OXAIIC ACID 4Aq) occurs in colorless, transparent, oblique, rhombic prisms, which have an intensely sour taste. and are soluble in nine parts of cold water, and much more freely in boiiimr water. When heated to 212', the crystals lose their four equivalents (or 28.5 per cent) of water, and the residue, consisting of the hydrated acid bnomes opaque; these two equivalents of water contained in the hydrated acid, cannot be expelled by mere heat, although they can be displaced by an equivalent amount of a metallic; oxide. When the crystallized acid is rapidly healed to about it is decomposed into a final mixture of carbonic acid, carbonic oxide, and water; formic acid being produced and again decomposed in the process.
crystanizod Oxalic Carbonic Acid. Acid. Water. Forndc Acid.
C411208 4110 = 4110 + 021102,110; Water, Carbonic and formic acid when heated yields 2110 + 2C0. When warmed with strong sulphuric acid, it is decomposed into equal volumes of carbonic acid and carbonic oxide gases, and into water; according to the equation.
Hydrated Oxalic Carbonic- Carbonic Water. Acid. Acid. Oxide.
= C204 + C202 + 2110 This reaction affords one of the best means of obtaining carbonic oxide for use in the laboratory. Oxidizing agents, such as binoxide of manganese, peroxide of lead, nitric acid. etc., convert oxalic into carbonic acid, end on this property is based a good imt hod of detcannining the commercial value of the black oxide of manganese.
Oxalic acid is one of the most powerful of the organic acids, and expels carbonic acid and many other acids from their salts. The acid and its soluble snits, are poison ous. This acid is very widely diffused throughout the vegetable kingdom. Sometimes it occurs in a free state (as in Theleta$ more frequently asst salt, either of potash, as in the different species of arali4 (from which genus the acid was originally olmlined and derives its name), and of r ineav or of soda, as in various species of salieornia and sca/sea; or of lime, as in rhubarb and many lichens. In the animal
kingdom, it never occurs except in minute quantity and in combination with lime.
Oxalate of lime is found in a crystalline shape, both in healthy and morbid urine. In the hitter, it constitutes the leading symptom of the affection termed oxaluria while in the former it occurs after the use of wines and beer containing much carbonic acid, of sorrel, rhubarb-stalks, etc., and after the administration of the alkaline bicar bonates. It is the constituent of the urinary calculus, known from its rough exterior as the mulberry calculus. Crystals of oxalate of lime have also been found in the mucus of the gall-bladder, on the mucous membrane of the impregnated uterus, and in morbid blood. They have likewise been detected in the binary vessels and excrements of cater pillars. In the mineral kingdom these crystals have been detected in association with, crystals of calcareous spar.
Oxalic acid is produced by the action of either hydrate of potash or of nitric acid upon most organic compounds of natural occurrence. Its most common mode of preps ration is by the oxidation of starch or sugar by nitric acid. The organic compound and the nitric acid are heated in a flask till all effervescence has ceased, after which the solu tion is evaporated, and the oxalic acid separates in crystals on cooling.
This acid forms three series of salts, viz.: neutral, acid, and super-acid, which, if M represents the metal entering into the salt, may be represented by the formula: Neutral Salt. Acid Salt. Salt.