VINEGAR

This term is applied to various modifications of the acetic acid. The simplest mode of obtaining vinegar is to excite a second or acetous fermentation in wine: in this case oxygen is absorbed, a variable proportion of carbonic acid is generally evolved, and the alcohol of the wine pa es into acetic acid. Very good vinegar is also made from strong beer, or from a wort or infusion of malt prepared for the purpose, or from a decoction of common raisins, or from a mixture of about 1 part of brandy with 8 of water and some sugar and yeast. When vinegar is distilled, various impurities which it contains remain in tlie still, and the liquid which pa es over is the acetic acid, nearly pure, but largely diluted with water. In this state it is usually called distilled vinegar, and is used chiefly in pharmacy. But though a considerable quantity of vinegar is made in wine countries by the first mentioned proce , and here and elsewhere by the second, in which malt is employed; yet for all the purposes of the arts and manufactures, as well as for domestic consumption, the market is chiefly supplied from another source, which is the destructive distillation of wood. It has long been known that when certain kinds of dry wood, especially beech and such woods as are not resinous, instead of being burned in the open air, are converted into charcoal in close ve els, so as, in fact, to be submitted to distillation, that the vapours which pa off yield, when condensed, a large quantity of tar, and of very acid water. The latter is, in fact, an impure vinegar; that is, it owes its acidity to acetic acid, which is formed during the proce out of the carbon, hydrogen, and oxygen of the wood, which elenients are also those of acetic acid, and, what is remarkable, not in very different proportions. When this impure acetic acid is freed from the tar and empyreumatic oils with which it is mixed, it is called crude pyroligneous acid. To convert it into pure acetic acid, that is, to separate from it the empyreumatic products with which it is intimately combined, is a somewhat circuitous proce , of which the following is an outline: — It is first distilled, by which pyroxilic spirit and oil of tar first pa over, and these are followed by a quantity of impure or rough acetic acid. This rough acid, which is used by dyers and calico-printers, and by makers of sugar of lead, is saturated with powdered slaked lime, and being filtered, yields a solution of impure acetate of lime, which is evaporated to dryne , and which, distilled with dilute sulphuric acid, yields a purer acetic acid than the former, but which still has a burned and disagreeable flavour; it is thereibre again saturated by lime, and this liquid acetate of lime is mixed with a solution of sulphate of soda, which acting by double decomposition, yields a precipitate of sulphate of lime, and acetate of soda remains in solution. The latter salt is procured by evaporation, and purified by torrefaction and crystallization. Tiie vinegar-makers, who purchase it, decompose it in retorts or proper stills, by means of sulphuric acid, by which a very pure and strong acetic acid pa es over, sulphate of 4 O [s. 1308]