The term “liquefied petroleum gas”, as used in this chapter, means and includes any material which is composed predominantly of any of the following hydrocarbons or mixtures of the same: Propane, propylene, butane, normal or isobutane and butylene. The term “liquefied natural gas”, as used in this chapter, means a fluid in the liquid state composed predominantly of methane and which may contain minor quantities of ethane, propane, nitrogen or other components normally found in natural gas.