive plate.
         [1913 Webster]