Manner of Evaporation of Water The evaporation of water from wood takes place largely through the ends, _i.e._, in the direction of the longitudinal axis of the wood fibres. The evaporation from the other surfaces takes place very slowly out of doors, and with greater rapidity in a dry kiln. The rate of evaporation differs both with the kind of timber and its shape; that is, thin material will dry more rapidly than heavier stock. Sapwood dries faster than heartwood, and pine more rapidly than oak or other hardwoods. Tests made show little difference in the rate of evaporation in sawn and hewn stock, the results, however, not being conclusive. Air-drying out of doors takes from two months to a year, the time depending on the kind of timber, its thickness, and the climatic conditions. After wood has reached an air-dry condition it absorbs water in small quantities after a rain or during damp weather, much of which is immediately lost again when a few warm, dry days follow. In this way wood exposed to the weather will continue to absorb water and lose it for indefinite periods. When soaked in water, seasoned woods absorb water rapidly. This at first enters into the wood through the cell walls; when these are soaked, the water will fill the cell lumen, so that if constantly submerged the wood may become completely filled with water. The following figures show the gain in weight by absorption of several coniferous woods, air-dry at the start, expressed in per cent of the kiln-dry weight: ABSORPTION OF WATER BY DRY WOOD --------------------------------------------------------------- | White Pine | Red Cedar | Hemlock | Tamarack --------------------------------------------------------------- Air-dried | 108 | 109 | 111 | 108 Kiln-dried | 100 | 100 | 100 | 100 In water 1 day | 135 | 120 | 133 | 129 In water 2 days | 147 | 126 | 144 | 136 In water 3 days | 154 | 132 | 149 | 142 In water 4 days | 162 | 137 | 154 | 147 In water 5 days | 165 | 140 | 158 | 150 In water 7 days | 176 | 143 | 164 | 156 In water 9 days | 179 | 147 | 168 | 157 In water 11 days | 184 | 149 | 173 | 159 In water 14 days | 187 | 150 | 176 | 159 In water 17 days | 192 | 152 | 176 | 161 In water 25 days | 198 | 155 | 180 | 161 In water 30 days | 207 | 158 | 183 | 166 --------------------------------------------------------------- Rapidity of Evaporation