OXALIC ACID. (Fa., Acide oxaliqu e; GER., Sauerkleesaure). Formula, ' Oxalic acid exists in the crystallized form in transparent, quadrangular prisms. The crystals are soluble in nine times their weight of cold water, hut require only their own weight of boiling water ; they are also soluble in alcohol. In cold sulphuric and hydrochloric acid, they may be dissolved without undergoing decomposition. When heated suddenly to a temperature of 100°, the crystals melt in their own water of crystallization ; but if the process be conducted gradually and gently, they fall into an opaque white powder, losing 28.5 per cent. of water. The residue remain ing, cannot be deprived of its lost equivalent of water by heating, but it may be replaced by some metallic oxides. If these dried crystals be placed in a retort, and heated by means of an oil bath of 150° to 160°, they slowly sublime unchanged, and may be condensed in the form of white needles. This sublimation commences at about 100°, and if the heat be allowed to exceed 160°, the crystallized acid will be decomposed.
If the crystallized acid be heated quickly, without having previously undergone dessication, it dissolves in its water of crystallization, and at 155° resolves, with apparent ebullition, into a mixture composed of carbonic anhydride, carbonic oxide, formic acid, and water. Thus:— = + (Formic acid), the carbonic oxide being derived from the formic acid, which yields on decomposition by heat car bonic oxide and water, becoming CO and Heated in contact with powdered charcoal, explosion accompanies its decomposition.
Bromine and chlorine decompose this acid, as do also iodic, nitric, phosphoric, and sulphuric acids on the application of heat. When heated with concentrated sulphuric acid (0.V.), or with phosphoric anhydride, it splits up into equal volumes of carbonic oxide and anhydride. Berthelot has proved that oxalic acid may easily he converted into formic acid by dissolving the former in glycerine and heating to about 150°, when formic acid slowly passes over, and carbonic anhy dride escapes ; hut on raising the temperature some 26° carbonic oxide is obtained.
This acid reduces chromic acid, as well as the peroxides of cobalt, lead, manganese, and nickel, with formation of carbonic acid and water. It precipitates metallic gold from an aqueous solution of the chloride, carbonic acid being evolved. The aqueous solution of the acid has an intensely sour taste, and even 1 part in 2000 of water still reddens litmus. If swallowed, it acts as a powerful poison, producing death in a very few hours ; but effective antidotes exist in chalk or magnesia suspended in water.
During a series of investigations into the physiological action of light upon minute organioms, Dr. Downes and Mr. Blunt have observed that a decinormal solution of oxalic acid was entirely destroyed when freely exposed to the influences of sunlight for a lengthened time, while a similar solution placed under similar conditions, except that the tube containing it was encased in opaque material, remained altogether unchanged. It was found at the end of two months (when the
solution was examined again) that the destruction of the acid had been so complete that it ceased to redden litmus paper, and yielded no precipitate with chloride of lime, while the reaction produced with permanganate of potash was so slight as to be barely recognizable. Mr. D. N. Hartley noticed the same phenomena when using a solution of oxalic acid for the analysis of air by Pettenkofer's method, hut it struck him that some solutions were more proof against destruction than others. He believes that the oxalic acid made by oxidizing sugar with nitric acid is more stable in solution than that obtained by recrystallizing the commercial article. Also, the mycelium of a fungus was found by him in every instance where decomposition had taken place in the liquid, and hence he has attributed the change to the action of a fungus. On the other laind, Dr. Downes and Mr. Blunt found no trace of such mycelium iu any case, the liquid being always quite clear, and they would not have suspected its development in strong sunlight. Scheming and Miiutz consider the change due to the action ef an organized ferment, and Warrington adds that darkness is apparently essential to the process, which may be explaiued probably by the fact that light is inimical to the development of such organisms. In order to preserve the voln. metric solution, Mr. Hartley prepares it with water containing from 10 to 25 per cent. of alcohol, which he finds efficacious for four months at least. Oxalic acid is widely diffused in a natural state, and in the vegetable kingdom especially it is more widely distributed than perhaps any other organic acid. Commonly, it is found combiued with limo, and in flab form it c,onstitutes the chief solid part of many lichens, especially the Parmelia and Varkil,zria. In one species of Parmalia, gathered on the Persian and Georgian sands after a period of drought, has been found as much as 66 per cent. of oxalate of lime, and towards the end of its growth the cells of the plant contain the excess of this salt, which is there deposited in a crystalline form. It occurs thus in Ficus Ben galensis, Tradescantia discolor, Iris liorentina, Fritillaria Meleagris, and others. As an oxalate of potash, it is found in oxalis acetosella (wood sorrel), from which plant the acid derives its name, and in Rumex acetosa (common sorrel), both of which plants have been used in the manufacture of the acid; and also in oxalis corniculata, R11771CX acetosella, Spinacia oleracea, Herba belladonna, and iu the various parts of eeveral other plants. Salsola kali and S. soda, besides several species of S‘tic,rnia, contain the acid as a salt of soda, while in the pods of the chick pea it exists in an uncombined state.