Oxalic acid, a most powerful acid, occurs combined chiefly with potash
juices of plants of the genus _oxalis_ and _rumex_. Artificially it
was obtained by the action of nitric acid upon sugar and starch, but
has been prepared latterly by treating spent dyestuffs with alkalies.
Oxalic acid forms colorless transparent crystals, which are inodorous,
intensely sour, and do not grow moist upon exposure. Should they become
damp, some nitric or sulphuric acid, used in the preparation, has not
been thoroughly removed. It is soluble in its own weight of boiling
water, but requires about eight times its weight of water at 65° Fah.
Oxalic is one of the largely used acids in feather dyeing, being used
in a number of light colors for the purpose of developing the color.
In developing blues it is invaluable. Other colors it will totally
destroy, violet or safranine, for example; and it is used in place of
sulphuric acid for the purpose of extracting color.