572 INDUSTRIAL USES OF WOOD. 



Wood of large dimensions, oakwood at any rate, is too 

 expensive for rail way- sleepers, so that only oaks of third class 

 are used. As a rule from 30 to 40 per cent, of the wood is 

 wasted. 



Oakwood formerly was considered essential for railway- 

 sleepers owing to its durability, extending to 10 16 years. 

 Narrow-ringed larchwood had an average duration of 10 years, 

 and close-ringed Scots pine with plenty of heartwood 7 to 9 

 years, no other European woods heing utilisable unless 

 impregnated with antiseptic substances. Now, owing to the 

 increasing scarcity and cost of oakwood and the advantages 

 of impregnating sleepers, impregnated pinewood as well as 

 impregnated wood of beech, spruce and silver-fir are pre- 

 ferred. Beechwood absorbs creosote fully and is now used 

 extensively. Experimental use is also made of pitch pine and 

 quebracho wood. The question of impregnating wood has 

 been dealt with already (p. 509). 



Young oakwood on account of its superior density is better 

 for railway-sleepers, when creosoted, than the wood of old 

 trees. If many oak sleepers have shown little durability, 

 that is due to the low class of timber used. The nature 

 also of the bedding in which the sleepers are laid exercises 

 considerable influence on their duration. 



Iron has come recently into competition with wood for 

 sleepers, the chief reason for its use being its great durability. 

 During the years 1891 to 1896 on the Prussian State Eailways, 

 which use annually about 3J million sleepers, the use of iron 

 sleepers has gone up from 17 per cent, in 1891 to 25'9 per 

 cent, in 1896. Of the wooden sleepers, in 1896, 71'3 per- 

 cent, were of pine and 28'7 per cent, of oak, in 1895, 90 per 

 cent, of the pine sleepers were imported but only 0*9 per cent, 

 of the oak sleepers. 



[The iron or steel sleepers are either trough- shaped or pot- 

 shaped, the trough-shaped form being the best. The chief 

 objection consists in a gradual change in the molecules due to 

 the action of the traffic that renders this metal brittle. 

 Wooden sleepers are heavier and more stable than metal 

 sleepers. Another objection lies in the greater cost of steel 

 sleepers ; often in India the saline nature of the soil is 



