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<br />Ir~n and manganese are also objectionable in water used <br />for sanitation because they stain porcelain, enamelware, and <br />fabrics. White clothing wa8h~d in water containing high con- <br />centrations of iron ~d manganese turns yellow or brawn. <br /> <br />Water for Heatinq and Coolinq <br /> <br />Millions of dollars are lost each year by water users through <br />corrosion of and scale formation in pipes, water heaters, boilers, <br />and other heat-exchange vessels. Corrosion is a very complex <br />process: among the many factors contributing to corrosion are <br />low pH, low alkalinity (indicated as bicarbonate in table 3), low <br />hardness, high content of free carbon dioxide, and high concen- <br />trations of iron sulfate or magnesium chloride. Scale formation <br />generally is caused by calcium and magnesium, which precipitates <br />with bicarbonate or sometimes with sulfate: it also can be caused <br />by silicates, oxides of iron, and other substances. Scale caused <br />by calcium or magnesium carbonates ordinarily is softer and less <br />adherent than scale caused by calcium sulfates or by certain <br />forms of silicates. <br /> <br />The tendency of a water to cause corrosion or to form scale <br />can be controlled by treatment. Some forms of treatment consist <br />only of aer~tion or deaeration to remove dissolved gases that <br />accelerate c~rosion. An important form of treatment involves <br />the careful regulation of the pH, alkalinity, and calcium content <br />of the water so that the water will be only slightly scale forming: <br />maintenance of a thin coating of scale insulates the metal from <br />the corrosive medium. Such treatment, however, may not be practi- <br />cal if the chemical composition of the water supplies fluctuates <br />widely. The "Langlier calcium carbonate saturation index" (Powell, <br />1954, p. 278) provides a method by Which the relative corosiveness <br />or scale-forming tendencies of a water can be estimated from the <br />chemical analysis of the water. <br /> <br />Water for Industrial Processinq <br /> <br />. <br /> <br />Water for industrial processing is the water that comes into <br />contact with a product or that is actually incorporated into the <br />product. The chemical-quality requirements for such water are <br />dependent on the product manufactured: for some products very <br />exacting limits must be maintained. Water for all industrial <br />processing should be free of offensive taste, odor, and appearance. <br />Differences in the chemical-quality requirements for the process <br />water is indicated by the following examples (california Institute <br />of Technology, 1957): <br /> <br />25 <br />