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 

 o'f 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. 



