Nitric Acid

Nitric acid, or strong water, HNO₃, in the form of ammonium, alkaline, and alkaline-earth salts, called nitrates, occurs universally in soil; known (only) deposits of nitrates exist in Chile. N. a. was obtained by Glauber in the 18th century; the composition of N. a. was determined by Gay-Lussac in 1816. Anhydrous N. a. is colorless, smokes slightly; sp. gr. at 15°-1.59; boils at 86°; from light or heating N. a. turns yellow due to the formation of nitrogen dioxide (NO₂). N. a. belongs to the strongest acids, dissolves or oxidizes all metals except gold, platinum, rhodium, and iridium. Organic substances are very strongly oxidized by N. a. N. a. is obtained partly from nitrates by distillation with sulfuric acid, but mainly from N of the air, burning N in the flame of an electric arc or by other means, or preparing from N ammonia. Raw N. a. is purified by distillation. Nitrogen dioxide from strong N. a. is removed by heating after diluting the acid with water. Qualitatively, N. a. is determined by the reactions described in analytical chemistry: 1) ferrous sulfate with sulfuric acid (brown coloring); 2) diphenylamine with sulfuric acid (blue coloring); 3) brucine with sulfuric acid (pink, turning yellow). Quantitative determination of N. a. with several mg is done colorimetrically, and with larger amounts volumetrically, converting nitric acid into ammonia. The effect of N. a. on the organism is expressed in the neutralization of blood alkalis, the formation of acid-albumins, local irritation, inflammation, and, depending on the concentration of the acid, greater or lesser destruction of tissues; N. a. has a specific effect on proteins, causing yellow coloring (so-called xanthoprotein reaction) at points of contact with the skin or mucous membrane. According to Ph (VII), the single highest dose for diluted nitric acid containing 16.2% anhydrous, -1.0, pro die-3.0. The lethal dose for concentrated N. a.-10.0. Medical significance is also attached to and adopted by Ph (VII): 1) Acid, nitric. pur., containing 32.4% anhydrous N. a.,- used for cauterizations; 2) Acid, nitric. dilut., containing 16.2% anhydrous N. a.; 3) Potassium nitrate; 4) Sodium nitrate; and 5) Nitroglycerin. sol. Technical significance is attached to nitrates, especially potassium (black gunpowder, fertilizer); a series of organic nitro compounds and explosives- smokeless gunpowder, dynamite, melinite, lyddite, erazite, etc.; also belong to these chloropicrin CCl₃(NO₂) and other nitro compounds used in gas warfare. N. a. fuming, Acid, nitric, fumans, or Acid, nitrosonitricum, represents 86% N. a., containing up to 8% nitrogen dioxide; gives off abundant suffocating fumes of nitrogen dioxide, has an oxidizing and destructive effect to a greater degree than non-fuming N. a. It is obtained 1) by passing NO₂ into concentrated N. a., 2) by distilling nitrates with sulfuric acid at elevated t° or with the addition of starch. It is used cautiously as a cauterizing agent. N. a. in forensic-medical respect. By its effect on tissues N. a. is almost identical with sulfuric and hydrochloric acids, but concentrated N. a. gives a yellowish coloration to burned tissues, mainly in the throat and esophagus, less frequently in the stomach and never in the intestines; here it, due to dilution, gives a simple gray coloration. A difference from poisoning with sulfuric and hydrochloric acids can also be the lesser intensity of coloring in N. a. burned tissues with hematine.-N. a. is volatile, and vomiting in poisoning with it is accompanied by eructation of suffocating fumes and difficulty in breathing, and subsequently lobular pneumonia often forms. Diluted N. a. is sometimes used under the name 'sharp water' as an abortifacient; abortion occurs in this case due to chronic poisoning with N. a., which often leads to death. At autopsy here one usually finds parenchymatous degeneration of internal organs and anemia. As for the reduction products of N. a., poisoning with fumes of N. a. and nitrous oxide are often observed. The symptoms of these poisonings are similar to ammonia poisoning, but appear only after some time (about 8 hours). At autopsy-acute inflammation of the respiratory tract and edema of the lungs.-Discovery in legal cases and in professional poisonings. Free N. a. is fixed on protein bodies: yellow coloring. The object (internal organs, food, etc.) is extracted with water (see Poisons). Part of the extract is evaporated with white woolen threads: yellow coloring of them, turning from ammonia to orange; the extract is subjected to distillation with copper sawdust (reducing agent) almost to dryness,-in the distillate nitrous acid is revealed.-For determination in the air 25-50 liters of it is drawn through absorption flasks (see Poisons) with 30% solution of caustic soda. The liquid is boiled (to remove possibly present ammonia), then heated in a Kjeldahl apparatus with zinc dust or Devarda's alloy (aluminum + zinc + copper); the ammonia formed by reduction is distilled into a titrated solution of sulfuric acid. If nitrous acid is present in the air, its amount is subtracted from the amount of N. a., calculated from the ammonia found.