3902. Dale's Process for Obtaining Oxalic Acid

3902.    Dale's Process for Obtaining Oxalic Acid. At present much of the oxalic acid of commerce is obtained by heating sawdust with a mixture of 2 parts caustic soda with 1 part caustic potassa. A watery solution of the mixed alkalies is evaporated to specific gravity 1.35, and then mixed with sawdust to a paste. This is heated on iron plates to 400° Fahr., and kept at that temperature for 1 or 2 hours, with constant stirring; the heat is continued until the mass is quite dry, but not charred. It now contains 28 to 30 per cent, of oxalic acid combined with the alkalies. By washing the powder on a filter with a solution of carbonate of soda, all traces of potassa are washed out. The oxalate of soda is converted, by heated milk of lime, into oxalate of lime, and the resulting oxalate of lime is treated with sulphuric acid, leaving a solution of oxalic acid, ready to be evaporated into crystals. Two pounds of sawdust yield 1 pound oxalic acid.

3903. Chemically Pure Oxalic Acid

3903.    Chemically Pure Oxalic Acid. Chemically pure oxalic acid is best prepared by precipitating a solution of binoxalate of potash with acetate of lead, washing the precipitate with water, and decomposing it, while still moist, with dilute sulphuric acid or sulphuretted hydrogen. Filter and evaporate gently, so that crystals may form as it cools.

3904. To Distinguish Oxalic Acid from Epsom Salts

3904.      To Distinguish Oxalic Acid from Epsom Salts. Oxalic acid has occasionally been mistaken for Epsom salts, with fatal results. They may be easily distinguished. Epsom salts taste extremely bitter and nauseous; oxalic acid tastes extremely sour. It is safer to taste a weak solution in applying this test. Epsom salts, dissolved in water and mixed with carbonate of soda, or carbonate of potash, turn milky, and, after a time, a white sediment subsides; oxalic acid, mixed with carbonate of soda or carbonate of potash, effervesces, and the liquid, in a few seconds, becomes transparent.

3905. Gallic Acid

3905.    Gallic Acid. When pure, gallic acid forms small, feathery, and nearly colorless crystals, which have a beautiful silky lustre. Commercial gallic acid has usually a pale yellow color, soluble in both water and alcohol. Its aqueous solution decomposes by exposure to the air. It blackens the salts of iron. Dissolved in hot oil of vitriol, it forms a deep, rich, red solution, which, when thrown into water, drops the gallic acid, deprived of some of its water. Gallic acid forms gal-lates with the bases.

3906. To Obtain Gallic Acid

3906.    To Obtain Gallic Acid. Mix 36 troy ounces nut-gall, in fine powder, with sufACIDS.

ficient distilled water to make a thin paste; expose the mixture to the air in a shallow glass or porcelain vessel, in a warm place, for a month, occasionally stirring with a glass rod, and adding sufficient distilled water to preserve the original consistence. Then press out the water, boil the residue in 8 pints distilled water for a few minutes, and filter while hot through purified animal charcoal. (See No. 1752 (To Prepare Animal Charcoal to Decolorize Vinegar and other Vegetable Liquids)). Set aside to crystallize, and dry the crystals on bibulous paper. If not sufficiently free from color, dissolve the crystals in boiling distilled water, filter through a fresh portion of the charcoal, and crystallize again. (U. S. Ph.)