Origin. - Prepared by heating in an iron crucible a mixture of exsiccated potassium ferrocyanide 8 parts and potassium carbonate 3 parts until effervescence ceases.

Description and Properties. - White, opaque, amorphous pieces, or a white, granular powder, odorless when perfectly dry, but in moist air exhaling the odor of hydrocyanic acid. The taste is sharp and somewhat alkaline, but should be tested with great care, as the salt is very poisonous. In moist air it deliquesces; soluble in about 2 parts of water and sparingly soluble in alcohol. Potassium cyanide should be kept in well-stoppered bottles.

Dose. - 1/16-1/8 grain (0.004-0.008 Gm.).

Antagonists and Incompatibles. - Atropine is a physiological antagonist; the diffusible stimulants also tend to counteract the effects of the drug. The metallic salts, particularly cobalt nitrate, are chemically incompatible.

Synergists. - The cardiac and motor depressants.

Physiological and Toxicological Action. - On the skin dilute hydrocyanic acid has little action - more concentrated solutions cause numbness. On mucous membranes it causes a sensation of warmth; in the mouth salivation occurs, due to its acrid burning and penetrating taste and odor. Numbness follows from the anesthetic action of the acid. On the mucous membrane of the stomach its has a similar action.

Circulatory System. - The heart is less affected than the medullary centers. The primary medullary irritation causes vagus stimulation and a slightly slowed heart - the blood-pressure rising at the same time; but on the advent of the medullary paralysis the pressure falls and the heart beats faster; but the oncoming of a true muscle-poisoning prevents it from beating very rapidly. Heart paralysis is secondary to medullary paralysis.

Nervous System. - In small doses it may cause a sense of giddiness, with temporary nausea and faintness. In toxic doses, however, it has a very pronounced action. The medullary centers are primarily involved, followed by other nervous centers. The respiratory center is primarily stimulated, rendering the respiratory movements fuller and more rapid. Convulsive respiratory movements and dyspnea supervene on larger doses - the rhythm being also influenced by the onset of generalized convulsive seizures which are characteristic of poisoning. Paralysis of respiration follows.

Consciousness is in the early stages clouded, headache and mental confusion are present, and complete unconsciousness soon develops if the dosage is large. Vasomotor and muscle paresis is later evident from the loss of blood-pressure and involuntary fecal and urinary evacuations.

Metabolism. - Hydrocyanic acid has a marked activity in intracellular metabolism. It seems to lock up, as it were, the vital processes - retarding them or completely destroying them, according to the grade of poisoning. It seems to prevent oxygen-absorption particularly. The venous blood retains its bright-red color because of the lack of reduction of the oxyhemoglobin.

Cyanide of potassium differs from hydrocyanic acid in no essential particulars.