slightly soluble in officinal ether; they are decomposed by acids and by alkalies. Heated to 210°-215° C. (410°-419° F.), in absence of water, it is sublimed as pyrogallic acid and carbonic anhydride; at higher temperatures, other products are formed. Gallic acid is characterized by its physical properties (as above given); by its reactions with iron salts (a), with alkalies (b), with tartrate of antimony and potassa and with alkaline arsenate in the air (c), and with molybdate of ammonium (d). It is distinguished from the tannic acids by negative results with gelatin, albumen, and starch (e); by not precipitating the alkaloids, and by its far weaker reducing power (f) (distinction from pyrogallic acid also).—Gallic acid is determined, if free from tannic acids, by absorption in recently ignited oxide of zinc, according to method b in determination of tannic acid. It is separated from tannic acids and determined by solution with carbonate of ammonium from the precipitate with acetate of copper (g). a. Ferric salts in solution give a deep blue color with gallic acid. Ferrous salts give a blue-black precipitate (distinction from gallotannic acid). b. Alkaline solutions of gallic acid turn yellow to brown and black in the air, from absorption of oxygen and formation of tannomelanic acid, greatly accelerated by boiling. The latter acid, on neutralizing with acetic acid, precipitates acetate of lead, black. Solution of lime with gallic acid, forms a white turbidity, changing to blue and then to green, in c. Tartrate of antimony and potassium is precipitated white very dilute solution. A faintly alkaline solution of arsenate of potassium or sodium, with gallic acid, exposed to the air, soon develops an intense green color, commencing at the surface. Dilute acids change the green to purple-red and a careful neutralization with alkalies restores the green color, but it is destroyed by excess of alkali.* *PROCTOR: Jour. Chem. Soc., 1874, p. 509. d. Molybdate of ammonium reacts as with tannic acid. e. Gallic acid does not precipitate gelatin, albumen, or starchpaste, but it forms a precipitate with a mixture of gum-arabic and gelatin. f. Gallic acid does not reduce alkaline copper solution, but reduces salts of gold and silver, and quickly decolorizes permanganate solution. Quantitative.―g. The prepared solution is fully precipitated with a filtered solution of cupric acetate; the precipitate washed and then exhausted with cold solution of carbonate of ammonium. The last solution, containing all the gallate of copper with a very little tannate, is evaporated to dryness, the residue moistened with nitric acid, ignited, and weighed as oxide of copper. This weight multiplied by 0.9 gives the quantity of gallic acid (the full ratio being 0.9126, but allowance is made for solution of a little tannate by the carbonate of aminonium. The ratio between oxide of copper and tannic acid is 1.304). (Method of FLECK modified by SACKUR and WOLF.) 15. PYROGALLIC ACID. CHO,. Pyrogalline. Pyrogallol.-Characterized by its physical properties (a); its peculiar avidity for oxygen (b); its reactions with alkalies, lime, iron, copper, etc. (c). It is distinguished from tannic acid by not precipitating gelatin or moderately dilute tartrate of antimony and potassium or cinchonia, and by its different reactions with both ferrous and ferric salts: from gallic acid by its greater solubility in cold water and its far greater reducing power (b). It may be determined gravimetrically as a lead precipitate (d), and volumetrically by permanganate. a. Pyrogallic acid crystallizes in long prismatic plates or needles, of a white or yellowish-white color, and an acid and very bitter taste. At 115° C. (239° F.) it melts, and at about 210° C. (410° F.) it sublimes with partial decomposition and formation of metagallic acid. It is soluble in three parts cold water, freely soluble in alcohol and in ether, not soluble in absolute chloroform. b. It is permanent in dry air free from ammonia, but in moist or ammoniacal air it gradually darkens, and in water solution it turns brown to black, sooner if boiled, still more rapidly in presence of alkalies, absorption of oxygen taking place to an extent proportional to the coloration, which is destroyed by oxalic acid. It quickly reduces the alkaline copper solution; also salts of the noble metals, and reduces acid solu tion of permanganate with evolution of carbonic anhydride. c. With lime solution, a purple-red color at first appears, afterward the brown color formed by alkalies as mentioned in b. With ferrous salts a blue color is formed; with ferric salts a red solution, brown when heated. Acetate of copper gives a browngreen precipitate; acetate of lead a white, curdy precipitate; both soluble in acetic acid. Quantitative.