hogshead vs tank wagon

hogshead

noun
  • A large barrel or cask of indefinite contents, especially one containing from 100 to 140 gallons. 

  • An English measure of capacity for liquids, containing 63 wine gallons, or about 52+¹⁄₂ imperial gallons; a half pipe. 

tank wagon

noun
  • A vehicle designed to transport liquids or gases in bulk; a tanker 

  • Synonym of tank car. 

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