244 TIMBEKS AND THEIK USES 



proportion of non-felting fragments of cellulose 

 cannot ,be avoided. It may be assumed that 

 the ideal condition of a hydrated pulp, whatever 

 may be the degree to which hydration is carried, 

 is one in which the fibres, almost unreduced in 

 length, are each surrounded by a gelatinized 

 envelope of their own ceU substance, gradually 

 merging towards the interior into unmodified 

 cellulose. In other words, the cementing sub- 

 stance, which is the valuable product of hydra- 

 tion, should be self-contained on the outside of 

 each individual fibre." 



Wood Distillation. A considerable amount 

 of wood is, especially on the Continent, subjected 

 to dry distillation, that is .to say heating for 

 several hours at a temperature of 600° F., for 

 the sake of the valuable distillates and residues 

 obtained. The distillates consist of water, crude 

 pyroUgneous acid, wood spirit and gases and the 

 residues of charcoal and tar. On the Continent 

 gas, approximating to coal gas, is obtained by 

 the destructive distillation of wood ; it consists 

 of hydrogen, carbon monoxide and various 

 hydrocarbons. Pyroligneous acid is subjected 

 to redistillation and yields acetic acid, and, 

 after further treatment, vinegar. It is also used 

 in the preparation of acetate of lime on a large 

 scale with naphtha from which, after treatment 



