FOREST PRODUCTS 177 



beech, birch, maple, yellow poplar, gums, and cottonwoods. The 

 pulping liquor in this process is caustic soda. 



Rayon. Large quantities of wood pulp are used in the manufac- 

 ture of rayon or artificial silk. Sulphite pulp, since it requires less 

 refinement and produces a higher yield than other wood pulps, is in 

 greater demand. Most of the rayon is manufactured by the viscose 

 process which is used also for the manufacture of cellophane. Other 

 methods used for the production of rayon are the nitrocellulose, cellu- 

 lose acetate, and cupro-ammonium processes. During a recent year 

 over 157 million pounds of pulp were used for rayon and cellophane. 

 Of this quantity, 60% was of wood pulp and 40% cotton linters. 

 Production is concentrated largely along the Atlantic seaboard states. 



Wood Fiber Insulating and Building Boards. An important appli- 

 cation for sawmill and woods waste has developed within recent years. 

 Enormous quantities of wood, formerly wasted, are now used for the 

 manufacture of fiber boards. They must be made from chemical or 

 mechanical pulp, originally derived from sawmill or woods waste in 

 large part, or they may be made of other materials or combinations 

 of wood and other materials such as asbestos, bagasse (sugar cane 

 stalks after sugar has been compressed from them), cork, cornstalks, 

 licorice roots, moss, gypsum, and several others. 



The principal types may be: 



1. Rigid, combining both insulating and strength properties. 



2. Semi-rigid, such as felts, which are somewhat flexible. 



3. Flexible, consisting of loose fibers and covered with paper or 

 fabric. 



4. Filler, made of powdered, shredded, or granulated material. 



The advantages and reasons for the wide introduction and in- 

 creased use of insulating boards and materials are: 



1. They lower fuel costs by preventing undue loss of heat. 



2. Smaller and more economical heating systems are necessary. 



3. Greater comfort is provided during both winter and summer. 



4. They are necessary for air conditioning. 



5. Fire hazard is reduced. 



4. Fuelwood furnishes fuel for a great variety of industrial and 

 domestic uses. For many years prior to the introduction and use of 

 coal, fuel oil, and natural gas, it was the only fuel available. The 

 threat of a fuel famine was the chief reason for the establishment of 

 forestry in Europe. Formerly fuel was the chief use of forest products 

 in this country. Within recent years, it has rapidly 1 decreased in im- 

 portance because of the competition from coal and other fuels. It 



