chroma

Pure water is colorless and transparent. Natural water contains soil, organic matter, plankton, and inorganic minerals, which give it a certain color. Industrial wastewater contains dyes, biological pigments, colored suspended solids, etc., and is the main source of coloring in environmental water bodies. Colored water can weaken the transparency of water bodies, affect the growth of aquatic organisms, and reduce the ornamental value of water bodies.

The color of water can be divided into two types: true color and surface color. True color refers to the color of water after removing suspended solids, which is called chromaticity; The color of water without removing suspended solids is called surface color. For clean or low turbidity water, its true color and surface color are similar; For industrial wastewater with deep coloring, there is a significant difference between the two. The color of water is commonly measured using the following methods.

（1） Platinum cobalt standard colorimetric method

This method involves dissolving potassium chloroplatinate and cobalt chloride in water to form a standard color chart (GB11903-89), and then visually comparing it with the water sample to determine its color. The color of 1mg platinum and 0.5mg cobalt per liter of water is defined as 1 degree, which serves as the standard color unit. This standard solution has stable properties and can be stored for a long time. However, potassium chloroplatinate is relatively expensive and can be dissolved in water with potassium dichromate and cobalt sulfate to form a standard series, but cannot be stored for a long time. If the water sample is turbid during measurement, it should be placed for clarification. Alternatively, centrifugation or filtration with a 0.45 μ m pore membrane can be used to remove suspended solids, but filter paper cannot be used.

This method is suitable for the determination of natural and drinking water that is relatively clean and has a yellow color tone. If there is soil or other finely dispersed suspended matter in the water sample, and it is still opaque after treatment with clarification, centrifugation, or other methods, the "color" shall be measured. If the water sample is not yellow, it cannot be compared using the platinum cobalt color column, and only appropriate text can be used to describe its color and chromaticity.

（2） Dilution ratio method

This method is suitable for determining the color of surface water and industrial wastewater contaminated by industrial wastewater. When measuring, first describe the type and depth of the water sample color in words, such as dark blue, brownish yellow, dark color, etc. Then take a certain amount of pre treated water sample and dilute it with distilled water until the color is barely visible. The chromaticity of the water sample is expressed according to the dilution factor (GB11903-89), and its unit is times.

The water sample taken should be free of leaves, dead branches, and other debris; After sampling, it should be measured as soon as possible, otherwise it should be refrigerated and stored. In addition, the International Commission on Illumination (CIE) has also established standards for determining the chromaticity of water samples using spectrophotometry.