To prevent, or rather to lessen, the production of fusel oil, it has been proposed to add a certain quantity of tartaric acid or bitartrate of potassa to the wort, or to arrest the fermentative process somewhat before the liquid has reached its utmost degree of attenuation. The best means of depriving the spirit of this and other substances of a similar nature is to largely dilute it with water, and to redistil it at a gentle heat. Agitation with olive oil, decantation, dilution with a large quantity of water, and redistillation, have also been recommended. An excellent method is filtration through newly burnt and coarsely powdered charcoal. This plan succeeds perfectly with moderately diluted spirit. On the Continent, the addition of about 10% of common vinegar, and a very little sulphuric acid, followed by agitation, repose for a few days, and redistillation is a favourite method. A solution of chloride of lime is also employed for the same purpose, and in the same way. In both these cases a species of ether is formed, which possesses a very agreeable odour. In the first, acetate of oxide of amyl (essence of jargonelle) is produced; and in the other, chloride of amyl, which also possesses a pleasant ethereal smell and taste. The affinity of the hydrated oxide of amyl (fusel oil) for acetic acid is so great, that they readily unite without the
intervention of a mineral acid. (Doebereiner). Thus, the oil of vitriol mentioned above, though always used in practice, might be omitted without any disadvantage.
According to Messrs Bowerbank, the distillers quoted by Dr Pereira, 500 galls. of corn-spirit yield about one gall. of corn-spirit oil. See Acetification, Alcohol, Brewing, Distillation, Fermentation, Fusel Oil, Spirit, Vinegar, Viscous Fermentation, Yeast, &c.
VI′OLET. Syn. Purple violet, Sweet v.; Viola (Ph. L. & E.), L. “The recent petals of Viola odorata, Linn.” (Ph. L.) It is chiefly used on account of its colour. See Syrup.
VIOLET DYE. Violet, like purple, is produced by a mixture of red and blue colouring matter, applied either together or in succession. The ‘aniline colours’ are now almost exclusively used for obtaining violet on silk and wool (see Aniline, Purple, and Tar colours). With the old dye stuffs, violet may thus be obtained:—A good violet may be given to silk or wool by passing it first through a solution of verdigris, then through a decoction of logwood, and, lastly, through alum water. A fast violet may be given by first dyeing the goods a crimson with cochineal, without alum or tartar, and, after rinsing, passing them through the indigo vat.—Linens and cottons are first galled with about 18% of gall-nuts, next passed through a mixed mordant of alum, iron liquor, and sulphate of copper, working them well, then through a madder bath made with an equal weight of root, and, lastly, brightened with soap or soda. Another good method is to pass cloth, previously dyed Turkey red, through the blue vat. Wool, silk, cotton, or linen, mordanted with alum and dyed in a logwood bath, or a mixed bath of archil and Brazil, takes a pretty, but false, violet.
VIS′COUS FERMENTATION. Syn. Mucilaginous fermentation, Mucous f. The peculiar change by which sugar, in solution, is converted into gummy matters, and other products, instead of into alcohol.
When the expressed juice of the beet is exposed to a temperature of 90° to 100° Fahr., for a considerable time, the sugar it contains suffers this peculiar kind of fermentation. Gases are evolved which are rich in hydrogen, instead of being exclusively carbonic acid, and when the sugar has, for the most part, disappeared, mere traces of alcohol are found in the liquid, but, in place of that substance, a quantity of lactic acid, mannite, and a mucilaginous substance, resembling gum Arabic, and said to be identical with gum in composition. By boiling yeast or the gluten of wheat in water, dissolving sugar in the filtered solution, and exposing it to a tolerably high temperature, the viscous fermentation is set up, and a large quantity of the gummy principle generated, along with a ferment of a globular texture, like that of yeast, but which is capable
of producing only the viscous fermentation, in saccharine solutions.
The peculiar cloudy, stringy, oily appearance of wine and beer, called by the French ‘graisse,’ and the English ‘ropiness,’ depends on the accession of the viscous fermentation. The mineral acids and astringent substances, especially the sulphuric and sulphurous acids, and tannin, precipitate the viscous ferment, and are, hence, the best cures for this malady of fermented liquors. It is the large amount of tannic acid in the red wines and well-hopped beer which is the cause of their never being attacked with ‘graisse,’ or ‘ropiness.’ See Vinous Fermentation, Wines, &c.
VI′′SION. The following means of preserving and restoring the sight may be appropriately inserted here:—