lation, are still greater. To this class belong all the different kinds of wine, which owe their peculiarities of flavour partly to the different varieties of grape, of which 500 or 600 are cultivated, and partly to the different flavour which even the same variety of grape* possesses in different climates, according as the saccharine, the aromatic, the acidulous, or the astringent principle of the fruit predominates: the grapes grown in the hottest climates furnishing the sweetest juice, but not the wines of finest quality; the flavour is also materially influenced by the manner in which the wine is prepared. For example, when fermentation is allowed to proceed until all the sugar is transformed into spirit, a dry wine is produced; when checked before this term is reached, the result is a rich fruity wine: and when bottled whilst the fermentation is still proceeding, a brisk effervescent wine like champagne is the result. It is the usual practice to add cane sugar to champagne before bottling. According to the experiments of Bence Jones, claret, Burgundy, and the wines of the Rhine and the Moselle, contain no sensible quantity of sugar; sherry yields from 1 to 5 per cent., port from 3 to 7 per cent., and Tokay as much as 17 per cent. of sugar. The ageing of wine and consequent change of flavour, depends partly upon the gradual fermentation of sugar still retained in rich wines, and partly upon the slow separation of saline matter, principally in the form of hydro-potassic tartrate (KHЄ,H ̧ ̧), which becomes less soluble as the proportion of spirit increases, and is deposited, particularly from port wines, as a crust of tartar, upon the sides of the bottle. An important part of the change of flavour appears also to be owing to the slow formation of minute quantities of fragrant and aromatic ethers, which are gradually produced by the reaction of the vegetable acids upon the alcoholic portion of the wine. It has been observed that the presence of a considerable amount of acidity favours the development of the bouquet' or aroma which is especially characteristic of the acidulous wines of the Rhine and the Moselle.

Some wines, instead of improving, become ropy by keeping. This occurs only with sweet wines, and is due to a peculiar species of fermentation in which the sugar passes into the uncrystallizable form of mucilage (1101, 1120).

The colour of the wine is dependent upon the mode in which

A certain variety of grape when grown upon the Rhine furnishes a species of Hock; the same grape when raised in the valley of the Tagus yields Bucellas; whilst in the island of Madeira it produces the wine known as Sercial, which has a flavour quite different from either of the others.

a

the fermentation is effected. Red grapes may be made to yield 'white' wine, if the husks of the grape be removed from the must before the fermentation begins, as in the preparation of champagne and sherry; but if the skins be left in the fermenting mass, the alcohol, as it is formed, dissolves the colouring matter, producing the different shades of 'red' wine. During the preparation of red wines the skins and stalks rise to the surface of the fermenting mass and form the chapeau, which is removed from the fermenting juice at an earlier stage in the making of clarets than in the preparation of ports, and this is one reason why port is the more astringent wine of the two.

The process of fermentation in making wine is much more gradual and protracted than in the preparation of malt liquors. After the grapes have been trodden in the press, the juice passes to the fermenting vessels; no addition of yeast is necessary, and after a short time a copious deposit of ferment granules or yeast occurs spontaneously. The fermenting vats are so constructed that when the active stage of the fermentation is over, they can be loosely closed by a bung. As soon as the winter frosts set in, the wine is decanted from the lees into casks, which are completely filled, and then closed with care. In order to supply the loss from leakage or evaporation, the casks are carefully filled up at intervals. Here a secondary very gradual fermentation occurs. It requires careful watching, exclusion of the air at this stage being indispensable in order to prevent the wine from becoming sour, owing to the formation of acetic acid by the oxidation of the alcohol.

Sometimes a wine acquires a peculiar flavour known as the 'taste of the cask.' This is attributed to the development of a peculiar essential oil during the growth of fungi, or 'mould,' upon the surface of the wine. It is said that it may be removed by adding to each pipe about a quart of olive oil, which dissolves the obnoxious flavouring matter, and carries it with it to the surface.

It is obvious that in wines and other fermented liquors which have not been submitted to distillation, all the soluble matter of the fruit is present in the beverage. Other saccharine juices, besides those of the grape, admit of being fermented, and thus a great variety of drinks may be produced. Beer and ale, for example, consist of an infusion of malt, flavoured by the aromatic bitter of the hop, and subsequently fermented. The different kinds of porter are similarly prepared, and owe their dark colour to the use of high-dried malt; cider is the fermented juice of the apple; perry is a similar liquid obtained from the pear; and nearly every fruit may be made to yield its own peculiar liquor. Even savage

TRITYLIC OR PROPYLIC ALCOHOL.

189

nations evince a knowledge of this fact. The natives of the islands in the Pacific, when discovered by Cook, not only knew how to prepare an intoxicating liquor from the juice of the cocoanut, but they were accustomed to rectify it by a rude process of distillation.

Since foreign matters are present in all fermented liquors, the specific gravity would, except in special cases,* be no guide to the quantity of spirit contained in them. A simple means of overcoming this difficulty was successfully practised by Brande ;-Potassic carbonate is soluble in water, but insoluble in alcohol: when perfectly dry potassic carbonate in powder is poured in excess into a mixture of alcohol and water, the salt becomes dissolved in the water, and the liquid separates into two layers, the upper of which consists of alcohol of sp. gr. o'825. By employing a graduated tube for the experiment, the volume of alcohol which is contained in any wine or liquor may be read off at once by inspection.

