sentences:  The density is given by
  
  where formula_17 and formula_18 are the densities the dry air and water vapor would respectively have when occupying the volume of the air parcel.Rearranging the standard ideal gas equation with these variables gives
  
  Solving for the densities in each equation and combining with the law of partial pressures yields
  
  Then, solving for formula_11 and using formula_23 is approximately 0.622 in Earth's atmosphere