238 TIMBERS AM) THEIR USES 



ably in the moist condition, containing fifty per 

 cent of air-dry pulp. It may be mentioned that 

 this practice is not a matter of mere convention. 

 It involves an obvious and serious addition to 

 freight and transport charges and some risk of 

 attack by moulds and micro-organisms. It is 

 based upon the retention of paper-making 

 quahty by the pulp, which is injuriously affected 

 not only by drying, but in the process of repulp- 

 ing with water. 



" The woods commonly employed are White 

 Pine, Spruce and Aspen. The last named yields 

 a finer pulp of a better colour, but of inferior 

 strength. 



" Paper containing mechanical wood piilp is 

 very liable to become discoloured by the action 

 of air and light, the ligno-celluloses being much 

 more readily acted upon than the celluloses iso- 

 lated from them. Such fibre is, moreover, of low 

 felting quahty, it has, in fact, httle to recommend 

 it but its comparative cheapness. It is never- 

 theless used in large quantities, some cheap 

 papers being made almost entirely from it." 



. In the manufacture of chemical wood pulp 

 the mechanical processes are reduced to a 

 minimum, and the pulp is extracted almost 

 solely by chemical means. It is hardly neces- 

 sary or advisable to enter into a discussion of 



