Below 200C. the main products moisture, tur- 

 pentine and pine oil are primary in nature. With 

 continued increase in temperature the wood itself 

 suffers decomposition, with formation of water 

 and small amounts of acetic and formic acids, 

 then light tar oils, gas and small amounts of methyl 

 alcohol, and finally heavy tar oils; charcoal is left 

 as a residue in the retort. At temperatures ap- 

 proaching 300C. rosin begins to decompose, the 

 successive products being water, light rosin spirits, 

 heavier rosin oils and pitch. 



The main problems in the destructive distillation 

 process are uniform distribution of heat and accu- 

 rate control of temperature. The types of retorts 

 are numerous and differ rather widely in methods 

 of heat application. 



The fractions obtained by the destructive dis- 

 tillation of resinous wood are for the most part 

 mixtures of the decomposition products of rosin 

 and wood. Purification of the products is for this 

 reason difficult and imperfect. The number of end 

 products is relatively large, but many of them are 

 of low inherent value. Destructive distillation has 

 the advantage, however, of adapting itself to rough 

 and even charred wood, without the necessity of 

 finely dividing the same. Furthermore, certain 

 valuable products, such as pine tar, tar oils and 

 creosote, can be obtained by this process alone. 



Steam Distillation 



Although the boiling point range of turpentine 

 lies above 155C., both turpentine and pine oil 

 are volatile with steam at temperatures above 

 94 96C. The steam distillation process aims to 

 remove the volatile oils from the wood by this 

 simple agency. The finely divided resinous wood 

 is subjected to the action of saturated or super- 

 heated steam in suitable retorts for several hours, 

 until the greater portion of the crude turpentine 

 has been carried over. The volatile oils are readily 

 separated from the aqueous layer in the distillate 

 and by a series of fractional distillations in a col- 

 umn still the end products, wood turpentine and 

 pine oil, are isolated in a favorable state of purity. 



9 



