potash vs sodium

potash

noun
  • An impure form of potassium carbonate (K₂CO₃) mixed with other potassium salts. 

  • A class of potassium minerals, of similar applicability to potassium carbonate, such as being a fertilizer. (ie. potassium chloride, potassium hydroxide) 

  • The water-soluble part of the ash formed by burning plant material; used for making soap and glass and as a fertilizer. 

verb
  • To treat with potassium. 

sodium

noun
  • Employing sodium. 

  • The chemical element (symbol Na) with an atomic number of 11 and atomic weight of 22.990. It is a soft, waxy, silvery, reactive alkali metal that is never found unbound in nature. 

How often have the words potash and sodium occurred in a corpus of books? (source: Google Ngram Viewer )