EXAMINATION OF VINEGAK. 213 



Vinegar prepared from spirits of wine leaves, when carefully 

 evaporated in a porcelain dish, a very small residue of a whitish 

 or very slight yellow color, which chiefly consists of the salts 

 contained in the water used for the preparation of the alcoholic 

 liquid, an accurate examination showing it to consist of calcium 

 acetate, gypsum, and a very small quantity of sodium chloride. 

 If the residue is of a dark brown color, swells up when heated, 

 and leaves a lustrous black coal, the vinegar has been colored 

 with sugar color. 



Beer and malt vinegars are dark yellow, generally with a red- 

 dish shade. On account of their content of dextrin they foam 

 when shaken, and, when carefully evaporated, leave a brown, gum- 

 like residue. The latter consists chiefly of dextrin, and contains, 

 besides, the other extractive substances occurring in beer and 

 malt vinegar, such as salts of ashes, especially much phosphoric 

 acid. On heating strongly an odor calling to mind that of 

 toasted bread is evolved. At a still higher temperature the resi- 

 due turns black and finally acts like caramel : it evolves pungent 

 vapors and leaves a lustrous coal. 



The great content of phosphoric acid characteristic of malt or 

 beer- vinegar may also serve for the determination of the deriva- 

 tion of such vinegar. By compounding beer or malt- vinegar 

 with some nitric acid and a solution of ammonium molybdate 

 and heating, the fluid, after standing, separates a yellow precipi- 

 tate, which contains the phosphoric acid present in the fluid. 



Wine-vinegar is best recognized by its characteristic odor, the 

 latter becoming especially perceptible by rinsing out a large tum- 

 bler with the vinegar, and after allowing it to stand for a few hours 

 examining the odor of the few drops remaining in the tumbler. 

 The greater portion of the acetic acid having then volatilized 

 the vinous odor becomes more prominent. Cider-vinegar, the 

 odor of which is somewhat similar to that of wine-vinegar, can 

 in this manner be plainly distinguished from the latter, the residue 

 in the tumbler having an entirely different odor. 



The presence of potassium bitartrate is a characteristic sign 

 of wine-vinegar. By evaporating wine-vinegar to a brownish 

 syrupy mass, boiling the latter with some water, rapidly filter- 

 ing the boiling fluid into a test tube, and adding double its volume 



