30 



differs from gum turpentine in all its properties. Turpentine pro- 

 duced by destructive distillation has a pungent, smoky odor, which 

 the most careful refining will not entirely eliminate, and is usually 

 more highly colored than the steam-distilled product. 



The general character of the turpentine is determined largely, 

 therefore, by the method of production, but it is further modified 

 by the care with which it is refined. Every precaution should be 

 taken to insure that the temperature does not rise sufficiently high 

 to drive over the heavy oils. If the refining still is heated directly 

 with fire, a thermometer may be placed in the liquid and the heat 

 so regulated that its temperature does not rise above 220 C. ; or, 

 if the still is properly constructed, the product may be controlled by 

 taking the specific gravity of the distilled and cooled turpentine with 

 an accurate hydrometer. 



If the crude turpentine is steam refined by passing a current of 

 live steam through it, water and turpentine distil together at from 

 97 to 99 C., and after the lighter portions of the crude oils have 

 distilled, heavier oils, which are always present in crude steam- 

 distilled turpentine (owing to the fact that these oils distil below 

 100 C. w r hen mixed with water), are also carried over, and these, in 

 proportion to the quantity present, seriously affect the specific grav- 

 ity, drying properties, and odor of the refined products. It is of the 

 utmost importance, therefore, that toward the close of the distilla- 

 tion the specific gravity be carefully noted, using an accurate hydrom- 

 eter, and when the gravity of the last portions distilling has risen to 

 0.875 the distillate should no longer be collected as turpentine. 



By whatever method it is refined, the redistilled turpentine should 

 be stored in a reservoir into which a large quantity is run, and from 

 which it is barreled from time to time. With these precautions, the 

 turpentine will be uniform in specific gravity, color, odor, flash point, 

 and drying properties, and will agree closely in many of the physical 

 tests with gum spirits, from which it will differ more or less in odor 

 and color, according to the method, of production. 



PINE OILS. 



In redistilling, below the temperature of 250 C. in the retort, the 

 crude oils obtained in the distillation of resinous woods, there is no 

 sharp distinction in properties or composition to be drawn between 

 the oils obtained. Thus the oils that pass above 185 C. differ from 

 the last fraction of turpentine but little; indeed, there is no clear-cut 

 distinction in these oils until rosin begins to break up into rosin 

 spirits and rosin oils. For convenience, therefore, all these oils dis- 

 tilling above turpentine (185) and below the temperature at which 

 rosin " breaks up" may be classified as pine oils, and they may be 



[Cir. 36] 



