3. Narcotics. These may be detected in the manner noticed at page 1630.
4. Lead. The presence of lead or litharge in wine may be readily detected by sulphuretted hydrogen, or a solution of any alkaline sulphydrate, which will, in that case, produce a black precipitate. See Wine-tests.
5. Potassa or SODA improperly present. A portion of the wine is evaporated nearly to dryness, and then agitated with rectified spirit; the filtered tincture, holding in solution acetate of potassa, is then divided into two portions, one of which is tested for acetic acid, and the other for the alkali.
6. Alum. A portion of the wine is evaporated to dryness, and ignited; the residuum is then treated with a small quantity of hydrochloric acid, the mixture evaporated to dryness, again treated with dilute hydrochloric acid, and tested with liquor of potassa. If a white bulky precipitate forms, which is soluble in an excess of caustic potassa, and which is reprecipitated by a solution of sal ammoniac, the sample examined contained alum.
7. Oil of vitriol.—a. A drop or two of the suspected wine may be poured upon a piece of paper, which must then be dried before the fire. Pure wine at most only stains the paper, but one containing sulphuric acid causes it to become charred and rotten. The effect is more marked on paper which has been previously smeared with starch paste.
b. According to M. Lassaigne, pure red wine leaves, by spontaneous evaporation, a violet or purple stain on paper; whilst that to which sulphuric acid has been added, even in quantity, only equal to 1⁄2000 to 1⁄3000th part, leaves a pink stain in drying.
8. Spurious colouring-matter.—a. Genuine red wine yields greenish-grey precipitates
with sugar of lead, and greenish ones with potassa; but those coloured with elderberries, bilberries, litmus, logwood, and mulberries, give deep blue or violet precipitates, and those coloured with Brazil wood, red sanders wood, or red beet, give red ones.
b. Pure red wine is perfectly decoloured by agitation with recent hydrate of lime.
c. Dissolve a piece of caustic potash in a small quantity of the liquid to be experimented upon. If no deposit is formed, and the wine assumes a greenish shade, there is no artificial coloration. A violet-coloured deposit indicates the presence of elderberries or mulberries, a red one indicates the presence of beetroot for Brazil wood, red violet that of logwood. If the deposit is blue violet, privet berries have been employed; and if of a pale violet the coloration is due to litmus.