Pyrogallol

“ When pyrogallol is made in the ordinary way by heating gallic or tannic acids to 410° F. (210° C.) , much of this body is formed, even if the process be conducted in a stream of carbonic acid, and the yield of pyrogallol usually amounts to only about 5 per cent. of the gallic acid employed (see p. 65) .
Catechol.—Pyrocatechol, pyrocatechin, oxyphenic acid, C6H4 (OH) 2.
Sources.—Beside that of the decomposition of certain tannins by heat (see p. 63) , catechol is produced by the dry distillation of catechin and some allied bodies which frequently accompany the tannins. ”

“ Assuming that this is true, how can we account for the anomalous fact that in high concentrations of oxygen, phosphorus will not luminesce or that in high concentrations of pyrogallol, there is no luminescence in presence of ozone or of oxidizer and H2O2. Of course with high active mass of oxygen (in case of phosphorous luminescence) or of pyrogallol (in case of pyrogallol luminescence) the reaction velocity must be [Pg 150] greater than the optimum. If that is the case, then lowering the temperature should reduce the reaction velocity to the optimum and light should appear. ”

“ It is, of course, comparable to luciferase and acts on the thermostable, dialyz [Pg 112] able pyrogallol-H2O2 mixture, which is comparable to luciferin. Curiously enough, although many hydroxyphenol and amino-phenol compounds can be oxidized by peroxidase and H2O2, only pyrogallol and gallic acid will oxidize with light production. Many other oxidizers can take the place of the peroxidase. ”

“ When pyrogallol is oxidized by K4Fe (CN) 6 and H2O2, it is not completely oxidized and probably only a small amount of the energy is converted into light; otherwise we should be able to see the luminescence of a very much weaker concentration of pyrogallol. As the reaction luciferin ⇆ oxyluciferin is so easily reversible, very little energy must be liberated, and, as experiments indicate, very little heat, if any, accompanies light production. Even though this be true, it is still possible for a very small amount of luciferin to produce a very large amount of light. ”

“ As the hæmoglobin does not lose this power on boiling, whereas luciferase does, the analogy is far from perfect. Many oxygen carriers are known, however, which may be destroyed on boiling their solutions, namely, the peroxidases of plant juices. Esculin will not luminesce with peroxidase and H2O2, but pyrogallol or gallic acid will. If one mixes a test tube containing pyrogallol solution + H2O2 with potato or turnip juice or almost any plant extract, a yellowish luminescence appears. The plant extract loses the power to cause such luminescence on boiling and the peroxidase will not dialyze. ”

“ We may, therefore, divide tannins broadly into derivatives of catechol, which yield no bloom, and usually give greenish-blacks with iron acetate, and which include hemlock, mimosa, cutch, gambier, quebracho, &c; derivatives of pyrogallol, which give bluish-blacks with iron, deposit bloom in leather, and embrace galls, sumach, divi-divi, myrobalans, pomegranate rind, &c., and tannins which contain both pyrogallol and catechol, such as oak-bark and valonia, and which, as is well known, yield bloom, and give blue-blacks with iron. ”

“ Table 11 shows this effect of temperature with K4Fe (CN) 6 and varying concentrations of pyrogallol, and Table 12 shows the effect of temperature with pyrogallol and varying concentrations of K4Fe (CN) 6. Table 10 shows the relation between temperature and intensity of luminescence with pyrogallol and various oxidizers. The terms faint, fair, good, and bright are purely relative designations of brightness as estimated by the eye, for accurate measurements of weak intensities are very difficult to make. ”

“ Guinchant (1905) has described oxyluminescence of uric acid and asparagine, Weitlaner (1911) of substances in humus and McDermott (1913) of substances in urine and the anaerobic alkaline hydrolysis products of glue and Witte's peptone. Pyrogallol is especially prone to luminesce, as was first noticed by Lenard and Wolf (1888) in developing a photographic plate with pyrogallol developer. Later the luminescence was studied in some detail by Trautz and Schloringin (1904-5) who developed the well-known luminescent mix [Pg 38] ture of pyrogallol, formaldehyde, K2CO3 and H2O2. ”

“ The sensitivity of our eye is largely responsible for the detection of so small an energy change. As we have seen, recent determinations have proved that the dark adapted eye can detect 18 × 10-10 ergs per second. From the heat of complete oxidation of pyrogallol it is possible to calculate the amount of pyrogallol necessary to give 18 × 10-10 ergs if completely oxidized. ”

