APHA / APHA Color Number

APHA stands for the American Public Health Association.

The APHA color number is a finely scaled measure used to determine the color of nearly colorless to pale yellow liquids. The terms “Hazen” or “Hazen color number” and “Platinum-Cobalt color number” (PtCo) are used interchangeably, as Allan Hazen defined this color scale based on a Platinum-Cobalt solution for the APHA.