IMPREGNATION. 303 



withdrawn. Steaming takes from about 40 to 80 hours, accord- 

 ing to the size of the wood, and generally makes the colour 

 darker than wood naturally seasoned. Oak turns dark-brown 

 and Maple reddish, while Beech turns brown to pinkish and is 

 then preferred for parquet-work. Steamed wood dries quicker, 

 is lighter, and is less liable to warp and split than unsteamed 

 wood of the same degree of dryness. While still warm and 

 moist as it comes from the steaming-box, it is very flexible ; and 

 in cooling and drying it retains the form given to it while still 

 warm and moist. This quality is made use of in bending wood 

 for ship's planking, carriage- and waggon -making, cooperage, 

 chair-making, &c. 



II. Impregnation with Antiseptics. The earliest methods 

 of preservation by antiseptic means were simple submersion of 

 converted wood in sea- water, or in a solution of common salt, 

 or in milk of lime (a l-in-40 solution of slaked lime in water), 

 or by charring and coal-tarring fence-posts and stobs at the 

 lower ends put near or below the surface of the ground. The 

 ideal preservative fluid would be one that preserves thoroughly, 

 penetrates easily and deeply into the wood, remains there per- 

 manently, is cheap and innocuous, and does not increase the 

 inflammability of the wood; but no such impregnating substance 

 has yet been discovered. For large timber the four oldest 

 antiseptic processes worked on any large scale are 



1. Kyaris method (1832), by simple immersion and imbibi- 

 tion of a 1-per-cent solution of corrosive sublimate (bichloride 

 of mercury), 1 Ib. dissolved in 10 gals, of water (100 Ibs.) being 

 sufficient to impregnate 50 cubic feet of well-seasoned timber ; 



2. Burnett's method (1838), by injecting a 2- to 3-per-cent 

 chloride of zinc solution under pneumatic pressure of 105 Ibs. 

 per square inch (7| atmospheres) at 230 F., the wood operated 

 on (chiefly for railway sleepers) being thoroughly seasoned ; 



3. BetheWs method (1838), by injecting creosote (crude heavy 

 oil of coal-tar) into thoroughly seasoned wood under a pressure 



