CHEMICAL PBOPEBTIES. 81 



from wood. The mineral matter in wood varies from '2 to 50 

 parts in a thousand ; according to species ; age of tree-parts 

 (younger organs containing proportionally more asli than 

 older ones); age of tree and nature of the soil in which the 

 tree grew. Silicic acid is so abundant in bamboos and palms, 

 especially near their outer rind, as to increase their hardne^ . 

 [Silica in the form of a hydrate is found in the hollows of 

 1 KID i boo culms and termed tnbaxhir, which is sold in Indian 

 ba/aars. Tr.] Briar- wood (Erica arborca), that is used for 

 pipes, is very rich in silica. Some tropical woods, such as 

 ebony, cocus, etc., are very rich in mineral matter. 



Water is the basis of the life of trees ; after they are felled 

 it is a worthless ballast in wood. Its great influence on the 

 economic value of wood will be described hereafter ; the 

 section on specific weight may be consulted for an account 

 of the distribution of water in a tree, and in its heart wood 

 and sapwood. 



Sugar, dextrin, albumen and tannin are decomposed 

 easily, and form the chief nutriment of the fungi that destroy 

 wood. The superior durability of winter-felled wood is ex- 

 plained by the fact, that during winter the above materials 

 are in a iixed or resting condition, in which they are more 

 resistant to decomposition. Wood that has remained for some 

 time in water (floated or rafted) is also supposed to be more 

 din-able, because the above materials, being soluble in water, 

 have been partly dissolved, and thus the fungi have lost part 

 of their nutriment and their aggressiveness is reduced. This 

 advantage is effective if followed by a subsequent complete 

 drying of the wood to its air-dry condition, but practically this 

 seldom happens, while the saturated wood requires prolonged 

 desiccation. Hence floated wood is more susceptible to fungi 

 than wood that has been transported by land. 



[The materials above referred to serve also as food for 

 insects, and bamboos that have been floated over long dis- 

 tances or soaked in tanks for several months are much more 

 immune from insect-attacks than bamboos transported by land. 

 The drying of floated wood after it has been landed is much 

 more rapid also in hot countries than in Europe, so that 

 floated wood is very durable under such conditions. Tr.] 



J.l. G 



