common salt vs seawater

common salt

noun

  • Ordinary salt (sodium chloride) 

seawater

noun

  • The saltwater of a sea or ocean. 

adj

  • Associated in some way with seawater, or intended for dealing with seawater. 

  • Consisting of seawater. 

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