CELLULOSE. 32 1 



Cellulose is the commercial product obtained from wood first 

 cut into thin slices and small chips by machinery, then ground 

 down between grooved rollers, and boiled under high pressure 

 in a solution either of soda (alkali process} or of calcium sulphite 

 (acid process, and usual method). The Alkali process is the 

 older, but the more expensive, and though it yields a finer 

 quality of cellulose, there is more loss of cellulose through the 

 wasteful action of the caustic soda (NaHO) in dissolving the 

 lignin ; and it has the further disadvantage of creating an 

 abominable stench. The Acid Process is therefore now gener- 

 ally used, in which the macerating agent is bisulphite of lime, 

 Ca(HS0 3 ) 2 , obtained by dissolving sulphate of lime, CaS0 3 , in 

 hydrated sulphurous acid, H 2 SO g , the sulphurous acid, S0 2 , 

 being the active agent in dissolving the ligneous matter encrust- 

 ing the cellular tissue of the woody substance, without wasting 

 the cellulose itself so much as in the alkali process ; while the 

 cellulose got thus is also easier to bleach than alkali-processed 

 cellulose, though it is less soft and pliable. All the wood used 

 has to be carefully cleaned, barked, and freed from branch-knots 

 and unsound parts, then chipped diagonally into small pieces 

 and ground up before being packed and boiled with bisulphite 

 of lime lye in large glazed barrel-shaped masonry vats. The 

 bisulphite of lime lye is obtained by burning sulphur or iron' 

 pyrites in furnaces and leading off the sulphurous acid evolved 

 into a lofty tower built up of wood and iron, and packed with 

 limestone down which water continually trickles from a per- 

 forated tank at the top, a weak solution of hydrated sulphurous 

 acid, H 2 S0 3 , being thus obtained, and acting upon the carbonate 

 of lime in the limestone, CaC0 3 , and forming bisulphite of lime, 

 Ca(HS0 3 ) 2 . The lye is led off into the large glazed masonry 

 vats packed with ground chips, which are then boiled under a 

 pressure of about 80 Ibs. per sq. in., the heating taking place 

 by hot steam at 260 or more for about 40-60 hours, when the 

 sulphurous acid is carried off again to the limestone-tower, and 



x 



