=Prussic Acid= is the most active of poisons. The diluted hydrocyanic
acid of the Pharmacopoeia contains 2 per cent. of hydrocyanic acid,
Scheele's 4 per cent. It is a colourless liquid, feebly acid, with
odour of bitter almonds.
=Cyanide of Potassium= is largely used in photography and in
electro-plating, and is also poisonous. It often contains undecomposed
carbonate of potassium, which may act as a cor
osive poison and cause
erosion of the mucous membranes of the lips, mouth, and stomach.
=Oil of Bitter Almonds=, used as a flavouring agent, may contain (when
improperly prepared) from 5 to 15 per cent. of the anhydrous acid.
Symptoms.--The symptoms usually come on in a few seconds, and are of
the shortest possible duration. There is a sudden gasp for breath,
possibly a loud cry, and the patient drops down dead. If the fatal
termination is prolonged for a few minutes, the symptoms are intense
giddiness, pallor of the skin, dilatation of the pupils, laboured and
irregular breathing, small and frequent pulse, followed by
insensibility. There may be convulsions or tetanic spasms, with
evacuation of urine and fæces. Death results from paralysis of the
central nervous system, but artificial respiration is useless, as the
drug promptly arrests the heart's action. It also kills the protoplasm
of the red blood-corpuscles, rendering them useless as oxygen-carriers.
Post-Mortem Appearances.--Skin livid, pale, or violet, with bright red
patches on the dependent parts. The gastro-intestinal mucous membrane is
bright red in colour, owing to the presence of cyanmethæmoglobin. Hands
clenched, nails blue, jaws fixed, froth about mouth. Eyes prominent and
glistening, odour of acid from body, venous system gorged.
Treatment.--Empty the stomach by the tube at once, and wash it out
with a solution of sodium thiosulphate. Strong ammonia to the nostrils.
Stimulants freely--brandy, chloric ether, ammonia, sal volatile ad
libitum. If patient cannot swallow, inject hypodermically either brandy
or ether. Hypodermic injection of 1/50 grain atropine. Douche to the
face, alternately hot and cold. Death commonly occurs so rapidly that
there is no time for treatment.
Fatal Dose (Smallest).--Half a drachm of the B.P. acid, equal to 0.6
grain of the anhydrous. Recovery from 1/2 ounce of the B.P. acid.
These records are fallacious, for in specimens the percentage of
anhydrous acid varies enormously. Practically, 1 grain of the anhydrous
acid is fatal.
Fatal Period.--From two to five minutes after a large dose, but may be
Method of Extraction from the Stomach.--Having previously carefully
fitted a watchglass to a wide-mouthed bottle, nearly fill the bottle
with the contents of the stomach, blood, secretions, etc. Place a few
drops of a solution of nitrate of silver on the concave surface of the
watchglass, and cover the mouth of the bottle with it. The vapour of
hydrocyanic acid, if present, will form a white precipitate which may be
tested. Other watchglasses, treated with sulphide of ammonium or
sulphate of iron and liquor potassæ, will give the reactions of the acid
with appropriate tests. This method removes all objections as to foreign
admixture. If the acid is not at first detected, gentle warming of the
bottle in a water-bath will assist the evolution of the vapour. The
vapour may be obtained by distillation, but this process is open to
objections to which the other is not. In some cases it becomes changed
in the body into formic acid, which should therefore be sought for.
Tests.--With nitrate of silver a white precipitate, insoluble in cold,
but soluble in boiling, nitric acid. The precipitate heated, evolves
cyanogen, having an odour of peach-blossoms, and burning, when lighted,
with a pink flame. Liquor potassæ and sulphate of iron give a
brownish-green precipitate, which turns to Prussian blue with
hydrochloric acid. Liquor potassæ and sulphate of copper give a
greenish-white precipitate, becoming white with hydrochloric acid.
Sulphide of ammonium gives sulpho-cyanide of ammonium. This develops a
blood-red colour with perchloride of iron, bleached by corrosive