The longitudinal flow rate of air through bar type specimens of fifteen species including domestic and imported woods was measured. From the results, the permeability characteristics for each species, and the effects of specimen length (l) and moisture content (u) on the permeability were discussed.
(1) In the longitudinal direction of wood, the permeability value calculated based on Darcy's law (kg) was a function of l with some exceptions, and a linear relationship was found between l and logarithm of kg in the range of 5-45cm sample length, as expressed by kg=K0exp(-bl), where kg is the superficial gas permeability.
(2) The longitudinal permeability of wood was extremely different from one species to another. In the case of air dried specimens of broad leaved trees, the values of K0 ranged from 0.02 to 180 darcy, and constant b was 0.03-0.56. In the case of those of coniferous trees, K0 was from 0.04 to 1.2 darcy and b was 0-0.03. Apitong (Dipterocarpus grandiflorus BLCO.) was the most permeable wood among the species tested and Balsa (Ochroma lagopus SW.) was also very permeable. Witch hazel (Distylium racemosum SIEB. & ZUCC.) had the least value of permeability. The heartwood of Cryptomeria (Cryptomeria Japonica D. DON) and Formosan cypress (Chamaecyparis obtusa ENDL. var formosana HAYATA) were less permeable than thier sapwood.
(3) The value of kg showed a low value for green specimens, but the value increased rapidly with drying at least below 25% of u with an exception of the heartwood of Siebold's beech (Fagus crenata BL.) and b became more or less smaller with decreasing u. This variation in permeability with u seemed to be reversible unless the specimens were dried to the moisture content below 5% with severe drying conditions.
