88 TECHNICAL PROrERTIES OF WOOD. 



very rapidly. Sal, teak, toon, ebony, sissu and some other hard 

 woods resist their attacks, but in the ca.se of building-timber it is 

 always best to saturate it with f/urjun- or wood-oil, e.xtracted from 

 species of Dipterocarjnm. Engineei-s in India should be careful only 

 to erect solid masonry-walls, and not leave crevices in them up 

 which the white ants may ascend to the roof of a building ; they may 

 also mix arsenic with their mortar with advantage. 



It has often been suggested that softer woods if injected with 

 sulphate of iron or zinc, or corrosive sublimate, would be found to 

 resist the attacks of white ants, but no serious attempts have as yet 

 been made in India to utilize injected wood. This subject will be 

 referred to again in Part III. — Tn.] 



(b) Wood used under Water. — "Wood used under water is very 

 durable, the action of the air which is indispensable for all 

 decay being thus preveuted. An essential condition for the 

 durability of wood under water is that the water should be 

 fairly pure, and not moving too rapidly, for rushing water 

 wears wood away. Oakwood, wood of resinous narrow-zoned 

 larch and Scotch pine, and alder-wood, are most durable under 

 water. These are the best woods for use in mill-dams and other 

 immersed works. Silver-fir lasts better than spruce for such 

 purposes. 



Even bceclnvood, otherwise so deficient in durability, may 

 last for centuries under water and has been used for the keels of 

 ships, and spruce and silver-fir last much longer under water 

 than when exposed to the air. In shipbuilding yards the best 

 pieces of timber are kept barked, or unbarked, for four to five 

 years under water, until they are required. Even logs intended 

 for sawmills may be best preserved in this way, and this 

 soaking does not prejudice the future durability of the timber. 

 In the year 1858, the water in the Rhine became exceptionally 

 low, and twelve oak piles of the Roman bridge near Aargau 

 came to the surface, and the wood was found to have become so 

 hard that there was considerable difficulty in turning various 

 toys, &:c., which w-erc made from it. Similar durability is 

 shown by oaken piles from the bridge built by the Romans 

 across the Danube, at the Iron Gates, in the time of Trajan, 

 and by oakwood dug from bogs in Ireland and elsewhere. 



