Oxalic acid

“ This acid may be thus recognised in solution:
1. Nitrate of silver throws down, with oxalic acid, [Pg 46] an abundant white precipitate (oxalate of silver) , which is soluble in nitric acid. The oxalate of silver, when dried and heated on platinum foil, detonates, and is dissipated in a white vapor.
2. Sulphate of calcium causes a white precipitate with oxalic acid (oxalate of calcium) which is soluble in nitric or hydrochloric, but not in any vegetable acid.
The solution containing the acid should be concentrated before testing, if it be not present in considerable quantity. ”

“ When a strong mineral acid is present, however, the ionization of the oxalic acid is much reduced by the high concentration of the H^{+} ions from the strong acid, the formation of the undissociated acid lessens the concentration of the C_{2}O_{4}^{—} ions in solution, more of the oxalate passes into solution to re-establish equilibrium, and this process repeats itself until all is dissolved. ”

“ Take an ounce of oxalic acid, dissolve it in a pint of soft water, and keep it in a bottle well corked; dip a soft sponge into the mixture to clean the tops with, and if there are any spots which refuse to disappear, rub them with a little fine Bath brick dust: sponge the tops afterwards with clean water. Take particular care always to have any mixtures, or powders for boot-tops, labelled with the word poison in large letters, as fatal accidents have arisen from oxalic acid, being so like Epsom salts in appearance, as to be often taken for them in mistake. ”

“ Oxalic acid can be prepared by an artificial process, with great ease, from sugar, and six times its weight of nitric acid,—the former affording the carbon necessary to its formation, and the latter the oxygen. It is only necessary to heat the nitric acid on the sugar; the sugar dissolves, and there is a violent effervescence, which must be moderated by immersion in cold water: when the mixture cools, crystals of oxalic acid form in abundance, which may be purified by a second crystallization. ”

“ The Effects of Oxalic Acid and Hydropotassic Oxalate on Man.—The cases of oxalic poisoning have been invariably due to either oxalic acid or hydropotassic oxalate, the neutral sodic or potassic oxalates having hitherto in no instance been taken. The symptoms, and even the locally destructive action of oxalic acid and the acid oxalate, are so similar that neither from clinical nor post-mortem signs could they be differentiated by anyone not having a previous knowledge of the case. ”

“ Oxalic acid is chiefly used in the arts of calico printing and bleaching; to remove ink-spots and iron moulds from linen, and to clean boot-tops. It is extremely poisonous. The treatment, in cases of its having been swallowed, is to promote vomiting, and to administer chalk, whiting, or magnesia, mixed up with water, in considerable quantities. The use of the alkalies or their carbonates must be avoided, as the compounds which these form with oxalic acid are nearly as poisonous as the acid itself. ”

“ Oxalic acid is the easiest to make of any. A sufficient quantity of pure crystallised oxalic acid is powdered and pressed between filter paper, so as to absorb the moisture which occasionally is retained in cavities of the crystals. 6·3 grm. is then weighed out and dissolved in water, exactly as was done with sodic carbonate, forming a decinormal solution. It is used in Löwenthal's tannin estimation process and may also be employed to determine alkalies, but forms insoluble calcium oxalate with lime salts, and does not give a sharp reaction with methyl orange indicator. ”

“ The external application of oxalic acid does not appear to cause illness; workmen engaged in trades requiring the constant use of the acid often have the nails white, opaque, and brittle; but no direct injury to health is on record.
A large dose of either causes a local and a remote effect; the local is very similar to that already described as belonging to the mineral acids, i.e., more or less destructive of the mucous membranes with which the acid comes in contact. The remote effects may only be developed after a little; they consist essentially of a profound influence on the nervous system. ”

“ The question before us is, what oxalate is being formed in the sense-organs? We know that in certain tissues in the bodies of animals oxalic acid, and other oxalates, are formed apparently through the incomplete oxidation of carbohydrates. Now we find that even so small a quantity as one part by weight of oxalic acid in one thousand parts of sea-water paralyzes the sense-organs and permanently prevents their giving rise to pulsation, although so weak a solution is not sen- sibly poisonous to the general tissues of the medusa. ”

