rub out vs send to the scaffold

rub out

verb
  • To kill, especially to murder. 

  • To delete or erase or remove (something) by rubbing. 

send to the scaffold

verb
  • To cause someone to be condemned to be hanged. 

  • To sentence to be hanged. 

How often have the words rub out and send to the scaffold occurred in a corpus of books? (source: Google Ngram Viewer )