This blue appears to the consumer in the form of crystals or coarse
powder of a purplish tint. It is not universally used among feather
dyers, although it is the most reliable aniline blue in use. It is used
in conjunction with oxalic acid to develop. It is fast to light, and
possesses a great many advantages of value. It is soluble in water,
either hot or cold, and is used in the production of the palest shades,
as well as in the darkest navy blues.