protean vs quicksilver

protean

adj
  • Exceedingly variable; readily assuming different shapes or forms. 

noun
  • A protein that has been slightly modified by water, dilute acid, or enzymes, but not modified to the extent of a metaprotein. 

quicksilver

adj
  • Unpredictable, erratic or fickle; mercurial. 

verb
  • To overlay with quicksilver. 

  • To treat with quicksilver. 

noun
  • The metal mercury. 

  • An amalgam of mercury and tin applied to the backs of mirrors, quicksilvering. 

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