-d. The alcoholic solution of pyrogallic acid is precipitated with excess of alcoholic solution of acetate of lead; the precipitate washed quickly with alcohol, dried by water-bath and weighed. Pb(CH,O,), 2C,H2O, 457: 252 :: 1: 0.55142, 16. QUINOTANNIC ACID. Cinchotannic acid. Kinotannic acid. See Tannic acids (13) for appearance, taste, sɔlubilities, and reactions with alkalies and with iron salts. It precipitates tartrate of antimony and potassium only in concentrated solutions. In oxidation with alkalies it forms a red-brown color, due to cinchona-red, which dissolves in alkalies and in acetic acid, but not in water. Concentrated sulphuric acid changes quinotannic acid to cinchona-red and glucose. In dry distillation, phenic acid is formed, recognized by the odor. Quinotannic acid is removed from solution by acetate of lead, and from its lead precipitate by hydrosulphuric acid. For separation from Cinchona bark, see under Quinic Acid, d. 17. CATECHUTANNIC ACID. Has the properties of tannic acids in general, giving a grayish-green precipitate with ferric salts, and distinguished by not precipitating tartrate of antimony and potassium. It softens when heated, and by dry distillation yields an empyreumatic oil. The product of its atmospheric oxidation in water is red. Catechutannic acid is separated from Catechu as follows: The aqueous infusion of catechu is heated with dilute sulphuric acid and filtered; the filtrate treated with concentrated sulphuric acid to precipitate the acid sought; the precipitate is washed on a filter with dilute sulphuric acid and pressed between paper. It may then be dissolved in water; the solution treated with carbonate of lead and filtered; the filtrate evaporated in vacuo. It may be farther purified by dissolving in alcoholic ether and evaporating off the solvent. 18. CATECHUIC ACID. Catechucic acid. Catechin. Tanningenic acid.—A white, tasteless powder, or in fine, silky needles, melting at 217° C. (423° F.), and in dry distillation yielding an empyreumatic oil. Very slightly soluble in cold water, soluble in three parts boiling water, moderately soluble in alcohol, sparingly soluble in ether. With alkalies and metallic salts, and as a reducing agent, it gives the reactions of the (irongreen) Tannic Acids, from which it is distinguished by not giving precipitates with tartrate of antimony and potassium or with alkaloids, or with gelatin (the last-named being a distinction from catechutannic acid). With strong sulphuric acid it forms a deep purple liquid. Catechuic acid may be separated from catechutannic acid and the other constituents of catechu by its sparing solubility in cold and ready solubility in hot water. Bengal catechu is digested twenty-four hours in cold water, and the (slightly washed) residue is then exhausted with boiling water. When the solution cools, a yellow deposit of catechuic acid appears. This is washed in cold water. It may be decolorized by hot filtration through animal charcoal. It is dried on bibulous paper by aid of the air-pump. 131 10 19. MORINTANNIC ACID. C,,H,,O,. Capable of crystallization; yellow, with great tinctorial power, and of an astringent, sweetish taste. Melts at 200° C., and at higher temperatures distils phenic acid. In reactions with alkalies, oxidizing agents, gelatin, tartrate of antimony and potassium, iron salts, etc., it behaves like other Tannic Acids (13). With ferric salts it gives a greenish precipitate; with acetate of lead a yellow precipitate; with sulphate of copper a yellowish-brown precipitate; with stannous chloride a yellowish-red precipitate. It is separated from Fustic by spontaneous deposition from the concentrated decoction. 20. CAFFETANNIC ACID. Caffeotannic acid. Has in general the physical properties of the Tannic Acids, but is not incapable of crystallization. It melts when heated, and then gives the odor of roasted coffee, and in dry distillation yields oxyphenic acid as an oil which solidifies in the cold. With fixed alkalies in solution it turns yellow to reddish-yellow, by oxidation; with ammonia, forms a green color, due to viridic acid, which, when neutralized, gives with acetate of lead a blue precipitate. Warmed with concentrated sulphuric acid, it dissolves with a blood-red color. Distilled with dilute sulphuric acid and binoxide of manganese, it evolves quinone—a pungent and irritating vapor, condensing to a golden-yellow to dingyyellow, crystallizable substance, heavier than water, in which it is but slightly soluble when cold. Caffetannic acid gives the green color with ferric salts. It reduces nitrate of silver, in the specular form, when heated. It is distinguished from the larger number of Tannic Acids by not producing precipitates with tartrate of antimony and potassium or with gelatin, but it precipitates cinchonia and quinia (distinction from Catechuic acid). It gives a yellow precipitate with barium salts. By gradual addition of acetate of lead, in decoction of coffee, it is precipitated next after (the very little) citric acid. Decom |