10 
BULLETIN 1485, U. S. DEPAKTMENT OF AGRICULTURE 
usually greater than that of bleached sulphite pulp. It thus becomes 
possible to obtain from sulphate pulp papers having printing proper- 
ties superior to those of papers from bleached sulphite pulp, unless 
the latter is combined with bleached soda pulp from hardwoods. 
The main drawback of the sulphate process lies in the disagreeable 
odors which characterize it; on this account the mills are usually 
located on the fringes of population. 
The wood is usually barked, although in some mills this step is 
omitted and any fragments of bark which pass the screening opera- 
tion are dissolved in the digester. The consequent high consumption 
of cooking liquor without any return, however, makes it more eco- 
nomical to bark the wood before chipping. Decayed wood does not 
affect the quality of the pulp as it does in the sulphite process, 
BLACK L 
STORAGE TANK 
300 GALLONS 
STEAM EJECTOf 
-MANHOLE COVER 
Fig. 1.— Digester used for alkaline cooks prior to 1916, and for sulphite cooks prior to 1911 
but it very seriously affects the yields and consumption of alkali 
to a ton of pulp. The durability of the wood used is therefore an 
important consideration from the economic standpoint. 
Charred wood is objectionable in this process (as well as in the 
others), since the particles of carbon survive the cooking operation 
and appear in the pulp. Pitch, fats, or waxes occasion no trouble, 
these being readily soluble in the sulphate liquors and furnishing 
to the cooking liquor combustible matter which helps later in the 
recovery of the soda. 
The penetrability of the wood is a considerable factor in the quality 
and uniformity of the pulp. The length of the fibers is of major 
importance, as sulphate pulps are ordinarily used for purposes 
where strength is required. The color of the wood is a secondary 
consideration except in a few instances where the coloring matter 
survives the cooking operations. The specific gravity of the wood 
is directly reflected in the yield of pulp obtained per cord. 