Christison submitted different wines to distillation, in order to determine their percentage of alcohol; he thus obtained a series of results, the most important of which are embodied in the following table. The numbers represent the weight of absolute alcohol contained in 100 parts of each variety of wine or fermented liquor:

from 690 to 8 40 5'70 " 6:06

This

(1128) 3. Tritylic (or Propylic) Alcohol (E,H,O). Sp. gr. of liquid 0817; of vapour 202; Rel. wt. 30; Boiling pt. about 206° (97° C.)—Although, during the ordinary process of the fermentation of fruit or grape sugar, the products are carbonic anhydride and ordinary (ethylic) alcohol, it usually happens that minute quantities of other homologous bodies are formed. is particularly the case when masses of the husk of the grape, from which the juice has been expressed (technically termed the marc of the grape), are thrown aside, and allowed to ferment. The saccharine matter which they still retain undergoes decomposition, and when the fermented liquor furnished by them is submitted to distillation, a mixture of tritylic, tetrylic, amylic, and hexylic alcohol is obtained.

*See "Report on Original Gravities" by Graham, Hofmann, and Redwood (Q. J. Chem. Soc. v. 229).

190

TRITYLIC AND TETRYLIC ALCOHOLS.

These different modes of fermentation admit of explanation by means of the following equations, in which it is assumed that in addition to the separation of carbonic anhydride, a certain quantity of water is eliminated at the same time :

2 € H, Ꮎ = 4 ᏟᎾ, + 2 Ꮋ Ꮎ + 2 €.ᎻᎾ ;

6

10

Tritylic alcohol, the third term of the alcoholic series, is obtained only in small quantity from the fermented marc. Its isomeride may be prepared by Berthelot's process of absorbing tritylene by oil of vitriol, diluting the solution with 5 or 6 times its bulk of water and distilling. It is a limpid, colourless liquid, lighter than water, with an agreeable fruity odour. Although freely soluble in water, it does not mix with it in all proportions.

(1129) 4. Tetrylic or Butylic Alcohol (H10). Sp. gr. of liquid 08032; of vapour 2·589; Rel. wt. 37: Boiling pt. 233° (112° C.)—Wurtz procured this fourth term of the alcohols during the rectification of fousel oil obtained from beet-root spirits; it is contained in that portion which boils below 266° (130° C.) By fractional distillation, this portion may be made to yield a liquid, the boiling point of which remains steady at 233°, and which is the desired alcohol. Tetrylic alcohol is a colourless liquid of high refracting power, lighter than water, and only partially soluble in water. It has an odour resembling that of fousel oil, but less oppressive. When heated with caustic potash, it is readily converted into potassic butyrate, with evolution of hydrogen; and when mixed with concentrated sulphuric acid, it forms tetrylsulphuric (or sulphobutylic) acid (H,,H,SO) without difficulty.

5

(1130) 5. AMYLIC ALCOHOL, Fousel Oil, or Potato Spirit (E,H12, or C10H12O2=88). Sp. gr. of liquid at 32°, 0·827; of vapour 3'147; Rel. wt. 44 ; Boiling pt. 269°·6 (132° C.) Kopp.-This substance, which constitutes the fifth term of the alcohol series,

FOUSEL OIL, OR AMYLIC ALCOHOL.

191

is a frequent impurity in brandies distilled from fermented potatoes,* barley, rye, and the marc of grapes, to which it communicates a peculiar offensive odour and taste. Since it is considerably less volatile than either alcohol or water, it accumulates in the last portions of the liquid when such brandies are submitted to distillation. Crude fousel oil is usually mixed with a variable amount of different ethers of the acids of the acetic series.

According to Liebig (Familiar Letters, 4th ed. p. 217), fousel oil is formed principally in the fermentation of alkaline or neutral liquids, and its production in the potato mash may be prevented, in great measure, by adding crude tartar to the fermenting liquid. Its formation, he says, never occurs in acidulous fermenting liquids which contain tartaric, racemic, or citric acid. The addition of hops to the liquid has a similar effect in checking the development of fousel oil.

Amylic alcohol is a colourless, limpid liquid, which has a persistent, penetrating, and oppressive odour, and a burning taste. It is but sparingly soluble in water, though it may be mixed with alcohol, ether, and the essential oils, in all proportions. Its vapour is very irritating when respired; it burns with difficulty with a bluish flame. The specific gravity of fousel oil at 59° is o8184. At about -4(-20° C.) it congeals into crystalline plates. Amylic alcohol causes a left-handed rotation of the plane of polarization in a ray of polarized light, but the extent of this power varies greatly in different specimens. According to Pasteur, ordinary amylic alcohol consists of a mixture of two metameric bodies, one of which is inactive on polarized light, but the other produces left-handed rotation of a polarized ray. The two modifications can be separated by converting the alcohol into amylsuphuric acid and combining this with baryta. Both the baric amylsulphates crystallize in the same form, but the inactive variety requires 24 times as much water for its solution as the active one. The active alcohol has a sp. gr. about greater than the inactive variety, and it boils between 260°6 and 262°4. The inactive alcohol boils at 264°2.

Under the influence of spongy platinum, amylic alcohol gradually absorbs oxygen, whilst hydrogen is eliminated in the form of water, and valeric acid is produced; this acid bears the same relation to amylic alcohol that acetic acid does to ordinary alcohol :

The amylic series has been so named from amylum, starch, the most abundant constituent of the potato.