of
super-tartrate of potash, and extractive matter, derived from the juice
of the grape. These substances deposit slowly in the vessel in which
they are kept. To this is owing the improvement of wine from age. Those
wines which effervesce or froth, when poured into a glass, contain also
carbonic acid, to which their briskness is owing. The peculiar flavour
and odour of different kinds of wines probably depend upon the presence
of a _volatile oil_, so small in quantity that it cannot be separated.

EASY METHOD OF ASCERTAINING THE QUANTITY OF BRANDY CONTAINED IN VARIOUS
SORTS OF WINE.

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 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.

_Tabular View, exhibiting the Per Centage of Brandy or Alcohol[40]
contained in various kinds of Wines, and other fermented Liquors._[41]

Proportion of Spirit