สิ่งแวดล้อม มลภาวะ ของเสีย
เอกสารมาตรฐาน
สหรัฐอเมริกา
APHA
SMWW 2340
Hardness
2023
4
Standard methods for the examination of water and wastewater 543.3 APHA 24th ed. Ref. (Treatises&monographs FL2)
Originally, water hardness was understood to be a measure of the capacity of water to precipitate soap. Soap is precipitated chiefly by the calcium and magnesium ions present. Other polyvalent cations also may precipitate soap, but they often are in complex forms, frequently with organic constituents, and their role in water hardness may be minimal and difficult to define. In conformity with current practice, total hardness is defined as the sum of the calcium and magnesium concentrations, both expressed as calcium carbonate, in milligrams per liter...