VINEGAR. Illustration: (‡ VINEGAR FERMENTATION YARD.) Vinegar is produced by fermenting and exposing to the air any liquor which contains sugar, such as wine, infusion of malt, cyder, &c.; by the addition of yeast, this sets up a fermentation, by means of which the sugar in any of these liquors is converted, first into spirit, and afterwards into vinegar; this contains a certain quantity of acetic acid, which makes the vinegar sour. In warm countries, vinegar is made by simply exposing the poorer kinds of wine to the sun’s rays, when they ferment and become sour. In England, all the vinegar produced is made by fermenting wort made of malt, this is fermented for three or four days, and is then put into casks, with the bunghole left open for several weeks, or until it is thoroughly sour. In ordinary vinegar, there is about five or six parts only in the hundred of real acetic acid, but this acid, when pure, is so strong as to blister the skin when dropped on it; it is often extracted from vinegar for chemical purposes, and to smell too; for when scented, it constitutes aromatic vinegar. Vinegar, besides acid and water, contains a little unchanged spirit, much coloring matter, and some mucilage. Illustration: BOILER OR COPPER. Illustration: COOLING APPARATUS. Vinegar is chiefly used as a condiment, and for making pickles, and has considerable powers of preserving vegetable or animal substances; if common vinegar be distilled, a weak colorless acid comes over, commonly known as white or distilled vinegar. It is a common thing to sprinkle a sick room with vinegar, under the impression that it has disinfecting properties, but this is an error; although the odour is very refreshing. Vinegar has, of late, been made by means of the vinegar plant, which is a fungus, causing a species of slow fermentation, and converting the sugar or treacle used into acetic acid. Illustration: FILLING CASKS. The heading of this section gives a good idea of the large scale on which vinegar is made; being an accurate representation of the extensive works of Messrs. Beaufoy & Co. at Lambeth. COAL GAS. Illustration: (‡ COAL GAS DISTILLERY.) Illustration: SECTION OF RETORT. Illustration: FIG. 1. (‡ RETORT FURNACE.) Illustration: FIG. 2. (‡ RECEIVER TUBE.) Illustration: FIG. 3. (‡ CONDENSER.) Illustration: FIG. 4. (‡ RESERVOIR.) Illustration: FIG. 5. (‡ GASOMETER.)