The field of force and the form of the carbon dioxide molecule. - Part II. The variation of the viscosity of carbon dioxide with temperature

• Published in: Proceedings of the Royal Society of London. Series A, Containing papers of a mathematical and physical character Containing papers of a mathematical and physical character, 1932-01, Vol.134 (825), p.628-635
• Main Authors: Ibbs, T. L., Wakeman, A. C. R.
• Format: Article
• Language: English
• Subjects: Capillary tubes; Carbon dioxide; Fall lines; Furnaces; Gas temperature; Mercury; Molecules; Room temperature; Thermal diffusion; Viscosity
• ISSN: 0950-1207; 2053-9150
• DOI: 10.1098/rspa.1932.0010

The variation of viscosity with temperature provides another method of investigating the forces between gas molecules. Chapman has obtained the following expression for n the coefficient of viscosity of a gas n0·499 mc¯/√2πσ2 where m = mass of molecule, c¯ = average velocity, and σ = molecular diameter. As c¯ is proportional to the square root of the absolute temperature T, it follows that the value of n must be proportional to √T for a gas in which the molecules are rigid elastic spheres. For a gas in which a decreases with rise of temperature, n) will increase more rapidly than this as the temperature rises. The variation in the value of a will depend upon the law of force between molecules. Our experiments on thermal diffusion in carbon dioxide mixtures led to the conclusion that a definite change occurs in the field of force of this gas at about 145° C. This change should influence the viscosity of the gas, and conse­quently should be demonstrated by its effect on curves showing the relation between nand √T. We may expect either (a) a discontinuity in these curves owing to a sudden change in the effective diameters of the molecules, or (b) a singularity at a point in the curve where the general slope changes as a result of the change in molecular hardness.