DRY rot: injuries from various causes. 177 



SOUND AS A MEANS OF DETECTING DISEASES AND DEFECTS IN TIMBER. 



Wood is an excellent conductor of sound, when in perfect condition. 

 The scrutch of a pin may be heard at the further end of along pine rod, 

 and a light blow with a hammer is conveyed through a beam of timber of 

 the greatest length with much distinctness. But if parts are decayed, 

 or tending to decay, the homogeneity is destroyed, and the sound-waves 

 are deadened. Hence we have an easy test of perfect condition, or, at 

 least, evidence that there is no considerable rottenness within a piece of 

 timber that might otherwise appear sound. 



THE dry-rot. 



This is one of the most formidable maladies in timber, beginning in 

 the interior and spreading toward the outside, changing the fiber into a 

 dry dust, and of course destroying it for every purpose. It is most likely 

 to appear in warm, close, and moist situations, where the wood becomes 

 covered with a brownish-white mold, which sends its fibers into the 

 tissues, and it is now generally regarded as caused by the development 

 of a fungus, known to botanists as the Mcrulius lachrymans} This veg- 

 etation first appears as delicate white filaments, interlacing with one 

 another, attacking the wood fiber, and changing the ligneous mass into 

 a loose, celular tissue, that readily falls into powder. The surface may 

 remain sound when it is nothing but rottenness within. It does not ap- 

 pear in the growing tree, and appears to be favored and developed by a 

 fermentation of the juices. 



Among the remedies are, thorough seasoning after immersion for a 

 time in water, and the filling of the pores with an antiseptic mineral 

 solution, as the chloride of mercury, and the salts of copper, zinc, or iron, 

 or with common salt, which, but for its deliquescent tendencies, would 

 answer very well. A cargo of salt, in bulk, is deemed desirable in 

 new vessels on account of its benefit to the timbers. 



Carbolic acid and other pyroligueous products are much used to 

 check this tendency to dry-rot. Peifect ventilation, where it can be 

 had, is an excellent means to prevent rotting.^ 



INJURIES to trees FROM FROST, DROUGHT, AND OTHER CAUSES. 



Intense frosts will sometimes split trees in the direction of their fibers, 

 and sometimes even with a loud report. Such trees are generally those 

 that have some excrescences formed by a cicatrix covering an old 

 cleavage containing water. These, when they are deep, seldom heal, 

 and the timber so affected loses much of its value for uses requiring 



1 This fungus is described by Dr. Greville as follows : " Whole plaut generally occu- 

 pinate, soft, tender, at first very light, cottony, and white. When the veins appear 

 they are of a fine yellow, orange, or reddish brown, forming irregular folds, most fre- 

 quently so arranged as to hare the api>earance of pores, but never anything like tubes, 

 and distilling, when perfect, drops of water." This last property gives it the specific, 

 name. It is often found in cellars where it is damp and unventilated, and in hollow 

 trees. 



Another fungns, the Polyporus Jiyhridns, constitutes the dry-rot of oak-built vessels,. 

 It is described by Berkeley as " white, mycelium thick, forming a dense membrane, 

 or creeping branched strings, hymeniam breaking up into areas ; pores long, slender, 

 minute." 



'A list of remedies for tho dry-rot would be a catalogne of most of the processes, 

 that have been devised for increasing the durability of timber. Many of these are no- 

 ticed in a volume by Tho. Allen Britton, entitled "A Treatise on ike Origin, Progress, 

 Prevention and Cure of Dry-Hot in Timbers," 1875, 12 mo., pp. 311. 



%ee also the" Traitt'de la Conservation des Bois, » " * by Maxime Paulct, Paris, 

 1874, pp. 414. Also the appendix of "A Treatise on the Resistance of Materials," by Prof. 

 De Volseu Wood, Bvo, N. Y., 1875, in which many antiseptic and preservative methoda. 

 are described. 



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