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days, converts the starch into gum instead of into sugar; at other times mannite is formed; in other cases the starch is converted first into sugar, and this compound if mixed with chalk is then rapidly transformed into calcic lactate; whilst the same infusion, at a still later period of its decomposition, becomes turbid, and acquires the power of exciting the alcoholic fermentation. These observations seemed to indicate that the same body during its different states of decay may give rise to the formation of products quite different in properties from each other, though all these products, except mannite, have the same ultimate composition. Hence it was concluded, that the formation of each of these compounds corresponds to a particular phase of decay in the ferment. The observations of Pasteur have, however, rendered it probable that each product of fermentation is produced by the action of particular fungi or organisms developed successively during the decay of the albuminous substance. If this explanation be admitted, it is easy to see why in many instances the products of fermentation are of a more or less mixed nature, according as the ferment itself has passed through more or fewer phases of its decomposition.

All substances susceptible of putrefactive decomposition—such as casein, albumin, mucous membrane, muscular tissue, and the albuminoid azotised principles of plants—may furnish a pabulum for the development of these special ferments, each of which has the power of inducing decomposition of a particular kind, in bodies-like sugar, starch, urea, and various others which undergo no change unless some agent susceptible of putrefaction be employed. All these azotised putrescible substances possess certain properties in common, whilst they are undergoing putrefaction; and some seem to have the power of producing special changes, each of them being susceptible of certain phases of decomposition peculiar to itself. For example, the synaptase of the almond (1431) acts upon starch and sugar in a way resembling that in which yeast and gluten act, converting starch into sugar, and sugar into alcohol and carbonic anhydride; but it has, in addition, the peculiar property, not possessed by yeast or gluten, of converting amygdalin into hydrocyanic acid and essential oil of bitter almonds, and also of changing salicin into saligenin and sugar.

We have still much to learn respecting the progress of putrefaction. Pasteur describes putrefaction as a peculiar species of fermentation produced and maintained by an animal ferment of the genus vibrio. Each of the six known species of this genus he

ACTION OF FERMENTS-PUTREFACTION.

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regards as possessing the property of producing special modes of putrescence. During putrefaction, the substance, if exposed to the air, always experiences slow oxidation. If a liquid susceptible of putrefaction and containing air in solution be sealed up in glass vessels and left to itself, infusoria (Monas crepusculum and Bacterium termo) are first developed. They absorb the oxygen of the air, and evolve carbonic acid, after which they die and produce a sediment. Then, if the germs of the vibrio are present, these become developed, and at the same time putrefaction commences. The vibriones cannot exist in a liquid which contains free oxygen.

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If the putrescible liquid be freely exposed to the air, the monads and bacteria are developed at first, and continue to be produced in great abundance. They form a pellicle over the surface of the liquid which is perpetually being renewed, and by absorbing oxygen entirely prevents its access to the interior of the liquid. Then putrefaction commences, but the newly-formed products of putrescence are partially decomposed under the influence of the superficial layer of infusoria; and by the agency of these monads they become oxidized and converted into water, carbonic acid, and ammonia.

Pasteur further considers that he has proved that the slow oxidation of animal and vegetable matters, such, for instance, as moistened sawdust, is dependent upon the influence of the lower cryptogamic and infusorial organisms, such as the myceliums, mucors, or moulds,' and monads and bacteria, without the presence of which dead organized matter would scarcely be subject to change; and he altogether rejects the theory of albuminoid ferments.

Lemaire has pointed out the important influence which the condition of the liquid exerts upon the products of putrefaction, the same ferment producing different results according as the liquid is neutral, acid, or alkaline.

The observations of Schröder (Liebig's Annal. cix. 35, and cxvii. 273) upon the processes of fermentation and putrefaction are remarkable. He has shown that any organic liquid may be prevented from fermenting or putrefying, if it be heated under pressure to about 266° (130° C.), then transferred to a flask and boiled, the mouth of the flask being plugged whilst boiling with a pellet of cotton wool. In this way he preserved, during a hot summer, various liquids, including freshly boiled wort, blood, white of egg, whey, urine, broth, and milk; but when afterwards the plug of cotton was withdrawn, these liquids in a few days began to undergo decomposition. He explains these results by supposing

126

PREPARATION OF MALT.

that the spores of some organism must find access to the substance in order to set up the process of decomposition; by a temperature of 260° any such spores which the substance itself might contain are destroyed, and as the air is filtered through the cotton before it reaches the interior of the flask, none of these organic germs can afterwards obtain access to the body under experiment. I have repeated some of these experiments with complete success. If air be transmitted with suitable precautions slowly through narrow ignited platinum tubes, so as to destroy all suspended organic particles, no fermentation or putrefaction will take place on admitting such air to contact with putrescible substances previously heated to 260° for an hour. Pasteur has shown the existence of these floating germs in the air by drawing a large volume of atmospheric air, by means of an aspirator, through a narrow tube obstructed with collodion wool. On subsequently dissolving this wool in a mixture of alcohol and ether, various microscopic sporules were left undissolved. An elaborate experimental discussion of the subject occurs in a paper of Pasteur (Ann. de Chimie, III. lxiv. 5).

