4 NOTES ON THE PROPERTIES OF WOOD. 



green-heart is exempt from the erosion by the teredo ; hut there is a 

 mollusc in this timber which we find alive in it when it arrives here 

 from the West Indies. The worm is found in sizes from the lymexylon 

 to the teredo ; but is of a different species, and seems not to live in this 

 wood when used in such constructions as dock-gates, &c, in this country. 



Green sap-wood will not retain its form and bend if it is 

 suspended horizontally by its two ends. The same will occur in 

 timber constructions where green wood has been used. I may 

 mention that the artificial process of drying wood should not be 

 extended beyond 10 per cent., because it will cause it to become 

 brittle and totally useless. A close examination of a beam sup- 

 ported by its two ends will tell that the upper half of the fibres are 

 stowing while the lower fibres are extending. The centre of gravity lies 

 in the middle of the cross section. All woods do not offer the same re- 

 sistance, and we can increase it by strengthening the centre of gravity. 

 M. Duhamel describes in his work, " De la Force des Bois," the follow- 

 ing experiment in elucidation of this fact : he took twenty -four sticks 

 cut from young willows of equal strength ; each stick was 3 feet (Paris) 

 long, and 1^ inch square. Six of these broke in the centre, with an 

 average weight of 256'909 kilogrammes (1 kilogramme equals 2-205 lb. 

 English.) In two other pieces he made a cut across, £ inch deep in the 

 centre, and filled it up with a piece of oak ; they broke with an average 

 weight of 269'718 kilogrammes. Two more were cut ^ inch deep, and 

 otherwise treated in the same manner ; they broke with 259 - 312 kilo- 

 grammes. Five were cut f inch, and broke with 265764 kilo- 

 grammes. From this it results that the smaller piece of harder wood 

 fixed across the centre, considerably increased the strength of the stems 

 when put in half and even three-quarters of the thickness. It is also 

 the reason why a beam composed of several'smaller pieces will bear as 

 much as if of one entire piece. And again, as the bearing poA¥er of the 

 timber varies, some advantageous results may be obtained by putting 

 stronger and weaker wood together in a construction. 



A round or square piece of a stem will offer about the same resist- 

 ance from each side ; but if we compare a timber cut with the yearly 

 rings vertically, with another having the rings horizontally, we find that 

 the former will bear more than the latter. 



The sap which protects the wood does not prevent its decay. Tur- 

 pentine, which is often in the sap, prolongs the preservation of the fibre. 

 According to Baron Liebig, the decay of wood takes place in the three 

 following modes : first, oxygen in the atmosphere combines with the 

 hydrogen of the fibre, and the oxygen unites with the portion of carbon 

 of the fibre, and evaporates as carbonic acid. This process is called 

 decomposition. Secondly, we have to notice the actual decay of wood 

 which takes place when it is broughtinto contact with rotting substances ; 

 and the third process is called putrefaction. This is stated by Liebig to 

 arise from the inner decomposition of the wood itself; it loses its 