“ From the liquor remaining after the first cristallization of the oxalic acid we may obtain malic acid by refrigeration: This acid is more oxygenated than the oxalic; and, by a further oxygenation, the sugar is convertible into acetous acid, or vinegar.
The oxalic acid, combined with a small quantity of soda or potash, has the property, like the tartarous acid, of entering into a number of combinations without suffering decomposition: These combinations form triple salts, or neutral salts with double bases, which ought to have proper names. ”

“ The combinations of acetous acid with the various salifiable bases are very readily formed; but most of the resulting neutral salts are not cristallizable, whereas those produced by the tartarous and oxalic acids are, in general, hardly soluble. Tartarite and oxalat of lime are [Pg 270] not soluble in any sensible degree: The malats are a medium between the oxalats and acetites, with respect to solubility, and the malic acid is in the middle degree of saturation between the oxalic and acetous acids. With this, as with all the acids, the metals require to be oxydated previous to solution. ”

“ No rule can be given to regulate the insolation, but after a few trials it is easy to judge when it is right by observing the progress of the reduction and the color of the image. The orange color indicates the complete reduction of the ferric oxalate. When the details in the lights are faintly visible, the exposure is generally right.
The developer consists of an almost saturated solution of potassium oxalate acidified by oxalic acid, and for use heated to 80—85 deg. 0. (176—184 deg. Fahr.) ,23 in an agate glazed [pg 76] iron tray placed upon a water bath at the above temperature. ”

“ On the other hand, the excess of oxalic acid should not be so large as to react with more of the permanganate solution than is contained in a 50 cc. burette. If the pyrolusite under examination is known to be of high grade, say 80 per cent pure, or above the calculation of the oxalic acid needed may be based upon an assumption that the mineral is all MnO_{2}. If the quality of the mineral is unknown, it is better to weigh out three portions instead of two and to add to one of these the amount of oxalic prescribed, assuming complete purity of the mineral. ”

“ The presence of Oxalic Acid 256may be inferred, if the solution, when added to that of sulphate of lime, produce a precipitate. Malic acid has the power of precipitating silver, mercury, and lead, from their solutions in nitric acid, but no doubt or difficulty can arise from this circumstance, for the fact of its forming a soluble salt with lime will prevent every chance of accidental intrusion, and its price at once secures us against its fraudulent introduction ”

“ By this ingenious process 2 lbs. of sawdust are made to yield 1 lb. of oxalic acid.
Prop., &c. Colourless, transparent, prismatic crystals, possessing a powerful sour taste and acid reaction; these effloresce in warm dry air, with loss of 28% (2 eq.) of water, and then form a white powder, which may be sublimed in part, without decomposition; the crystals are soluble in 8 parts of water (9 parts, “and form a solution of sp. gr. 1·045,”—Ure) at 60° Fahr., in their own weight or less of boiling water, and in about 4 parts of alcohol; with the acids, it forms salts called oxalates. ”

“ Acids of Series II. may also be converted into saturated acids by heating to 300°C. with solid caustic potash, which decomposes them into acids of the stearic series with liberation of hydrogen. This reaction, with oleic acid, for example, is generally represented by the equation—
C18H34O2 + 2KOH = KC2H3O2 + KC16H31O2 + H2,
though it must be really more complex than this indicates, for, as Edmed has pointed out, oxalic acid is also formed in considerable quantity. ”

“ Some prefer to make oxalic acid by acting upon 4 parts of sugar, with 24 parts of nitric acid, of specific gravity 1·220, heating the solution in a retort till the acid begins to decompose, and keeping it at this temperature as long as nitrous gas is disengaged. The sugar loses a portion of its carbon, which combining with the oxygen of the nitric acid, becomes carbonic acid, and escapes along with the deutoxide of nitrogen. The remaining carbon and hydrogen of the sugar being oxidized at the expense of the nitric acid, generate a mixture of two acids, the oxalic and the malic. ”

