Dry Rot - Encyclopedia

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DRY ROT, a fungoid disease in timber which occasions the destruction of its fibres, and reduces it eventually to a mass of dry dust. It is produced most readily in a warm, moist, stagnant atmosphere, while common or wet rot is the result of the exposure of wood to repeated changes of climatic conditions. The most formidable of the dry rot fungi is the species Merulius lacrymans, which is particularly destructive of coniferous wood; other species are Polyporus hybridus, which thrives in oak-built ships, and P. destructor and Thelephora puteana, found in a variety of wooden structures.

The felling of trees when void of fresh sap, as a means of obviating the rotting of timber, is a practice of very ancient origin. Vitruvius directs (ii. cap. 9) that, to secure good timber, trees should be cut to the pith, so as to allow of the escape of their sap, which by dying in the wood would injure its quality; also that felling should take place only from early autumn until the end of winter. The supposed superior quality of wood cut in winter, and the early practice in England of felling oak timber at that season, may be inferred from a statute of James which enacted "that no person or persons shall fell, or cause to be felled, any oaken trees meet to be barked, when bark is worth 2S. a cartload (timber for the needful building and reparation of houses, ships or mills only excepted), but between the first day of April and last day of June, not even for the king's use, out of barking time, except for building or repairing his Majesty's houses or ships." In giving testimony before a committee of the House of Commons in March 1771, Mr Barnard of Deptford expressed it as his opinion that to secure durable timber for shipbuilding, trees should be barked in spring and not felled till the succeeding winter. In France, so long ago as 1669, a royal decree limited the felling of timber from the 1st of October to the 13th of April; and, in an order issued to the commissioners of forests, Napoleon I. directed that the felling of naval timber should take place only from November 1 to March i s, and during the decrease of the moon, on account of the rapid decay of timber, through the fermentation of its sap, if cut at other seasons. The burying of wood in water, which dissolves out or alters its putrescible constituents, has long been practised as a means of seasoning. The old "Resistance" frigate, which went down in Malta harbour, remained under water for some months, and on being raised was found to be entirely freed from the dry rot fungus that had previously covered her; similarly, in the ship "Eden," the progress of rot was completely arrested by 18 months' submergence in Plymouth Sound, so that after remaining a year at home in excellent condition she was sent out to the East Indies. It was an ancient practice in England to place timber for thrashing-floors and oak planks for wainscotting in running water to season them. Whale and other oils have been recommended for the preservation of wood; and in 1737 a patent for the employment of hot oil was taken out by a Mr Emerson.

For the modern processes of preserving timber see Timber.

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