“ It is not decomposed by concentrated hydrochloric acid; by melting hæmatoxylin with potash, pyrogallol (pyrogallic acid, C6H6O3) is obtained. Alum and the salts of lead throw down precipitates from solutions of hæmatoxylin, the latter being of a bluish-black colour. Logwood affords upon incineration 3·3 per cent. of ash.
The colouring matter being abundantly soluble in boiling water, an Extract of Logwood is also prepared on a large scale. It occurs in commerce in the form of a blackish brittle mass, taking the form of the wooden chest into which it is put while soft. ”

“ Two well-known developing agents, pyrogallol—commonly called pyro—and hydrochinon, are composed of the same chemical elements, carbon, oxygen, and hydrogen, the only difference in their composition being that a molecule of pyro contains one more atom of oxygen than the hydrochinon. The chemical formula for pyro is C6H6O3, and the chemical formula for hydrochinon is C6H6O2.
The chemical compounds employed in photography are used in the form of solutions. A solution is the liquid combination of a liquid and a solid. ”

“ They all give a black in lieu of that dark olive-green deposit of silver which is so often found with pyrogallol developers. All are alkaline developers, and the image is built up from the sensitive salt within the film. They are applicable to gelatin or collodion plates, but for the latter rather more bromide o an alkali is added, to retard fogging. ”

“ Products of the Decomposition of Tannins by Heat.—Pyrogallol, « 66 » pyrogallic acid, C6H6O3, has a bitter, but not sour taste, and feebly reddens litmus, but the addition of the smallest trace of alkali gives it an alkaline reaction. It is poisonous, 2 gr. having killed a dog. It is soluble in less than 3 parts of cold water, and still more freely in hot. It is also soluble in alcohol, ether, acetone, ethyl acetate, and glycerin, but not in absolute chloroform, or petroleum spirit. It fuses at 268° F. (131° C.) (Etti) , and sublimes at about 410° F. (210° C.) . ”

“ Pyrogallol tannins give a blue-black coloration or precipitate with ferric salts, and catechol tannins a green-black; and whereas bromine water gives a precipitate with catechol tannins, it does not with pyrogallol tannins. ”

“ Among the essential oils, the oil of cloves yields a strong, clear image, and good results are also obtained from oil of Roman camomile and oil of peppermint. The organic bases exhibit little developing power. Concerning pyrogallol the author writes that with potassium formate it gives better results than with any other substance. ”

“ About a dozen distinct compounds producing different shades of pink, crimson and red, and all derived from fluoresceïn, are at present in the market, and a few other phthaleïns formed by heating phthalic anhydride with other phenolic compounds instead of resorcinol or pyrogallol (e.g. diethylamidophenol) , are also of industrial importance. ”

“ Any excess of ammonia produces an amethyst-red, and acetic acid restores the blue. Its solution is turned brown by traces of nitrous acid. With lime-water it produces a beautiful but evanescent purple, rapidly turning brown. In presence of alkalies it absorbs oxygen from the air with great avidity, turning orange, brown, and black. Pyrogallol does not precipitate gelatin. Its solution rapidly reduces permanganate, Fehling's solution, and salts of gold, silver, [F] mercury, and platinum. ”

“ The following hypothesis has been suggested to explain the relative resistance of the three species: In the American chestnut bark the concentration of the available toxic tannin never reaches a level where it can stop the advancing parasite. The tannins in the Japanese species, although of the same type as in the native tree, are more soluble and reach a level toxic to the fungus. In the Chinese trees all the tannins of the bark belong to the toxic pyrogallol groups, and this, combined with their high solubility, results in the high degree of resistance in this species (4) . ”

“ Bismuth salt of nosophen.—Odorl., tastel., insol. powd.; 52.9% iodine.—Intest. Antiseptic and Astringent.—Dose: 4—10 grn., 3—5 t. daily.
Eugallol.
Pyrogallol Monoacetate, Knoll.—Syrupy, transparent, dark-yellow mass.—Sol. in water readily.—Succedaneum for Pyrogallol in obstinate chronic psoriasis; very vigorous in action.—Applied like pyrogallol.
Eugenol Merck.—Pure.
Eugenic Acid; Caryophyllic Acid.—Colorl., oily liq.; spicy odor; burning taste.—Sol. in alcohol, ether, chloroform, solut. caustic soda,—Antiseptic, Antitubercular, Local Anesthetic.—Uses: Extern., oint. ”

