18 MISC. PUBLICATION 16 2, U.S. DEPT. OF AGRICULTURE 



fibers. Among the woods most frequently used for paper pulp are 

 spruce, hemlock, southern yellow pine, poplar, balsam fir, jack pine, 

 white fir, beech, birch, maple, gum, and larch. 



Four commercial processes of making paper pulp from wood are 

 in general use ; three chemical — the sulphite, sulphate, and soda 

 processes — and one mechanical — the ground-wood process. In each 

 of the chemical processes the chipped wood is cooked with a chemical 

 under steam pressure in a specially designed cooker, or " digester ", 

 where the portion of the wood known as lignin is removed, leaving 

 fibers of almost pure cellulose. In the ground-wood process the 

 uncooked wood is mechanically ground into a pulp. Each process 

 is adapted to the manufacture of certain grades of paper or to the 

 pulping of certain woods. The stronger and better grades of paper 

 are made from the three chemical processes. 



The United States uses more paper than all the rest of the world ; 

 in 1930, over 13,000,000 cords of pulpwood were used. The paper 

 industry in this country was first established in the Northeast, where 

 today a large part of our paper products are manufactured. From 

 there, however, the industry has spread to other sections. 



Another product of wood pulp is rayon, which in the past few 

 years has come into extensive use for clothing. Rayon, like paper, 

 can be made from cotton and other forms of plant cellulose, but much 

 of it is made from wood. The manufacture of this artificial silk is 

 a rapidly developing industry. The annual production of rayon 

 now amounts to about 200.000,000 pounds. 



After wood, the most important forest products are turpentine 

 and rosin. They are obtained by the distillation of the gum that 

 exudes from the longleaf and slash pines of the South. The gum 

 is drained from the trees and carried to a still, where it is cooked 

 in closed iron retorts. The turpentine is given off in the form of 

 volatile oils, which are collected and condensed in a condensing 

 worm. The rosin is the part of the gum left after the turpentine 

 has been stilled off. Turpentine is essential in the manufacture of 

 paints and varnishes. It also goes into the making of waterproof 

 cements for rubber, glass, and metals, and of liniments, disinfectants, 

 celluloid, explosives, drawing crayons, patent leathers, and numerous 

 other articles. Rosin is used in the manufacture of high-grade 

 paper, in soap making, and shipbuilding, and in soldering opera- 

 tions. Turpentine and rosin obtained from southern pines are 

 worth millions of dollars each year. If conservative methods of 

 turpentining are used, the trees may produce gum for a number of 

 years and still be valuable for lumber. 



Not so valuable commercially, but with a domestic importance all 

 their own are the sugar and sirup made from the sap of the sugar 

 maple and its close relative, the black maple. The trees are tapped 

 in February or March by boring small holes in the sapwood. A 

 spout is inserted in each hole and a bucket hung beneath it to catch 

 the sap which drips out. The collected sap is carried to the sugar- 

 house, where it is boiled down to the proper consistency for sirup 

 or sugar. Most of the maple products come from the Northeastern 

 and Northern States, but a few other States also produce them in 

 commercial quantities. 



