The value of oak bark depends upon the amount of tannin contained in it, which varies much, depending not only on the growth of the tree but on the care bestowed on the preparation of the bark itself, as it soon ferments and spoils by exposure to wet, while too much sun-heat is injurious.
The bark and young cones afford a tanning material, inferior indeed to oakbark, and hardly equal to that of the larch, but of value in countries where substances more rich in tannin are not abundant.
The wood contains no tannin, and for this reason quassia, like chiretta and calumba, may be preserved with iron.
An astringent fluid, known as shibu, rich in tannin, is expressed from the green fruit and used in various industries.
In addition to their use for timber or basket-making, willows contain a large quantity of tannin in their bark.
Chinese galls examined by Viedt 12 yielded 72% of tannin, and less mucilage than Aleppo galls.
A comparatively new product in this region is that of canaigre, which is grown for the tannin found in its root.
It contains, in addition to tannin, a peculiar principle called larixin, which may be obtained in a pure state by distillation from a concentrated infusion of the bark; it is a colourless substance in long crystals, with a bitter and astringent taste, and a faint acid reaction; hence some term it larixinic acid.
Thus the protoand per-salts of iron, as well as the protoand per-salts of tin, including also a large variety of tannin, sumac, divi-divi, chestnut, valonia, the acacias (Areca Catechu and Acacia Catechu from India), from which are obtained cutch and gambier, &c., are no longer used solely as mordants or tinctorial matters, but mainly to serve the object of converting the silk into a greatly-expanded fibre, consisting of a conglomeration of more or less of these substances."
The principal chemicals in tea are: caffeine, tannin and essential oil.
The amount of tannin found in green teas appears to be FIG.
Tannin is a hardening and astringent substance, and in large quantities impairs digestion.
Apart from the literary characteristics which clearly differentiate this narrative from the preceding accounts of J and E, the following points of variation are worthy of consideration: (I) The people refuse to listen to Moses; (2) Aaron is appointed to be Moses' spokesman, not with the people, but with Pharaoh; (3) one sign is given (not three) and performed before Pharaoh; (4) the rod is turned into a reptile (tannin), not a serpent (n(thash).
Among other contents of the cell, fatty substances and tannin are known.
The presence of tannin has been established in the case of a great number of freshwater algae.
The bark of various Australian species, known as wattles, is also very rich in tannin and forms an important article of export.
Are also rich in tannin and used by tanners.
The proteid matter combines with a part of the tannin in the wine, forming an insoluble tannate, and this gradually subsides to the bottom of the cask, dragging with it the mechanically suspended matters which are the main cause of the wine's turbidity.
Some wines, particularly those which lack acid or tannin, are very difficult to fine.
The character of the acidity, however, changes, the free tartaric acid gradually disappearing, forming bitartrate of potash and being otherwise broken up. On the other hand, the free malic acid increases and the tannin decreases.
When the grape is ripe, the sugar has attained to a maximum and the acidity is very much reduced; the tannin has entirely disappeared.
In the case of red wines colouring matter is dissolved from the skins and a certain amount of mineral matter and tannin is extracted.
The tannin in young red wines may amount to as much as 0.4 or 0.5%, but in white wines it is much less.
As the wine matures the most noticeable feature in the first instance is the reduction in the acidity, which is mainly due to a deposition of tartar, and the disappearance of tannin and colouring matter, due to fining and the action of oxygen.
The softening effect of age is due to the deposition of a part of the tartar together with a part of the tannin and some of the colouring matter.
This disease is also caused by the wine lacking alcohol, acid and tannin, and to the presence of an excess of albuminous matters.
As a rule this disease is due to a lack of tannin (hence its more frequent occurrence in white wines).
Frequently alcohol, tannin, glycerin, and similar wine constituents are also added.
It is to this relatively large amount of body and absence of an excess of acid and of tannin that the peculiarly soft effect of the Bordeaux wines on the palate is due.
Comparing the fine wines of the better vintages with, for instance, the red wines of the Gironde, the main features of interest are the relatively high proportions of acid and glycerin and the low proportion of tannin which they contain.
TANNIN, or Tannic Acid, the generic name for a widely disseminated group of vegetable products, so named from their property of converting raw hide into leather.
Oak tannin; whilst others yield protocatechuic acid and phloroglucin, e.g.
Moringa-tannin; common tannin, however, is a digallic acid.
Common tannin, or tannic acid, C, 4 H, 0 0 9.2H 2 O, occurs to the extent of 50% in gall-nuts, and also in tea, sumach and in other plants.
It may be obtained by extracting powdered gall-nuts with a mixture of ether and alcohol, whereupon the tannin is taken up in the lower layer, which on separation and evaporation yields the acid.
The tannin of oak, C/9H16010, which is found, mixed with gallic acid, ellagic acid and quercite, in oak bark, is a red powder; its aqueous solution is coloured dark blue by ferric chloride, and boiling with dilute sulphuric acid gives oak red or phlobaphene.
The tannin of coffee, C3,H,80,6, found in coffee beans, is not precipitated from its solutions by gelatin.
Moringa-tannin or maclurin, C1,H1006 H20, found in Morus tinctoria, hydrolyses on fusion with caustic potash to phloroglucin and protocatechuic acid.
Catechu-tannin occurs in the extract of Mimosa catechu; and kino-tannin is the chief ingredient of kino (q.v.).
Frequent doses of a teaspoonful of tannin dissolved ' in water should be administered, together with strong tea and coffee and mucilaginous fluids.
The bark of the horse-chestnut contains a greenish oil, resin, a yellow body, a tannin, C26 H 24012, existing likewise in the seeds and various parts of the tree, and decomposable into phloroglucin and aesciglyoxalic acid, C 7 H 6 O 3, also aesculetin hydrate, and the crystalline fluorescent compound aesculin, of the formulaC21H24013 (Rochleder and Schwarz), with which occurs a similar substance fraxin, the paviin of Sir G.
An excess of the precipitant is shown by a drop of the solution imparting a yellow colour to a solution of tannin, prepared by dissolving one part of tannin in 300 of water; drops of this solution are placed on a white porcelain plate, and as the precipitant is added to the lead solution a drop of the latter is removed from time to time on a glass stirring-rod and added to one of the drops on the porcelain plate.
Colloidal silver is the name given by Carey Lea to the precipitates obtained by adding reducing solutions, such as ferrous sulphate, tartrates, citrates, tannin, &c., or to silver solutions.
Gallic acid is most readily obtained by boiling the tannin procured from oak-galls by means of alcohol and ether with weak solution of acids.
Owing to the quantity of tannin they contain, no harmful miasma exhales from the Irish bogs.