Processes for Wood- preservation. 189 



which these antiseptic processes tend to destroy, and that those 

 methods are most certain that accomplish this result most uniformly 

 and effectually throughout the wood. 



745. Charring. We have elsewhere noticed the extreme durabil- 

 ity of charcoal. By slowly scorching the outside of a post or stake 

 before setting it in the ground, its durability is much increased. 

 This is sometimes done with the railway ties in Europe, and two 

 methods are employed. 



74(>. By one of them, the stick is laid upon an iron frame, that ad- 

 mits of an easy sliding motion in all directions, and a tongue of flame, 

 either from a gas-jet or from air blown through flame, is passed over 

 every part. By this means the degree of torreh'cation may be reg- 

 ulated at will. The process may be applied to all kinds of wood- 

 work, and it may be so managed as not to destroy the sharpness of 

 any work upon the surface. 



747. By another process, a long iron tube is filled with flame, and 

 railway ties or other wood may be passed slowly through it oil a 

 broad iron chain. Piles charred before using will last for a long 

 period. It was the practice employed at Venice for the piles on 

 which that city was built. In whatever manner the scorching is 

 done, the timber must be first thoroughly seasoned ; if not, it will 

 only hasten its decay. 



748. There is an advantage in plunging the wood newly chanvd 

 into coal-tar or melted pitch, or by painting it thoroughly with three 

 or four coats of these substances. The charring process is in favor 

 upon the Belgian railways. It has the advantage of preventing 

 injuries from gnawing animals or white ants, and hence its value in 

 India and other countries where these insects are destructive, as also 

 in the wood work of basements, where thei-e is much humidity, 

 without proper ventilation. It is a most effectual remedy against 

 the dry rot. 



749. It was formerly customary to slightly char the outside of 

 ship timber after it was prepared for framing, but before it was put 

 together. The " Royal William," one of the most long-lived ships 

 in the British navy, was thus prepared. The fires used in this pro- 

 were made of shavings or straw, and accidents would sometimes 



happen. 



750. In some timbers used for railway ties, such as oak, it is not 

 easy to inject with mineral salts or other antiseptic substances, and 



