Modified Mercury Immersion Method in Determining Specific Gravity of Small, Irregular Wood Specimens

This paper reports a modified mercury immersion method in which a given pressure is created on the mercury to insure good contact with the wood at all points including jagged and irregular surfaces on the small particles. The pressure is controlled by the size of a hole through which excess mercury is forced out of the apparatus during displacement. This volume measuring device consists of three parts: the cap, the lid, and the container. A fine hole or bore of a given size is made in the lid. The relation given the pressure required to force mercury into and through the bore is given by an equation. Dry volume specific gravities of sixty 1- by 1- by 1-inch loblolly pine blocks were determined. After specific gravity, determinations, each block was broken to chip size of approximately 1 by 1/2 by 1/8 inch. Chips were then used in estimating the specific gravity by the modified mercury immersion method and its value was compared with that obtained from the original 1- by 1- by 1-inch block. The average volume deviations of 0.648 and 0.594 percent from using a 184 micron bore and a smaller hammered bore were as good as that obtained from the 1-inch blocks. Hence it is apparent that for practical purposes, both bore sizes may be used in determining specific gravity of loblolly pine specimens without the need of correction for the error due to mercury penetration. This of course means time saving and less work than if a correction is required.

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