A comparison of two methods for determining the basic density of small irregular samples of old waterlogged wood

Abstract

Introduction In sound wood the relationship between maximum moisture content (max.m.c.) and density was established and described in a simple mathematical function, which can be used to estimate the basic density of wood (Smith 1954). The basic density (R, g/cm 3) is based on dry weight and water saturated volume, and can be calculated from the maximum moisture content (Vmax, %) by the formula: R = lO0/[Vmax + 100/rw] where r~, = is the density of cell-wall substance (g/cm3). This method is based on the assumption that the density of cell-wall substance is constant for all species. A value of 1.50 or 1.53 g/cm 3 is usually assumed. To a certain degree, this variability has been attributed to differences in extractive content and related to the relative chemical (holocellulose-lignin) composition, and the densities of each component substance (Table 1). For conservation of waterlogged woods it is important to know the degree of wood degradation. Maximum moisture content and density is often used by conservators as a measure of solid wood loss. They assume that within a given species a higher max.m.c, and a lower density indicates greater deterioration of wood substance. Basic density is especially appropriate for degraded waterlogged wood Table 1. Density values of cell-wall substance and of cell-wall chemical constituents Tabelle 1. Dichte der Zellwand und ihrer chemischen Bestandteile Material Density, g/cm 3 Softwoods Hardwoods Cell-wall substance 1) 1.526 (1.517-1.529) 1.509 (1.497-1.517) Holocellulose ~ 1.595 (1.590-1.602) 1.533 (1.544-1.563) a-Cellulose 2) 1.520 1.520 Hemicellulose 2) 1.666