Sweetgum and black gum, in contrast to the oaks, are diffuse porous woods and do not show a dis-
tinctive grain pattern. Sweetgum heartwood has a reddish-brown color. The sapwood is a pale flesh
color and frequently has a pinkish tinge or is discolored with blue stain. The transition zone be-
tween heartwood and sapwood is sometimes variegated (Figure 3-2). Black gum, by contrast, has a
white to grayish white sapwood which merges gradually into the darker, greenish or brownish-gray
heartwood. Both species lack distinctive rays as compared to the oaks, have interlocked grain and
are moderately heavy in weight.
An easy-to-use chemical test separates white oak from red oak. When a ten percent solution of
sodium nitrite (NaNO2) is either brushed or sprayed on freshly cut sound heartwood, the heartwood
of white oak turns yellow-orange, then red-brown, and then dark green or purple to black while the
red oak heartwood is just slightly darkened.
Sodium nitrite is available from chemical supply stores. A 10 percent solution is prepared by
mixing 3.34 ounces per quart (104 grams per liter) of either tap or distilled water. The solution
remains effective for several months. At 80F the color reaction takes place in about 5 minutes.
The reaction time decreases as the temperature is lowered. At 50F the rate is about 20 minutes,
and below freezing, almost 24 hours. In cold weather 20 percent ethylene glycol can be added to
the sodium nitrite solution to prevent freezing. The solution can be heated to 194 degrees fahren-
heit, or the localized area of the wood heated to accelerate the reaction. The test will work on wood
with a moisture content ranging from green to six percent. In green or fresh material, the reaction
time is faster; the yellow, orange, and red shades seem more brilliant; and the color sequence is
3.2 SPECIES DESCRIPTIONS DETAILED. The detailed descriptions for selected species are
3.2.1 Softwoods. Softwoods refer to those tree species called conifers or evergreens, as
described in Chapter 2. They are commonly used for poles, piling and construction lumber and tim-
bers. Anatomically, softwoods are characterized by tracheids. Tracheids are large, slender,
lightweight cells which add greatly to the strength of wood. Figure 3-1 shows four of the five
domestic species discussed below.
Douglas-fir (Pseudotsuga menziesii) grows in most forests
from the Rocky Mountains to the Pacific coast, and from the Mexican border north through Canada.
The permeability, physical and mechanical properties of Douglas-fir vary with geographic location
(Figure 2-9 and Table 2-2). Botanically, it is not a true fir. It reaches its largest size and fastest rate
of growth in Washington and Oregon, where large trees form very dense forests.
Most old growth Douglas-fir from the Pacific coast and northern Rocky Mountain states is
moderately heavy, very stiff, moderately strong, and moderately shock resistant. It weighs about 33
pounds per cubic foot (air-dried condition) and the average specific gravity (oven-dry weight and
volume at 12 percent moisture content) of the coast type is 0.48. The wood is also moderately hard.