liquid gold vs natural gas

liquid gold

noun
  • Crude oil. 

  • Water. 

  • Beer. 

  • Urine. 

  • Sandalwood oil 

  • A kind of liquid preparation used to decorate ceramic ware with gold or gold colour. 

  • Any liquid that is yellow in color, such as beer, olive oil or a liquid cheese. 

  • Colostrum. 

natural gas

noun
  • A mixture of gaseous hydrocarbons associated with petroleum deposits; mostly methane with smaller amounts of ethane, propane and butane; principally used as a fuel. 

How often have the words liquid gold and natural gas occurred in a corpus of books? (source: Google Ngram Viewer )