Volatile Acids

Those are to bo estimated by distillation in a current of steam, and not indirectly, and reported as acetic acid (C2H2O2). The amount of the "fixed acids" is found by subtracting from the amount of "free acids" found, the amount of tartaric acid corresponding to the "volatile acids" found.

Bitartrate Of Potash And Free Tartaric Acid

(a) Qualitative detection of free tartaric acid: 20-30cc. of the wine are treated with precipitated and finely powdered bitar-trate of potash, shaken repeatedly, altered off after an hour, and 2-3 drops of a 20 per cent. solution of acetate of potash added to the clear filtrate, and the solution allowed to stand twelve hours. The shaking and standing of the solution must take place at as nearly as possible the same temperature. If any considerable precipitate forms during this time free tartaric acid is present, and the estimation of it and of the bitartrate of potash may be necessary.

(b) Quantitative estimation of the bitartrate of potash and free tartaric acid: In two stoppered flasks two samples of 20cc. of wine each are treated with 200cc. ether-alcohol (equal volumes), after adding to the one flask 2-3 drops of a 20 per cent. solution of acetate of potash. The mixtures are well shaken, and allowed to stand 16-18 hours at a low temperature (0 - 10° C), the precipitate filtered off, washed with ether-alcohol, and titrated. (The solution of acetate of potash must be neutral or acid. The addition of too much acetate may cause the retention of some bitartrate in solution.) It is best on the score of safety to add to the filtrate from the estimation of the total tartaric acid a further portion of 2 drops of acetate of potash to see if a further precipitation takes place.

In special cases the following procedure of Nessler and Barth may be used as a control :

Fifty cubic centimeters of wine are evaporated to the consistency of a thin sirup (best with the addition of quartz sand), the residue brought into a flask by means of small washings of 93 per cent. alcohol, and with continual shaking more alcohol is gradually added, until the entire quantity of alcohol is about 100cc. The flask and contents are corked and allowed to stand four hours in a cool place, then filtered, and the precipitate washed with 93 per cent. alcohol; the filter paper, together with the partly flocculent, partly crystalline, precipitate, is returned to the flask, treated with 30cc. warm water, titrated after cooling, and the acidity reckoned as bitartrate. The result is sometimes too high if pectinous bodies separate out in small lumps, inclosing a small portion of free acids.

In the alcoholic filtrate the alcohol is evaporated, 0.5cc. of a 20 per cent. potassic acetate solution added, which has been acidified by a slight excess of acetic acid, and thus the formation of bitartrate from the free tartaric acid in the wine facilitated. The whole is now, like the first residue of evaporation, treated with (sand and) 96 per cent. alcohol, and carefully brought into a flask, the volume of alcohol increased to l00cc., well shaken, corked, allowed to stand in a cold place four hours, filtered, the precipitate washed, dissolved in warm water, titrated, and for one equivalent of alkali two equivalents of tartaric acid are reckoned.

This method for the estimation of the free tartaric acid has the advantage over the former of being free from all errors of estimation by difference. The presence of considerable quantities of sulphates impairs the accuracy of the method.

Malic Acid, Succinic Acid, Citric Acid

Methods for the separation and estimation of these acids cannot be recommenced at the present time.

Salicylic Acid

For the detection of this, 100cc. of wine are repeatedly shaken out with chloroform, the latter evaporated and the aqueous solution of the residue tested with very dilute solution of ferric chloride. For the approximately quantitative determination it is sufficient to weigh the chloroform residue, after it has been again recrystallized from chloroform.

Coloring Matter

Red wines are always to be tested for coal tar colors. Conclusions in regard to the presence of other foreign coloring matters drawn from the color of precipitates and other color reactions are only exceptionally to be regarded as safe. In the search for coal tar colors the shaking out of l00cc. of the wine with ether before and after its neutralization with ammonia is recommended. The etherial solutions are to be tested separately.

Tannin

In case a quantitative determination of tannin (or tannin and coloring matter) appears necessary the permanganate method of Neubauer is to be employed. As a rule the following estimation of the amount of tannin will suffice: The free acids are neutralized to within 0.5 grams in l00cc. with standard alkali, if necessary. Then 1cc. of 40 per cent. sodic acetate solution is added, and drop by drop a 10 per cent. solution of ferric chloride, avoiding an excess. One drop of ferric chloride is sufficient for the precipitation of 0.05 per cent. of tannin. (New wines are deprived of the carbonic acid held in solution by repeated shaking.)

Sugar

The sugar should be determined after the addition of carbonate of soda by means of Fehling's solution, using dilute solutions, and, in wines rich in sugar (i. e. wines containing over .5 gram in 100cc.), with observance of Soxhlet's modifications, and calculated as grape sugar. Highly colored wines are to be decolorized with animal charcoal if their content of sugar is low, and with acetate of lead and sodium carbonate if it is high.

If the polarization indicates the presence of caue sugar (compare under polarization) the estimation is to be repeated in the manner indicated after the inversion (heating with hydrochloric acid) of the solution. From the difference the cane sugar can be calculated.

Polarization