of HCl and its subsequent reaction with surface oxides. Zinc chloride reacts with metal oxides (MO) to give derivatives of the idealized formula MZnOCl2. This reaction is relevant to the utility of ZnCl2 solution as a flux for soldering — it dissolves passivating oxides, exposing the clean metal surface. Fluxes with ZnCl2 as an active ingredient are sometimes called "tinner's fluid". Zinc chloride forms two salts with ammonium chloride: (NH4)2ZnCl4 and (NH4)3ClZnCl4, which decompose on heating liberating HCl, just as zinc chloride hydrate does. The action of zinc chloride/ammonium chloride fluxes, for example, in the hot-dip galvanizing process produces H2 gas and ammonia fumes. In textile and paper processing Concentrated aqueous solutions of zinc chloride (more than 64% weight/weight zinc chloride in water) have dissolving starch, silk, and cellulose. Relevant to its affinity for these materials, ZnCl2 is used as a fireproofing agent and in fabric "refresheners" such as Febreze. Vulcanized fibre is made by soaking paper in concentrated zinc chloride. Smoke grenades The zinc chloride smoke mixture ("HC") used in smoke grenades contains zinc oxide, hexachloroethane and granular aluminium powder, which, when ignited, react to form zinc chloride, carbon and aluminium oxide smoke, an effective smoke screen. Fingerprint detection Ninhydrin reacts with amino acids and amines to form a colored compound "Ruhemann's purple" (RP). Spraying with a zinc chloride solution forms a 1:1 complex RP:ZnCl(H2O)2, which is more readily detected as it fluoresces more intensely than RP. Disinfectant and wood preservative Dilute aqueous zinc chloride was used as a disinfectant under the name "Burnett's Disinfecting Fluid". From 1839 Sir William Burnett promoted its use as a disinfectant as well as a wood preservative. The Royal Navy conducted trials into its use as a disinfectant in the late 1840s, including during the cholera epidemic of 1849; and at the same time experiments were conducted into its preservative properties as applicable to the shipbuilding and railway industries. Burnett had some commercial success with his eponymous fluid. Following his death however, its use was largely superseded by that of carbolic acid and other proprietary products. Safety Zinc chloride is a chemical irritant of the eyes, skin, and respiratory system. Additional reading N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, 2nd ed., Butterworth-Heinemann, Oxford, UK, 1997. The Merck Index, 7th edition, Merck & Co, Rahway, New Jersey, USA, 1960. D. Nicholls, Complexes and First-Row Transition Elements, Macmillan Press, London, 1973. J. March,