METALLIC IMPURITIES
Vinegars containing free mineral acids are sometimes found to contain poisonous metals.
Evaporate 200 to 400 cc. of the vinegar to dryness, add a little sodium hydroxid to this residue and burn to an ash over a low flame. It may be necessary to add a little potassium nitrate once or twice. Add a little dilute hydrochloric acid and saturate with hydrogen sulfid and test for lead, zinc, copper, and arsenic according to [Allen’s method] given under canned meats.
Spices to Increase Pungency
Leach.—Neutralize a portion of the vinegar with sodium carbonate. The presence of spices is easily detected by tasting this mixture.
Another Test.—Exactly neutralize a little of the vinegar as above, evaporate to smaller bulk and taste as before, then shake the concentrated liquid with ether, separate the ethereal layer and evaporate it, and taste the residue.
Tartar in Wine Vinegar
The presence of tartar in vinegar proves it to be wine vinegar.
Allen’s Method.—Evaporate a portion of the vinegar and treat the residue with alcohol; a granular residue of tartar remains undissolved. To prove that it is tartar, decant the alcohol and dissolve the residue in a little hot water, cool, rub the inside of the vessel with a glass rod, and if tartar was present acid potassium tartrate will be deposited where the rod touched the vessel. The test will be more sensitive if an equal volume of alcohol is added.
Free Tartaric Acid in Wine Vinegar
Test as for Tartar.—Treat the alcoholic solution of the extract with an alcoholic solution of potassium acetate. Rub the sides of the vessel as before, and if tartaric acid is present the streaks and sometimes a precipitate forms where the rod touches the vessel.