TURNING FORESTS INTO PULP
Before we proceed to describe the modern Fourdrinier machine, we must look into present day methods of preparing pulp. The finest papers are still made from linen and cotton rags. Esparto grass is largely used in Europe. This comes from Spain and North Africa. But by far the greater part of the paper produced to-day is made from the fiber of trees. Particularly is this true of our own country, which consumes half of the world’s output of paper.
It used to be that only the poorest grades of paper were made from wood pulp; now however not only newspapers but nearly all books and magazines are printed on a forest product. Formerly only spruce wood was considered suitable for paper manufacture, but the rapid depletion of this raw material led to the employment of many other species of trees and our Government scientists are constantly searching for and experimenting with new woods for this purpose.
Because of the insatiable appetites of our large newspaper printing presses and because a newspaper is not intended to be an imperishable document but a fleeting record of passing events, quality is of little importance in the preparation of pulp for newsprint and everything must be sacrificed for speed. The pulp is made of “ground” wood as distinguished from the chemically prepared wood pulp known as “sulphite.” The wood is first stripped of its bark and then cut into pieces running from two to four feet in length, depending upon the size of the magazine of the grinder. The wood is pressed against a revolving grindstone by hydraulic pressure and at such an angle that the fibers torn off will be as long as possible. The fibers are borne off by a stream of water which carries them through a set of screens. These remove any unground slivers, and eventually the pulp is drained of water and pressed into laps, or, if it is to be used immediately, it goes directly to the beating engine. Here it is mixed with a certain amount of “sulphite pulp,” usually from 20 to 25 per cent. To correct the yellowish color of the pulp, a small amount of blue and red coloring is added. To give body to the paper from 5 to 15 per cent of clay is mixed into the pulp and, to bind the fibers together and give the paper a finish that will be at least partly nonabsorbent, a quantity of rosin and soda ash is added with enough alum to precipitate the rosin upon the fibers. The beater thoroughly mixes the mass of material and converts it into a fluid of the consistency of thin milk, which then passes on to the Fourdrinier machine.