Meaning of salt cake

salt' cake"

Pronunciation: [key]
— Chem. Chem.
  1. an impure form of sodium sulfate, esp. as obtained by the interaction of sulfuric acid and common salt in the synthesis of hydrochloric acid: used chiefly in the manufacture of glass, ceramic glazes, soaps, and sodium salts.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.