In making “mechanical pulp” the blocks of wood, mostly spruce and hemlock, are simply pressed sidewise of the grain against wet grindstones.  But in wood fiber the cellulose is in part combined with lignin, which is worse than useless.  To break up the ligno-cellulose combine chemicals are used.  The logs for this are not ground fine, but cut up by disk chippers.  The chips are digested for several hours under heat and pressure with acid or alkali.  There are three processes in vogue.  In the most common process the reagent is calcium sulfite, made by passing sulfur fumes (SO_{2}) into lime water.  In another process a solution of caustic of soda is used to disintegrate the wood.  The third, known as the “sulfate” process, should rather be called the sulfide process since the active agent is an alkaline solution of sodium sulfide made by roasting sodium sulfate with the carbonaceous matter extracted from the wood.  This sulfate process, though the most recent of the three, is being increasingly employed in this country, for by means of it the resinous pine wood of the South can be worked up and the final product, known as kraft paper because it is strong, is used for wrapping.

But whatever the process we get nearly pure cellulose which, as you can see by examining this page under a microscope, consists of a tangled web of thin white fibers, the remains of the original cell walls.  Owing to the severe treatment it has undergone wood pulp paper does not last so long as the linen rag paper used by our ancestors.  The pages of the newspapers, magazines and books printed nowadays are likely to become brown and brittle in a few years, no great loss for the most part since they have served their purpose, though it is a pity that a few copies of the worst of them could not be printed on permanent paper for preservation in libraries so that future generations could congratulate themselves on their progress in civilization.

But in our absorption in the printed page we must not forget the other uses of paper.  The paper clothing, so often prophesied, has not yet arrived.  Even paper collars have gone out of fashion—­if they ever were in.  In Germany during the war paper was used for socks, shirts and shoes as well as handkerchiefs and napkins but it could not stand wear and washing.  Our sanitary engineers have set us to drinking out of sharp-edged paper cups and we blot our faces instead of wiping them.  Twine is spun of paper and furniture made of the twine, a rival of rattan.  Cloth and matting woven of paper yarn are being used for burlap and grass in the making of bags and suitcases.