mollify vs pour oil on troubled waters

mollify

verb
  • To ease a burden, particularly worry; make less painful; to comfort. 

  • To appease (anger), pacify, gain the good will of. 

  • To soften; to make tender 

pour oil on troubled waters

verb
  • To calm, appease or quieten a person or situation. 

How often have the words mollify and pour oil on troubled waters occurred in a corpus of books? (source: Google Ngram Viewer )