ratory, so that the whole of the vapors may be condensed; the distillate is then treated as in the preceding case.]

§ 87. [Several plants, which chiefly belong to the division of Drupaces, and of which the most important are the bitter almond, cherry laurel, bird cherry, and peach, yield by distillation with water liquids which contain hydrocyanic acid and a peculiar essential dil, the essential oil of bitter almonds. It appears that neither the hydrocyanic acid, nor the essential oil, exist ready formed in the plant, but that they owe their origin to the action of a peculiar albuminaceous substance, emulsine, on a peculiar crystalline principle, named amygdaline, both of which are found in the various parts of the plant. When almond pulps, or the leaves of the cherry laurel, etc., are bruised with water, these two principles come in contact, and the amygdaline is decomposed into hydrocyanic acid, essential oil, and sugar. A gentle heat favors, but a boiling heat prevents, the reaction; alcohol and ether, which, like boiling heat, coagulate the emulsine, also prevent the decomposition. The pure oil of bitter almonds does not possess any poisonous properties, but the crude commercial article exercises 'poisonous effects in proportion to the amount of free hydrocyanic acid which it contains. The various distilled waters, as bitter almond water, cherry laurel water, peach water, etc., contain very variable quantities of prussic acid, rarely more than 1.5, frequently only 0.1 per cent.

The presence of hydrocyanic acid in these waters

is easily shown, and, if required, the amount quantitatively determined after the method given § 88. To detect its presence in the essential oil of bitter almonds, the oil is gently heated and well agitated with a watery solution of caustic potassa; cyanide of potassium is formed, which may be subjected to the usual tests. Or the oil is mixed, and well agitated with water and some finely pulverized red oxide of mercury. After some time the mixture is distilled, when the oil passes over, and cyanide of mercury remains in the retort.]

CHAPTER IV.

ON THE DETECTION OF OXALIC ACID.

[$ 88. OXALIC acid, when introduced into the system, is very rapidly absorbed; it has been found in the blood of the heart of men who died within half an hour after the administration of the poison; it has also been detected in the urine. It is, therefore, quite possible that in a case of poisoning with this acid, nothing of the poison is to be found in the primæ viæ, part of it having been removed by vomiting, etc., and the rest having entered into the blood.

To detect the presence of oxalic acid in the contents, or the vomited matters (which should be treated. separately), we proceed, according to Orfila, in the following manner :

§ 89. The substances under examination are placed into a large porcelain dish, and boiled with distilled water; the liquid, while hot, is filtered through paper, or cloth. The operation is repeated once more, the two filtrates are united, and evaporated to dryness at a gentle heat. The residue is repeatedly treated with small portions of cold concentrated alcohol, the alcoholic solutions are united and evapo

rated, at a gentle heat, to a small volume. On cooling, oxalic acid separates in crystals, if it was present in sufficient quantity. The presence of a large amount of organic matter may prevent crystallization. In this case, the organic substances may first be precipitated by the addition of some tincture of nut-galls (previously tested for oxalic acid); the precipitate is separated by filtration, the filtrate evaporated to dryness, and the residue treated with concentrated alcohol-(Schneider); on evaporating the alcoholic solution, crystals are deposited. The crystals are dissolved in water, and the solution tested with the proper reagents.

90. The solution shows a strong acid reaction. Soluble lime-salts produce a white precipitate of oxalate of lime; if the quantity of oxalic acid is very small, a few drops of ammonia are added; the precipitate, in this case, appears sometimes only after a while. The precipitate is soluble in free hydrochloric or nitric acid, when added in sufficient quantity; it is but very slightly soluble in oxalic, acetic, and other organic acids; it is insoluble in chloride of ammonium, and other ammoniacal, salts. The precipitate is even produced with a solution of sulphate of lime, and by this reaction, which is the most characteristic, oxalic acid is distinguished from all other acids, racemic acid only excepted. Nitrate of silver produces a copious white precipitate of oxalate of silver, insoluble in an excess of oxalic acid, with difficulty soluble in nitric acid, more readily dissolved by ammonia. The precipitate may be collected on a filter, dried, and heated in a porcelain capsule; it is decomposed with a slight detonation and emission of

escence.

thick, white fumes, metallic silver remaining behind. When mixed with a solution of chloride of gold, metallic gold is deposited, sometimes in the shape of a yellow crystalline powder, coating the sides of the tube; heat facilitates the reduction; if the solutions were concentrated, carbonic acid escapes with effervIf there is sufficient material, a portion of the crystallized acid is introduced into a small flask, provided with a delivery-tube; some pure, concentrated sulphuric acid is poured on the crystals, and a gentle heat applied. The oxalic acid is completely decomposed into carbonic acid and carbonic oxide, which are collected, over water, in a small bell-jar; the remaining liquid is colorless, if the oxalic acid is pure. The mixture of the gases is shaken with limewater, which, by absorbing the carbonic acid becomes milky from carbonate of lime; the remaining gas, when kindled, burns with a blue flame.

91. If not free oxalic acid, but an alkaline oxalate was used for poisoning, this will not enter into the alcoholic solution, but remain in the residue, obtained by evaporating the watery extract to dryness (v. § 89). This residue may, besides, contain some free oxalic acid, which was left undissolved by ; the alcohol. It is, for this reason, always advisable, whether free oxalic acid has been detected by the method just described, or not, to subject this residue to the following treatment:

The residue is treated repeatedly with small portions of cold water; the liquids are united, filtered, and the filtrate precipitated with chloride of calcium. The oxalate of lime is collected on a filter, washed with water, and boiled for about half an hour with a