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Chemical formula HCN. Colorless gas, melting point –13°C, boiling point 26°C. It condenses into a colorless liquid at room temperature, is highly volatile, has a bitter almond odor, and is highly toxic. In cases of poisoning, mild symptoms include an itchy throat, dizziness, and weakness. Severe dyspnea on the affected side, slow pulse, dilated pupils, coma, leading to spasms, loss of consciousness, muscle relaxation, and ultimately death. The lethal dose is 0.001 g/kg body weight. It is miscible with solvents such as ethanol, ether, glycerol, ammonia, benzene, chloroform, and water. Hydrogen cyanide burns in air with a blue flame. The explosive limit is 5.6–40% (by volume). When hydrogen cyanide is present in the air, it causes the aniline-copper acetate test strip to turn blue; it changes the methyl orange-mercuric chloride(II) test strip from orange to pink; and it causes the picric acid-sodium carbonate test strip to change from yellow to brown. The above test strips can all be used to detect hydrogen cyanide in the air. Gaseous hydrogen cyanide exists as molecules, while in the liquid state the molecules are strongly associated with each other. Therefore, hydrogen cyanide has the highest dielectric constant among all liquids (116 at 20°C). Liquid hydrogen cyanide or its aqueous solution undergoes polymerization under conditions such as alkalinity, high temperature, prolonged storage, exposure to light, discharge, and electrolysis. The polymerization releases a large amount of heat, which triggers a chain reaction until a violent explosion occurs. An aqueous solution of hydrogen cyanide is called hydrocyanic acid; it is an acid that is weaker than carbonic acid (K=2.1×10-9). It reacts with alkalis to form salts. It adds with aldehydes to form cyanohydrins. The product obtained together with propylene is the main raw material for plexiglass. Catalyzed by cuprous cyanide, it adds to acetylene to yield acrylonitrile. Hydrocyanic acid is an insecticide for fruit trees, and it is also commonly used for disinfection and pest control on ships. It is an important reagent in the mechanistic preparation and synthesis. When dilute acid is dropped on solid cyanide, hydrogen cyanide is produced immediately. Industrially, it is produced by using platinum as a catalyst to burn a mixture of ammonia and methane: 2NH3+2CH4+3O2 → 2HCN+6H2O; the HCN generated can be absorbed by NaOH.