Gallic acid

“ If the picture will not develop, from too short exposure in the camera, a solution of pyrogallic acid, as Dr. Diamond recommends, after the gallic acid has done its utmost, greatly increases the strength of the blacks: it slightly reddens the whites, but not in the same ratio that it deepens the blacks.
After the first wash with gallo-nitrate, it is essential to develop these strongly iodized papers with gallic acid only: the half-and-half mixture of aceto-nitrate and gallic acid, which works well with weaker papers, turns these red. ”

“ I excite my paper with equal proportions of saturated solution of gallic acid and aceto-nitrate of silver, one or two drops of each to the drachm of distilled water. I always plunge the bottle of gallic acid solution into hot water when first made, which enables it to take up more of the acid; on cooling, the excess crystallises at the bottom. This ensures an even strength of solution: it will keep any length of time, if a small piece of camphor be allowed to float in it. ”

“ Gallic acid was discovered by Scheele in 1786, and exists ready formed in the bark of many trees, and in gall-nuts. It is always associated with tannin, a substance to which it is allied in a manner hitherto unexplained. It is distinguished from tannin by causing no precipitate in a solution of gelatine. With a salt of iron it forms a dark blue coloured compound, which is the basis of ink. The finest colour is procured when the peroxide and protoxide of iron are mixed together. This character distinguishes gallic acid from every other substance excepting tannin. ”

“ Apple juice was used in medicine in the sixteenth century, and the soda salt of its characteristic acid (malic acid) was prepared by Donald Monro in 1767.
It was known to the ancients that extract of gall nuts acquired a black colour when mixed with a solution of iron vitriol; and Boyle and Bergmann ascribed this phenomenon to the presence of a peculiar acid. Gallic acid was first isolated by Scheele in 1785, and its composition established by Berzelius in 1814. Tannic acid was definitely recognised as distinct from gallic acid by Seguin in 1795. ”

“ It is better, as soon as the gallic acid has been applied, to put the picture away from the light of the candle in a box or drawer, there to develop quietly, watching its progress every three or four minutes; the surface is to be refreshed by a few light touches of the brush, adding more gallic acid if necessary. ”

“ Hydrolysis of leucogallic acid yields gallic acid and gallic aldehyde; oxidation by means of hydrogen peroxide yields ellagic acid and luteic acid, and oxidation with potassium persulphate and sulphuric acid, in acetic acid solution, yields purpurotannin (see below) [Footnote: Liebig's Ann., 1912, 386, 318.] .
Another distinct difference between digallic acid and leucodigallic acid is the fact that the formaldehyde condensation product of the former resembles gallic acid, whereas that of the latter resembles tannin ”

“ You inform me that some persons doubt whether I really obtain gallate of silver when using an infusion of gall-nuts, and that one of Mr. Talbot's friends raises the question. It is sufficient to reply, that though gallic acid is largely formed by a long exposure of an infusion of gall-nuts to the atmosphere, as first proposed by Scheele, yet this acid does exist in the gall-nut in its natural state, and in a sufficient quantity to form gallate of silver as a photogenic agent ”

“ By boiling gallic acid with solution of arsenic acid, Schiff obtained a product which precipitated gelatin, and otherwise reacted like tannin, and he regards this as digallic acid, but « 77 » other experimenters have failed to obtain digallic acid by this means, and have found that on complete removal of arsenic, the compound was reconverted to gallic acid. ”

“ For further identification, some of the acid was converted into an ester by the following process: it was dissolved in 80 per cent. alcohol, hydrochloric acid gas was passed in, and the solution was heated an hour on the water bath. It was then evaporated to a small bulk, neutralized with barium carbonate and extracted with ether. The ether, on evaporation, left the ester which was crystallized from water and dried in a desiccator over sulphuric acid. The anhydrous ester agreed in melting point (156° to 159°) and other properties with the ester of gallic acid described by Grimaux. ”

