The estimation of glycerine in wines, if it could be made with exactness, would be a very important one, as the glycerine is produced by the fermentation of the sugar, and the quantity formed is presumably fairly constant for the same amount of sugar fermented. This being the case, the quantity of glycerine in a wine should be a good index of the quantity of sugar which had undergone fermentation, and would thus show whether alcohol had been added to the wine. Unfortunately, the amount of glycerine present is so small, and its exact estimation so difficult on account of its volatile nature, that it is rather an unsafe reliance. The Germans attach considerable weight to the determination in establishing the character of a wine, using the following method :

One hundred cc. of wine (sweet wines excepted) are evaporated in a roomy, not too shallow, porcelain dish, to about 10cc, a little sand added, and milk of lime to a strong alkaline reaction, and the whole brought nearly to dryness. The residue is extracted with 50cc. of 96 per cent. alcohol on the water bath with continual stirring. The solution is poured off through a filter and the residue exhausted by treatment with small portions of alcohol. For this 50 to 150cc. are generally sufficient, so that the entire filtrate measures 100 to 200cc. The alcoholic solution is evaporated on the water bath to a sirupy consistence. (The principal part of the alcohol may be distilled off, if desired.) The residue is taken up by 10cc. of absolute alcohol, mixed in a stoppered flask with 15cc. of ether and allowed to stand until clear, when the clear liquid is poured off into a glass-stoppered weighing glass, filtering the last portions of the solution. The solution is then evaporated in the weighing glass until the residue no longer flows readily, after which it is dried one hour longer in a water jacket. After cooling, it is weighed.

In the case of sweet wines (containing over 5 grams of sugar in l00cc.), 50cc. are taken in a good-sized flask, some sand added and a sufficient quantity of powdered slacklime, and heated with frequent shaking in the water bath. After cooling, l00cc. of 96 per cent. alcohol are added, the precipitate which forms allowed to separate, the solution filtered, and the residue washed with alcohol of the same strength. The alcoholic solution is evaporated and the residue treated as above.

In regard to the performance of the official method, as given above, Dr. Barth1 adds the following commentaries and cautions :

In case the residue from the first evaporation with lime becomes entirely dry it should bo moistened with a little alcohol, the residue removed from the sides of the dish with a spatula, and the entire mass rubbed up with a pestle to a uniform pasty mass, the pestle and spatula being rinsed with a little alcohol; in heating up the alcoholic paste with lime, bumping and spurting may be avoided by careful stirring; the heating and subsequent washing out with hot alcohol is necessary, however, to dissolve out the glycerine properly. In evaporating with both the alcoholic and the ether-alcohol solution, all violent boiling of the liquid must be avoided, or mechanical losses will occur. The best way is to place the vessels containing the solutions inside of beakers filled with water on the bath. The clearing up of the ether-alcohol solution can be hastened by energetic shaking in the stoppered flask containing it. The vessel in which the ether-purified glycerine is finally weighed should have vertical walls at least 40mm. in height. The losses which are caused by the volatility of glycerine cannot be entirely avoided, but may be reduced to a minimum by a careful observance of all the directions, even those which are apparently unimportant. That the loss of glycerine is smaller by heating in a drying oven than on the open water bath has been noticed in the estimation of the extract; the choice of weighing tubes also with proportionally high, vertical walls has for its object the lessening of the possibility of losses in weight.

1 Die Weinanalyse, p. 17.

For the estimation of the glycerine in sweet wines the following precautions should be observed: Sufficient powdered lime must be added to the wine to convert the whole of the sugar into its lime compound. The formation of the latter takes place gradually during the heating on the water bath. "The mass becomes at first dark brown (special care is necessary to prevent its foaming over the neck of the flask), but when the saturation with lime is complete it becomes somewhat clearer, and, together with the characteristic smell of the sugar-lime, a caustic odor becomes manifest.

If the residue obtained from the concentration of the alcoholic solution remains somewhat thin even after cooling, it is not necessary to repeat the treatment with lime. The purification with ether-alcohol in the way described will be all that is necessary.

The above described method for glycerine estimation is intended to obtain the glycerine in a state of purity by its separation from all the other constituents of wine, either by their volatility, by their insolubility in alcohol, or their lime combinations, or finally by their insolubility in a mixture of one volume of alcohol with 1 1/2 volumes of ether. If pointed crystals appear on cooling, the presence of mannite is indicated. Since the separation of glycerine in an insoluble condition in a form or union peculiar to itself has not yet been accomplished, the extraction method must serve for its estimation, but the latter is only useful for the conclusions which are drawn from its results, when it is carried out with a strict observance of the preceding conditions.

Several methods have lately been proposed for the estimation of glycerine, and it was with the hope of some of them proving more exact and less tedious than the above that a somewhat hasty examination of these methods has been made.