The authors review the atomic and molecular data to analyze flow experiments on the onset of turbulent flow in gases. They use published and unpublished data from pipe flow experiments and calculate ratios of critical velocities obtained from identical apparatus. In contrast to the use of derived quantities for characterizing the onset of turbulence, such as the Reynolds number, we restrict our data and analysis using observable quantities such as molecular properties and critical velocities. We find a rationale for a molecular origin of turbulence, in contrast to the exclusive use of continuum theory. Several new predictions are made from the molecular theory of turbulence.