wood oil," is the produce of the "Artemisia absinthium." Other flavouring oils are always present, such as peppermint, angelica, cloves, cinnamon, and aniseed. The green colour is produced by the juice of spinach, nettles, or parsley, or, in other words, it is due to chlorophyll. The absorption-spectrum of properly made absinthe, is the same as that of chlorophyll. Most samples of absinthe contain sugar. The average composition of the liqueur as consumed in London (where its use is on the increase) is as follows:

On diluting absinthe the essential oils are thrown out of solution, and the liquid becomes turbid. The reaction is always slightly acid, due to a trace of acetic acid.

Adulterations of Absinthe.-The composition of absinthe appears to be fixed by no definite standard of strength; therefore, practically, the analyst has to look only for such substances as injurious colouring-matters and metallic impurities. Sulphate of indigo with turmeric is not unfrequently employed as a colouring agent, and similarly picric acid has been detected, and salts of copper. The latter is readily discovered by diluting the liqueur and adding ferrocyanide of potassium, which, if copper be present, will give a brown colouration; picric acid and indigo are detected in the way elsewhere described. (See Index.)

Analysis of Absinthe. The alcohol may be determined by distillation, after diluting the liqueur to cause the oils to separate, and getting rid of some portion by filtration. To make an estimation of the essential oils, a measured quantity of the liqueur is diluted to twice its volume by the addition of water; carbon disulphide is added, and the mixture shaken up in the tube described at p. 69. The carbon disulphide dissolves all the essential oils, and on evaporation leaves them in a state pure enough to admit of their being weighed. Absinthe, when taken habitually and for a lengthened time, produces a peculiar train of nervous symptoms which the French physicians affect to distinguish from the similar symptoms produced in inebriates by alcohol. In epilepsy caused by indulgence in absinthe, M. Voisin states, as the results of clinical observation, that the number of fits is far greater than in alcoholic epilepsy.

FERMENTATION: FERMENTED LIQUORS.

“The chemical act of fermentation is essentially a correlative phenomenon of a vital act beginning and ending with it. I think that there is never any alcoholic fermentation without there being, at the same time, organisation, development, and multiplication of globules, or the continued consecutive life of globules already formed.”—Pasteur.

§ 250. Fermented liquors are those manufactured by fermentation-i.e., a peculiar, low vegetable growth has been allowed to grow and multiply, assimilating material in one form, and excreting it in another, and this process has evolved, with other by-products, carbon dioxide and alcohol. Fermentation used to be considered as a sort of special action; but modern research recognises a great variety of ferments, and it is a question whether all animal and vegetable cells, in the exercise of their normal functions, do not act in a similar manner to the environing fluids, as do the organisms more distinctively called "ferments."

In normal alcoholic or spirituous fermentation, as in the manufacture of beer, a minute unicellular plant, "yeast," grows and multiplies, and splits up the sugar, as in the following equation:

C6H12O6=2C2H6O+2CO2,

that is, one molecule of sugar furnishes two of alcohol and two of carbon dioxide. In ordinary practice this complete reaction never occurs, but if by the constant removal of carbon dioxide and alcohol, by means of a mercury pump, atmospheric air be excluded, the equation is nearly realised. M. Pasteur, in his quantitative research on the products of ordinary fermentation,* found that 100 parts of cane-sugar, corresponding to 105.26 parts of grape-sugar, gave nearly

The method adopted by M. Pasteur to detect and measure quantitatively the glycerin and succinic acid contained in a fermented liquid, was as follows: "The liquid, when the fermentation was over, and all the

M. Monoyer has represented Pasteur's results in the form of the following equation :

:

4(C12H24O12)+6H2O=2(C4H6O4)+12(C3H8O3) +4CO2 +02,

the free oxygen being supposed to serve for the respiration of the yeast cells. Pasteur's equation is far more complex, and represents no free oxygen as produced; yet the fact of fermentation going on briskly in a vacuum, as well as other considerations, points to the probable correctness of Monoyer's supposition.

As a secondary product, there is also constantly acetic acid. This is generally considered to originate from the ferment itself. With ethyl-alcohol there is also produced, when complex matters are fermented, several other homologous alcohols. For example, if potatoes are fermented, on distilling off the more volatile portions, and collecting separately the final distillate, this is found to consist of propyl, butyl, amyl, caproic, œnanthyl, and caprylic alcohols.†

§ 251. Yeast.-There are no less than three methods of causing the wort of beer to ferment, but none of the three presents any very distinct variety of the yeast ferment. The one generally employed in England is what is called surface fermentation, in which the starch of the malt is changed into sugar by successive infusions, and the fermentation takes place at from 15° to 18°. This in breweries is done in large open vats; the yeast floats on the surface, and can be removed by skimming.

