114 INDUSTRIAL USES OF WOOD. 



but by cross-breaking clue to lateral bending. The thrust which 

 can be safely borne varies from j of a ton per square inch of 

 section in struts of a length equal to 8 times their diameter, to 

 one half of that amount when the length is 24 times the 

 diameter. 



(d) Deg-ree of Soundness and Durability. — All pieces of timber 

 used in constructions must be perfectly sound and sufficiently 

 durable, and in all cases none but thoroughly seasoned timber 

 should be used. Some of the pieces used in buildings are more 

 exposed to decay than others, such as those used for cellars, 

 wash-houses, breweries, stables and other damp jilaces, whilst 

 roofing timber is less endangered. 



It is not surprising to find, if green timber be used, that 

 destructive fungi attack the beams, &c., and early rejjairs are 

 necessitated. 



[In countries where white ants abound, only wood wliicii they do 

 not attack should be used in constructions, an exception being made 

 for rafters, when the masonry, or half-timbered walls arc secure 

 against the passage of the ants. It is also usual to smear the timber 

 externally with wood- oil, extracted ft-om species of Dipierocarpiis, 

 which is a great preservative against insects. — Tit.J 



(e) Weight. — Weight is now-a-days avoided as much as 

 possible, especially in the roofs of buildings, which were formerly 

 made of heavy oakwood. In substituting light coniferous wood 

 instead of oakwood for roofs, fairly durable wood should be 

 used, such as narrow-zoned and not broad-zoned wood — at least, 

 for the principal roof-timbers. The price of this fine-zoned 

 timber is usually considerably higher than the inferior material. 

 Greater ease in construction is also a cause of the preference of 

 light to heavy wood. 



[In India, bamboos are largely used for roofing, under thatch 

 they should be at least three years old shoots, and thoroughly 

 soaked in water for a month or two before being used, in order to 

 avoid insect-attacks. — Tn.] 



In Europe, the woods of spruce, larch, silver-fir, and Scotch 

 pine, are chiefly used in buildings on account of their light- 

 ness and other qualities, and good larchwood is the best material 

 of them all. These woods arc straight and strong, and if not 