(1098) Preparation of Malt.-Upon the proper management of the process of malting much of the success of the subsequent brewing depends. The seasons most favourable for malting are spring and autumn, when the temperature is neither very high nor very low. The barley first undergoes the operation of steeping. This is effected in stone troughs, where the grain is covered with water to a depth of about 6 inches (15 centimetres). The lighter and decayed seeds float, and are skimmed off, whilst the sound grain, being heavier than the water, subsides. The steeping is continued until the grain becomes uniformly soft, and this occupies generally from 40 to 60 hours, the water being changed twice or thrice. During this stage the barley swells considerably from the moisture which it imbibes, and increases in weight nearly one-half. After a final washing it is drained, and then couched, or placed in heaps of about 15 inches in height upon the floor. In these heaps it becomes warm, and continues to swell for the next twenty-four hours; by this time it begins to sprout; as soon as the first whitish protuberance shows itself, the heaps are evenly distributed over the floor of a darkened apartment, and the process termed sweating follows. In this state it is allowed to remain several days, usually fourteen; the workmen turning it twice or thrice daily with wooden shovels. This step is employed for the purpose of equalizing the heat, in order that the process of germination may proceed at all points with equal

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rapidity. By this manipulation the temperature is maintained at a point varying between 55° and 62°. In from 10 to 20 days, according to the heat of the weather, the germination is complete; as soon as the radicle, or acrospire, as the maltster calls it, has shot to the length of about half an inch, when it bifurcates, and just as the plumula or leaf-shoot is about to make its appearance, the vitality of the seed is extinguished by rapidly drying the grain. In order to effect this object, the malt is spread to the depth of about 2 inches, upon floors made of perforated metallic plates. Here it is left to dry in a current of air for some hours, at a temperature not exceeding 90° (32° C.); and at the end of this time fire is lighted underneath. It is necessary that the greater part of the moisture be expelled before the fire be kindled; afterwards the heat is allowed to rise gradually, but not to exceed 140° (60° C.) otherwise the starch of the grain would be acted on, and much of the diastase would lose its efficacy. High dried malt is subjected to a much higher temperature, and is actually scorched on the outside. Such malt, however, is used only in small quantity as a colouring ingredient, to give the customary deep brown tinge to porter. During the drying, which occupies two or three days, the grain requires frequent stirring, in order that the desiccation may take place regularly. Barley generally yields about 80 per cent. of malt after drying and sifting from the radicles. According to Thomson, 12 per cent, of this loss is due to water, only 8 per cent. being actually wasted in the form of carbonic anhydride and trimmings. During the germination, oxygen is absorbed, and a large quantity of carbonic anhydride is set at liberty. Other grains, such as wheat, oats, rye, and even Indian corn, may be malted, but experience has shown that barley is the grain best adapted to this process. It yields the largest quantity of diastase, although this does not exceed of the weight of the grain. The diastase appears to be developed at the expense of the azotised constituents of the grain. It is generated chiefly in the neighbourhood of the young germ, not of the rootlet.

It

According to the experiments of Lawes, 100 parts of dry barley yield 9022 of malt, and 3'99 of malt and kiln dust. is remarkable that the malt dust, consisting chiefly of the radicles of the seed, carries off with it a great deal of the nitrogen of the grain, amounting to nearly one-ninth of the entire quantity contained in the barley. The loss in nitrogen which barley suffers in becoming converted into malt rises to as much as 13.5 per cent. of the total quantity of nitrogen contained in 100 parts of dry barley. Lawes found the nitrogen in the barley to amount to

178 per cent. of the weight of the dry grain: that contained in dry malt being 1.70 per cent.

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(1099) DEXTRIN (ЄH10) is a transparent, brittle solid, with a vitreous fracture, and is indeed an artificial gum produced by a transformation of starch. It is soluble in water and in dilute alcohol, but is insoluble in anhydrous alcohol or in ether; wood spirit dissolves it freely. Dextrin is distinguished by producing right-handed rotation upon a ray of polarized light, and it derives its name from this property. It differs from starch in not yielding any coloration with iodine. It does not reduce cupric potassiotartrate on boiling. It is not susceptible of fermentation. By boiling for several hours with dilute sulphuric acid, it combines with water, and is converted into dextrose. It may be distinguished from gum by yielding with nitric acid, oxalic acid only, and no mucic acid. Payen has contrived a method of preparing crude dextrin on a large scale, which consists in moistening 10 parts of starch with 3 of water containing of its weight of nitric acid, allowing the mixture to dry spontaneously, then spreading the starch upon shelves in layers of an inch and a-half in depth, and heating them for an hour or an hour and a half in an oven to about 239° (115° C.) It consists of a mixture of dextrin with glucose and unchanged starch. When pure dextrin is required, Musculus recommends it to be prepared as follows:-Starch is diffused through water and boiled with diluted sulphuric acid till it gives no blue or red coloration with tincture of iodine. Well washed yeast is then added to destroy the glucose by fermentation. When this process is complete, the solution is filtered, evaporated, and the residue treated with absolute alcohol; the undissolved residue is dextrin, nearly pure. Dextrin is likewise largely manufactured in a form more or less coloured by heating starch to about 400° (p. 118), when it yields British gum. It may also be obtained by heating an infusion of ground malt in water to 165° (74° C.), and adding starch in small quantities at a time; as soon as the starch is dissolved the liquid is rapidly heated to 212°, filtered, and evaporated, with constant agitation, until it has acquired a syrupy consistence. Pure dextrin gives no precipitate with basic acetate of lead (Musculus).

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(1100) INULIN (dried at 212°, H100; Dubrunfaut).—The roots of many plants, among which are those of the dahlia, elecampane (Inula helenium), colchicum, dandelion, and chicory, contain a variety of starch, to which the name of inulin has been