Tonqua Bean (also written Tonquin, Tonga, and Tonka), an Asiatic name applied to a South American product, the seeds of dipterix odorata, a tree belonging to the leguminosm or pulse family. The genus dipterix (Gr. δίς, double, and πτερόν, a wing) comprises about eight species, all large trees of the forests of Brazil, Guiana, and neighboring countries, and belongs to a tribe of the family of which there are no representatives in northern localities; the trees have pinnate leaves and large panicles of flowers, which are succeeded by (what is very unusual in the family) a pod containing only a single seed. The Tonqua bean tree grows 60 to 90 ft. high, with a trunk sometimes 3 ft. in diameter; the indehiscent pods, about 2 in. long, are almond-shaped and very thick; the single seed is over an inch long, shaped somewhat like a large kidney bean; it has a wrinkled skin, which is shiny black. The odor, which is remarkably strong, resembles that of the me-lilot or sweet clover and the sweet-scented vernal grass (anthox-anthum), and is due to the same principle, coumarine, a concrete crystallizable, volatile, neutral substance, with the composition C18H6O4, very soluble in alcohol and ether, and somewhat so in boiling water, from which it crystallizes on cooling; the beans are often frosted with crystals of this, which show very distinctly on their black surface.
Formerly the beans were much used to scent snuff, and they are often called "snuff beans," a few of them being placed in a jar with the snuff, or a single one kept in the snuff box; they were also formerly used in smoking tobacco, but a much cheaper substitute is found in the "wild vanilla" (liatris odoratissima) of Florida. (See Vanilla.) The odor of the bean bears some resemblance to that of the true vanilla, and much of the extract of vanilla sold for flavoring ice cream and articles of cookery is adulterated with it, and in some of the cheaper flavoring extracts it is entirely substituted for that costly material; any one with a nice sense of smell can readily detect the least admixture. The wood of the Tonqua bean tree is remarkably close-grained, hard, and heavy, and, though redder, much resembles lignumvitae, and in some parts of South America it is called by that name; it is valued for fine cabinet work. Another species, D. eboensis, is the eboe tree, the fruit of which is without odor; its timber is hard and valuable.
Tonqua Bean (Dipterix odorata). Half of the one-seeded pod.