The second method, more in use in Germany, is fermentation

sugar had disappeared (which required from fifteen to twenty days under good conditions), was passed through a filter, accurately weighed against another made of the same paper. After having been dried at 100°, the dried deposit of the ferment collected at the bottom of the vessel was also weighed. The filtered liquid was subjected to a very slow evaporation (at the rate of from twelve to twenty hours for each half litre); when reduced to 10 or 20 cc. the evaporation was completed in a dry vacuum. The syrup obtained was next exhausted with a mixture of alcohol and ether (1 part alcohol of 30° and 15 parts ether), which extracted completely all the succinic acid and glycerin. The ether-alcohol was distilled in a retort, then evaporated in a water-bath, and afterwards in a dry vacuum. To this was added a little lime water, to fix the succinic acid, and again the mixture was evaporated, and then the glycerin was separated from the succinate of lime by ether-alcohol, which only dissolved out the glycerin. This etheralcohol solution on evaporation, which was finished as before in a dry vacuum, left the glycerin in a state fit to be weighed, and the calcium succinate was purified by treatment with alcohol of 80 per cent., which only dissolved out the foreign matters."-Schützenberger on "Fermentation.' Lond., 1876.

"Thèse de la Faculté de Médecine de Strasbourg."

†M. Jeanjean has separated camphyl-alcohol (C10H160) from the distillate of madder.

by sedimentary yeast (Unterhefe). The starch is transformed by decoction, and the temperature (12° to 14°) is much lower than the former. The yeast forms a sediment on the bottom; and when the first and most active fermentation is over, the clear liquid is run off into proper vessels; but the yeast not having been all deposited, a slow fermentation still goes on for a long time.

A third method, employed in Belgium, is to leave the wort to itself, having first placed it under proper conditions.

The microscopical appearance of yeast is that of a number of round or oval cells, from 00031 to 00035 in. (008 to 009 mm.) in their greatest diameter. They are transparent, with one or two vacuoles; contain often a somewhat granular protoplasm, and occur together, united two by two; or, if in active growth, in groups, of which seven is a very common number. These groups are derived from offshoots or buds from a single cell, which will be found somewhere near the middle, and can be identified by its greater size. The usual teaching as to the mode of propagation has been hitherto that this growth is effected by a true budding; but according to Dr. de Vaureal, the supposed budding is an optical delusion. He considers the utricle of yeast as allied to the spermogones of Tulasne. The nucleolar elements of the cell are spermatic; and being set free by the rupture of the cell-wall, produce new cells. This explanation would at all events account for the ready manner in which yeast germs are carried about by the air.

Schlossberger and many other chemical composition of yeast. of two analyses as follows [the removal of ash]:

chemists have determined the Schlossberger gives the mean elementary composition after

The ultimate principles contained in yeast appear to be, certain albuminoid substances, tyrosine, leucine [neuclein ?], cellulose, and some other hydro-carbons, but the matter is not yet fully worked out.

The ash of yeast has been analysed by Mitscherlich, and Schutzenberger arranges his analyses as follows:

The researches of Ergol, Rees, Pasteur, and others have shown that there are a great variety of alcoholic ferments: the wine ferment is distinct in size and shape from the beer-yeast ferment; while the ferment of fruit-juice, again, differs in the figure of its cells from either; and to the various alcoholic ferments names have been given-e.g., Saccharomyces ellipsoideus, S. exiguus, S. conglomeratus, S. apiculatus, &c. All of them, however, are of quite the same general type as yeast ferment.

P

T

§ 252. When liquids become sour, ropy, or putrid, in each case the change has been produced by a particular ferment. The lactic acid ferment, e.g., decomposes sugar into lactic acid; the butyric acid ferment attacks fatty matters, and separates in a free state butyric acid; and putrid ferments, by their avidity for oxygen, split up complex organic matters into a variety of substances. Of these ferments, the most important in reference to beer is the lactic acid ferment. In normal alcoholic fermentation, M. Pasteur has proved that there is not the smallest production of lactic acid, and when this does appear, it is certain that it has originated in and contaminated the yeast used. These ferments can be recognised by the microscope, and they should be looked for generally in the sediment. For the purpose of collecting the sediment of beers, wines, water, &c., the author has devised the following tube (fig. 65). The tube is of the capacity of a litre, and at the lower end is conical and open; on to this conical end is ground a glass cap, C, which is in point of fact a shallow cell about an inch in depth; P is a glass rod, the end of which fits easily into the narrow part of the tube, and is ground so as to make. a perfect joint. The use of the tube is as follows:The liquid under examination is placed in the tube closed by the cap, and the plunger P is removed; when the sediment has all collected in C, the plunger is very slowly and carefully inserted, so as to stopper the lower end of the tube; the cap may then be removed for microscopical examination.

Fig. 65. Fig. 66 is a representation, after Pasteur, of the ferments which characterise sour or turned beer.