THE SUITABILITY OF AMERICAN WOODS FOR PAPER PULP 7 
decay, is, therefore, of great importance. Not only the color but also 
the physical properties of the pulps, as well as their paper-making 
qualities, are seriously influenced by decay, which often causes con- 
siderable loss of material. Decay has more serious effects in this 
process than in any of the chemical processes. 
CHEMICAL PROCESSES 
Of the chemical processes the sulphite, soda, and sulphate pro- 
cesses are standard, and all the wood pulp made by chemical means 
on a commercial scale is the product of one of the three. 
SULPHITE PROCESS 
The sulphite process is by far the most important from the stand- 
point of annual tonnage. It consists of the removal of the incrusting 
matter in the wood by means of a solution of sulphur dioxide in an 
aqueous solution of calcium or magnesium bisulphite or a mixture of 
the two. The pulp is usually light colored and in many products 
.may be used without bleaching. The wood is first barked and then 
chipped to suitable dimensions to permit proper contact and cir- 
culation of the cooking liquor during digestion. As the liquor will 
not dissolve bark, great care must be exercised in the barking oper- 
ation; for this reason the size and shape of the wood as received at 
the mill must be taken into consideration. Round wood down to 3 
inches in diameter is used in some instances, but the cost of removing 
the bark and the relatively large proportion of wood lost in the oper- 
ation have greatly retarded the use of small material. The same 
reason has discouraged the use of mill waste from lumbering or wood- 
working operations, and the quantity of such material reported as 
having been used in the manufacture of paper pulp in 1920 was actu- 
ally less than that reported in 1914. 
Decay often gives considerable trouble in the manufacture of 
sulphite pulp, since certain fungi prevent the wood from being com- 
pletely acted on by the liquor. Discolorations in the wood appear 
in the pulp, the wood affected is incompletely pulped, and trouble 
from uncooked portions is encountered. 
On account of the acid character of the process, resinous matter, 
tannins, and other extractive substances are not dissolved, and their 
presence, by resisting the penetration of the cooking liquor, often 
prevents complete pulping. In the mill they cause trouble on ac- 
count of shives or excessive screenings. The pitch particles them- 
selves, either alone or combined or agglomerated with the cooking 
base, create difficulties on the paper machine in numerous ways 
familiar to the paper maker. 
The spruces, firs, and hemlocks are all capable of reduction by the 
sulphite process without undue trouble from pitch. Most of the 
pines, cedars, larches, cypresses, and sequoias, and Douglas fir are 
too resinous or contain other extractive matter which retards the 
penetration of the cooking liquor. A few of the pines are used to a 
limited extent, and it seems probable that with more definite infor- 
mation in regard to the fundamental scientific principles governing 
the sulphite process the rapidly growing and more easily pulped 
species such as jack pine, loblolly pine, and Virginia pine will come 
into more general use, especially when the wide range of some of 
