VINEGAR. 65 



the number of cubic centimeters of alkali added in the first place and the number 

 of cubic centimeters needed to titrate the ash represents the equivalent of the free 

 acid present. 



11. DETERMINATION OF OXALIC ACID. 



The presence of oxalic acid may be detected and its quantity determined by 

 addition of a solution of calcium sulphate to a measured quantity of the vinegar. 



12. DETERMINATION OF ALCOHOL. 



Domestic fruit vinegars are often incompletely acetified; if the specific gravity be 

 abnormally low, a determination of the alcohol present is desirable. Owing to the 

 small quantities usually present, it is best to concentrate the distillates. Carefully 

 neutralize 100 cc of the vinegar and distill over 40 cc; redistill the distillate until 20 cc 

 has passed over; cool to 15.5 C. and make up to 20 cc with distilled water. Determine 

 the specific gravity by means of a pycnometer and calculate the percentage by weight, 

 by Table II. The percentage in the last distillate, divided by 5, represents the 

 amount in the original vinegar. 



13. DETECTION OF COLORING MATTERS. 



The principal coloring matter used for tinting imitation vinegars in America is 

 caramel. To detect this use Amthor's method (p. 120) . A further test of the caramel 

 may be made by boiling the aqueous solution of a portion of the precipitate obtained 

 by Amthor's method, with Fehling's solution; caramel has a reducing action. 



In the case of wine vinegars, test for foreign red colors may be made according to 

 the methods given on p. Ill and following. 



14. DETECTION OF FOREIGN PUNGENT MATERIALS. 



Exactly neutralize a portion of the vinegar (the residue from determination of 

 total acidity may be used), evaporate off a portion of the water, and test the concen- 

 trated solution by taste for pungent substances; then agitate the liquid with ether, 

 in a separatory funnel, remove and evaporate the ethereal layer, and apply the same 

 test to the residual ethereal extract. The perfect identification of the specific 

 substance employed is rarely attained. 



15. DETECTION AND DETERMINATION OF METALLIC POISONS. 



Evaporate from 200 to 500 cc to dryness. In case of cider, malt, and other vine- 

 gars rich in solids, add a little sodium hydroxid and potassium nitrate, and incinerate. 

 The ash thus obtained, or the solids themselves, in case of vinegars low in extract, 

 is carefully dissolved in hydrochloric acid and the solution subjected to examination 

 by methods indicated for the analysis of canned vegetables (p. 52). 



16. DETECTION OF PRESERVATIVES. 



Preservatives are sometimes, though rarely, added to vinegar. Salicylic and ben- 

 zoic acids may be separated by agitation with ether and detected in the residue left 

 upon evaporation of the ether. Boric acid may be detected in the ash left upon the 

 evaporation and incineration of the vinegar after neutralization by alkali. 



Most of the tests for the detection of formaldehyde are excluded from use in test- 

 ing vinegars, since the indicative reactions are usually produced by acetaldehyde also, 

 which is frequently present in normal vinegar. From 100 cc of the vinegar distill 

 20 cc. To a portion of the distillate add a few drops of milk; float the liquid upon 90 

 to 94 per cent sulphuric acid to which a little ferric chlorid has previously been added. 

 A violet ring appears at the point of separation of the liquids, if formaldehyde is 

 present. Acetaldehyde does not produce this reaction, the color being yellowish 

 green changing to brown. 



16648 No. 6502 5 



