Canada Pitch. Pix Canadensis. U. S. 1880. Hemlock Pitch.—The Tsuga canadensis (L.) Carr, Hemlock or Hemlock Spruce of the United States and Canada, when of full growth, is often seventy or eighty feet high, with a, trunk of two or three feet in diameter, and of nearly uniform dimensions for two-thirds of its length. Its leaves are scattered, short, linear, obtuse, from 8 to 13 mm. in length, whitened beneath and appearing as two-ranked. The strobiles are ovate, little longer than the leaves, terminal and pendulous.
The tree is abundant in Canada, Nova Scotia, and the more northern parts of New England, and is found in the elevated and mountainous regions of the Middle States. Its bark is much used for tanning, an extract being made for the purpose. The tree contains much less juice than some other of the Pinaceae, and very little flows from incisions made into its trunk. But in the trees which have attained their full growth, and are about to, or have begun to, decay, the juice exudes spontaneously, and hardens upon the bark, in consequence of the partial evaporation or oxidation of its volatile oil. The bark thus incrusted is stripped from the tree, broken into pieces, and boiled in water.' The pitch melts, rises to the surface, is skimmed off, and is still further purified by a second boiling in water. Hemlock pitch is hard, brittle, quite opaque, of a dark reddish-brown color, becoming still darker by exposure to the air, of a weak peculiar odor, and scarcely any taste. It softens and becomes adhesive with a moderate heat, and even at ordinary temperatures takes the form of the vessel containing it, and melts at 92.2° C. (198° F.).
The constituents of this pitch are resin and a minute proportion of volatile oil. It is sometimes known by the incorrect name of 'hemlock gum. Canada pitch is a gentle rubefacient, closely analogous to Burgundy pitch in its properties, and employed for precisely the same purposes. It is, however, more readily softened by heat, and is sometimes almost too soft for convenient application at the temperature of the body. A volatile oil obtained from Tsuga canadensis, and called oil of spruce or oil of hemlock, has been employed to & considerable extent in veterinary liniments. It has also been used as an abortifacient, with the effect of endangering the life of the woman. (J. S. Paige, N. Y. M. J., viii, 184.)
W. Zinn (M. M. W., Oct., 1902) reports a case of stupor and involuntary evacuation of urine, and collapse with subsequent psychic disturbance, as produced by the inhalation for many hours of the emanations from branches of Pseudotsuga taxifolia (Lamb.) Britton. (P. Douglassi Car.).
The U. S. Pharmacopoeia of 1880 gave the following directions for preparing the Hemlock or Canada Pitch Plaster (Emplastrum, Picis Canadensis, U. S., 1880) : "Canada Pitch, ninety parts [or nine ounces av.]; Yellow Wax, ten parts [or one ounce, av.], to make one hundred parts [or ten ounces av.]. Melt them together, strain the mixture, and stir constantly until it thickens on Cooling." U. S., 1880.
The Dispensatory of the United States of America, 1918, was edited by Joseph P. Remington, Horatio C. Wood and others.