1863 The manufacture of liquors, wines, and cordials

MANUFACTURE OF VINEGAR.

278

white precipitate, if nitric acid be present

an im-

probable may be detected by its producing a yellow color when boiled with indigo. The acrid substances usually introduced into vinegar are red pepper, long pepper, Guinea pepper, pelli- tory, and mustard. These may be detected by eva- porating the vinegar to an extract, which will have an acrid, biting taste, if any one of these substances should be present. By far the most dangerous impurities in vinegar are copper and lead. The former may be detected by a brownish precipitate on the addition of ferro- cyauuret of potassium to the concentrated \inegar. The latter by a blackish precipitate with sulphuret- ed barium, and a yellow one with iodide of potas- sium. Pure vinegar is not discolored by sulphureted hydrogen. The essential ingredients of pure vinegar are acetic acid and water ; but, besides these, it con- tains various other substances derived from the particular vinous liquor from which it may have been prepared. Among these may be mentioned coloring matter, gum, starch, gluten, sugar, a small portion of alcohol, and frequently malic and tartaric acids, with a minute proportion of alkaline and earthy impurity. It

salts.