Sept. 2i, 1914 
Density and Porosity of Wood 
425 
EXPERIMENTAL METHODS AND APPARATUS 
The method used in the present research was the same in principle as 
that followed by Sachs and by Hartig in similar studies on a few European 
woods 30 years ago. Small blocks were boiled in water until sufficient air 
was expelled to make them sink. Thin sections were then cut with a 
sharp knife across the grain. These sections were placed in a solution of 
calcium nitrate and boiled for a few seconds to complete expulsion of the 
air; then they were transferred to cold solutions of the same salt. The 
densities of these cold solutions averaged about 1.6, which was a little 
greater than the anticipated density of the wood, so that the sections 
floated on the surface. Water was added, a few drops at a time at inter¬ 
vals of four hours or more, and the solutions held at constant tempera¬ 
ture until equilibrium was established and the wood hung suspended in 
the solution. 
A specific-gravity bottle was then submerged in the solution and 
filled; after a few minutes it was withdrawn, washed, dried, cooled to 
room temperature, and weighed. The volume of the bottle was deter¬ 
mined by filling it with freshly boiled distilled water at the same tem¬ 
perature as the solutions measured, cooling to room temperature, and 
weighing. These relative densities of the solutions were divided by the 
density of air-free distilled water at the temperature in question, and a 
result was obtained expressing the density of the solutions (and also of 
the wood suspended) in terms of water at its maximum density. 
Preliminary experiments showed that accurate results could not be 
secured without control of the temperature of the solutions. For this 
purpose a tank 50 cm. on each edge was hung in a wooden box so as to 
leave a 10-cm. space on four sides and the bottom. This space was 
filled with sawdust. The tank was open above, but was partially cov¬ 
ered with a board when the temperature of the room fell more than io° 
C. below the temperature of the water in the tank. A shaft extended 
through the center of the bottom, and a stirrer made from a 30-cm. 
electric fan was mounted on this shaft. The stirrer was driven by a 
>£-horsepower electric motor at a speed of 65 revolutions per minute by 
a belt and through an intermediate shaft for reducing the speed. 
The tank was filled nearly full of water. Heat was supplied by a 175- 
watt carbon filament incandescent lamp submerged in one corner of the 
tank. The temperature was controlled automatically by an ether ther¬ 
moregulator—an ether reservoir inverted and sealed with mercury. 
The recession of the mercury column as the ether contracted broke a 
dry-cell circuit through a relay and turned on the lamp. A rise in tem¬ 
perature beyond a certain point extinguished the lamp. In this way 
the temperature of the water in the tank was kept within a range of 
yi degree centigrade. 
