THE "BLUE" WOOD. 13 



Numerous white strands of fungus mycelium make their appearance 

 after six months or more. As the wood of the trunk dries, the bark, 

 loose at first, tightens, so that in the " black-top" stage it adheres 

 quite firmly to the trunk. When cut into, it peels off in large sheets 

 very readily, however. 



The " blue " wood differs very little from the sound wood in general 

 appearance, except its color. It is full of moisture at first, but loses 

 this rapidly, so that in two years after the beetle attacks the wood 

 it may be almost perfectly seasoned, even when completely covered 

 with its bark. The ' 4 blue " wood is said to be very much tougher 

 than the green wood, so much so that the tie makers in the Black 

 Hills can be induced to cut wholly blued wood only with difficulty. 

 This toughness and a possible reason therefor are discussed hereafter. 



STRENGTH OF THE "BLUE" TIMBER. 



Ever since its first appearance there has been considerable discussion 

 as to the strength and durability of the "blue" timber when com- 

 pared with sound timber. It was universally believed that it would 

 prove very much inferior in both respects. A test was made in the 

 testing laboratory of the department of civil engineering of Washing- 

 ton University, St. Louis, 05 to determine the comparative strength of 

 the "blue" and the healthy timber. Sections of tree trunks 5 feet 

 long were cut from trees at points 10 to 15 feet from the ground, and 

 were shipped to St. Louis, where they were sawed into blocks of sev- 

 eral sizes. For the compression tests, blocks 2 by 2 by 4 inches and 

 3 by 3 by 6 inches were cut and planed to the exact dimensions, or as 

 nearly so as possible. 



For the cross-breaking strength, sticks 2 by 2 inches by 4 feet, and 

 3 by 3 inches by 4 feet were prepared. The blocks for these tests were 

 kiln-dried at a temperature of 172 F. until an approximately constant 

 weight was reached. It was found that completely dried blocks would 

 not shear at all. The moisture content of the green blocks was slightly 

 higher than that of the "blue" blocks. 



Three kinds of timber were used: A Green timber; B "Blue" tim- 

 ber taken from "sorrel-top" trees, i. e., trees dead about one year; 

 C "Blue" timber taken from "red tops" and "black tops" (mostly 

 the latter), i. e., trees dead about two years. 



The tests were made with the machinery described by Johnson 

 in early reports 6 of the Division of Forestry. Every block was 

 carefully measured. The results, reduced to the average crushing 

 strength and the average cross-breaking strength per square inch, are 



The machinery was put at the writer's disposal through the courtesy of Prof. J. L. 

 Van Ornum. 



& Timber Physics, Bulls. Nos. 6 and 8, Division of Forestry, U. S. Department of 

 Agriculture. 



