caustic soda vs potash

caustic soda

noun
  • sodium hydroxide (NaOH), a strong alkaline substance used in the manufacture of paint, soap and detergents, or as a drain cleaner. 

potash

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

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

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

verb
  • To treat with potassium. 

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