MOLECULAR-SIZE EXCLUSION BY SOIL ORGANIC MATERIALS ESTIMATED FROM THEIR SWELLING IN ORGANIC-SOLVENTS

A published method previously developed to measure the swelling charac teristics of powdered coal samples has been adapted for swelling measu rements on various peat, pollen, chitin, and cellulose samples. The sw elling of these macromolecular materials is the volumetric manifestati on of absorption, that is, sorption by dissolution (or partitioning) o f the sorbed liquids into cross-linked macromolecular solid phases. Di rect evidence for the existence of this additional category of sorbed materials has been obtained for soil organic materials by the present research; however, it seems to be limited by molecular size-exclusion effects to fairly small molecules. Liquids with molar volumes greater than about 93 cm3 mol-1 appeared to be strongly excluded from sorption inside most cross-linked soil organic materials studied in this work. Cellulose excluded liquids with molar volumes greater than about 88 c m3 mol-1.