hell on earth vs purgatory

hell on earth

noun
  • A very unpleasant situation; torment, particularly when widespread. 

purgatory

noun
  • Any situation where suffering is endured, particularly as part of a process of redemption. 

adj
  • Tending to cleanse; expiatory. 

How often have the words hell on earth and purgatory occurred in a corpus of books? (source: Google Ngram Viewer )