SUITABILITY OF LONGLEAF PINE FOR PAPER PULP. 3 



The waste wood mentioned is not as a rule the clean, clear material 

 to which pulp mills have been accustomed. But when the soda and 

 sulphate processes are employed, the presence of knots, pitch pockets 

 and streaks, and remnants of decayed wood and bark are not very 

 objectionable. The expense of handling and preparing slabs and other 

 irregular sizes and shapes, however, is greater than for round pulp- 

 wood, so the initial cost of such material must be low enough to offset 

 the extra cost incident to its use. 



PULP MAKING PROCESSES APPLICABLE TO LONGLEAF PINE. 



Four or five mills are at present using southern pine mill waste 

 for the manufacture of wrapping paper and similar products, three of 

 which employ the sulphate process. Several other sulphate mills 

 are either projected or in course of construction. Because of the 

 resinous nature of the wood the preparation of paper pulp from long- 

 leaf pine is confined to the soda and sulphate processes, unless special 

 extraction treatments are employed preliminary to cooking. 



The soda process consists in digesting suitably prepared wood with 

 caustic soda (NaOH) solution. The cooking results in dissolving 

 the lignin and resin constituents of the wood, and separating the 

 individual fibers from one another. The action depends partly upon 

 the direct solvent and saponifying power of the caustic soda, and 

 partly upon the hydrolysis of the wood in the presence of water at 

 high temperatures, forming organic acid products which unite with 

 the alkali present. Cellulose, of which the fibers are chiefly composed, 

 withstands the cooking action, except under very severe treatment. 



The spent cooking liquor, or " black liquor," is separated from the 

 pulp fibers and evaporated; the residue is calcined in a furnace, and 

 the soda compounds are recovered as " black ash," an impure sodium 

 carbonate (Na 2 C0 3 ) . This ash is dissolved in water, and the solution 

 is causticized with freshly burned lime; the resulting caustic soda is 

 again used in cooking. The losses of soda occurring in the operations 

 are made up by adding fresh soda ash (commercial sodium carbonate) 

 previous to causticizing. 



The sulphate process is similar to the soda process, except that 

 sodium sulphide (Na 2 S) is employed as a cooking chemical in addi- 

 tion to the caustic soda. The sodium sulphide is derived from sodium 

 sulphate (Na 2 SO 4 ), which is added during the recovery operations to 

 make up for the losses, and it is from this chemical that the process 

 derives its name. The sodium sulphate is mixed with the black ash 

 and subjected to a high temperature in a "smelter"; this treatment 

 reduces it to sodium sulphide, although the reaction is not complete. 

 The "smelt," containing sodium carbonate, sodium sulphide, and 

 unreduced sodium sulphate, is dissolved in water and the solution is 

 causticized, as in the soda process, with lime, which has, however, 



