Now, green wood can have moisture content anywhere from 30% (denser woods) to over 200% (lighter woods). The most commonly referenced "heaviest wood", lignum vitae ( Guaiacum officinale), has a specific gravity of 1.05 when green, which makes its weight about 1365 kg/m 3, or 85 pounds per green cubic foot. And like a sponge, most woods float, and therefore have specific gravities less than 1.0 a few of the denser tropical hardwoods are actually heavier than water and sink. Actual woods, the amazing composite of cell matrix in infinitely different shapes, sizes, and arrangements, much like a sponge made of lignocellulose, have much lower specific gravity than the theoretical maximum due to the amount of space in the matrix filled with air and water. Wood of course, is comprised of cells, of which only the cell walls have the specific gravity stated above. Thus far, we have been talking only of solid wood substance, which is not really wood as we know it. Together, the amount of ash and extractives in wood can vary from trace amounts to 30% and therefore affect the weight of wood differently according to species. Ash, which makes up 0.5% to 2.0% of most woods, has a specific gravity of 1.6 to 2.8 the specific gravity of extractives varies depending on the substance. These extractives and infiltrates impregnate the lignocellulosic matrix and fill parts of the cavities of the wood. In addition, inorganic compounds such as silicates, carbonates, and phosphates appear in the wood as "infiltrates" and result in ash as the wood substance is decomposed. Wood also contains measurable quantities of organic "extractives" such as such as terpenes, resins, and polyphenols such as tannins, sugars, and oils. ![]() With the specific gravity around 1.5, solid wood "substance", or lignocellulose as it is commonly called today, weighs around 1500 kg/m 3 (93.6 lb/ft 3), at theoretical most…no air, water, or other fluids in cell pores, which would decrease the weight of the wood per unit of volume. ![]() ![]() The nice thing about using water as the reference measure was that early scientists could easily classify materials by whether they float on water (specific gravity less than 1.0) or whether they sink (specific gravity greater than 1.0). Since water conveniently weighs about 1 g/cm 3, variable with temperature, specific gravity was derived as an index metric to state the weight of other substances relative to water.
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