212 VINEGAR, CIDER, AND FRUIT-WINES. 



little importance in a hygienic respect, that of copper, zinc, or tin 

 is more serious, the combinations of these metals having a poison- 

 ous effect upon the organism. Copper can be detected in vinegar 

 by evaporating to dry ness about 1 quart of the vinegar to be 

 examined and dissolving the residue in a few drops of nitric acid. 

 By compounding a portion of this solution with ammonia in 

 excess the fluid acquires a perceptible blue coloration in the 

 presence of copper; the latter can be shown with still greater 

 sharpness by dipping polished iron into another portion of the 

 fluid. If the iron becomes coated with a perceptible red film 

 (consisting of actual copper), the presence of this metal is shown. 

 Tin. Evaporate to dryness at least 2 or 3 quarts of the vine- 

 gar ; dissolve the residue in hydrochloric acid, and conduct sul- 

 phuretted hydrogen through it until the fluid has acquired a 

 strong odor of the latter. If a precipitate is formed, it is filtered 

 off, dissolved in strong hydrochloric acid, and the solution divided 

 into several portions. Compound one of these portions with 

 dilute solution of chloride of gold ; if after some time it becomes 

 rod and precipitates red flakes, the vinegar contains tin. The 

 presence of tin is also indicated if another portion of the solution 

 of the precipitate in hydrochloric acid does not acquire a blue 

 color after the addition of potassium ferrocyanide. The behavior 

 of the fluid towards solution of potassium permanganate may 

 serve as a controlling test ; if the fluid contains tin, the solution 

 of potassium permanganate becomes discolored. 



Determination of the Derivation of a Vinegar. 



The examination of a vinegar as regards the materials used in 

 its preparation is generally effected by the senses of odor and taste ; 

 there are, however, many easily executed tests which assist the 

 judgment of the tongue and nose. 



Vinegar prepared from dilute spirits of wine is colorless or only 

 colored slightly yellowish. If such vinegar has a dark yellow 

 color resembling that of wine, it is generally due to the addition 

 of sugar color, the addition being chiefly made on account of the 

 erroneous opinion prevailing among the public that vinegar clear 

 as water or only slightly colored lacks strength. 



