UTILIZATION OF BLACK WALNUT. 8 



purplish brown. The annual rings of growth are usually broad and 

 are marked off' from each other by the presence of many pores at 

 the beginning and a somewhat dense growth at the end of each 

 annual ring, as well as by a fine light-colored line between adjacent 

 rings. This contrast between the growth rings is especially marked 

 on tangential cuts and gives a somewhat coarse figure to the wood. 

 The pores are compartively large and in cross sections easily visible 

 to the naked eye ; they appear as fine dark and generally short lines 

 over the entire longitudinal surface. Figured wood is in demand for 

 different kinds of finish. Its handsome effect is often produced by 

 dark-colored streaks or alternate stripes of lighter and darker 

 shades. The striped figure in quartered stock is caused by the 

 alternate light and dark shades of the growth rings. Another kind 

 of figure is that formed by the wavy or curly grain which is found 

 near a knot or other defect. Abnormal or irregular growths, crooks, 

 forks, and twists produce a special figure in the wood. Highly 

 figured walnut, with a great variety of design, is cut from the walnut 

 burl — an abnormal growth of wood tissue. 



PHYSICAL AND MECHANICAL PROPERTIES. 



Black-walnut wood is heavy, hard, strong, and stiff. It is easy 

 to split, has good shock-resisting ability, shrinks moderately in 

 seasoning, is susceptible of a good polish, and takes paint, stain, and 

 other finishes exceedingly well. 



The results of certain Forest Service experiments on black walnut 

 tested green are shown in Table 1 in comparison with oak. The 

 strength values of the green wood are considered the best basis for 

 comparison. Walnut compares still more favorably with oak when 

 their dry weights are taken into consideration. For instance, black 

 walnut, which has a dry weight of 85 per cent of the dry weight of 

 oak, has shock-resisting ability 27 per cent greater and strength 

 in bending 14 per cent greater than that of oak. As to strength in 

 compression parallel to the grain, walnut rates 21 per cent higher, 

 and in stiffness 14 per cent more. The shearing strength of walnut 

 is only slightly less than that of oak. The hardness values of wal- 

 nut and oak are in the same proportion to each other as their specific 

 gravities — 85 per cent. As to strength in compression perpendicular 

 to grain, walnut has a lower value than oak. The shrinkage of 

 black walnut in volume is less than that of oak, which is about 16 

 per cent. Shrinkage in the radial direction is about the same in 

 both woods; but in the tangential direction the shrinkage of black 

 walnut is less than that of oak. The ratio of radial to tangential 

 shrinkage is much less in black walnut than in oak. In weight, and 

 likewise in dimension, walnut changes slowly with changes in 

 atmospheric conditions. 