“ Hence the younger barks, which alone are medicinal, are widely different from the older in structure and appearance.
Chemical Composition—The most interesting constituent is a peculiar kind of tannin. Stenhouse pointed out in 1843 that the tannic acid of oak bark is not identical with that of nutgalls; and such many years afterwards was proved to be the case.
The first-named substance, now called Querci-tannic Acid, yields by destructive distillation pyrocatechin, and according to Johanson (1875) very little pyrogallol. ”

“ Pyridine Merck.—C.P.
Colorl., limpid, hygroscopic liq.; empyreumatic odor; sharp taste.—Miscible with water, alcohol, ether, fatty oils, etc.—Respiratory Sedative, Antigonorrhoic, Antiseptic.—Uses: Asthma, angina pectoris, dyspnea, gonorrhea, etc. Contra-indicated in heart weakness.—Dose: 2—10 drops, several t. daily in water. Usually by inhalation; 45—75 ♏, evaporated spontaneously in room. As urethral injection, 1/3% solut.; as paint, 10% solut.
Pyrogallol,—see Acid, Pyrogallic. ”

“ It is resinified by the action of concentrated mineral acids. On warming solutions of pyrrol in dilute acid, ammonia is evolved, and an amorphous powder of variable composition, known as pyrrol-red, separates out. The pyrrol ring is easily broken, e.g. hydroxylamine gives the dioxime of succinic aldehyde. Pyrrol is readily converted into pyridine derivatives by acting with bromoform, chloroform, or methylene iodide on its potassium salt, β-brom-and β-chlorpyridine being obtained with the first two compounds, and pyridine itself with the last. ”

“ Should the picture be very tardy, either from an insufficient exposure, want of light, or other cause, a few drops of a solution of pyrogallic acid, made with 3 grains to the ounce of water, and a drachm of acetic acid, will act very beneficially. It sometimes gives an unpleasant redness upon the surface, but produces great intensity upon looking through it. Until the pyrogallic solution was added, there was scarcely anything visible upon the specimen exhibited, the failure having in the first instance happened from the badness of the iodized paper. ”

“ Ether when shaken with the concentrated aqueous solution and left to evaporate, leaves colourless crystals of pyrocatechin which after purification are devoid of acid reaction. They have a peculiar burning persistent taste, and are very pungent and irritating when allowed to evaporate. A solution of pyrocatechin yields with perchloride of iron a dark green coloration changing to black after a few moments, and becoming red on the addition of potash. ”

“ Guaiacol may be obtained directly from beechwood tar, from pyrocatechin by methylation with potash and potassium methyl sulphate at 180°, or from anisol by nitration, reduction of the ortho-nitroanisol to amino-anisol, which is then diazotized and boiled with water. It melts at 28° and boils at 250°. It is employed in medicine as an expectorant. The dimethyl ether or veratrol is also used in medicine. Many other pyrocatechin derivatives have been suggested for therapeutic application. Guaiacol carbonate is known as duotal, the phosphate as phosphatol, the phosphate as guaiaco-phosphal ”

“ They are easily sublimed at some degrees above their fusing point (104° C.) , or removed by acetic acid, in which as well as in water they are readily soluble. Hence in some sorts of tar this substance does not occur, it having probably been removed by water.
Pyrocatechin, C6H4 (OH) 2, can be obtained by the destructive distillation of many other substances, as catechu, kino, the extracts of rhatany and bearberry leaves, and other extracts rich in that form of tannin which produces greenish (not blue-black) precipitates in salts of iron. ”

“ It is not necessary to make up the full amount of 2 oz. pyro at one time.
In the foregoing two formulæ will be found all that is necessary for making good negatives by either process.
Every box of plates that is put up for sale carries p177 with it the formula supposed to be best for that plate. There are other forms of development that produce good work. The following is one of them:
FERRO-CYANIDE OF POTASSIUM DEVELOPER.
Make a saturated solution of yellow prussiate of potassium and dilute with an equal bulk of water; add 2 drops of ammonia and 2 grains of dry pyro to each ounce used. ”