142 



[March 1907. 



Pulp and Paper Making. 



Daring the nineteenth century there were remarkable changes and improve- 

 ments in the methods employed for converting paper stock into paper pulp and 

 paper. These advances have been due to two causes— one, the revolution in the 

 nature and supply of the raw material itself, and the other, the increased demand 

 for the finished product. The method of preparation of paper pulp or half-stuff has 

 thus far largely been dependent upon the nature of the material treated, where 

 as the making of the pulp into finished paper in sufficient quantities to meet the 

 marvelous growth of the industry has caused the laborious hand process to be 

 superseded by the huge automatic machines of the present time. However, the 

 principles involved in the making of paper remain unaltered, regardless whether 

 the material is removed from a vat with a small hand sieve and turned out a single 

 sheet at a time or is allowed to flow on to an endless wirecloth web under heavy rolls 

 and over the steam-heated drying cylinders of a Fourdrinier machine. Generally 

 speaking, the purpose is just the opposite of that which obtains in the isolation 

 of fibres for the textile and cordage industries ; instead of so treating the fibrous 

 substance as to preserve the fibre bundles or filaments in their greatest length, it is 

 necessary, by some mechanical or chemical means, to convert them to the invidual 

 fibres or cells of which the filaments are composed. 



There are five distinct steps in the preparation of paper pulp from any 

 vegetable material. Two of these are entirely mechanical, whereas the remainder 

 are of a distinctly chemical nature. Arranged in their order of procedure, they are : 



1. Cleaning. — A purely mechanical process which consists in removing all 

 foreign matter such as sand, dirt, weeds, chaff, etc., either by hand or machinery. 



2. Boiling or digesting.— This results in eliminating the soluble plant con- 

 stituents and incrusting matter by chemical means. 



3. Bleaching consists in further chemically purifying the resistant cellulose 

 by removing adhering coloring matter. 



4. Beating or refining. — This procedure mechanically disintegrates the pulpy 

 mass of fibres into fragments of requisite length. 



5. Loading, sizing, and, coloring so modify the bleached and beaten pulp 

 by the addition of mineral or animal substances, that a non-porous resistant of the 

 required shade is given to the finished product. 



Boiling or Digesting. 

 At tlie present time there are two main groups of processes in general use 

 for the isolation of paper cellulose, namely, the alkaline and acid treatment. Tiie 

 first and older methods depend upon the action of solutions of caustic soda, soda ash, 

 caustic lime, or mixtures of these chemicals, under varying conditions of strength of 

 solution, pressure, andf duration of digestion.* Therefore it is evident that in 

 valuing an unknown material for use as paper stock these differences need carefully 

 to be considered. The second method for the resolution of raw fibres is of com. 

 paratively recent origin and consists in cooking then under strong pressure with 

 sulphurous acid, either free or combined with soda, lime, or magnesia in the form of 

 the bisulphites of these bases. The development of this process has been slow, 

 owing to the many mechanical difficulties involved, the strong chemicals employed 

 attacking and soon rendering the digesters worthless. However, within recent years 

 resistant digester linings have been invented and now this process is established as 

 the leading method for the preparation of chemical wood-pulp. Comparatively 

 little has been done to show its adaptability to materials other than wood, but the 



* Esparto grass is invariably subjected to the alkaline method of treatment, but the pressures 

 carried vary from 5 to 60 pounds, the time of digestion from one to six and one-half hours, and the strength 

 of the caustic liuuor from 10 to 20 per cent, calculated upon the gross weight of the material, 



