Permeance, Diffusion and Partition Coefficients: Units and Their Conversion

Since 1960, units of measurement have been based on the SI (Systéme International) system, and we shall be using it in this book. Basic units in this system are (among others) metre (m), kilogram (kg), mol, seconds (s), Pascal (Pa) and Kelvin (K). This has not always been the case, and before 1960 the CGS system (cm, g, s) was common in the natural sciences. In engineering, a great variety of non-metric units (i.e., inch, pound, fluid ounce, and horse-power) are still in use, particularly in the Anglo-Saxon countries.

In Chap. 2, mass transfer across membranes was characterised by permeance, diffusion coefficients and first-order rate constants.We shall use these parameters to explain why permeability of cuticles from different plant species to various solutes differs greatly. Permeability depends on chemistry and structure of membranes, and we shall relate chemistry and structure of cuticles to their permeability. To this end, we have incorporated studies by physical scientists, engineers and biologists on permeability of natural and synthetic membranes published during the last 7 decades. This necessitates converting older units into SI units.