The strength of all wines depends upon the quantity of alcohol or brandy which they contain. Mr. Brande, and Gay-Lussac, have proved, by very decisive experiments, that all wines contain brandy or alcohol ready formed. The following is the process discovered by Mr. Brande, for ascertaining the quantity of spirit, or brandy, contained in different sorts of wine.
EXPERIMENT.
Add to eight parts, by measure, of the wine to be examined, one part of a concentrated solution of sub-acetate of lead: a dense insoluble precipitate will ensue; which is a combination of the test liquor with the colouring, extractive, and acid matter of the wine. Shake the mixture for a few minutes, pour the whole upon a filtre, and collect the filtered fluid. It contains the brandy or spirit, and water of the wine, together with a portion of the sub-acetate of [Pg 93]lead. Add, in small quantities at a time, to this fluid, warm, dry, and pure sub-carbonate of potash (not salt of tartar, or sub-carbonate of potash of commerce), which has previously been freed from water by heat, till the last portion added remains undissolved. The brandy or spirit contained in the fluid will become separated; for the sub-carbonate of potash abstracts from it the whole of the water with which it was combined; the brandy or spirit of wine forming a distinct stratum, which floats upon the aqueous solution of the alkaline salt. If the experiment be made in a glass tube, from one-half inch to two inches in diameter, and graduated into 100 equal parts, the per centage of spirit, in a given quantity of wine, may be read off by mere inspection. In this manner the strength of any wine may be examined.
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