SUITABILITY OF LONGLEAF PINE FOR PAPER PULP. 25 
SUMMARY OF CONCLUSIONS FROM THE AUTOCLAVE TESTS. 
(1) The effective cooking chemicals in sulphate cooking liquors 
are caustic soda and sodium sulphide, the former being the more 
drastic in its action. Sodium sulphate and sodium carbonate, which 
unavoidably occur in the commercial liquors, are of no assistance in 
cooking, at least so far as the wood of longleaf pine is concerned. 
(2) Increases in the amounts of either caustic soda or sodium 
sulphide, or both, result in more thorough cooking. The same effect 
may be obtained by increasing either the cooking pressure, the dura- 
tion of cooking, or the initial concentrations of the chemicals in the 
cooking liquors. 
(3) More thorough cooking is evidenced by decreased yields and 
by lighter colored pulps until a condition of very thorough cooking is 
reached, after which the color of the pulp is not affected. 
(4) The best, or well-cooked, sulphate kraft pulps will have good' 
strength and wearing properties, will be light brown in color, and 
will have a smooth, firm, leather-like feel when properly beaten. 
Undercooked pulps are characterized by a darker brown color, 
brittleness, lack of strength, and poor wearing properties. Over- 
cooked pulps are light gray in color and may have good strength 
and wearing properties when properly beaten, but the yield will be 
low. Pulps much overcooked, in addition to being light gray in 
color, will be soft and fluffy, with little strength. 
(5) With each different combination of the cooking conditions 
there is a definite minimum amount of sodium sulphide which must 
be used in conjunction with the caustic soda present to impart to 
the product the high strength and good wearing properties char- 
acteristic of properly cooked sulphate kraft pulps. 
(6) The use of sodium chloride in conjunction with caustic soda 
improves the quality of the pulp to a slight extent only. The similar 
use of sulphur results in pulps having properties practically the same 
as those of sulphate pulps, 
(7) As the proportion of sodium sulphide in the digester charge is 
increased, the disagreeable odor produced in the cooking operations 
becomes more pronounced. 
PRACTICAL SIGNIFICANCE OF THE EXPERIMENTS. 
While the present experiments are not complete, they show con- 
clusively (1) that longleaf pine is well adapted for the manufacture 
of natural-color kraft pulps and papers; (2) that the sulphate process 
of pulp making applied to this wood affords products of better quality 
and of higher yields than the soda process; (3) that kraft papers can 
be made from longleaf pine equal or superior in quality to the 
imported and domestic kraft papers now on the market; and (4) 
