This section is from the book "A Treatise On Beverages or The Complete Practical Bottler", by Charles Herman Sulz. Also available from Amazon: A Treatise On Beverages.
Wintergreen oil enters largely into the composition of many beverages, both carbonated and fermented. It is distilled from the leaves Gaultheria procumbens, while fresh, with water or the aid of steam. It is largely made in New York, Pennsylvania, and some of the New England States. The average yield is about from 0.5 to 0.8 per cent. When wintergreen is scarce, the young shoots of sweet black or cherry-birch (see Oil of Birch) are often used as a substitute. Kennedy (1882) showed that much of the commercial oil of wintergreen is obtained therefrom, the shoots being distilled after having been cut into short pieces, and subjected to brief maceration with water.
Oil of wintergreen is usually of a reddish color, but may be obtained colorless by rectification. According to Leonard (1884), the color is usually due to the presence of a little iron, and is readily removed by citric acid. It has a strong and agreeable aromatic odor, and a sweetish, warm, aromatic taste, and begins to boil at a little above 200° C. (392° F.). It is the heaviest of the volatile oils, its density being 1.180 at 15° C, which is also that of oil of sweet birch. - (N. D.) Kennedy, however, asserts that the specific gravity of oil of gaultheria is 1.0318, and that of birch 1.180. The oil is neutral or faintly acid to test paper, and dissolves readily in alcohol, and but to a small degree in water. Proctor (1842) recognized the presence of salicylic acid in this oil, but Cahours (1843) proved it to consist to the amount of about 90 per cent, of methyl salicylic acid (methyl salicylate or mono-methyl salicylic ether), which is now also artificially prepared for use in the arts. Pettigrew (1883) showed the oil of sweet birch to be pure methyl salicylate, and to boil constantly at 218° C. (424.4° F.). Where oil of wintergreen or birch is used, if they are good, there is no occasion for using salicylic acid as a preservative, as the oil itself, if pure, is an antiseptic.
The great density of this volatile oil prevents its adulteration with most cheaper ones, which would reduce its specific gravity. A mixture of alcohol and chloroform has been employed for the purpose, but is readily detected by the low boiling point, and the character of the first fractional distillate. The most common adulterant is oil of sassafras, which is colored dark-red, and converted into a brown-red resinous mass by strong nitric acid. The pure oil yields nearly colorless crystals of methyl nitro salicylate. - N. D. When heated to about 80° C. (176° F.) the oil should not yield a colorless distillate having the characteristics of chloroform or of alcohol. On mixing five drops of the oil with five drops of nitric acid, the mixture should not acquire a deep-red color, and should not solidify to a dark-red, resinous mass (absence of oil of sassafras). - U. S. P.
It is said that oil of wintergreen is frequently adulterated with camphor oils, and three methods for testing for the adulterant are given. First, specific gravity test. Oil of wintergreen has a specific gravity of 1.180, camphor oil, 0.900. Second, gently agitate a few drops of the suspected oil in water; if it be pure it wholly subsides in a few seconds, but if it contains camphor oils, several minutes elapse before it subsides, and time is given to notice that the particles of oil assume different forms, other than globular. Third, nitric acid changes the color of adulterated oil to red, but has little effect upon pure oil.
This artificial product is obtained by heating a mixture of methyl (wood) alcohol, sulphuric and salicylic acid. The rising ether is treated with water, and separates as the artificial wintergreen oil. It is said that it does not differ in its properties from the natural oil. We understand that it is made in Germany, minus the terpene present in the natural oil. The quality of the artificial oil is said to be at least equal to that of the natural, and its price is lower, whereby all competition of the natural oil would be excluded. Some experts expressed the opinion that the artificial oil will in the future displace nearly all the natural oil, and that the artificial product answers very well, while still others are against it. The artificial oil has the color and density of pure oil, but it is claimed, that by close application to the nose, a distinct odor of wood alcohol will be noticed in the synthetic article. We think (from a chemical point of view) that if the artificial product is properly prepared, it will answer for the natural product; however, we reserve our opinion until the artificial product has gone through experimental practice.
This is identical with the essence of birch. Oil of wintergreen, or birch, one ounce; alcohol 95°, eight ounces; water, eight ounces. Cut the oils as directed.