ter. The chances of obtaining a decisive result decrease in proportion to the time which elapses between the administration of the poison and the dissection of the body. It would appear from repeated experiments that, under ordinary circumstances, the chemical examination is not likely to be attended with success when made three days after death, or eight days after death in bodies that have been buried; this, however, should not detain the analyst to undertake an examination at even a later period, since there are a few cases on record where the poison has been found seven, and even twelve, days after death.

A chemical examination of the body is useless, and cannot possibly yield any result if death was produced by inhalation of hydrocyanic acid vapor, or if chlorine or a hypochlorite (ex. gr. bleaching liquid) has been administered as antidote.-Schneider.]

[§ 86. From the preceding remarks it is evident that the analyst can never be expected to determine, with the slightest degree of accuracy, the quantity of hydrocyanic in a body; to show its presence is all he can do. Even if the analytical methods for its determination were sufficiently accurate to separate and determine the whole amount of the poison contained in the various organs, the blood, the secretions, etc., a considerable quantity would escape detection on account of its volatility. But there are other cases in which a quantitative determination may be desired. Thus ex. gr. the analyst may be required to examine rests of food and drink for hydrocyanic acid, and to determine whether the

quantity of the poison which they contain is sufficient to have caused death. This question can only be answered by a quantitative analysis, which is conveniently executed in the following manner:

The substance under examination, if a liquid, is accurately weighed, then precipitated with nitrate of silver, afterwards a few drops of nitric acid added, just sufficient to produce a weak acid reaction, and the precipitate collected on a filter; the precipitate is washed with distilled water, dried at 212° and weighed; 100 parts of cyanide of silver correspond to 20.15 parts of hydrocyanic acid. If the liquid contains chlorides, besides cyanides, the precipitate is a mixture of cyanide and chloride of silver. In such a case the liquid has to be divided in two equal parts. With one of them we proceed as just mentioned, and thus obtain the sum of chloride and cyanide. The other is mixed with some borax, evaporated to dryness, and the dry residue exposed to a moderate heat (the heat ought never be driven so high as to cause fusion); the hydrocyanic acid vaporizes, while hydrochloric acid unites with the soda of the borax. The residue is dissolved in water, the solution acidulated with nitric acid, and afterwards precipitated with nitrate of silver; the precipitate is dried and weighed. By deducting the weight of the chloride of silver from the weight of the chloride and cyanide, as obtained by the first experiment, we obtain the weight of the latter.

Solid substances are treated as directed (§ 74), care being taken to connect the retort with a good refrige

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 Drupaceæ, 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 oil, 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 pri mæ 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