FLAVIN is an extract or preparation of quercitron bark (Quercus tinctorza), used as a yellow dye in place of the ground and powdered bark. Flavin is not a definite chemical compound, and the commercial product is found to vary greatly in composition and tinctorial value, according, probably, to the nature of the varied processes employed in its preparation. The manufacture of flavin is principally carried on in the United States under various patents; and while some kinds appear to be little other than finely powdered and sifted bark, others are almost pure quercitrin, the chemical principle peculiar to quercitron bark. A kind of flavin made in England is obtained by exhausting the bark in a weak alkaline solution, and precipitating the colouring matter by neutralization with either sulphuric acid or hydrochloric acid. Flavin of good quality ought to possess about 16 times the tinctorial strength of the bark from which it is extracted.