OXALIC ACID, the most highly oxygenated of all the vegetable acids, is also the most rapid and certainly fatal of any which are capable of being crystallised. As the crystals are not unlike those of the sulphate of magnesia, or Epsom salts, mistakes between the two are of very frequent occurrence. Being likewise much used in the arts, and commonly known by the name of acid of sugar, it is taken either accidentally, or under the supposition that it is akin to sugar, and therefore pleasant and innocent.
To prevent confusion of the crystals of this formidable acid with those of the sulphate of magnesia, it has been proposed that the former should be coloured while in the course of preparation, an expedient which has not been adopted. But on the other hand, the crystals of Epsom salts have been manufactured of a different shape by &peculiar process of crystallisation. The taste is very different, a solution of oxalic acid being intensely sour, while that of sulphate of magnesia is extremely bitter. Attention to this point, in previously tasting a small quantity, may prevent very serious casualties. Oxalic acid not only acts with violence, but produces nearly the same effects to whatever texture of the body it is applied. The concentrated acid, if taken in considerable dose, may cause death in from two to twenty minutes. "After death the stomach is found to contain black extra vasatecl blood, exactly like blood acted on by oxalic acid out of the body ; the inner coat of the stomach is of a cherry-red colour, with streaks of black granular warty extravasation ; and in some places the surface of the coat is very brittle and the subjacent stratum gelatin ised. Such are the effects of the concentrated acid. When con siderably diluted the phenomena are totally different. When dissolved in twenty parts of water, oxalic acid, like the mineral acids in the same circumstances, ceases to corrode ; 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. When the quantity is large, the most prominent symptoms are those of palsy of the heart ; when less, fits of violent tetanus ; and when still less, the spasms are slight or altogether wanting, and death occurs under symptoms of pure narcotism, like those caused by opium." Very few persons have recovered when the quantity taken was con siderable. (Christison, 'On Poisons.) To counteract the very rapid effects of this poison, the most prompt treatment is necessary. Chalk, magnesia, or even the plaster of the room diffused through water, should be given without delay. The other alkalies are improper, as they form soluble salts with the acid, and oxalic acid is an example of a poison which acts through all its soluble chemical combinations. Emetics may be given, if vomiting
has not spontaneously taken place ; but it is highly inexpedient to give much warm water, as dilution only facilitates the absorption of the poison, and induces its remote but equally fatal effects.
Notwithstanding the formidable properties of this acid, the agreeable cooling effects it displays have led to its employment in the form of lozenges, or in a dilute solution as a refrigerant. Both in this country formerly, and still in France, it is used to quench thirst, and allay the heat of the stomach, which prevails towards the later stages of consump tion. But for this purpose citric acid or lemonade is preferable, as well as safer.
Besides the immediate danger from an overdose, there is yet a remote source of risk which requires notice. Oxalic acid exists in many vegetables, in combination with lime or potass, or free, as in the case of the titer arietinum. Many of these plants are used in differ ent parts of the world, as salads, on account of their refrigerating quality. Their frequent employment by persons disposed to calculous diseases is highly dangerous, as they give rise to the formation of the mulberry or oxalate of lime calculus, which is not only the most pain ful of all the stones found in the human kidneys or bladder, but also the most insidious, for, owing to the insolubility of this compound, no deposit or sediment is observed in the urine at an early period, so as to occasion a suspicion of what is taking place. (Majendie, On Gravel,' 2nd French edit.) [Cieen.] The now well-ascertained connection between the existence of the oxalic acid diathesis, rheumatism, indigestion, and other painful diseases, renders a popular knowledge of this point of much importance. Not only the free use of some of the vegetables alluded to, but saccharine fruits, sugar, and starch, especially potato starch, give rise to the formation of oxalic acid, and its attendant evils. Rhubarb (stalks, not powder), sorrels of different sorts, tomatoes, common barberry, should all be avoided by persona prone to rheumatism or stone in the bladder. Hard 'waters, containing lime, should be eschewed. The excessive use of sugar, either in the ordinary states, or in sweet preserves, is improper. Where any calculus of this sort is detected in the bladder, the employ ment of bicarbonate of potass in solution gives great rel'ef, by coating the very angular stone with a smooth surface. Its use must not be too long persevered in. (See 'Front on Stomach and Renal Diseases.')