The chief ingredient in all saccharine aerated drinks is the syrup. This is formed by making concentrated solutions of sugar in pure water, or in water containing the principles of various flavouring substances; the former are called simple, and the latter compound syrups. There are many precautions to be taken in order to ensure the production of good syrups, the most important being, perhaps, the selection of the sugar. Cane-sugar only should be used, and that should be perfectly refined. The least shade of colour in the sugar is due to the presence of impurities, and syrup prepared from such sugar not only has an unpleasant flavour, but is also very difficult to keep. The use of common or brown sugar may be regarded, in many cases, as an adulteration. Syrups are very easily prepared. A hemispherical copper basin, not tinned, but well polished, and kept scrupulously clean, is the apparatus employed. This basin stands on three legs, and is furnished with a false bottom, which is also hemispherical. The two hemispheres are surrounded by a copper cylinder, fitted with a lid; the three parts of the apparatus are fixed together by means of two circular iron rings, which are fitted to the circumference of the hemispheres and to the bottom of the cylinder, the whole being well pinned or bolted together. A stop-cock in the outer hemisphere communicates by means of a short pipe with the inner one, and serves to withdraw the contents. Another cock, placed almost at the top, serves for the admission of steam between the two bottoms; and the condensed water is drawn off by means of a third cock communicating only with the outer bottom, and placed at a short distance from the first. The whole apparatus may be of any convenient size. Its chief advantage is that the syrup can be heated to the required degree with the utmost nicety; the steam is admitted until this degree is reached, and the supply may then be stopped in a moment, thus ensuring perfect regularity of working. There are many circumstances which tend to produce changes in syrups when made, and to cause them to degenerate and become worthless; these must be carefully guarded against. The most common is fermentation; this may be either the result of too short or too long-continued boiling; or of the presence of an excess of mucilaginous substances; or an imperfect clarification of the syrup will also produce it in the course of time. But the most frequent cause of fermentation is found in leaving the syrup in a warm place, or in vessels which are not completely filled, and especially if they happen to have been wet when the syrup was introduced. In order to guard against under or over-boiling of simple syrups, it should be laid down as a rule that they stand at 32° B. when boiling, and when cold at 34° B. in winter, and 35° B. in summer. They should then be bottled, and stored in a cool cellar.