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TEXT 12Reaction of Metals Most elements are combined with oxygen to form compounds with oxygen or oxides under some conditions. The behaviour of metals is very important. In the case of ordinary metals such as iron, copper, zink, etc., this chemical reaction is slow at normal air temperatures and only noticeable as rusting or corroison. At heigher temperatures, however, all these metals will burn in air or oxygen in a manner similar to that of carbon. In some cases, however, the burning of the metal is continuous only if steps are taken to keep the temperature of the metal high enough. On the other hand the metal sodium at air temperature combines with oxygen readily and also rapidly decomposes cold water. Magnesium is another example of a metal which readily burns. Magnesium, like many other metals, decomposes water. Sodium does this rapidly at air temperature, but magnesium requires a high temperature before the process becomes equally rapid. It must be heated to high temperature to burn in air. TEXT 13 Smoke Smoke consists of finely divided particulate matter and suspended liquid droplets known as aerosols. Carbonaceous particulate matter is formed from the burning of most materials under conditions of incomplete combustion. Under these conditions, incompletely burned organic materials are also evolved in dispersed aerosol and contribute to visible smoke. Since the average size of particulates and aerosols is about the same as the wavelength of visible light, the scattering of the light occurs and vision through smoke is obscured. There are certain combustion conditions under which some materials burn without producing visible products of combustion. However, visible smoke generally accompanies fire, and like flame, is evidence of fire. Smoke frequently provides the early warnings of fire, but at the same time contributes to panic conditions by the very nature of its blinding and irritating effects. Smoke particulates and aerosols can be harmful when inhaled, and long exposure may cause damage to the respiratory system. Particulates and irritants in the eyes induce tears. When present in the nose and throat, they can cause sneezing and coughing. Smoke particulates are often of a sufficiently small size that enables them to be inhaled deep into lungs where adsorbed toxicants may produce profound respiratory system damage. These effects have not been sufficiently studied to enable the understanding of their consequences.
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