54 OUR VANISHING FORESTS 



into a huge barrel-shaped container which constantly 

 tumbles them against rows of spikes; but hand labor 

 is also needed for a thorough job. There are two 

 general types of wood pulp; that made by grinding 

 the wood billets against huge stones under a con- 

 tinuous jet of water or steam, and that obtained 

 from dissolving chips in an acid. The first method 

 is the simpler, but since the grind-stone tends to 

 break the wood fibres, paper made from ground- 

 wood alone would not possess much strength. 

 Where acid is used, the fibres come out whole. Or- 

 dinary newspaper is a mixture of about one part 

 chemical pulp to three or four parts of groundwood, 

 while writing paper, book paper, wrapping paper 

 and the like are chiefly made from chemical pulp 

 only. 



The secret of paper manufacture lies in having 

 the pulp absolutely clean and free from impurities. 

 It has to be washed, stirred and beaten, and washed 

 again and again before the material is ready to mix 

 with the necessary rosin or other sizing material and 

 be rolled into paper. A large supply of thoroughly 

 fresh and clean water is therefore absolutely essen- 

 tial. The pulp, carried about in liquid form, 

 eventually comes into the paper room and sprays 

 onto a thin screen which leads over and under a 

 series of very hot rollers until the pulpy sheet has 



