52 BULLETIN 983, U. S. DEPARTMENT OF AGRICULTURE. 
of the acetyl and formyl groups in the lignin. Bergstrom obtained 
as much as 1.53 per cent acetic acid and 0.23 per cent of formic acid 
from spruce boiled in water at a pressure of 6 atmospheres for two 
hours without any catalyst, whereas cellulose produced from spruce 
yielded only 0.08 per cent of combined acids under similar treatment. 
This being true, the maximum amount of acid obtainable from 
wood is the sum of the acid produced by the destructive distillation 
of the cellulose and the hydrolysis of the lignin. This would be 5.7 
per cent total acid, which, so far as the writer's knowledge extends, 
has never been obtained by the destructive decomposition of wood. 
Undoubtedly secondary decomposition products are formed, such as 
2CH 3 COOH = (CH 3 ) 2 CO plus H 2 plus C0 2 , 2 HCHO plus H 2 = CH 3 OH 
plus HCOOH, and similar reactions, which may account for the 
acetone and in part for the formic acid obtained from destructive 
distillation. 
A series of destructive distillations has been made at the Forest 
Products Laboratory on spruce and spruce-digester residues cooked 
with sulphuric acid for sugar and alcohol production. These dis- 
tillations were made, some slowly and some quickly, some very 
wet and some very dry, to determine whether the hydrolytic effect 
noted above could be reproduced in the destructive-distillation 
process. The details of this work are being reserved for later pub- 
lication; but it may be stated here that the distillation of either 
wet wood or wet residue produced more total acid than was ob- 
tained from the dry wood or dry residue under similar distillation 
conditions, showing that there was a hydrolytic effect from the 
added water. The increased amount of acid, however, was not 
sufficient to pay for its recovery from the more dilute pyroligneous 
acid produced. 
Aside from the scientific interest of the subject and its bearing 
on the chemistry of wood, the technical importance of the recovery 
of these acids is to be considered. As outlined previously, this has 
been attempted in France and in the processes covered by the 
patents granted to Cohoe in this country. Cohoe, however, worked 
with broad-leaved woods, which would give even larger amounts 
of these acids. The table in the Appendix, however, shows that 
the amount of acid which might be recovered in the condensed 
blow-off averages only about 10 per cent of each, and this would 
yield a condensate of little value. As the average concentration of 
acetic acid in the condensed blow-off was only about 0.20 per cent, 
it is questionable whether recovery in commercial amounts is pos- 
sible. If some means could be devised, however, for washing out 
the volatile acids with steam and making a practically complete 
recovery of them without too great expense or delay to the digester 
cycle, these acids might form a valuable by-product of this industry. 
