Potassii Cyanidum. Potassium Cyanide. Kcn = 65.01. Source. - Heat in an iron crucible dried Potassium Ferrocyanide, 8; with

Potassium Carbonate, 3; until effervescence ceases.

Characters

White, opaque, amorphous pieces, or a white, granular powder, odorless when perfectly dry, but in moist air exhales the odor of Hydrocyanic Acid. This salt is very poisonous. Solubility. - In about 2 parts of water and sparingly in alcohol.

Dose, 1/20 to 1/4 gr.; .003 to15 gm.

Preparation

Acidum Hydrocyanicum Dilutum

Diluted Hydrocyanic Acid. - Hcn = 26.98. Synonym. - Prussic Acid. A liquid compound of 2 per cent., by weight, of absolute Hydrocyanic Acid, and 98 per cent. of water. Source. - Distil a mixture of Potassium Ferrocyanide, 20; Sulphuric Acid, 8; and water, 65, into distilled water. K4FeC6N6 + 2H2So4 = 2K2S04 + H4FeC6N6. On the application of heat the Hydroferrocyanic Acid reacts with the remaining Potassium Ferrocyanide and Sulphuric Acid, and Hydrocyanic Acid distils over. H4FeC6N6+ K4FeC6N6+ H2So4 = 6Hcn + K2So4 + K2Fe(FeC6N6). The distillate is diluted with distilled water until the official strength is obtained. Diluted Hydrocyanic Acid may also be prepared, extemporaneously, in the following manner: Mix Hydrochloric Acid, 5, with distilled water, 55; add Silver Cyanide, 6, and shake the whole together in a glass-stoppered bottle. When the precipitate has subsided, pour off the clear liquid. Scheele's Prussic Acid is a 4 or 5 per cent. solution.

Characters

A colorless liquid, of a characteristic odor and taste, resembling that of bitter almond. Very unstable; to preserve it best, it should be kept in inverted blue-stoppered bottles. Old specimens may be inert.

Incompatibles

Salts of silver, copper and iron, red mercuric oxide and sulphides.

Impurities

Sulphuric and hydrochloric acids.

Dose, 1 to 3 m.; .06 to .20 c.c.

Hydrocyanic acid belongs chemically to the Carbon compounds, but on account of its physiological and therapeutical relationship to Potassium Cyanide it is considered at this place.

Action of Potassium Cyanide and Diluted Hydrocyanic Acid

External

Hydrocyanic acid can pass through the epidermis, and then it paralyzes the terminations of the sensory nerves; thus it is a local anaesthetic and sedative. It is very rapidly absorbed from raw surfaces, and may cause poisoning if applied to them. Potassium cyanide may possibly give the same results. It also produces a dermatitis on local application to the epidermis.

Internal

Alimentary tract. - Hydrocyanic acid is quickly and potassium cyanide less rapidly absorbed by mucous membranes, and has the same anaesthetic and sedative effect on the mouth and stomach as on the skin. It must always be employed well diluted. A single drop of the pure acid placed inside the eye of even a moderately large animal will kill it instantly.

Blood

If death takes place almost immediately after the administration of the drug, all the blood in the body is a bright arterial tint; but if death does not occur for some little time (within half an hour), the blood is of a dark venous color. The primary transitory reddening of the venous blood is due to the fact that the haemoglobin in it is oxidized; we do not know the cause of this. The subsequent darkening of the arterial blood is due to the fact that it has lost its oxygen, and contains carbon dioxide gas; why this should be is not certain, but probably it depends upon the asphyxia consequent upon the action of hydrocyanic acid on the respiratory centre. If blood be shaken up with hydrocyanic acid, after some time oxyhaemoglobin is converted into cyanohaemoglobin, the oxygen being turned out. Hydrocyanic acid added to drawn blood alters the shape of the red blood-corpuscles. Neither of these actions is seen in life, for sufficient hydrocyanic acid to cause them would kill before they could take place.

Heart

Large doses cause instantaneous diastolic arrest. As this is also true if the drug is applied locally, we may conclude that large doses paralyze the heart directly. But hydrocyanic acid acts also on the cardiac centre in the medulla. A small dose will cause a slowing of the pulse from stimulation of the vagus centre, and the stoppage from larger doses is due both to the direct action on the heart and to that on the medulla.