_Free Tartaric Acid and Potassium Bitartrate._--In the presence of a small amount of free acids, the detection of a considerable proportion of free tartaric acid may fairly be considered as strong evidence that the wine is artificial. Nessler recommends the following qualitative test:--20 c.c. of the sample are repeatedly shaken with a little freshly prepared and finely ground cream of tartar. After standing one hour, the solution is filtered, 3 or 4 drops of a 20 per cent. solution of potassium acetate are added, and the mixture is allowed to remain at rest for twelve hours, when, in presence of free tartaric acid, a precipitation will take place. The quantitative estimation of free tartaric acid and potassium bitartrate is made by Berthelot’s method, as follows:--Separate portions of the wine (20 c.c. each) are introduced into two flasks, a few drops of 20 per cent. solution of potassium acetate being added to the second flask. 200 c.c. of a mixture of equal parts of alcohol and ether are then added to both flasks, their contents repeatedly shaken and finally set aside for eighteen hours at a temperature between 0° and 10°. The separated precipitates are now removed by filtration, washed with the ether-alcohol mixture, and then titrated with 1/10th normal alkali solution. That formed in the first flask corresponds to the potassium bitartrate originally contained in the wine; the second represents the total tartaric acid present. The addition of a small quantity of clean sand will assist in the separation of the precipitates. _Malic Acid._--A slight excess of lime-water is added to 100 c.c. of the wine, and, after standing for some time the solution is filtered, concentrated by evaporation to one-half its original volume, and treated with an excess of absolute alcohol. The resulting precipitate (consisting of calcium malate and sulphate) is collected upon a filter, dried and then incinerated. The proportion of malic acid contained is now estimated by volumetrically determining the amount of calcium carbonate present by means of a normal acid solution: 1 part of calcium carbonate represents 1·34 parts of malic acid (C_{4}H_{6}O_{5}). _Tannic Acid._--10 c.c. of the sample are taken, the free acids present neutralised with normal alkali solution, and a few drops of concentrated sodium acetate solution (40 per cent.) added. A solution of ferric chloride (10 per cent.) is then added, drop by drop, carefully avoiding an excess. A single drop of the iron solution represents 0·05 per cent. of tannic acid. The method of tannin determination described under Tea (see p. 22) can also be applied.