320 PLANTS AND MAN 



chemical pulps are dissolved out by chemical action. The princi- 

 pal wood used in this process is spruce, with smaller amounts of 

 hemlock and balsam fir. 



The soda process. — ^The soda process uses mostly poplar, 

 Douglas fir, gum, and small amounts of beech, maple, and birch. 

 The chips are cooked in a solution of caustic soda for four to six 

 hours, after which the pulp is washed, screened, and compressed. 

 This process yields a soft, weak, bulky fiber which is mixed with 

 sulphite for strength and used for manufacture into book and 

 magazine papers. 



In the conversion of pulp to paper, the pulp, together with 

 all the materials that are added to make up the particular paper, 

 is placed into large beating machines which separate and spread 

 the fibers. A rosin compound, or sizing, is added to make the 

 fibers resistant to wetting; fine clay, or filler, to make a smooth 

 paper; and dyes to give the paper its desired color. The final step 

 in the manufacture of paper is the spreading of a thin suspension 

 of pulp, about 99% water, on a moving endless belt of wire 

 cloth which drains ofT most of the water, leaving a thin wet mat of 

 fibers. This wet sheet is compacted by passing through a series 

 of steel and rubber rollers (fig. 227), and dried by passing be- 

 tween and around numerous steam heated drying cylinders. 

 Finally the sheet is run between heavy steel rollers, known as 

 calenders, which give it a smooth finish. This paper machine is the 

 most expensive piece of machinery in the industry, a large one 

 often costing a million dollars or more. Some of the large news- 

 print machines are capable of turning out a sheet almost twenty 

 feet wide at the rate of a thousand feet per minute. 



Fiber boards. — Many types of fiber, wall, or building boards 

 are in use today, a number of which are of wood composition. 

 These are made of pulp, pulp screenings, shredded bark, com- 

 pressed shavings, etc. Such boards are put to a wide variety of 

 uses, including principally partitions, ceilings, sheathing, drawer 

 bottoms, doors, shelving, store fixtures and trunks. 



Rayon. — For many years cotton linters were used in the 

 manufacture of rayon, or artificial silk, but today it is made al- 

 most entirely from wood which is cheaper and more readily 

 available. The manufacture and use of rayon has increased 



