THE SUITABILITY OF AMERICAN WOODS FOR PAPER PULP 9 
from such species. It is not, however, handicapped by the disagree- 
able odor characteristic of sulphate mills, which is probably the reason 
it has not been supplanted entirely by the more recent process. 
The soda process consists of the disintegration and solution of the 
incrusting matter in the wood by means of an aqueous solution of 
sodium hydroxide, the wood being prepared in a manner similar to 
that used in the sulphite process. It is not so important, however, 
to remove entirely the bark, knots, or decayed portions, because 
under proper conditions the soda liquor disintegrates them. Never- 
theless, the wood is usually peeled so as to avoid the consumption of 
alkali in the solution of the bark or of decayed portions which yield 
no pulp. 
Pitch is not objectionable in the soda process, as it is readily dis- 
solved in the cooking liquor. Tannins, however, consume caustic 
soda and make necessary the use of larger quantities. Also tannins 
not removed (by means of water extraction) before the cooking 
operation usually darken the pulp and render it much more difficult 
to bleach. 
Although fiber length is important, it is not so much so as in the 
sulphite process, because soda pulp is used almost entirely in the 
manufacture of printing papers where printing qualities outweigh 
strength. The color of the wood is also a minor factor, since the 
coloring matter is in many cases dissolved by the liquor and removed 
from the pulp. With some woods, however, the coloring matter 
persists throughout the cooking action, and is apparent in the pulp. 
The specific gravity of the wood has the same importance as in the 
sulphite and mechanical processes. 
SULPHATE PBOCESS 
The sulphate process, only recently introduced into America, 
was first used in continuous commercial operation in Quebec in 1907. 
Since that time the production of sulphate pulp has increased very 
rapidly. In 1914 about 52,000 tons were produced in the United 
States. By 1922 production had risen to over 243,000 tons. The 
reasons for this increase are the larger yields of pulp and the greater 
strength of the paper. 
It is a modification of the soda process in which the active ingredi- 
ents of the cooking liquor consist of caustic soda and sodium sulphide, 
usually in the proportion of 2 to 1. Its use is confined almost entirely 
to conifers. There is no reason why it should not be applied to hard- 
woods; with the majority of these species easier bleaching pulps 
are obtained with equal yields. The unbleached pulp from conifers 
is commonly used in the manufacture of kraft wrapping paper or, 
in combination with waste papers, for high-test container board. 
Although the practice of bleaching sulphate pulp is not very preva- 
lent, work at the Forest Products Laboratory has demonstrated 
that by using modified methods of bleaching with the standard solu- 
tions, and with quantities of bleaching powder not in excess of common 
commercial practice, very satisfactory results may be obtained. 
Although the pulp obtained by ordinary methods of bleaching is 
yellow and does not approach the brilliant white characteristic of 
bleached sulphite pulp, pulp comparable in brightness is obtained 
by the modified methods. The opacity of the bleached pulp is 
