Sept, si, 1914 
Density and Porosity of Wood 
427 
Table II. — Results of 21 determinations , giving density of various species of wood 
Species at wood. 
Density (referred to water at 4 0 C.). 
Soaked in acid at 
35° C. 
Soaked in water at— 
35 ° C. 
30* c. 
Longleaf pine. 
fl I. 6197±0. OOO7 
i. 59i5±o. 0012 
5534 
i- 557 ° 
1. 5929^0. 0005 
I. 5060 
I- 5639 
Douglas-fir.. 
1.5698 
Pacific yew. 
Mockemut hickory. 
1. 55 2 5 ±0.0003 
1. 4990 ±0. 0002 
1* 5395 ±0. °°04 
1. 55°6 
Beech. 
Red oak. 
Sugar maple. 
1. 6170 
* This is not the ''probable error;” the mean values in this column rest on only two observations, and 
the actual deviation of the two from the mean is indicated. 
Table II shows, in the first place, that there are significant differences 
between the densities of the wood substance from various species of 
trees. The difference between beech and Douglas fir indicates that the 
extreme range for these seven species is nearly 4^ per cent. 
Those sections which had been soaked in hydrofluoric acid as a step 
in their preparation for sectioning on the microtome showed a higher 
density than those which were merely boiled in water. It appears that 
either some constituent with a density less than 1.55 was removed or 
some foreign substance with a density greater than 1.55 was added to 
the wood, or else some molecular rearrangement took place in the wood 
under the influence of the acid. The chemical analysis which might 
indicate the actual nature of this change was not undertaken. 
The table also gives comparable results of determinations on one spe¬ 
cies at two temperatures, and from these the thermal expansion of wood 
substance is shown to be negative. This means that wood substance 
contracts and becomes denser on heating, instead of expanding and be¬ 
coming lighter in weight. If this is true, wood substance differs from 
other substances for which records are available. Moreover, it is diffi¬ 
cult to reconcile this anomalous behavior with the well-established fact 
that, in the aggregate, blocks of wood expand when heated. 
The observed increase in density between 30° and 35 0 C. amounts to 
one-third of 1 per cent, or one-fifteenth of 1 per cent per degree centigrade. 
This apparent contraction is about twice as large as the expansion which 
water undergoes between 30° and 35 0 C. 
