68 PEOVISIONAL METHODS FOK ANALYSIS OF FOODS. 



4.6 to 17.1, average 9.0; that of pure spirit malt and wine vinegar averages 5 to 8; 

 but upon addition of cider jelly to a vinegar, low in solids, the ratio becomes 17.1 

 to 80. 



The quantity of nitrogen serves to distinguish malt vinegars from such as are derived 

 from saccharine liquids, low wines, or wood acids. Calculated as albuminoids, the 

 amount in malt vinegars is 0.65 to 0.7 per cent; a in cider vinegars, 0.006 to 0.024 per 

 cent; b in sugar, glucose, spirit, and wood vinegars, much less. 



The presence of alcohol in vinegars derived from alcoholic liquids often serves to 

 distinguish them from wood vinegar; its absence is not conclusive against their deri- 

 vation from the former class of materials. 



The presence of tartar distinguishes wine vinegar, though its absence is not con- 

 clusive of other origin. c Allen's method for this test is as follows: d Treat the residue 

 left from evaporation of the vinegar, with alcohol; a granular residue of tartar re- 

 mains undissolved; to prove its character, pour off the alcohol and dissolve the residue 

 in a small quantity of hot water. On cooling the aqueous solution, and stirring the 

 sides of the vessel with a glass rod, the acid tartrate of potassium will be deposited 

 in streaks on the track of the rod. An addition of an equal bulk of alcohol makes 

 the reaction more delicate. 



The adulteration of wine vinegar by addition of free tartaric acid is proved in a 

 similar manner, the alcoholic solution of the extract is treated with an alcoholic 

 solution of potassium acetate; upon stirring the mixture with a glass rod in a beaker, 

 streaks and probably a distinct precipitate of tartar will be deposited. Quantitative 

 results can be obtained upon titration of the precipitate by standard alkali. 



The presence of malic acid distinguishes cider vinegars, though the quantity is often 

 small. Failure to obtain a precipitate upon the addition of a few drops of neutral 

 lead acetate to 10 cc of a vinegar, proves it not to be cider vinegar; if a precipitate be 

 obtained, parallel tests with silver nitrate and barium chlorid to determine the 

 absence of chlorids and sulphates should be made, before the presence of malic acid be 

 considered proved. 



Dextrin is often found in glucose vinegar and is precipitated from the concentrated 

 vinegar upon addition of three or four four volumes of strong alcohol; the precipitate 

 may be identified by the physical properties and by its color reaction with iodin 

 solution. Dextrin is also of general occurrence in malt vinegar. 



Wood vinegar is quite commonly marked by the presence of empyreumatic matters; 

 these are sometimes sufficient to impart their characteristic flavor to the vinegar. It 

 has been recommended that the method of Cazeneuve and Cotton e be used for their 

 detection; this depends upon the immediate reduction of 1 cc of a 0.1 per cent solu- 

 tion of potassium permanganate when added to 10 cc of the liquid to be tested. 

 Obviously this test is not applicable in the presence of caramel or the reducing sugars 

 of fruit and malt vinegars; both the distillate and the ether extract of cider vinegars 

 cause rapid reduction. The test is not applicable therefore to mixtures of wood vine- 

 gar with that from other sources, but may be useful in completing the examination of 

 a vinegar shown by other evidence to be wood vinegar. 



Microscopic examination may establish the absence of alcoholic and acetic ferments; 

 in such event, the article is shown to be distilled vinegar. 



Blyth, Foods, Their Comp. and Anal., 4th edition, p. 587. 



>Frear, Kept. Pa. Dept. of Agr., 1898, p. 145. 



'Tretzol (Forschungsber, 1896, 3, 186: Vtjschr. Chem. Nahr., 1898, 11, 257) states that true wine vine- 

 gars are occasionally found without tartar or more than traces of it. H. Eckenroth (Pharm. Ztg., 

 1889, 34, 14; Vtjschr. Chem. Nahr., 1891, 4, 88) claims that it is always found, if from 500 cc to 1 liter of 

 the vinegar be used for the test. Von Bitteryst (Op. cit., 1896, 9, 425) gives 0.04 gram per 100 cc as a 

 minimum. 



''Commercial Organic Analysis, 2d ed., vol. 1, p. 389. 



Vereinbarungen zur einheitlichen Untersuchung und Beurtheilung von Nahrungs und 

 Genussimitteln, II, 83. Bui. soc. chim., 1881, [2], 36, 102. 



