SUITABILITY OP 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 S0 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, 