“ Section II.—On the Action of Oxalic Acid and the Symptoms it causes in Man. The action of oxalic acid on the animal economy is very peculiar.
When injected in a state of concentration into the stomach of a dog or cat, it causes exquisite pain, expressed by cries and struggling. In a few minutes this is succeeded by violent efforts to vomit; then by sudden dulness, languor, and great debility; and death soon takes place without a struggle. The period which elapses before death varies from two to twenty minutes, when the dose is considerable,—half an ounce, for example. ”

“ The addition of powdered oxalic acid to the reaction mixture did not seem to be of advantage, because no visible reaction commenced until this had been driven off or decomposed. It is usually added in producing sulphonic acids by baking the sulphates of the amines to increase the porosity of the mass and thus facilitate removal of the product. However here the only effect seemed to be to retard the reaction, as the product was the sane hard grayish mass as without the acid, and it was just as difficult to dig it out. ”

“ In the animal kingdom oxalic acid is always present in the intestinal contents of the caterpillar. In combination with lime, it is constantly found in the allantois liquor of the cow, the urine of man, swine, horses, and cats. With regard to human urine, the presence or absence of oxalate of lime greatly depends upon the diet, and also upon the individual, some persons almost invariably secreting oxalates, whatever their food may be. ”

“ Sometimes a little nitric acid is added to the solution of the coloured crystals, for the purpose of bleaching them, but in this way a minute quantity of oxalic acid is formed. A more general plan is to bleach the citrate of lime by covering it with a weak solution of chloride of lime, exposing it in shallow vessels to the sun’s rays, and rewashing it before decomposing it with sulphuric acid. A safer plan is to dissolve the crude citric acid, digest with animal charcoal, and again concentrate the solution to the crystallising point. ”

“ Poisoning with the Oxalates.—Oxalic acid is one of the best examples of a poison that acts through all its soluble chemical combinations. Dr. Coindet and I found that the oxalates of potash and ammonia are little inferior in energy to the acid. They do not corrode, indeed, and scarcely ever irritate; but they produce tetanus and coma, like the diluted acid. Half a drachm of oxalic acid neutralized with potass will kill a rabbit in seventeen minutes; ninety grains of neutral oxalate of ammonia will kill a strong cat in nine minutes. ”

“ In any case, it must be remembered, that although rhubarb has been eaten for centuries, and every schoolboy has occasionally chewed small portions of sorrel, no poisoning has resulted from these practices. When oxalic acid has been taken into the stomach, it will invariably be found partly in combination with lime, soda, ammonia, &c., and partly free; or if such antidotes as chalk has been administered, it may be wholly combined. Vomiting is nearly always present, and valuable evidence of oxalic acid may be obtained from stains on sheets, carpets, &c. ”

“ Nitric acid makes it red, and if heated upon it, converts it into oxalic acid. If mixed by slow degrees with one third of its weight of sulphuric acid, an acid liquor is formed, at whose bottom a resin of a fine purple colour is found. After being washed, this resin becomes hard and brittle. Alcohol dissolves it, and takes a red colour; and water precipitates it of a blood red hue. It dissolves also in ether. When we agitate a mixture of strong caustic soda lye and oil of cloves in equal parts, the mass thickens very soon, and forms delicate lamellar crystals. ”

“ If the stomach is examined immediately after death, little corrosion will be found, compared with what is seen if the inspection be delayed a day or two. [401]
Such are the effects of the concentrated acid. When considerably diluted, the phenomena are totally different. When dissolved in twenty parts of water, oxalic acid, like the mineral acids in the same circumstances, cease to corrode; nay it hardly even irritates. But, unlike them, it continues a deadly poison; for it causes death by acting indirectly on the brain, spine, and heart. The symptoms then induced vary with the dose. ”

“ Oxalate of calcium falls as a precipitate, and soda remains in solution. This soda is boiled down, and again made use of with fresh sawdust. This recovery of alkali is also practised with the potassium salt which filters through in the last stage. (6) The oxalate of calcium is now decomposed in leaden vessels with sulphuric acid. Sulphate of calcium is precipitated, and oxalic acid is in solution, which is now evaporated, and the acid separates in crystals, which now need only to be recrystallised to make them quite pure, and fit the acid for all the purposes for which it is employed. ”