Also, because it refers primarily to water, the term “APHA Color” is undesirable.

It is therefore recommended that the incorrect term “Hazen Color” should not be used. The parts per million nomenclature is not used since color is not referred directly to a weight relationship.

Subsequently, in their first edition (1905) of Standard Methods for the Examination of Water, the American Public Health Association, using exactly the same concentration of reagents, assigned the color designation 500 (parts per million) which is the same ratio. Hazen in the American Chemical Journal 5 in which he assigned the number 5 (parts per ten thousand) to his platinum-cobalt stock solution. This test method is similar to the description given in Standard Methods for the Examination of Water and Waste Water 4 and is referred to by many as “APHA Color.” The preparation of these platinum-cobalt color standards was originally described by A. This was accomplished in 1952 with the adoption of Test Method D1209 using the platinum-cobalt scale. Several expressions for defining “water-white” gradually appeared and it became evident that a more precise color standard was needed. 3.2 For a number of years the term “water-white” was considered sufficient as a measurement of solvent color.

Apha standard methods 21st edition pdf