There are various processes for obtaining gallic acid, one of which is to moisten the bruised galls and expose them for four or five weeks to a temperature of 80 degrees Fahr.; by which a mouldy paste is formed, which is pressed dry and then digested in boiling water, which after evaporation yields the acid, and mixed with the solution of green copperas, makes the, ink. A quicker process, however, is to put the bruised galls into a cylindrical copper of a depth equal to its diameter, and boil them in nine gallons of water--taking care to replace the water lost by evaporation. The decoction to be emptied into a tub, allowed to settle, and the clear liquid being drawn off, the lees are emptied into another tub to be drained. The green copperas must be separately dissolved in water, and then mixed with the decoction of the galls. A precipitate is then formed in the state of a fine black powder, the subsidence of which is prevented by the addition of the gum, which, separately dissolved in a small quantity of hot water, combines with the clear black liquid. Besides its effect in keeping the fine insoluble particles in suspension, the gum mucilage improves the body of the ink, prevents its spreading or sinking too much into the paper in writing, and also acts beneficially by forming a sort of compact varnish in it, which tends to preserve its colour, and shield it from the action of the air. If, however, too much mucilage is used, the ink flows badly from quill pens, and still more so from steel pens, which require a very limpid ink. The addition of sugar increases the fluidity of ink, and permits the quantity of gum to be increased over what it would bear without it; but, on the other hand, it causes it to dry more slowly, and besides it frequently passes into vinegar, when it acts injuriously on the pens. The dark- coloured galls, known as the blue Aleppo ones, are said by Ribaucourt, and others who have given much attention to the ingredients for ink-making to be the best for that purpose, and they are generally used by the best makers.