“ The solution of acetate of ammonia decomposes that of this salt, in consequence of the carbonic acid which is generally diffused through it. It has lately been discovered that Gallic acid and Tannin are capable of combining with lead in solution, and of forming a perfectly insoluble substance, which falls to the bottom of the vessel; hence all vegetable astringents must be considered as incompatible with this medicine. On this account, liquors which have been kept in oak casks, [603] for a certain time, must be freed from lead. ”

“ I have generally put a little camphor in the gallic acid solution, as recommended by Laborde. It prevents the decomposition of the gallic acid, and renders the image clearer and free from spots. A piece about the size of a pea for four or five ounces of solution.
As to the third difficulty, I believe nothing but replacing the porcelain dishes by glass ones will prevent the dirty marbled appearance in the bottom of the dishes made of porcelain; they are generally rough and uneven on the surface, and there are often what is called "kiln-cracks" in the angular parts. ”

“ The antimony must be in solution as antimonious chloride, and must not be accompanied by an excess of hydrochloric acid. To ensure these conditions, the solution is treated with potassium iodide until no more iodine is evolved, and is then evaporated to remove the excess of hydrochloric acid. To the concentrated, and nearly neutral, solution a freshly-prepared solution of gallic acid is added in slight excess. A bulky white precipitate is formed that settles rapidly. The solution is diluted with hot water and washed by decantation. ”

“ 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. When pure the acid forms a colourless, amorphous mass, very soluble in water, less so in alcohol, and practically insoluble in ether. Common salt precipitates it from aqueous solutions. It forms a penta-acetate. It may be obtained artificially by heating gallic acid with phosphorus oxychloride or dilute arsenic acid (cf. P. Biginelli, Gazetta, 1909, 39, ii. pp. 268 et seq.) ”

“ In all the works on photography, the directions given run generally as follow:—'Put an excess of gallic acid into distilled water, shake the mixture for about five minutes, allow it to deposit, and then pour off the supernatant fluid, which is found to be a saturated solution of the acid.'
"Now I have found by constant experiment, that by keeping an excess of acid in water for several days, the strength of the solution is greatly increased, and its action as a developing agent materially improved. ”

“ After having ascertained that the gallic acid produces this uniform colour on the impression, only because it is combined in small quantity with the aceto-azotate of silver, M. Blanquart-Evrard removes all the difficulty. After taking the proof from the camera obscura, he plunges it into a vessel of large dimensions, covered with a layer of one centimètre of gallic acid of cold saturation. ”

“ The phthaleïn formed from gallic acid and phthalic anhydride really results from the union of the latter with pyrogallol. It is now manufactured under the name of “galleïn,” and is largely used [Pg 147] for imparting a bluish grey shade to cotton fabrics. By heating galleïn with strong sulphuric acid, it is transformed into another colouring-matter which gives remarkably fast olive-green shades when dyed on cotton fibre with a suitable mordant. This derivative of galleïn is used to a considerable extent under the name of “cœruleïn.” ”

“ A strong aqueous solution of tannic acid (tannin) is added to sulphuric acid as long as a precipitate falls; the powder is collected, washed, and dissolved by the aid of heat in dilute sulphuric acid; the solution, after being boiled for a few minutes, deposits, on cooling, crystals of gallic acid in considerable quantity.
4. (Scheele.) A filtered decoction of galls is exposed for some months in an open vessel; after a time it grows mouldy, and becomes covered with a thick, glutinous pellicle ”

“ In the Red bark, Fourcroy detected also a portion of citric acid, some muriate of ammonia, and muriate of lime. Upon which of these principles the tonic and febrifuge virtues of bark depends, has ever proved a fruitful source of controversy. Deschamps attributed them to Cinchonate of Lime, and asserted that two doses of thirty-six grains each, would cure any intermittent. Westering considered Tannin as the active constituent; while M. Seguin assigned all the virtues to the principle which precipitates gallic acid, and which, as it has been before stated, he mistook for gelatine. ”

