Pickles.—These should be of a dull-green color. The bright emerald green sometimes observed is due to the presence of the salts of copper; this may be proved by dipping the blade of a penknife in the liquor, as described under the heading of "Canned Goods."
Alum is sometimes used as a preservative and in order to make the pickles crisp. Its presence may be demonstrated by means of the "logwood" test mentioned under the heading of "Flour."
VINEGAR.—Cider vinegar is of a brownish-yellow color and possesses a strong odor of apples.
Wine vinegar is light yellow if made from white wine, and red if made from red wine.
Malt vinegar is brown and has an odor suggestive of sour beer.
Glucose vinegar has the taste and odor of fermented sugar.
Molasses vinegar has the distinctive odor and taste of molasses.
OLIVE OIL.—Pure olive oil has a pleasant, bland taste and a distinctive and agreeable odor, unmistakable in character for that of any other oil. The finest virgin oil is pale green in color, the cheaper grades are light yellow.
The adulterants consist of cotton-seed, corn, mustard, and peanut oils.
When pure olive oil is shaken in a glass or porcelain dish with an equal quantity of concentrated nitric or sulphuric acid[7] it turns from a pale to a dark green color in a few minutes; if under this treatment a reddish to an orange or brown color is produced the presence of a foreign vegetable oil is to be suspected.