MOST INTERESTING FOREST PRODUCTS 139 



by hand was very durable but quite expensive. "With 

 the rapid increase in the number of newspapers in 

 order to fill the demand for an elastic free-running 

 paper, the process of manufacturing paper from wood 

 was invented. 



Spruce on account of its long strong fiber is especially 

 desirable as a source of wood pulp and at present sup- 

 plies more than half the stock used for paper. How- 

 ever, more than a score of species furnish material for 

 wrapping paper and fiberboard. 



Manufacturers divide the kind of pulp made from 

 wood into two classes mechanical and chemical. In 

 the manufacture of pulp by the mechanical process the 

 wood is ground up into bits by pressing each piece of 

 the tree trunk they are called "bolts 53 against a 

 rapidly revolving grindstone. These wood fragments 

 make a very coarse pulp from which fiberboard and 

 ordinary pasteboard boxes are made. This ground 

 wood may be mixed with chemical pulp to make news- 

 paper stock, about three-fourths of the paper being com- 

 posed of ground wood. The ease with which such paper 

 is torn is largely due to the presence of the untreated 

 pulp, but the discoloration of a newspaper after a short 

 time is due to the presence of sulphur in the chemical 

 pulp. 



In the manufacture of paper by use of chemicals the 

 wood is first chipped instead of being ground, as the 

 fiber must be kept whole. The chips are then treated 

 with soda or sulphurous acid which dissolves away all 

 the impurities and leaves behind nothing but the wood 

 fibers. This part of the manufacture the "cooking" 

 is done in large upright cylinders called digesters. 

 After the cooking is finished the pulp is washed, beaten 

 and then diluted with water until it is very thin, in 



