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timber less than squared timber. The splitting of timber being caused by unequal 

 shrinkage in a radial direction and along the rings, may be avoided, in great part, by 

 sawing the logs through the heart ; or by making a longitudinal cut, from the surface to 

 the heart, which relieves the superficial tension and opens up steadily as the log dries. 



Sawn timber should be stacked in a dry place, sheltered from sunshine and high 

 winds. The seasoning shed or yard should be floored or paved and well drained, as 

 otherwise " stack rot" may result from the piling of timber on damp soil. The mode of 

 stacking should be such as to allow of a free circulation of air all round each piece, while 

 resisting warping. 



2. PKESEKVATION OF TIMBER. 



The decay of timber is generally due to the growth of the mycelium of various fungi 

 which derive their nutriment from the tissues of the wood ; it is also aided by bacteria. 

 An excess of moisture is favourable to the development of " wet rot," and warm and 

 stagnant air to that of " dry rot." Timber is most lasting when kept constantly dry and 

 freely ventilated, while alternations of dryness and wetness are the most unfavourable 

 conditions. 



Protection from decay is afforded by seasoning and ventilation, and by coatings of 

 oil-paint or tar applied when the wood is dry, but impregnation with antiseptic substances 

 that prevent the spread of the fungi of rot is a more effectual method. 



The various processes which have been adopted from time to time for the preservation 

 of timber are mainly the following : 



a. Creosoting. 



This consists in impregnating timber with the oil of tar called creosote. The 

 cut up timber, which must be sufficiently dry, is packed on small wagons that are run 

 along .a light line of rails into a long cylinder, the headpiece of which is then closed and 

 rnnde air-tight. The air inside is exhausted by means of an air-pump ; .the highest 

 vacuum is reached after half-an-hour's pumping, but a longer interval is required to make 

 the wood give up all the air it contains. The creosote is next admitted and allowed to be 

 forced in by the pressure of the atmosphere, the air-pump being kept going to prevent 

 the accumulation of air, in the upper part of the cylinder as it becomes filled up, which by 

 penetrating into the pieces of wood near the top would render these incapable of absorbing 

 the creosote. The creosote is usually heated to a temperature of 100 to 120 by coils of 

 pipes placed in the reservoir, through which a current of steam is passed, in order to 

 render it fluid enough to penetrate the wood freely, but in a warm climate this precaution 

 is unnecessary. When the cylinder is nearly full, the supply of creosote is .cut off, but 

 the air pump is left to work a little longer. More creosote is then forced in by means of 

 a force-pump, until a pressure of 120 to 150 Ibs. per square inch is registered. This 

 pressure is maintained from two to sixteen hours, according to the kind of wood and the 

 depree of saturation required. When the impregnation is sufficient, the creosote is run 

 off, the lid of the cylinder opened, and the wagons drawn out. 



Creosote is a product of the distillation of coal tar. Coal tar yields about one-fourth 

 of volatile oils, which can again be separated into lighter oils containing benzine, and 

 heavier oils containing carbolic acid. The latter constitute the raw creosote of commerce. 

 The proportion of carbolic acid in coal-tar is about 3 per cent. ; in creosote it should be 

 at least 8 or 10 per cent, for purposes of impregnation, bat it is frequently very much 

 less in some of the creosote used for the impregnation of sleepers for export, and unsatis- 

 factory results follow. A simple method of testing creosote consists in shaking a 

 portion, with a 10 per cent, solution of caustic soda, in a graduated glass tube, and 

 allowing the mixture to settle. The carbolic acid combines with ihe alkali in the solution^ 

 and the volatile oils float in a layer on the surface. The diminution in volume of the 

 latter indicates the quantity of carbolic acid which they contained. Creosote is one of 

 the best substances used for impregnation. Apart from its antiseptic qualities, due to 

 the carbolic acid which it contains, "it fills the pores of the wood with a bituminous sub- 

 stance that excludes both air and moisture ; it resists the lixiviating action of water better 

 than metallic salts ; and, unlike the latter, which render wood somewhat more brittle, it 

 rather increases if anything the strength of soft woods. Greosoting, when properly per- 

 formed, about doubles the life of a sleeper. 



The quantity of creosote usually forced into wood is : . 



For railway sleepers, telegraph poles, and construction .on land, 8 Ibs. ,or '8 galls, 

 per cubic foot. . 



