16 BULLETIN 983, Uj S. DEPARTMENT OF AGRICULTURE. 
hydrolysis is of little or no importance, except where it varies the 
actual ratio of acid to wood; the concentration of the catalytic 
agent expressed in per cent, or other terms, of the dry wood is the 
decisive factor. 
In view of these facts, it was decided to reinvestigate certain of 
the variables studied heretofore, in addition to such others as might 
be considered necessary to the technical solution of this problem. 
This bulletin presents the results of the first part of such a systematic 
study. 
The variables under investigation were: (1) Influence of the 
temperature and pressure of digestion; (2) length of the time of 
digestion; (3) ratio of the water to the dry sawdust; (4) ratio of the 
catalyzing agent to the dry sawdust; (5) concentration of the 
catalyzing agent in water; (6) size of the sawdust, hogged slabs, 
etc.; (7) effect of adding the catalyzing agent (acid) after the prelim- 
inary heating of the wood; (8) effect of varying the amount of bark 
in the sawdust: or, more specifically, the tannin and other ingre- 
dients in the bark; (9) special chemical treatments other than or in 
addition to acid catalysis; (10) yields from different species and 
mixtures; (11) the fermentation variables; (12) steam consumption 
for each ton of sawdust digested. 
APPARATUS AND PROCEDURE. 
The apparatus used and the method of procedure in each experi- 
ment were as follows : The hydrolysis of the wood was carried on in 
a rotary digester consisting of a thin cast-iron inner shell lined with 
acid-proof enamel and an outer shell of steel, the two being separated 
by several inches. The inside length of the inner shell was about 5 
feet, the diameter about 2\ feet, and the total capacity about 22 
cubic feet. Steam was admitted simultaneously to the inner shell 
and to the space between the inner and outer shells, the digester being 
similar to a steam-jacketed apparatus, except that the inner shell 
could be readily taken out and replaced. After a cook had been 
completed, the digester was blown off, the blow-off vapors being 
condensed in a quartz coil. A cast-iron tank, also lined with acid- 
proof enamel, was connected with the digester in such a way that its 
contents might be introduced into the digester when the latter was 
under pressure. The steam flowed to the inner shell and to the space 
between the two shells through separate pipes. The one leading to 
the inner shell connected with the acid tank. All pipes in contact 
with acid liquor or acid vapor were enamel-lined,- and the valves were 
of special bronze, so as to reduce corrosion to a minimum and avoid 
as much as possible those complications in fermentation that arise 
from the presence of iron, copper, and zinc salts. The pressure was 
