Ammonia

Ammonia, NH₃, a chemical compound found in small amounts in air, atmospheric precipitation, river and sea water, and soil. Ammonia is a colorless gas with a sharp, pungent odor that irritates mucous membranes; specific gravity at 0° and 760 mm = 0.589 (air = 1); under a pressure of 7 atm at room temperature or under ordinary pressure and cooling to -40°, ammonia turns into a liquid that boils at -34° and crystallizes at -75°; critical temperature +130°; liquid ammonia conducts electric current (dielectric constant D = 21.22), and the electrical conductivity of many salts in it is higher than in aqueous solution. It is easily soluble in water (at 0° - 1050:1); a saturated aqueous solution is usually prepared, which contains about 33% NH₃; in this solution there is a small amount of easily dissociated ammonium hydroxide NH₄OH (=NH₃+H₂O); when heated to boiling, all the ammonia evaporates from the aqueous solution. Ammonia is now obtained in enormous quantities synthetically, mainly by the following methods: the German method of F. Haber (Haber, 1913): a mixture of H and N under a pressure of 200 atm is heated to 600° in the presence of a catalyst (iron oxide); yield up to 25%; in the French method of Claude (G. Claude, 1922), a pressure of 100 atm is used and work begins at 360°, then the temperature is maintained by the reaction itself, and conversely, the apparatus is cooled with molten lead; yield up to 97%; the third method (Frank and Caro, 1895), especially common in the United States and Japan, consists in obtaining calcium cyanide CaCN₂ from calcium carbide and nitrogen (at 700° in the presence of catalysts), which is widely used as fertilizer and also gives ammonia when decomposed by water with heating (the cheapest method); the fourth method (Serpeck) consists in obtaining aluminum nitride, AlN, which gives ammonia when acted upon by water vapor; the old method consists in saturating water from gas works with hydrochloric or sulfuric acids, through which illuminating gas (from dry distillation of wood) is passed. Synthetic ammonia is significantly cheaper, but the initial installation is expensive. Determination of ammonia is usually done with mercury salts, with which it gives characteristic precipitates; a very sensitive test is "Nessler's reagent" (a solution of mercuric iodide in potassium iodide in the presence of caustic potash), which gives a red precipitate of basic amido-iodide of mercury [Hg(NH₂)I] HgO. Ammonia is quantitatively determined by titration with acids using methyl orange as an indicator. Liquid ammonia is used in small ice-making machines to obtain sterile ice. In industry, synthetic ammonia is used in enormous quantities to convert it into nitric acid and saltpeter. Ammonium salts are also widely used. Ammonia, both in gaseous state and in solution, has a strong local irritating effect on mucous membranes and skin; penetrating through it, it first excites and then paralyzes the endings of sensory nerves, being a typical representative of so-called anaesthetica dolorosa. The effect of ammonia solution on the skin, depending on concentration and duration, is expressed as hyperemia, formation of blisters and a scab, which is difficult to separate, leaving behind a persistent scar. Ammonia acts more strongly on mucous membranes: inhaling it in concentrated form causes burning pain, suffocating cough, spasm of the glottis, edema and strong irritation of the mucous membrane of the larynx and trachea with swelling and formation of exudate; in poisoning with ammonia solution per os, besides the oral cavity, pharynx and entrance to the larynx, the esophagus and gastrointestinal tract are affected, which is accompanied by vomiting, sometimes bloody, and diarrhea. In acute poisonings, phenomena from the gastrointestinal tract predominate, but sometimes death occurs after several hours from acute edema of the larynx. The resorptive effect of ammonia can be best observed in experimental poisoning of an animal by rapid introduction of a solution of ammonium salts, for example, ammonium carbonate, directly into the blood, because when introduced per os no poisoning occurs, as the introduced salt is detoxified by the liver as it is absorbed, converting it into urea. The phenomena of poisoning with ammonium salts (resp. ammonia) are expressed by strong excitation of the central nervous system, especially the medulla oblongata, as well as the motor apparatus of the heart. This is the cause of the deepest and most frequent breathing, a sharp increase in blood pressure and attacks of clonic convulsions, which then pass into true tetanus with opisthotonus, but, unlike strychnine, they have not only a reflex but also an autonomous character. At the same time, there is a darkening of consciousness due to the suppression of the higher centers of the cortex. The convulsive attacks last for a short time, then followed by a state of complete relaxation due to the subsequent paralyzing effect of ammonia on the central nervous system, and in this state death occurs due to paralysis of the respiratory center. The local irritating effect of ammonia finds therapeutic application for reflex excitation of vasomotor centers by irritating the endings of n. trigemini and n. laryngei superioris when inhaling ammonia released from its solution or from its volatile salts. For therapeutic purposes, ammonia and its salts are used: externally - in the form of spirits of hartshorn as a skin irritant and local anesthetic in ointments and liniments; for smelling in fainting and comatose states - in the form of spirits of hartshorn and ammonium carbonate; internally - as an expectorant, for which purpose ammonium anisate drops are prescribed - Liq. Ammonii anisat. 15-20 drops, ammonium carbonate 0.2-0.5, ammonium chloride 0.3-1.2 pro dosi; the last two salts are also used for inhalations in a 2% aqueous solution. Detection in judicial cases and in professional poisonings. Toxicological significance is attached to finding only free ammonia in fresh objects (internal organs, food, etc.), since as a result of putrefaction of protein bodies, ammonia is formed. In a flask, place the crushed object (internal organs, stomach contents, etc.), the neck of the flask is stoppered, to the lower surface of which are attached 1) moistened red litmus paper, 2) paper moistened with a solution of mercurous nitrate, 3) a solution of copper sulfate (1:1,000) and 4) a solution of lead acetate (to confirm the absence of hydrogen sulfide, in which case the detection of ammonia loses significance). From ammonia, the litmus paper turns blue, with mercurous nitrate it turns black, with copper sulfate it turns blue. For quantitative determination of ammonia in air, a certain volume of it is drawn through absorption bottles with ^v/₁₀ sulfuric acid solution using an aspirator with indicators: lacmoid (with added malachite green), cochineal infusion or methyl red, and the excess acid is back-titrated with ^{v/₁₀ caustic soda solution.}