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s as a yellow amorphous substance, C14H10O9, having an astringent taste, and forming with ferric salts a bluish-black compound, which is the basis of common ink. Called also tannin, and gallotannic acid.

The double cyanide of ferrous and ferric iron, a dark blue amorphous substance having a coppery luster, used in dyeing, calico printing, etc. Cf. Prussian blue, under Prussian.

he consistency of oil. -- Red vitriol, a native sulphate of cobalt. -- Vitriol of Mars, ferric sulphate, a white crystalline substance which dissolves in water, forming a red solution. -- White vitriol, zinc sulphate, a white crystalline substance used in medicine and in dyeing. It is usually obtained by dissolving…