EFFECTS OF UK AT. 



75 



and therefore useless for casks, except those containing butter 

 and other more or less solid substances. In split oak or 

 chestnut palings, the fibres and vessels are not cut, and 

 they are therefore much less permeable by water than sawn 

 palings. Tr.] 



( J. Effect * ut 11 cat on Wood. 



(a) Change of NHIJIC. 



The coefficient of linear expansion of a rod is the incivase 

 in its length for 1 C. divided by its original length. Thus, if 

 a rod one meter long, at C., receives an increased tempera- 

 ture of 100 J and thereby expands 1 mm. in length, its co- 

 efficient of expansion would bo -,,,,, 1 ,,,,,,, or O'OOOl. It 

 should be noted that for wood, this expansion longitudinally 

 is only a fraction of its radial expansion, and that the former 

 is less than in metals or glass, which being homogeneous, 

 expand equally in all directions. 



[Where iron girders are used in buildings, in case of the 

 house being burned, the expansion of the girders tends to knock 

 down the walls ; this is not the case with wooden beams. Tr.] 



In order to determine exactly the effects of heat on wood, 

 the wood and the air in which it is placed must be absolutely 

 dry. If this is not the case, as in the wood of a living tree or 

 of one recently felled, or in converted wood, heat always 

 produces contraction. This is because the heating of the 

 contained water not only counteracts the expansion due to 

 heat, but produces even a reduction in volume. 



Frozen wood, according to Mayr, is affected by heat quite 



