The process to detect the presence of alum in wine, is to take some fresh prepared lime-water, and to mix the suspected wine with it, in about equal proportions; if after the mixture has stood about a day, a number of crystals is found deposited at the bottom of the vessel, the wine is genuine; but, if alum is present in the wine, there will be no crystals, but a slimy and muddy precipitate. Or the presence of alum may be detected, by dropping some solution of subcarbonate of potash into the wine, when, if the alum be present, there will be a violet coloured precipitate, or at least cloudiness, which will vanish again if a few drops of caustic, potash, or of muriatic acid are added to the mixture. Where artificial colouring matter is suspected in wine, put a quarter of a pint of the liquor into a phial, with an ounce of fresh charcoal finely pulverized. Then shake the mixture well for a few minutes, when, if the wine is impregnated only with its own natural colouring, that colour will be chemically destroyed, and the wine, when filtered, will yield a clear limpid fluid; but, if the wine is artificially coloured, such artificial colours will not be acted on by the charcoal, and the mixture will appear unchanged. Extraneous colours in wines may also be detected by means of acetate of lead. If this test produces, in red wine, a greenish grey precipitate, it is a sign that the wine is genuine. Wine coloured with the juice of bilberries, or elderberries, or Campeachy wood, produces, with acetate of lead, a deep blue precipitate; and fernambouk wood, red saunders, and the red beet, produce a red precipitate by the agency of the acetate of lead. According to Cadet (Dictionnaire de Chimie, art. Vin.) this species of adulteration may be detected by pouring into the suspected wine a solution of sulphate of alumine, and precipitating the alum by potash. If the wine is pure, the precipitate will have a bottle green colour, more or less dark, according to the natural hue of the wine. But if the colour has been artificial the following will be the results:— Tournesol will give a precipitate of a bright yellow colour. Brazil wood a brownish red colour. Elderberries or privet a brownish violet colour. Wortleberries the colour of dirty wine lees. Logwood a lake red colour.