28 BULLETIN 1003, U. S. DEPARTMENT OF AGRICULTURE. 
pounds. Of them all, water is the compound formed in the greatest 
quantity, because of the fact that oxygen and hydrogen constitute 
55 per cent of cellulose, the principal wood constituent. This water, 
holding in solution numerous other compounds, produced simultane- 
ously with its formation, is referred to in this bulletin as the “ acid 
liquor,” an exceedingly complex liquid of a wine-red color, having 
a sharp, tarry odor and strong acid reaction. In addition to water, 
it is largely made up of acetic acid, methyl or wood alcohol, tar acids, 
oils, esters and acetone aldehyde bodies, together with small propor- 
tions of numerous other compounds of an unknown nature. | 
It is not meant to convey the idea that these changes occur in 
clear-cut stages. Neither is it strictly true that the charge in the 
retort is in reality made up of cellulose, lignin, and abietic acid or 
rosin at any time during the distillation, for these compounds, owing 
to their instability toward heat when dry, undergo progressive 
changes as the moisture is more and more completely driven out 
of the wood, before the recovery of turpentine is complete. Though 
the period during which the distillation products do not result from 
decomposition of the wood substances and the destructive stages of 
the distillation merge into each other or overlap, the nature of the 
changes taking place is essentially as set forth. 
DISTILLATION OF Woop (EXOTHERMAL) AND OF ROSIN (ENDOTHERMAL). 
The chemical reactions brought about during the destructive dis- 
tillation of cellulose are exothermal, that is, heat is given off during 
the changes taking place once the action, for which a temperature of 
270° C. is necessary, has been started. The amount of heat thus lb- 
erated was found by Klason, Heidenstam, and Norlin® to be equiva- 
lent to 4.6 per cent of the calorific or fuel value of the wood (pine). 
The reactions involved in the decomposition of rosin by destructive 
distillation, in the course of which rosin oils are formed, however, 
cease unless an adequate supply of heat is maintained throughout the 
distillation. This is due to the fact that the changes taking place, 
instead of liberating, take up heat, being “ endothermic” reactions. 
These facts are of significance in view of the difference in behavior 
observed when the more highly resinous wood and that containing 
but little resinous matter, such as “bull pines,” are distilled. In the 
case of the more highly resinous wood a decided exothermic effect: 
was observed while the destructive stage of the distillation was in 
progress, continuance of the high temperature (343° C.) being neces- 
sary to carry the distillation to completion. In the distillation of 
“bull pine” in the same state of dryness, however, the reaction be- 
5 Arkiy. Kemi. Min. Geol., Band 3, No. 10, Heft 2. Published by the Royal Academy of 
Sciences at Stockholm. 
