bolk vs bowk

bolk

verb
  • To vomit; retch. 

  • To belch out; give vent to; ejaculate. 

  • To heave. 

  • To belch. 

  • To gush out. 

bowk

verb
  • To vomit. 

  • To belch, to burp. 

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