86 OF WOOD IN GENERAL. 



Carbonizing, or charring the outer surface of wood, destroys all 

 fungus-germs at the surface ; and, charcoal resisting the solvents 

 of fungi, this process renders the wood little liable to subsequent 

 infection. Thus it is stated that the stakes found in the bed of 

 the Thames, near Weybridge, and supposed to have been used to 

 oppose the invading Eomans, and the piles upon which the city 

 of Venice was built, had alike been charred. M. de Lapparent, 

 who introduced this process into the French dockyards forty 

 years ago, held that the durability of carbonized timber is secured 

 by the absence of fermentation in the juices of the interior of the 

 wood. The results are satisfactory, but care must be taken not 

 to cause surface splitting. M. de Lapparent's process is carried 

 out by means of a jet of gas. 



Another important series of methods of seasoning are those 

 which may be termed impregnation-methods, which all depend upon 

 the principle that the sap may be replaced by some substance that 

 is antiseptic or poisonous to fungus-germs. The most primitive 

 of these is merely to paint the substance, such as tar, as thickly 

 as possible over dry wood and leave it to soak in, and this 

 undoubtedly has a great preservative effect, even on sapwood or 

 wood very imperfectly dried ; but the chief drawback to this, and 

 the chief difficulty in several other impregnation processes, is the 

 very small distance that the liquid soaks, so that slight cracks 

 expose unprotected wood to fungus attack. Whilst it is compara- 

 tively easy to inject sapwood in a longitudinal direction, it is far 

 more difficult to inject heartwood ; and it is vastly easier to force 

 liquids through wood tangentially than radially. 



An improvement on any painting process is to submerge the 

 timber in a bath of the preservative, which may be tar, sulphate 

 of iron or of copper, chloride of zinc or creosote ; and in these 

 processes the replacement of the air and sap in the wood by the 

 liquid will generally be hastened by heat. Penetration is, how- 

 ever, slight, and long submergence renders the timber brittle. 



Of the materials employed for impregnating timber, the most 

 effective is corrosive sublimate (mercuric chloride), the use of 

 which is known, from its inventor, Kyan, as kyanizing. It forms 



