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45. Hydrocyanic acid (prussic acid)

46. Hydrogen sulphide

45. Hydrocyanic acid (Prussic Acid).

Physical and chemical characteristics. - Hydrocyanic acid is a clear, colourless liquid of low boiling point (260 C. or 78.80 F.), very volatile and smelling strongly of bitter almonds. (Some persons,- as an idiosyncrasy, are unable to distinguish the smell of hydrocyanic acid.)

It is very soluble in water and in alcohol, but such solutions decompose rapidly. Watery solutions do not redden litmus paper.

The vapour of hydrocyanic acid is somewhat lighter than air and diffuses rapidly when released. In closed spaces it is extremely toxic; in the open, however, the dispersion of the gas is so rapid that relatively low concentrations result which are not lethal. This fact explains the failure of hydrocyanic acid gas shells in the Great War in the open field, where they caused but few casualties. Nevertheless, a study of the gas is essential as it may be used again in different circumstances.

Mode of action.- The gas arrests the activity of all forms of living matter by inhibiting oxidation. In high concentration, such as may be found in a confined space, this gas may well be considered a fulminant poison, as it may cause death with dramatic rapidity through paralysis of the respiratory centre in the brain.

In open warfare, however, the gas loses much of its potential activity through diffusion; moreover, in low concentrations, the gas may be detoxicated in the body, as quickly as it is absorbed, to products which are relatively harmless. The failure of this gas in open warfare is therefore not surprising.

Attention may be drawn to a danger in the use of hydrocyanic acid gas when it is employed for the destruction of vermin, such as rats in ships, or in the disinfection of rooms. A suitable respirator eliminates the danger of its inhalation, bu, 'since this gas may be absorbed by the skin, it is dangerous to remain for long in the high concentrations employed against vermin even with a respirator.

Owing to the ease with which the gas dissolves in water, the skin absorption danger is greatly increased if the weather be hot and the skin bathed in sweat.

Symptoms. - With high concentrations the effects are rapid. The symptoms are ushered in by uneasiness and vertigo, palpitation and hurried breathing; unconsciousness and convulsions follow quickly, and death occurs through paralysis of the respiratory centre and failure of the circulation.

Concentrations that are not lethal may yet produce headache or giddiness, and sometimes nausea or inability to concentrate; recovery, however, is usually rapid and complete.

Protection.-Ordinary charcoal respirators give only limited protection against hydrocyanic acid gas, but special containers Containing pads impregnated with caustic soda, etc., are available which give effective protection; these depend on the neutralization of the gas by chemical action, and are fitted with indicating devices which give timely warning when the useful life of the respirator is nearing its end.

After the employment of hydrocyanic acid gas for the destruction of vermin or the fumigation of closed spaces, it is essential that the ventilation of such compartments be thorough, not only to remove possible pockets of gas, but also to allow bedding and all material into which the gas may be absorbed ample time to eliminate the poisonous vapour.

An indirect form of protection applicable to confined spaces, is the employment of susceptible animals (such as canaries, pigeons, or dogs) to indicate the presence of the gas; canaries are particularly susceptible, as they succumb in about two minutes when exposed to a concentration which is not rapidly harmful to man.

Treatment must be immediate and the primary urgent necessity after removing the victim from the poisonous atmosphere is to reduce the concentration of the gas in the circulation. This can he achieved by artificial respiration, preferably in conjunction with the administration of oxygen with an admixture of 5 to 7 per cent. of carbon dioxide, as the latter, through central stimulation, will help to secure thorough ventilation of the lungs.

Various prophylactic and antidotal methods have been suggested based on the laboratory neutralization of hydrocyanic acid gas by certain chemicals, such as sodium thiosulphate, methylene blue, glucose, etc., but very little success has, so far, followed their adoption. The main essential in successful treatment is immediate artificial respiration.

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46. Hydrogen sulphide (Sulphuretted Hydrogen).

Physical and chemical characteristics - Hydrogen sulphide is a colourless gas with a foetid odour resembling that of rotten eggs, more offensive in weak than in strong concentrations. Although the characteristic odour can be detected in concentrations low enough to be harmless, fatigue of the sense of smell occurs early, and the odour may cease to serve as a warning. Again, very high concentrations, though irritating to the eyes and throat, may be unrecognizable by the sense of smell and may, like hydrocyanic acid gas, be rapidly fatal. The gas, which is inflammable, is heavier than air, and may form explosive mixtures in tunnels, cellars, dug-outs, and other confined spaces. Hydrogen sulphide was tried in the Great War as an offensive gas, but its use was abandoned.

Mode of action. - Hydrogen sulphide acts both as a local irritant and as a systemic poison. Local irritation is confined to the tissues and exposed mucous membranes of the eyes, throat and respiratory tract while systemic poisoning follows the invasion of the lungs by moderate or high concentrations of the gas.

High concentrations of the gas produce unconsciousness with the same dramatic suddenness as with hydrocyanic acid, due in both cases to paralysis of the respiratory centre in the brain. Moderate concentrations give rise to symptoms of pulmonary oedema. There is no evidence that abnormal combinations with haemoglobin are formed.

Symptoms. - Symptoms of acute poisoning are usually ushered in by panting respiration, pallor and rapid unconsciousness; this is quickly followed by cessation of breathing, often accompanied by convulsive movements. The heart continues to beat for some minutes, and unless the victim is extracted from the gassed area and artificial respiration employed immediately, cardiac failure and death may result. In less acute cases of poisoning violent irritation of the eyes and severe inflammation of the respiratory tract, which may prove fatal, are the most prominent symptoms.

Subacute cases of poisoning, as met with occasionally in industrial life are not likely to be seen frequently in war time; they give rise to symptoms of general ill-health, with chronic

conjunctivitis and affections of the respiratory and digestive tracts.

Protection. - Adequate protection against its use in the field is provided ly the respirator. If concentrations of the gas are suspected in dug-outs, cellars or other closed spaces, they may be readily detected, apart from smell, by exposing lead acetate paper, sheet copper or slightly moist silver articles, which are all blackened in the presence of hydrogen sulphide.

Treatment. - As in the case of poisoning by hydrocyanic acid gas, treatment must be prompt. It consists essentially in the immediate removal of the victim from the poisonous atmosphere and the administration of artificial respiration, preferably with inhalation of air or oxygen mixed with 5 to 7 per cent. of carbon dioxide. The latter stimulates the respiratory centre in the brain, and the rapid oxidation of the residual hydrogen sulphide in the blood ensures that no lasting after-effects follow the exposure.

Artificial respiration should be persisted in for a long period, even though there may be no signs of life. The effectiveness of this has been proved by industrial practice.

The treatment of the subacute type is symptomatic; recovery is usually complete if permanent freedom from further exposure can be secured.

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