impure vs strengthening

impure

adj
  • Unchaste; obscene (not according to or not abiding by some system of sexual morality) 

  • Containing undesired intermixtures 

  • Unhallowed; defiled by something unholy, either physically by an objectionable substance, or morally by guilt or sin 

strengthening

noun
  • The process by which something is strengthened. 

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