According to Medinger and Michel,1 when 15 c.c. of wine are shaken with a few c.c. of concentrated solution of sodium nitrite, a bright yellow or yellowish-brown coloration is obtained if the wine is pure, whereas cider or perry is coloured dark-brown or brownish-black, and a brownish-black precipitate separates. This precipitate is insoluble in water, alcohol, or ether, but dissolves to a red solution in aqueous alkali. Wines when treated with both sodium nitrite and potassium hydroxide give a yellow coloration, whilst cider and perry and mixtures of these with wine yield a pure red coloration.

1 Chem. Zeit, 1918, 42, 230. See also Schulte, ibid., 537, 557,