Mercurial BALLS, in Pharmacy, are an amalgam of mercury and tin, sufficiently solid to be moulded, and to preserve a given form. The method of making them is by adding mercury to melted tin, and pouring the fluid mass into a round hollow mould. These balls are employed to purify water, in which they are boiled; for which purpose travellers often carry some along with them. Nothing, however, can be more pernicious than such a practice, should the water contain any nitrous acid, which it very often does.