In case the wine to be examined contains substances other than water and alcohol, which would affect its density, it is necessary, before making use of the alcoholmeter, to distil the sample and subsequently examine the distillate, which will consist of a simple mixture of water and alcohol. Usually the distillation is discontinued as soon as one-third of the sample has passed over, and a quantity of distilled water, sufficient to render the volume of the mixture equal to the original volume of the wine, added to the distillate: the fluid remaining in the flask will be entirely free from alcohol. The addition of water to the distillate is not indispensable, but otherwise it is necessary to divide the degrees indicated by the alcoholmeter by 3, in order to reduce the result to the original volume of the wine taken.
M. Salleron offers for sale a small apparatus (Fig. 20) used in examinations of this character, consisting of a flask, closed with a gutta-percha cork, containing a tube which connects with a worm passing through a cooler. The flask is supported by an iron stand, and heated with a gas or spirit lamp.
Fig. 20.
In order to estimate the cream of tartar, the wine is evaporated to the consistency of an extract, alcohol of 82° B. added, and the residue obtained calcined in a crucible. The amount of salt present in the fused mass is then determined by the alkalimetric method, as directed in all works on quantitative analysis. The carbonate obtained from 1 gr. of cream of tartar exactly saturates 9.75 cubic centimetres of a solution containing 100 grammes of sulphuric acid of 66° B., and 1800 grammes of distilled water.
The detection of toxical substances, often contained in wine, is accomplished by the methods described under the head of detection of poisons.
VINEGAR.
Vinegar is frequently adulterated with water, and occasionally sulphuric acid is added to artificially increase its acidity.
The ordinary reagents—such as chloride of barium, or nitrate of silver—are not adapted to the direct detection of sulphuric acid, or of other mineral acids, as sulphates and chlorides, which are as readily precipitated as the free acids, may also be present.
The following method, proposed by M. Payen, is usually employed: