Tannic acid

“ Tannins are either free phenol-acids or, more commonly, glucosides of these acids. Common "tannin," when hydrolyzed, yields from 7 to 8 per cent of glucose, which indicates that it is a penta-acid ester of glucose, i.e., each glucose molecule has five acid groups attached to it. The formula for such a tannin is, therefore, as follows,
in which the R represents a complex phenol-acid like tannic acid, or digallic acid. ”

“ Having described the products of decomposition, something must be said of the way in which these constituents are combined to form the unaltered tannins. The only tannin of which we have as yet anything approaching complete knowledge is that obtained from galls, sumach, and myrabolans, and which is thence called gallotannic acid.
Gallotannic, or digallic acid exists as the principal tannic acid of the galls of oak, tamarisk, &c.; and, in mixture with more or less ellagitannic acid, in myrabolans, divi-divi, sumach, pomegranate rind, and many other plant-products. ”

“ Weak tincture of the iodine yields a white precipitate, which acquires an olive color with excess of the tincture. Pure and concentrated sulphuric acid does not alter it; when the mixture is heated it acquires a greenish brown color, and if the heat be continued it becomes blood-red and afterwards black. Nitric acid imparts to it a topaz color, which is not changed by the action of heat. Hydrochloric acid yields white vapors as ammonia does, and renders it violet, especially when heated. Tannic acid gives a white precipitate, and chloride of platinum a yellow precipitate. ”

“ Tannic matter was long supposed to be of one kind, namely that found in the oak gall, but the researches of later years have proved the tannin of different plants to possess distinctive characters: hence the term gallo-tannic acid to distinguish that of galls, from which it is principally derived. It was however shown by Stenhouse as far back as the year 1843, again in 1861, as well as by still more recent unpublished experiments, that the tannic acid found in Sicilian sumach, the leaves of Rhus Coriaria L., is identical with that of oak galls. ”

“ Of the rest the sulphuric-acid plant was most thriving, then the hydrochloric-acid plant, and last, and just alive, the plant treated with formic acid. Analyses of the ashes of the plants showed that the acid waters tended to introduce organic ingredients into their tissues. Of hyacinth-bulbs treated in a similar way, only the one treated with tannic acid developed roots. The hydrochloric-acid bulb died, and the sulphuric-acid bulb a month later. After the tannic-acid one, a bulb treated with oxalic acid did best. Tannic acid seemed to increase the intensity of the color of the flower. ”

“ Acid. Tann.) , Troches of Tannic Acid, U.S.P.—Each troche contains tannic acid (0.06 Gm. or 1 grain) , with sugar and tragacanth, flavored with orange flower. [Pg 14]
Unguentum Acidi Tannici (Ung. Acid. Tann.) , Ointment of Tannic Acid, U.S.P.—Tannic acid (20%) , in glycerin and ointment.
Acidum Tartaricum (Acid. Tart.) , Tartaric Acid, U.S.P.—Obtained from wine lees or argol.
A white, odorless powder, with an acid taste. Very soluble in water (1:0.75) and in alcohol (1:3.3) .
Action and Uses: Mild acid; used in the manufacture of effervescent salts.
Dosage: 0.5 Gm. or 8 grains, diluted. ”

“ In cold water it disintegrates, and in boiling water, alcohol, acetic acid and strong caustic alkali it is completely dissolved. Chemically it consists of a mixture of a peculiar variety of tannin termed catechu-tannic acid with catechin or catechuic acid, and a brown substance due to the alteration of both these principles. Catechu-tannic acid is an amorphous body soluble in cold water, while catechin occurs in minute, white, silky, needle-shaped crystals, which do not dissolve in cold water. ”

“ The tannic acid contained in the tablets could not be determined with accuracy but it was much less than 1 per cent. (or 1⁄8 grain per tablet) yet it is said to add valuable astringent qualities to Formitol Tablets! (The U. S. P. lozenge of tannic acid contains 1 grain of tannic acid.)
The quantity of guaiac (as resin) is but a fraction of 1 per cent. Yet it is said to impart to Formitol Tablets “stimulant resolvent” properties and it is intimated that there is sufficient to be of value in “cases of abscess of the throat and inflammation of the tissues.” ”

“ The presence of free gallic acid, fisetin, and rhamnose in the plant can be readily explained by a series of assumptions for which there is a considerable amount of experimental evidence. There is reason to believe that tannin-like bodies are formed at the expense of chlorophyll, [41] that complex tannin bodies can be broken down by acetic acid (also found in Rhus toxicodendron) into a tannic acid and a glucoside (for example, the "fustin-tannide" mentioned above yields tannic acid and fisetin-glucoside) ”

“ This is a fact that general practitioners often use to their own satisfaction and to their patient’s advantage, if it happen to be that kind of patient who does not object to make some sacrifice in order to be rid of troubles. The alkaloid which tea contains appears to be less easily absorbed than that of coffee, owing to the very large quantity of tannic acid present. The tannic acid in tea is doubtless one of the causes why it is as a drink so attractive. ”

“ Many are inclined to believe that both changes take place, and this view is probably correct, as a pure tannic acid produces a thin, empty leather, while a tanning material which contains a fair proportion of non-tannin matters, yields a full and firm leather. The practical tanner who adapts his work to the theory that tanning is a process of feeding the hides with gradually increasing strengths of tannin, is, in any event, on the right track. The suspender liquors are always weak in tannin, and are pumped from "handler" liquors through which packs of hides have already passed. ”

“ Tann′ate, a salt of tannic acid.—adjs. Tann′ic; Tannif′erous, yielding tannin.—n. Tan′-ride, an enclosure spread with tan for riding.—Tannic acid, an acid forming the astringent principle of the bark of oak and other trees, used in tanning and in medicine. [Fr. tannin.]
Tanrec=Tenrec (q.v.) .
Tansy, tan′zi, n. a genus of composite plants allied to Artemisia—Common tansy is a bitter, aromatic plant with small yellow flowers, common on old pasture: a pudding or cake flavoured with tansy, eaten at Easter. [O. Fr. tanasie, through Late L., from Gr. athanasia, immortality.] ”

“ Chemical Composition—The aqueous infusion of the herb exhibits a slight acid reaction, and has an intensely bitter taste, which appears due to an indifferent, non-basic principle, for the usual reagents do not indicate the presence of an alkaloid. Tannic acid on the other hand produces an abundant precipitate, a compound of itself with the bitter principle. ”

“ In fine, among exotic or indigenous woods, soft or hard, the most resistant are the richest in tannic acid, as among indigenous woods the oak and the chestnut; the first remarkably hard, the second soft enough, are both preserved during many years, and we cannot doubt that this is owing to the influence of the tannic acid with which they are impregnated, which, after the cutting of the wood, reacts upon the azotic and albuminous materials contained in their capillary vessels. ”

“ When men were skin-dressed animals they knew little or nothing of tanning. Tannic acid is found in nearly every plant that grows, and its combination with the fresh skins spread or thrown thereon, may have given rise to the observation of the beneficial result and subsequent practice. But whether discovered by chance, accident or experience, or invented from necessity, the art of tanning should have rendered the name of the discoverer immortal. ”

“ These are caustic soda, soda ash, and tannic-acid compounds, the last being derived from sumac, catechu, and the exhausted bark liquor from tanneries.
Caustic soda in large excess is injurious to boiler fittings, gaskets, valves, {122} etc. That it is injurious, in reasonable excess, to the boiler tubes themselves is yet to be proved. Foaming and priming may be caused through excess of caustic soda or soda ash, as is well known by every practical engineer. Tannic acid is to be condemned and the use of its salts is not to be recommended. ”

“ The outer cortical layer, as well as the zone of the nucleus-sheath, contains a little tannin, and a watery infusion of the drug is coloured greenish by perchloride of iron. Neutral acetate of lead precipitates some mucilage as well as the bitter principle, which latter may also be obtained by means of tannic acid. It is an amorphous, bitter substance, which deserves further investigation. By an alkaline solution of tartrate of copper the presence in serpentary of sugar is made evident. ”

“ Other elements also are used, such as gallic acid, alum, sulphate of iron, and copper, salt, and other agents."
"What are the chemicals for?"
Fig. 13. Tanning Vat.
"The tannic acid or the chemicals act on the skins, or, rather on the gelatin, glutin and albumen in the skins, and thus harden the texture and preserve it. Where tannin is not used and only the chemicals are employed, it is called 'tawing' the leather, instead of 'tanning.'"
"Well, we can get the bark; I know where there are several oak trees, and also a number of beech trees." ”

“ From galls, in tolerably fine powder, 8 oz., and a mixture of sulphuric ether, 3 pints, with water, 5 fl. oz.; by percolation, in successive portions, like the last; the aqueous solution of tannic acid being evaporated, and finally dried at a heat not exceeding 212° Fahr.
Prop., &c. Pure tannic acid is perfectly white, but as ordinarily met with it has a slight yellowish colour, owing to the action of the air; it is uncrystallisable; possesses a powerful and purely astringent taste, without bitterness; is freely soluble in water, less so in alcohol, and only very slightly in ether ”

“ Dissolved in tannic acid to the condition of a soluble salt, in proportions which vary according to the degree of hardness to be given to the wood, it is rapidly transformed under the influence of air, and is deposited in the cells of the wood in a solid state, which it petrifies, so to speak, thus increasing the preservative effects of the tannic acid. ”

“ In another case, by thirty minutes' active boiling, so much tannin as 1112 per cent of the tea-leaf was obtained in solution. Black teas are necessarily steeped longer than green, as they yield all their soluble matters more slowly. In coffee the proportion of tannin is not over one third, perhaps on an average not over one fourth or one fifth, of that in tea. The cacao-nib and its preparations are free from tannin. Guarana is heavily charged with a specific variety of tannic acid, and the mate is even more astringent than the tea-leaf. ”

“ The following gives the relative proportions of the various substances containing tannin:—1 lb. tannic acid equals 4 lbs. sumach, 18 lbs. myrobalans, 14 lbs. divi-divi, 11 lbs. oak galls. [Pg 48]
Examples from various recipes:
For 10 lbs. cotton use 12 ozs. tannic acid.
" 50 " " " 10 lbs. sumach.
" 40 " " " 10 lbs. "
" 20 " " " 2 lbs. yellow (or black) catechu.
" 20 " " " 3 lbs. catechu with 3 ozs. blue vitriol.
Some recipes soak the cotton 24 hours, others 48.
RECIPES FOR DYEING (1) INDIGO VAT
Take 3 oz. well ground indigo, mix into a paste with hot water. Slake 3 oz. ”

“ Whereas the catechol tannins (i.e., fir, gambir, hemlock, cutch, mangrove, and quebracho) are coloured black, those of the pyrogallol class (i.e., algarobilla, dividivi, valonea, gallotannic acid, myrabolams, and sumac) bluish-black, and the "mixed" tannins (i.e., canaigre, oak, and mimosa bark) bluish-purple by iron alum, Neradol D is coloured a pure blue. How sensitive this reaction is, the following comparative analyses illustrate: to each litre of tan liquor containing 4 gm. tanning matter prepared from (a) quebracho extract and (b) Neradol D, 10 c.c. of a 10 per cent. ”

“ Simand gives 61·1 grm. as the equivalent of quercitannic acid. Commercial "pure tannin" always gives results higher than the truth, as the gallic acid which it contains consumes more permanganate than an equal weight of tannin, or even than the tannin which would yield it if boiled with acid. When this is done the equivalent used should be definitely stated, or it will certainly lead to confusion. Neubauer's equivalent is only properly applicable to gall nuts, and possibly to sumach and myrabolans. For oak bark Oser's number or that of oxalic acid is most likely nearly correct ”

“ Calling this d, as c is to (b - d) , so is 6·3 to the percentage of non-tannins in terms of oxalic acid, and for the present it is best invariably to calculate results in this way, since we do not actually know the relation of any single tannin to permanganate, even Neubauer's number for gallotannic acid being probably too high, according to the recent investigations of Councler and Schroeder, [M] and Oser's for quercitannic being at most only approximate. ”

“ The fact that a positive reaction is given with aniline hydrochloride [Footnote: This reaction is carried out as follows:—5 c.c. of the tannin solution to be examined (about 4 gm. tanning matter per litre) are shaken violently in a test tube with 0.5 c.c. aniline and 2 c.c. concentrated HCl added. All natural tannins are unaffected by this treatment, ligninsulphonic and other sulphonic acids cause opalescence. Note.—Employing formic acid in lieu of hydrochloric acid (Knowles) renders the reaction no more reliable.—Transl.] is very puzzling ”