Understanding the Platinum-Cobalt Color Scale
The Platinum-Cobalt Scale (Pt/Co scale, Apha-Hazen Scale, or APHA Scale ) is a color scale that was introduced in 1892 by chemist Allen Hazen (1869–1930). The index was developed as a way to evaluate pollution levels in waste water. It has since expanded to a common method of comparison of the intensity of yellow-tinted samples as defined by ASTM D1209. The scale for APHA color goes from 0 to 500 in units of parts per million of platinum cobalt to water. Zero on this scale represents distilled water, or what is more commonly called white water. APHA standards can be used for both visual comparison and instrumental measurements. The original purpose of the APHA scale was to assist in the determination of the quality of public water supply, however other uses of APHA color have been demonstrated in chemical, pharmaceutical, beverage, plastic and petroleum industries.
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