What is the APHA Color Scale?

The color intensity of liquids may be estimated rapidly by using platinum-cobalt standards as described in ASTM (D1209).  These platinum-cobalt standards are also called APHA (for American Public Health Association) and Hazen standards.  This method is particularly applicable to those materials in which the color-producing substances have light absorption characteristics nearly identical with those in the standards. Colors having hues other than light yellow or reddish yellow cannot be determined with these standards. The scale reads zero to twenty for most ACS or SEMI grade chemicals with zero indicating a water white solution.

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