28 



oil may be again distilled to recover any alcohol it contains, leaving 

 the light wood oil, which is very inflammable and for which no profit- 

 able use other than burning has been devised. 



ADDITIONAL OILS OBTAINED FROM RESINOUS WOODS. 



Resinous woods are distinguished from hardwoods in yielding a 

 much larger percentage of oils when distilled. Some of these oils 

 exist naturally in the wood, while others are derived from the break- 

 ing up of natural resins. When wood is gradually heated as in de- 

 structive distillation, and the temperature in the retort rises above 

 100 C., these oils mixed with water begin to pass over or distil, and 

 continue with rising temperature until the distillation of the wood is 

 complete. The oil passing from the retort at any moment may be 

 different from that which passed previously and from that which fol- 

 lows it, so that in practice the distillate is a mixture of compounds 

 having closely related chemical and physical properties, and this 

 mixture increases in density and the boiling point rises with the 

 temperature in the retort. Below the temperature of 250 C. the 

 oils are almost colorless, and there is but little if any breaking up 

 of the natural resins, those that have distilled being naturally in 

 the wood. When, however, the temperature in the retort rises above 

 200 C., the wood substance begins to char,, giving to the products 

 their characteristic smoky odor. Consequently, in order to obtain a 

 turpentine free from this odor the temperature of the retort must not 

 rise above 200 C. until the turpentine is completely distilled.* At 

 approximately 250 C. or above the lighter resins begin to break up, 

 yielding oils which boil at from 97 to 250 C. When the tempera- 

 ture in the retort rises above 300 C. the heavy resins or rosin breaks 

 up, yielding 3 to 7 per cent of light oils, known commercially as " rosin 

 spirits" or "pinoline," boiling at from 97 to 250 C.; 75 to 85 per 

 cent of heavy oils, boiling at from 250 to 450 C., known as " rosin 

 oils," and water containing about 1 per cent of acetic acid. The oils 

 distilling above 200 C. are contaminated by products derived from 

 the breaking up of the wood substance, and these products mask 

 especially the odor of the oils specified so that they do not have the 

 characteristic rosin-oil odor. l3y proper methods of treatment and 

 fractional distillation oils of different physical and chemical proper- 

 ties may be obtained, and a number of such oils are on the market 

 under various trade names. Some cf these oils have not yet found a 

 regular sale, however, owing to the fact that their composition is not 

 definitely known. 



[Cir. 36] 



