94 TIMBER AND SOME OF ITS DISEASES. [CHAP. 



Then, subtracting the dry volume and the water 

 from the fresh volume, we get 



8. The volume occupied by the air-spaces in the wood. 



But we have still to determine how much of the 

 total water is imbibed in the cell-walls, and how much 

 exists in the liquid state in the cavities of the tra- 

 cheides, &c. It may be safely assumed that as long 

 as any liquid water exists in the lumina, the walls will 

 be saturated. Sachs' method of hanging a piece of 

 wood, dried at 105 C. in an atmosphere saturated 

 with moisture, was employed. The temperature was 

 kept constant, and it was found that in two days the 

 wood had absorbed water to the extent of half the 

 quantity it was capable of absorbing, and it then went 

 on absorbing it more and more slowly, until it took 

 no more. 



Hartig concluded that the capacity for imbibing 

 stands in intimate relation to the presence or absence 

 of cells containing substances which swell in water. 



For instance, the inner wood ( " heart-wood " ) of 

 beech continued to imbibe for forty-seven days, and 

 then had taken up 57 per cent, of its substance- 

 volume ; while the alburnum of beech, which contains 

 much starch, continued to imbibe for fifty-seven days, 



