mercilessness vs purgation

mercilessness

noun
  • The property of being merciless. 

purgation

noun
  • The process or act of purging, such as by the use of a purgative. 

  • The process or act of cleansing from sin or guilt. 

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