72 OF WOOD IN GENERAL 



hammered to their outline, the ends of the bands being turned out 

 at right angles and bored for a screw bolt, by means of which the 

 bands can be tightened up every few days. 



The various steaming processes justly claim that the high tempera- 

 tures employed destroy disease germs and coagulate the albuminous 

 constituents of the sap. The two most important methods are, per- 

 haps, the Erith and the Haskin. The former consists in the circu- 

 lation of warm but very moist air round the timber, so as to avoid 

 case-hardening and to remove the moisture from the centre out- 

 wards. Haskinizing consists in submitting the wood to circu- 

 lating superheated air under considerable pressure, " causing the 

 constituents to organize into an oleaginous compound, saturating 

 the fibre, and filling the pores." This process is costly, and the 

 drawbacks to all such methods are the danger of a deterioration of 

 the wood by a separation of its fibres and the removal of some of 

 its substance without any replacement. 



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 Httle hable to subsequent 

 infection. It also dries the surface, destroys any tendency to fer- 

 mentation, and distils such antiseptic substances as acetic acid and 

 creosote out of the surface wood, leaving them free to act as pre- 

 servatives. 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 Romans, 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. 



The most 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 un- 

 doubtedly 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 Hquid soaks, so that slight cracks expose 

 unprotected wood to fungus attacks. Whilst it is comparatively 

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



