52 



FOREST PRODUCTS 



pulp is a pinkish gray color and is used directly in grayish papers. The 

 mechanical pulps which are gray or brown in color according to the 

 method of manufacture are used in papers which are generally not re- 

 quired to be white and, therefore, are seldom bleached. 



Whenever sulphite, sulphate, or soda pulps are to be bleached they 

 are put through a process of oxidation. The compounds used generally 

 are hypochlorites, usually suspensions of chloride of lime, or electrolytic 

 bleach consisting of calcium or sodium hypochlorite solutions, etc. The 

 bleaching process, which is rather expensive, increases the value of the 

 paper to a considerable degree. 



Beating. 



After bleaching, or in case the pulp is not put through the bleaching 

 process, the complete separation of the individual fibers is necessary. 



Photograph bv U. S. Forest Service. 



FIG. 8. Beating machines. 



This is done by beating which gives the pulp evenness of texture so that 

 proper felting and an interlacing of the fibers can be secured in the final 

 process of papermaking. The fibers are also made flexible and of uniform 

 length and the ends are frayed out so that they will enmesh more readily. 

 The machine used for the reduction of the pulp by beating is called 

 the " Hollander," or more commonly the beating engine. It consists 

 of an oblong trough with semi-circular ends, and " midfeather," running 



