Oleum Betulae lentae. - Birkenrindenol (Wintergrunol). - Essence de Betula.
Origin and Production. Sweet birch, black birch or cherry birch, Betula lenta, L. (family Betu/aceae), is a tree 15 to 20 m. in height that grows in good forest soil throughout southern Canada and the northern United States, westward as far as Minnesota and Kansas and southward as far as Georgia and Alabama.
The oil is mostly distilled in Tennessee, in the north western counties of Ashe, Watanga and Mitchell, also in the south eastern part of the state. As a rule there are about 10 to 20 trees on an acre. These the distiller occasionally buys for 10 cts. a piece.
The trees, which have a diameter of 12 to 24 inches, are cut down while the sap is in the trunk and are deprived of their bark. This is comminuted with the aid of a cutting machine. Frequently, so-called mountain tea or wintergreen is added, occasionally the twigs are also used for distillation.
The still is of the most primitive type. It is made of planks and is about 21/2 ft. wide, 3 ft. deep and 7 to 8 ft. long. The bottom consists of galvanized iron, is nailed to the wooden box and made watertight. The still is placed on a stone foundation which serves as fire-box. The bark rests on a false bottom of laths, which is about 4 in. above the iron bottom. Iron pipes about one inch in diameter connect the still with the condenser, which is fed by the water of a creek. The receiver consists of a tin can which stands in a larger container. The water which flows over and is saturated with oil is returned to the still by a separate pipe.
The principal season for distillation is from May to the latter part of September.
As soon as the distiller has obtained about 2 to 10 lbs. of oil, he sells it to the nearest general merchant. Occasionally he goes somewhat farther in order to obtain a better price. These merchants send the oil either direct to New York or sell it to herbalists.
The oil enters the market at Wilkesborro (North Carolina), Lenoir, Elk Park and Marion, Virginia, also at Abingdon, Virginia and Johnson City, Tennessee1).
W. Procter2) had already observed that the volatile oil does not occur as such in the bark, but results by the interaction of two substances in the presence of water, similar to the formation of bitter almond oil, of mustard oil and other ferment oils. According to later investigations, these two substances were found to be the enzyme betulase3) and the glucoside gaultherin4) which crystallizes with 1 mol. of water. The latter is hydrolyzed to sugar and methyl salicylate.
These changes must be taken into consideration in the production of the oil. According to Kennedy5) a twelve hour's maceration should precede the distillation in order to obtain a satisfactory yield. Every ton of 2240 lbs. of birch bark should yield about 5 lbs. of oil = 0,23 p. c, whereas a like amount of wintergreen leaves yields about 18 lbs. of oil = 0,83 p.c. A more rationally conducted distillation, however, may yield as much as 0,6 p.c. of oil.
In order to ascertain the most favorable conditions for the production of the oil, E. F. Ziegelmann6) made a series of experiments. The best results were obtained when working with small amounts, 0,62 p.c. being obtained after a twelve hour maceration period at room-temperature. Longer standing did not influence the yield. If the maceration was conducted at 40 to 50°, the yield was somewhat smaller. When distilled without previous maceration, the yield was much smaller. When working with larger amounts, birch bark yielded 0,306 p.c. Upon cohobation of the aqueous distillate an additional amount of 0,076 p.c. of oil was obtained.
1) Report of Schimmel & Co. October 1900, 64. 2) Americ. Journ. Pharm. 15 (1843), 241.
3) A. Schneegans, Journ. d. Pharm. v. ElsaB-Lothr. 23 (1896), No. 17; Chem. Zentralbl. 1897, I. 326.
4) A. Schneegans and ). E. Gerock, Arch. der Pharm. 232 (1894), 437. 5) Americ. Journ. Pharm. 54 (1882), 49.
6) Pharm. Review 23 (1905), 83.
Properties. Inasmuch as sweet birch oil and wintergreen oil have practically the same properties, the two oils were not always kept apart formerly, moreover birch bark and wintergreen leaves were frequently distilled together. Since 1906, the Pure Food and Drugs Act demands that they be kept distinct in the United States, the designation of sweet birch oil as wintergreen oil being regarded as a violation of the law.
Sweet birch oil is a colorless or yellowish liquid which is at times colored red by traces of iron. As to odor and taste it can scarcely be distinguished from methyl salicylate; its odor differs, however, materially from that of Gaultheria procumbens. The sp. gr. fluctuates between 1,180 and 1,1881). Whereas gaultheria oil is slightly laevogyrate, sweet birch oil is optically inactive. With 5 to 8 vol. of 70 p.c. alcohol, it yields a clear solution at ordinary temperature. In moderately concentrated solution of potassium hydroxide, it dissolves readily with the formation of the readily soluble so-called potassium ester salt. From this solution it can be separated unchanged upon the addition of acids. The so-called sodium ester salt, however, is difficultly soluble. When heated with an excess of alkali, both ester salts are saponified.
Water shaken with sweet birch oil yields a deep violet color with ferric chloride. When distilled over a direct flame, sweet birch oil passes over between 218 and 221°.
Composition. As already pointed out, no distinction was formerly made in commerce between sweet birch oil and gaul-theria oil, indeed this holds true to a large extent to-day. Hence it is doubtful whether the salicylic acid of A. Cahours2) was discovered in a sweet birch oil or in a gaultheria oil. However, it may be definitely assumed that Procter made a distinction between the two oils. It is also certain that Cahours worked with an adulterated oil, for he found 10 p.c. of a terpene boiling at 160° (presumably turpentine oil), which he designated gaul-therilene. From recent investigations, however, made with unquestionably genuine oils, it is evident that neither of the oils contains terpenes.