exchange of contracts vs exchanging contracts

exchange of contracts

noun
  • The point or stage at which a conveyancing contract comes into existence between negotiating parties for the carrying out of a disposition of an estate in land; usually requiring the payment of a deposit. 

  • The act of exchanging contracts. 

exchanging contracts

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