« EdellinenJatka »
Turpentine No. 27-A refined steam turpentine...
FIG. 1. Percentage weight-steam temperature curve for a mixture of two oils distilled in the ordinary manner................
2. Percentage weight-steam temperature curve for a mixture of two oils
3. Percentage weight-steam temperature curve for a nearly pure oil
4. Apparatus used in turpentine analysis...
5. Working drawing of dephlegmator...........
6. Percentage weight-specific gravity curve for a gum turpentine....
10. Percentage weight-index of refraction curve for a crude steam-distilla-
11. Percentage weight-steam turpentine curve for a crude steam-distilla-
12. Percentage weight-specific gravity curve for a refined steam-distilla-
13. Percentage weight-index of refraction curve for a refined steam-distillation turpentine..............
14. Percentage weight-steam temperature curve for a refined steam-dis
15. Percentage weight-specific gravity curve for a crude destructive-dis
16. Percentage weight-index of refraction curve for a crude destructive-
17. Percentage weight-steam temperature curve for a crude destructive-
This work was begun at the Sheffield Scientific School of Yale University, New Haven, Conn., where a laboratory was placed at the disposal of the Forest Service through the courtesy of Prof. Russell H. Chittenden, director, to whom acknowledgments are made.
THE ANALYSIS OF TURPENTINE BY FRACTIONAL DISTILLATION
FORMER METHODS OF TURPENTINE ANALYSIS.
In the course of the studies by the Forest Service concerning the utilization of waste yellow pine wood by distillation processes," it was found that the "wood turpentines" produced by these methods were extremely variable in composition and properties, and that an accurate method for comparing and grading them was very necessary for the further progress of the work. Most of the methods of turpentine analysis in use were devised simply to detect adulterations in gum turpentine, and there was no satisfactory method applicable to all classes of turpentines which would give an accurate idea of their relative compositions and characteristics. Fractional distillation with subsequent examination of the individual fractions appeared the best for this purpose, but some modifications seemed advisable. This general method is ordinarily carried on as follows: The liquid to be distilled is heated in a flask, the vapors are condensed, and the distillate is collected in several portions or fractions; the temperatures between which the various fractions distill are recorded, and sometimes one or more physical properties of the fractions are determined. In this manner a general idea of the composition of a turpentine can be obtained, but, as will be shown later, the completeness of the separation, the ease of interpretation of the results, and the reliability of the data can be increased by extending and modifying the ordinary
The four following important changes were made:
(1) A new still head was introduced.
(2) Steam distillation was used instead of the ordinary distillation
with direct heat.
(3) The graphical method of expressing results was employed. (4) More physical properties were determined.
These changes will be discussed in order.
(1) If a mixture of two liquids with different boiling points be distilled, each of the first fractions will contain a larger proportion of the
a Forest Service Circular 114, "Wood Distillation.??
lower boiling liquid, and each of the last a larger proportion of the higher boiling liquid; all the fractions will contain both liquids in varying proportions, and it will be impossible to separate the two liquids completely by one such distillation. By repeated distillations of the several fractions, however, and by combination of those fractions which distill between the same temperatures, a fairly complete separation can eventually be made. This is usually a long and tedious operation and not readily applicable to an analytical method.
By taking advantage of the well-known principle of dephlegmation these difficulties are largely removed and in many cases one operation will suffice to separate two liquids in practically pure condition. This principle is applied by placing between the distilling flask and the condenser a new form of column still head or dephlegmator (fig. 4). This is of such construction that the vapors are partly condensed before they reach the condenser, and the uprising vapors are therefore washed by the reflowing liquid. When a mixture of light and heavy a oils, such as might occur in turpentines, is distilled through this apparatus, the tendency is for the vapors of the light oil to pass freely out into the condenser, while the vapors of the heavy oil are condensed and return to the still, to be carried over only after all the light oil has been distilled. The results are the same as though repeated distillations were made.
(2) When distilling high boiling oils over a direct flame, it is difficult to regulate the temperature, and there is always danger of superheating. It is true that this superheating may be slight when the distillation is carefully carried on, but if the operation is hastened the danger may be greatly increased. In the case of turpentine and other liquids which contain unstable substances, like terpenes, superheating may cause decomposition or alteration of the oil, and for this reason a study of the properties of the distillate may not clearly show the composition of the original oil.
Not only does superheating tend to cause decomposition of the turpentine, but it introduces errors in temperature readings. Further, the rate of distillation may not be constant. These several sources of error involved in an analysis by ordinary direct heat distillation can be largely eliminated by distillation with steam, since the process can be carried on at a much lower temperature and with a more certain regulation.
The fundamental principles of distillation with steam may be outlined as follows: If a pure liquid, such as benzine, which does not dissolve in water be placed in a flask and water added, the two will upon
a "Light" and "heavy" are terms used synonymously with low boiling and high boiling. The terms arise from light and heavy weight—that is, low and high specific gravity which usually accompany low and high boiling points respectively.