1. Strong sulphuric acid produces a yellow colour, changing to red, produced rapidly if heated.
2. Strong hydrochloric acid and heat produces a red colour.
3. Sulphomolybdic acid produces a reddish colour, changing to dirty brown, greenish, and finally blue.
These tests should be done with the solid veratrine.
HYDROCYANIC ACID
Hydrocyanic acid is a compound of cyanogen and hydrogen. It was first obtained by Scheele in 1782, but it was not until 1815 that Gay-Lussac pointed out its real nature. Anhydrous hydrocyanic acid may be obtained by passing over cyanide of mercury, gently heated, a stream of dry sulphuretted hydrogen. It is now made by mixing ferrocyanide of potassium with dilute sulphuric acid, and applying heat, when the acid is distilled over and collected in a cooled receiver.
Dilute hydrocyanic acid, the only important form of the acid from a toxicological point of view, is a colourless, feebly acid liquid, with a peculiar odour, like that of bitter almonds or peach kernels (specific gravity, 0.997). The Pharmacopœial acid contains 2 per cent. of anhydrous acid; that of Scheele 5 per cent. According to Taylor, however, the percentage of the acid varies from 1.3 to 6.5. Taking into consideration the smallness of the dose, and the shortness of the time before death occurs, it is the most deadly of all known poisons. Prussic acid is not regarded as a cumulative poison—that is, it does not gradually accumulate in the body and then break out with dangerous or fatal violence.
Symptoms.—These will be more or less modified by the quantity of the dose, and in some cases closely resemble an attack of epilepsy. In most cases, the symptoms of poisoning are seldom delayed beyond one or two minutes; and if the dose be large, the symptoms of poisoning may come on while the person is drinking. Giddiness, followed by almost complete insensibility, mark the accession of the symptoms. The eyes are fixed, staring, and glassy; the pupils are dilated, and insensible to light. The muscles of the extremities are relaxed, and the limbs flaccid. A white or bloody froth surrounds the mouth, and the jaws are fixed. The surface of the body is cold and clammy to the touch; the respiration is sometimes long-drawn and spasmodic; and the pulse so reduced as to be almost imperceptible. The breathing is sometimes stertorous in character. This is an important fact; for, in ignorance of the occasional presence of this symptom, it was argued that Walter Palmer, whose breathing was stertorous, died of apoplexy, and not from prussic acid as was alleged. When the dose is small (between twenty and thirty drops of the dilute acid), the patient complains of nausea, giddiness, and a feeling of constriction round the head. The mind is confused, the pulse hurried, and the breathing irregular. Salivation may also be present. Tetanic spasms and involuntary evacuations precede the fatal termination. When the dose is from ten to twenty drops, the patient complains of nausea, giddiness, and a feeling of impending suffocation. These symptoms under treatment may soon pass off, or leave the patient more or less confused and listless. In most cases, where the dose is very large, death takes place suddenly, without convulsions; but the period of death does not appear to be as short in man as in the lower animals.
External Application.—Applied to the unbroken skin, prussic acid does not appear to have caused any alarming symptoms; but it should be used with the utmost caution where the skin is at all abraded or ulcerated.
Post-mortem Appearances.—In making an inspection, care should be taken; for, if the dose be large, the vapour from the corpse on opening it has been known to produce giddiness and fainting. Externally, the skin is pale, livid, or of a violet colour. The hands are clenched, and the nails blue. The jaws are firmly set, and there is usually some froth around the mouth. The internal organs are greatly congested, and the venous system gorged with fluid dark-coloured blood. The stomach and intestines are sometimes inflamed, but in many cases they present no material alteration in colour.