amass vs buy up

amass

verb
  • to gather a great quantity of; to accumulate. 

  • To accumulate; to assemble. 

  • To collect into a mass or heap. 

buy up

verb
  • To buy the whole of; to purchase the entire stock of something. 

  • To buy off; to pay in blackmail money or similar. 

  • To buy whatever is available of something. 

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