Platin chloride throws down a reddish crystalline precipitate, soluble on warming; and gallic acid gives a flocculent precipitate.
For ink-making the tannin has first to be transformed into gallic acid.
The gallic acid will fall down in crystals as the liquid cools.
gallic acid acts in the same manner, but yet more feebly than tannin.
Chemists have extracted from it an astringent liquor containing tannin and gallic acid.
The image is to be brought out with gallic acid and acetic acid, laid over with a brush, and requires no heat.
It contains a little tannic acid, gallic acid and a volatile oil.
The water of the former is strongly impregnated with iron, that of the latter with gallic acid.
Contains neither tannic nor gallic acid, but abounds with a yellow, bitter principle, soluble in water and alcohol.
The texture of the paper was not injured, but the iron basis of the ink, as well as the gallic acid, was entirely removed.