What Forests Give

WOOD PULP

To make wood useful to himself, man always has to take it apart and put it together again in some other shape. A tree, left to itself, will not do much for him except to offer shade, a little shelter from the rain, a refuge, and possibly food. A tree cut into large pieces with saws or axes or knives can be reassembled into houses or boats or carriages. But wood taken apart by grinding, wood dissected into the smallest particles which are still wood—wood that has been "pulped"— can be put together in a far greater number of shapes for a far wider use.

If you ask your grandmother what she did her sums on in school she will answer, "a slate." This was not because we did not know how to make paper when she was a girl, but because we did not know how to make it out of wood. The art of paper making is so old that we do not know when or where it began. It came to us from the Chinese, but the Chinese learned many of their arts from the people of India, who began to live in cities and manufacture cloth so long ago that the historians have no date for it. That early paper was made of rags—of the fibers that grow in flax or cotton, sometimes even of silk fibers—used first in cloth, and then as a second use, made into paper. In the early days of our country the paper mills advertised for rags, and when they did not get them they had to stop running. Not until we learned from the wasp, who has made his nest from paper as long as he has been on earth, that paper could be made from wood, did we have all the paper we needed. We had to learn to do what the wasp does to pulp wood.

This is, roughly speaking, to continue the process of dividing it up. There are two ways of doing this. One is to cook the wood in water in which a little caustic soda or acid has been added. This separates the wood fibers without breaking them and is used in making the strongest paper. The other way is to put wood chips into a grinder—a sort of glorified extension of a coffee mill. This mill grinds so effectively and so exceedingly fine that the mere friction makes the pulp too hot to touch. It comes from this grinder a grayish substance, moist and sticky like bread dough with too much flour in it.

Pulping Wood

The pulp can be put back into solid form because wood is composed of cells, most of which are shaped like slender fibers, and the walls of these cells are made up of smaller threadlike bodies called "fibrils"; the fibrils are formed of infinitesimal spindle-shaped bodies. Wood is composed of short tiny threads within threads. They can be made to stick together again in the same way that felt is made from rabbits' hairs.

In the modern process of making paper, wood pulp made by either of these processes is mixed with water till it looks like skim milk, beaten like an egg, and then in a slow stream floated out above a moving belt of cloth or fine wire mesh through which, as it moves on and on, the liquid drains away, leaving a thin layer of wet pulp like undissolved sugar in the bottom of a cup. The belt passes between steel rollers, as clothes are put through a wringer, and more water is squeezed out. It goes on between hot rollers as sheets go through a hot mangle, and the water that has not been wrung out is steamed out. On and on it goes between more rollers that squeeze it and dry it and polish it, and finally, if it is newsprint paper, as most of it is, it is rolled up and sent to the printers. Paper is a tangled mass of wood fibers—it is felted wood.

If it is true that we Americans are great and civilized and happy because we can read, that we are a democracy because we have a free press, and that we have a wide culture because we grow up in the presence of books, it is because we live in a land of plentiful forests. We live and grow, intellectually speaking, on a diet of wood pulp, and wood pulp is a forest product.

Wood pulp is used for many things besides paper—3,000,000 tons every year are made into paperboard for wall coverings which might otherwise be made of larger boards, into boxes and containers and other things, which would certainly be made of wood as it comes from the tree, if paper had not been invented.

The use of wood in the form of pulp has all come since our grandfathers' time. In 1865 none of it was made in the United States. Thirteen million tons were pulped in 1930. This is a vast amount of wood, but it is not necessarily the wood that makes good boards or even the wood that makes good plywood—almost any part of a tree will make wood pulp.

Making Paper

Most of our paper is made from spruce, fir, and hemlock, a little from birch and beech. We could grow crops of these trees that would give us all the paper we need year after year after year, just as we grow all the potatoes we need and all the apples, but we have not begun to do it yet, and every year we bring in pulpwood from Canada, and many ship loads from Norway, Sweden, Finland, and some from the Union of Soviet Socialist Republics.

Another way of taking wood apart without changing its nature is to explode it. Chips are fed into an explosive chamber or "gun", tightly closed in, and steam at 350 pounds pressure turned upon them which—on the same principle as a pressure cooker on the kitchen stove—sends the temperature up to 375° F. for about half a minute. Then for 5 seconds the steam pressure is raised to 1,000 pounds, and the temperature goes up to 540°. All the moisture inside those chips of wood is so hot that it would become gas but for the terrific pressure which prevents its expanding. Then the lower part of the gun opens, the chips drop out, the pressure upon them is suddenly removed, and the water expands instantly into gas, ripping the wood into the fibers of which it is made.

But the fibers are of the same substance as the log, or the shingle or the sawdust—they are wood and they too are felted into boards as wool is felted into hats. The wide sheets which are made from them are as truly wood as though they were cut from the heart of a 400-year-old pine.