Water-BALLS, those which swim and burn a considerable time in the water, and at length burst therein. These are made in a wooden shell, the cavity of which
is filled with refined saltpetre, sulphur, saw-dust boiled in water of saltpetre, and dried; to which sometimes other ingredients are added, as iron filings, Greek pitch, amber dust, powdered glass, and camphor. The ingredients are to be ground, mixed up, and moistened with linseed oil, nut oil, olive oil, hempseed oil, or petrol. At the bottom is placed an iron coffin, filled with whole gunpowder, that the ball may at last burst with a greater noise: and, lastly, the ball is by the addition of lead or otherwise, made of the same specific gravity with water.