A Note On The Diffusion of Water Across Oil And Wax Layers and Insect Cuticles

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Abstract
The terms diffusion and permeability are frequently confused and misused. For example, Barrer (1941) in the preface of his book defines permeability constant in contradictory ways in successive sentences and both are incorrect. In the case of diffusion of gases and water, confusing systems of units have been employed. Taylor et al. (1936) define a coefficient as g/hr/cm/mmHg and Barrer (1941) uses cc(vapour at N.T.P.)/sec/cm2/cmHg/mm thick. The use of more than one solidus leads to ambiguity and may, for example, disguise that the thickness term is in the numerator and Machin (1980) does, indeed, manage to invert this term. Other errors can also easily occur. Thus Beament (1958) writes mmHg when cmHg is intended and this is repeated by Machin (1980). Also Machin & Lampert (1987) use both the coefficients mg h−1 cm−2 torr−1 and cms−1 without relating them.