66 PROVISIONAL METHODS FOR ANALYSIS OF FOODS. 



A portion of the distillate prepared as above may, after the addition of a few drops 

 of milk, be treated with a drop of concentrated aqueous ferric chlorid solution, agi- 

 tated and well mixed with a nearly equal volume of concentrated hydrochloric acid. 

 Warm below boiling with constant agitation. Shortly before ebullition a purple 

 coloration of the casein appears, if formaldehyde be present; it is not produced by 

 acetaldehyde. 



17. DETERMINATION OF THE SOURCE OF A VINEGAR. 



It is not always possible to make this distinction with entire certainty. The prin- 

 cipal vinegar of the United States is cider vinegar, though malt vinegar finds prefer- 

 ence with many. The substitutes are chiefly (a) low wine vinegar, either sold under 

 the name "white wine vinegar" or colored by addition of caramel, or even given 

 color and body by addition of cheap apple jelly; (b) vinegar from sugarhouse wastes; 

 (c) wood vinegar, or preparations from vinegar essence, with or without coloring 

 matters. Grape, or true " wine vinegar, " is important in few localities outside of 

 California. Glucose vinegar is sometimes found. 



The nature of the vinegar is commonly indicated, if it be pure of its kind, by its 

 flavor and odor. The fruity quality of cider vinegar is usually very conspicuous; the 

 odor of malt vinegar is characteristic; and impure wood vinegar often shows a very 

 perceptible empyreumatic quality. Even when these qualities are distinctly indic- 

 ative of the source of the vinegar, additional evidence is desirable for legal proof; 

 often slight impurities mask them. 



The quantity of the solids is often distinctive. The range for the principal vinegars 

 is: Cider vinegar, 1.18 to 8.04; average, about 2.5. Malt vinegar, 1.75 to 6.0; average, 

 about 3.0. Spirit vinegar, 0.13 to 0.78; average, about 0.3. Wine vinegar, 1.38 to 

 3.19; average, 1.9. a The quantity of solids in sugar and glucose vinegars varies with 

 the conditions of manufacture, sometimes corresponding closely with that of fruit 

 vinegars. That of wood vinegar resembles the quantity in spirit vinegars. By the 

 addition of foreign solids to spirit or wood vinegar the value of this criterion is 

 often destroyed. 



The quality of the vinegar solids, as a whole, is usually characteristic. The consistency 

 of that from cider is thick and viscid or mucilaginous; that from sugar, glucose, or 

 malt is somewhat more glutinous. The odor of baked apples is notable in cider- 

 vinegar solids, that of molasses is often apparent in sugar-house vinegar, and that of 

 malt vinegar is usually distinctive. The flavor of cider-vinegar solids is acid and 

 somewhat astringent; in these respects wine vinegar resembles it. The bitter taste 

 of caramel is usually observed in sugar-house vinegar solids and in those from col- 

 ored spirit and wood vinegars. On burning the solids, the apple odor is developed 

 by cider vinegar, that of burnt sugar by sugar-house vinegar, and that of scorched 

 corn b by glucose vinegar. The solubility of the solids in alcohol marks fruit vinegars 

 except a granular residue of tartar in grape vinegar while the solids of malt and 

 glucose vinegars are only very slightly dissolved. c By addition of cheap cider jelly 

 to spirit or wood vinegar, the characteristic apple quality is, however, given to the 

 vinegar solids. d 



The quantity of the ash is useful in distinguishing spirit and wood vinegars from fruit 

 and malt vinegars, the quantity in the former case rarely exceeding 0.1 per cent; in 

 the latter rarely falling below 0.2; the range for pure cider vinegar is 0.19 to 0.57; 

 average about 0.35 per cent. 



The quality of the ash is far more indicative. That of fruit vinegars and malt vine- 

 gars is distinctly alkaline; that of spirit and wood vinegars very slightly so. The 



'According to Blyth. Eckenroth gives 0.35 to 1.51 per cent. 



i> Davenport, 26th Ann. Kept. Milk Inspector, City of Boston, 1885. 



"Allen, Com. Organic Anal., Vol. I, p. 389. 



a Frear, Kept. Pa. Dept. of Agr., 1898, p. 138; Leach, Kept. Mass. State Bd. of Health, 1898, p 633. 



