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On Sun. 25 Mar. 2001, Thomas Barr wrote "...3KH/GH => to about
50ppm or mg/l."  I had earlier made a note of a definition from (I believe)
Paul Sears to the effect that one degree of hardness (1 dGH) corresponds to
10 mg/l of calcium oxide in the water.  By that definition, 3 dGH would be
30 mg/l, not 50.

I'm not a chemist, so I'm skating on thin ice in the following analysis.
But is the difference because Barr's definition is in terms of calcium
carbonate rather than calcium oxide?

Since the molecular weight of CaO is 56 and that of CaCO3 is100, you would
need 100/56 x 10 mg/l = 17.9 mg/l of the latter to achieve the same number
of calcium ions.  In that case 3 dGH = 53.7 mg/l, which is close to Barr's
number of 50.

I would appreciate correction if I'm wrong.

John T. Fitch
E-mail: JTFitch at FitchFamily_com
Web Page: www.fitchfamily.com