The rate of absorption of a chemical through a cell membrane and through a
tissue depends of both the size of the molecule and the lipid:water partition
coefficient for that molecule. The lipid:water partition coefficient is determined
by dissolving the chemical in a mixture of lipid and water and
measuring the concentration of the chemical in each solvent. Lipid
is usually represented by the solvent octanol. The lipid:water
partition coefficient is the ratio of the concentration of the chemical
in octanol to the concentration in water: coeff. = [conc. in octanol] ÷
[conc. in water]. The logarithm of the coefficient is called the log
Kow. The relation between rate of absorption for a chemical and
the log Kow for that chemical is given in Figure 5 on the next page