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solution of carbonate of potassa. Insoluble carbonate of lime and soluble oxalate of potassa are formed. The former is removed by filtration, the filtrate precipitated with acetate of lead (oxalate of lead is thrown down), the precipitáte collected on a filter, and washed with water. To separate the oxalic acid from the lead, the precipitate is suspended in water, and a current of sulphureted hydrogen gas passed through the mixture, until the liquid smells distinctly of the gas. It is then placed at a moderately warm spot, until the excess of the gas has passed off, filtered, and the filtrate, which contains free oxalic acid, evaporated to crystallization. The crystals are tested as above described.

$ 92. The investigation becomes much more complicated when an alkaline earth, as magnesia, or a lime-salt has been administered as an antidote. In this case, a large portion, or the whole, of the oxalic acid remains in the insoluble residue left after boiling the substances with water. By washing with water, the finer particles are separated from the organs, and the mass thus obtained repeatedly treated with water, to effect as complete as possible a separation of the heavy powder from the lighter organic substances, which remain suspended in the liquid and are poured off with it. The impure oxalate is collected and treated with hydrochloric acid, if magnesia was the antidote used. The solution is filtered, and the filtrate neutralized with ammonia; oxalate of magnesia being soluble in ammoniacal salts, no precipitate will be produced. The magnesia is now removed by precipitation with oarbonate of potassa; the liquid, separated from the precipitate by filtration, contains oxalate of potassa ; from this the oxalic acid is obtained in the free state by the method above given.

$ 93. If lime, or a lime-salt, was the antidote, the separation of the acid from the base becomes still more difficult. In this case, the impure oxalate (v. $ 92), is dissolved in moderately concentrated nitric acid; the solution is gently heated to effect a partial destruction of the organic matters, and, after cooling, precipitated with ammonia.

The precipitate, consisting essentially of oxalate of lime, is digested with acetic acid, which dissolves any phosphates which might be present. The oxalate of lime, thus purified, is treated with carbonate of potassa, etc., as described in $ 91.

It is not admissible to treat the impure oxalate with carbonate of potassa, because the organic matters which it contains, on being boiled with the alkali, may give rise to the formation of oxalic acid. This objection cannot be raised against the treatment with nitric acid; for, even if oxalic acid should be formed, it will remain in the liquid as oxalate of ammonia; only the pre-existing oxalate of lime being precipitated on the addition of ammonia.]

CHAPTER V.

ON THE DETECTION OF PHOSPHORUS.

$ 94. CHEMICO-LEGAL investigations for the detection of phosphorus are not of very rare occurrence, especially since friction-matches, and pastes containing phosphorus for killing rats, mice, etc., have come into general use. It is difficult to conceive how willful murder can be perpetrated by poisoning with phosphorus, on account of the very extraordinary and disagreeable odor which it imparts to all kinds of food and drink. [There are, however, cases of this kind on record ; one mentioned by Orfila, where two persons, cautioned by the peculiar odor, escaped death, but the third, swallowing the poisoned soup, died of the effects; another case, that of Jean Riehl, is mentioned by Flandin.] Two cases of intended poisoning have come under my observation ; in one case it was a paste used for killing rats, and in the other the mass used for friction-matches which were ployed; but the odor, in both cases, served as a warning.

$ 95. The odor of phosphorus, undergoing slow oxidation, is so characteristic that its presence in

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food, contents, etc., may by this means alone be with certainty ascertained. Food, and other matters, containing phosphorus, become luminous in the dark when agitated and gently heated. Lipowitz remarks that the luminosity is destroyed by ammonia, and that, consequently, in substances which have become ammonial by putrefaction, the phenomenon does not take place. By an addition of dilute sulphuric acid, until the mass shows an acid reaction, the luminosity is restored.

To collect the finely divided particles of phosphorus which are often intimately mixed with, and disseminated through organic and other substances, Lipowitz proposes the use of sulphur. If matters containing phosphorus are heated with some small pieces of sulphur, the latter takes up the phosphorus and forms a compound in which the presence of the poison is readily demonstrated. If the experiment is performed in a retort, the distillate frequently possesses the odor of phosphorus, and its presence here may also be easily detected.

$ 96. The mode of procedure, according to Lipowitz, is as follows: The substances are acidulated with dilute sulphuric acid and introduced into a tubuJated retort. A few pieces of sulphur are then added, and, the receiver being loosely fitted on, the distillation is commenced. The contents of the retort having been kept boiling for about half an hour, the operation is discontinued. The distillate is mixed with a little fuming nitric acid, introduced into a porcelain dish, and evaporated; thus the phosphorous acid, originating from the oxidation of the vapors of phosphorus, is converted into phosphoric acid. The residue is diluted with water, filtered if necessary, and mixed with ammonia in excess. The resulting liquid is tested with a solution of chloride of ammonium-magnesium, or with a solution of sulphate of magnesia previously mixed with a solution of chloride of ammonium. If phosphoric acid is present a white, granular and crystalline precipitate of phosphate of magnesia-ammonia is thrown down.

The contents of the retort are, after cooling, emptied into a porcelain dish, and the small pieces of sulphur taken out and washed with water. If these are placed into a porcelain dish, heated over a water-bath, they become luminous when phosphorus is present; when treated with fuming nitric acid a liquid is obtained in which the presence of phosphoric acid is detected, as above described. A few of the pieces of sulphur may be enclosed in a glass tube filled with water, and handed, as corpus delicti, to the authorities. It ought to be remarked here that, with long keeping, the luminosity of the sulphurpieces is lost, but then phosphoric acid may always be detected in the water.

Lipowitz states that he has detected by this method Taobao of phosphorus in poisoned food with certainty, and even in cases where not a trace of phosphorous acid could be found in the distillate, the presence of phosphorus in the sulphur was satisfactorily shown. (Lipowitz in Pogg. Annalen, vol. xc., p. 600; Pharm. Centralblatt, 1854, p. 157; Schacht in Archiv für Pharmacie, vol.lxvi., p. 165.) Experiments, conducted after this method in my laboratory, have yielded very satisfactory results.

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