natural gas vs vapor

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. 

vapor

noun
  • The gaseous state of a substance that is normally a solid or liquid. 

  • Cloudy diffused matter such as mist, steam or fumes suspended in the air. 

  • Something insubstantial, fleeting, or transitory; unreal fancy; vain imagination; idle talk; boasting. 

verb
  • To emit vapor or fumes. 

  • To give (someone) the vapors; to depress, to bore. 

  • To become vapor; to be emitted or circulated as vapor. 

  • To turn into vapor. 

  • To use insubstantial language; to boast or bluster. 

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