acidity vs mordancy

acidity

noun
  • Sourness; tartness; sharpness to the taste. 

  • The quality or state of being acid. 

  • A caustic, sour, biting, or bitter quality. 

  • Excessive acid quality, as in gastric secretions. 

mordancy

noun
  • The state or quality of being mordant. 

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