alkali vs caustic soda

alkali

noun
  • One of a class of caustic bases, such as soda, soda ash, caustic soda, potash, ammonia, and lithia, whose distinguishing characteristics are dissolving in alcohol and water, uniting with oils and fats to form soap, neutralizing and forming salts with acids, turning to brown several vegetable yellows, and changing reddened litmus to blue. 

  • Soluble mineral matter, other than common salt, contained in soils of natural waters. 

caustic soda

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

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