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.
This volatile oil is obtained from Betula Lenta, sweet, black or cherry-birch, which is indigenous to Canada and the northern part of the United States, but grows in the mountains as far south as Georgia. The bark and leaves yield a volatile oil, which Procter (1843) found to be identical with oil of gaultheria or wintergreen, and which Kennedy showed is largely sold in place of the latter (see Oil of Winter-green). Pettigrew (1883) found it to be pure methyl salicylate, and to have the spec. gr. of 1.180 at 15° C, and the boiling point to be constant at 218° C. (424.4° F.).
In regard to adulterations see Oil of Gaultheria or Wintergreen.