I have found that when this process was applied to a decoction of an ounce of beef in six ounces of water, with which one grain of anhydrous oxalic acid had been mixed, all the tests acted characteristically on the solution ultimately procured. I have farther found, that when two grains of oxalate of lime, which correspond with one grain of oxalic acid, were mixed with a similar decoction in which some fragments of beef were purposely left to complicate the process, a solution was eventually obtained, which gave with muriate of lime a white precipitate insoluble in a little muriatic acid, with sulphate of copper a greenish-white precipitate also insoluble in a little muriatic acid, and with nitrate of silver a white precipitate which fulminated and was almost all dispersed, but left a little charcoal, owing to its containing a small proportion of animal matter. In a case which lately happened in London, every test acted as here described, except that the oxalate of lime did not fulminate, owing to the presence of organic impurities.[[396]] In order to try the test of fulmination in such circumstances, it is essential to dry the precipitated oxalate of silver thoroughly before raising the temperature to the point at which fulmination usually occurs.
The process now recommended is both delicate and accurate. An objection has been advanced against it,—that acetate of lead will throw down chloride of lead as well as the oxalate of lead; that both will subsequently be decomposed by the sulphuretted-hydrogen? and that the hydrochloric acid thus brought into the solution with the oxalic acid will be precipitated by the nitrate of silver, and form a mixture of salts which will not fulminate characteristically.[[397]] This objection is not well founded. Chloride of lead being soluble in thirty parts of temperate water, it will seldom be thrown down from such fluids as occur in medico-legal inquiries; and besides it is easily removed, as I have ascertained, by washing the precipitate with moderate care on the filter.
Professor Orfila has advanced another objection,—that the process will yield all the indications mentioned above, if binoxalate of potash be present, or sorrel-soup, which contains a little of that salt.[[398]] The objection is valid, were these substances apt to come in the way. But the binoxalate of potash is not put to any medicinal use in Britain, and English cookery does not acknowledge the “soupe à l’oseille.” The process he recommends to meet the difficulty, an important one in France, is the following: 1. Having made a watery solution as above, evaporate nearly to dryness, agitate the residue with cold pure alcohol, repeatedly during a period of several hours; decant the tincture, and repeat this step with more alcohol; evaporate to obtain crystals, if possible; dissolve these again in cold pure alcohol, and crystallize a second time by evaporation. If crystals do not form on first concentrating the alcoholic solution, evaporate it till a pellicle begins to form, agitate the residue with cold pure alcohol, and concentrate again to obtain crystals. Lastly, examine the crystals by the tests for pure oxalic acid. The object of these steps in the process is to separate binoxalate of potass, oxalate of magnesia and oxalate of lime, which, he says, are all either not soluble, or very sparingly so, in absolute alcohol. 2. More oxalic acid may be got by acting with distilled water on the matter left by the action of alcohol, evaporating this watery solution nearly to dryness, agitating the residuum with cold alcohol as before, and so on. 3. The preceding operations may have left oxalate of magnesia and oxalate of lime unacted on by the water among the solids remaining on the filter. The former compound may be dissolved out by cold hydrochloric acid diluted with four times its volume of water; and by an excess of pure carbonate of potass, the oxalate of magnesia in the solution is converted into insoluble carbonate of magnesia and soluble oxalate of potass, from which oxalic acid is to be obtained by a salt of lead and sulphuretted-hydrogen, as explained in my own process. 4. Oxalate of lime, which may still remain, is to be sought for by boiling the residuum of the action of hydrochloric acid with solution of bicarbonate of potash, so as to obtain here also an oxalate of potass in solution. I have not had an opportunity of trying this method. But I find, that, contrary to Orfila’s statement, binoxolate of potass, though sparingly soluble in cold alcohol of the density of 800, is sufficiently so to vitiate the principle on which the process is founded.
Caustic potass must not be used for decomposing oxalate of lime or magnesia, because the pure alkali, as Gay-Lussac has shown, produces oxalic acid in acting on animal substances at a boiling temperature. Carbonate of potass has no such effect.
The discovery of oxalic acid in the form of oxalate of lime in the stomach or vomited matter is exposed to a singular fallacy, if a material quantity of rhubarb has been taken recently before death, or before the discharge of the vomited matter. For according to the researches of M. Henry of Paris, rhubarb root always contains some oxalate of lime, and some samples yield so much as 30 and even 33 per cent.[[399]]
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. After death the stomach is found to contain black extravasated 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 gelatinized, evidently by the chemical action of the poison.[[400]] 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. When the quantity is large, the most prominent symptoms are those of palsy of the heart; and immediately after death that organ is found to have lost its contractility, and to contain arterial blood in its left cavities. When the dose is less the animal perishes after several fits of violent tetanus, which affects the respiratory muscles of the chest in particular, causing spasmodic fixing of the chest and consequent suffocation. When the dose is still less, the spasms are slight or altogether wanting, and death occurs under symptoms of pure narcotism like those caused by opium: the animal appears to sleep away.
This poison acts with violence, and produces nearly the same effects to whatever texture of the body it is applied. It causes death with great rapidity when injected into the sac of the peritonæum, or into that of the pleura; it acts with still greater quickness when injected into a vein; and it also acts when injected into the cellular tissue beneath the skin, but with much less celerity than through any other channel. Eight grains injected into the jugular vein of a dog occasioned almost immediate death: Thirty-three grains injected into the pleura killed another in twelve minutes. The same quantity did not prove fatal, though it caused violent effects, when retained in the stomach by a ligature on the gullet. One hundred and sixty grains injected under the skin of the thigh and belly did not prove fatal for about ten hours. The symptoms were nearly the same in every case.[[402]]