Quercitron, a dyestuff, the bark of the black oak, quercus coccinea, var. tinctoria (Q. tinctoria of authors), in some localities called the yellow-barked oak. (See Oak.) The black outer portion of the bark being removed, the inner portion is found to contain a coloring principle which stains the saliva yellow when the bark is chewed; this is extracted by boiling water, giving to it a brownish yellow color, which is deepened by alkalies and brightened by acids. The bark is largely employed in-the United States as a dye, and it is also reduced to a coarse powder and shipped to Europe in great quantities for the same use, particularly in calico printing. When this decoction has been deprived of tannin by means of glue, a fine yellow color is obtained upon fabrics mordanted with alum, and various shades of olive with iron mordants. The coloring principle is called quercitrine, or from its acid reaction quercitric acid. Black-oak bark is used for tanning also, but its yellow color makes it objectionable. Its astringent and tonic properties have led to its use in medicine, but white-oak bark, having similar medical properties without the color, is preferred.