“ The presence of other plant [Pg 19] substances in the solution also interferes with the color tests, and finally, a substance which gives a blue color with iron salts and one giving a green color may be found together in the same plant. [19] Further tests with a solution of the resin in dilute alcohol, and with a water solution of the acid precipitated by adding sulphuric acid to a solution of the resin in potassium hydroxide, led to the conclusion that the acid is gallic acid. ”

“ The former of these precipitates extractive, without materially acting upon gallic acid, which is thrown down by the latter: the greatest care, however, must be taken not to add the iron in excess, as in that case the black precipitate formed will be redissolved, and an olive-coloured and clear fluid be only obtained.
He details the results of a number of experiments made upon galls, and ascertains the relative proportions of their several elements; and he proves that tannin may exist in such a state of combination in different substances as to elude the test of gelatine ”

“ The contents of the three gallic acid derivatives decreased remarkably with the development of leaves. For instance, the content of β-glucogallin and galloylquinic acid in the fourth leaf decreased to 10.37% and 11.69%, respectively, when compared to the bud. The accumulation of HCA derivatives was found to be developmentally regulated in leaf. The content was high in the first leaf, followed by the bud, and reduced significantly in the fourth leaf. The accumulation of GA and HCA derivatives in both stem and root were trace, but quinic acid was highly accumulated in the stem. ”

“ Tincture of galls, or instead of this, what is simpler, gallic acid, is used in lithography. It contains plenty of tannin, and is one of the most efficacious means of preventing the combination of the stone or zinc plate with fatty substances. ”

“ These observations were in accordance with the accumulation patterns of gallic acid derivatives, HCA derivatives, anthocyanidins, and galloylated catechins (Fig. 4) . Some genes in this subgroup had proved to be involved in the biosynthesis of gallic acid derivatives and galloylated catechins. For instance, CsUGT75E2 and CsUGT75E3 could be gathered in group L of the phylogenetic tree together with Arabidopsis UGT75B1 (data were not shown) ”

“ The essential ingredients of ordinary black ink are—first, tannin-yielding bodies, for which Aleppo or Chinese galls are the most eligible materials; second, a salt of iron, ferrous sulphate (green vitriol) being alone employed; and third, a gummy or mucilaginous agent to keep in suspension the insoluble tinctorial matter of the ink. For ink-making the tannin has first to be transformed into gallic acid. In the case of Aleppo galls this change takes place by fermentation when the solution of the galls is exposed to the air, the tannin splitting up into gallic acid and sugar. ”

“ When it has floated a short time, "it does not require so long a time as the acid process." It is, while wet, floated again upon a weak solution of free iodine for about half a minute; it may then be dried, and is ready for the sensitive solution. This last must be acid, and any of the approved formulæ will suit it; but the solution, whatever it is, must be allowed to dry before placing between the white glasses, nor on any account ought it to be touched with blotting-paper. The image is to be brought out with gallic acid and acetic acid, laid over with a brush, and requires no heat. ”

“ A 1⁄4 of an ounce of gallic acid put into such a 3-ounce bottle, and quite filled up with distilled water as often as any is used, will serve a very long time.
I would also recommend that the paper should be excited upon the morning of the day upon which it is intended to be used; no doubt the longer it is kept, the less active and less certain it becomes. I have, however, used it successfully eight days after excitement, and have a good negative produced at that length of time. The general medium time of exposure required is five minutes. ”

“ The infusion and tincture of galls possess habitudes with which it is very important for the medical practitioner to be acquainted, not only for the purpose of directing their exhibition with success, but because the elements which impart to them their characteristic traits, viz. Gallic Acid and Tannin, [512] are very widely diffused through the products of the vegetable kingdom, and will be found to be constantly active in their chemical, medicinal, and pharmaceutical relations. ”