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MgSO4.7H20? or MgSO4.1H20?

	This morning I picked up a pound of "Rite Aid 100% Natural Mineral
Epsom Salt, Magnesium Sulfate U.S.P."  It's pharmaceutically pure
MgSO4.7H2O, right?  On the side of the box, however, it says, "Magnesium
Sulfate U.S.P. MgSO4.H20" -- not the heptahydrate, but a monohydrate.  I
assumed that this was simply an error, but just to be sure, I looked it
up.  It turns out that in addition to "Epsomite", MgSO4.7H2O, there's
also "Kieserite", MgSO4.H2O.
	In an attempt to figure out which of the two I actually had, I made a
solution with a final concentration of 219 mg of the mystery powder per
liter.  This should (by the arithmetic below) give a GH of 5 with the
heptahydrate, or a GH of 9 with the monohydrate.  My Tetra GH kit took
14 drops in 10 mls, for a reading of 7, exactly midway between my 2
predicted results. :(  Since my analytical equipment consists of kitchen
utensils, a postage scale, and a bucket (carefully) calibrated in
gallons, it's not surprising that the result was inconclusive.
	For now I plan to err on the safe side, and assume that this really is
MgSO4.H2O.  But I'm still wondering: 
1. What's the correct answer?
2. How many people out there are mixing their PMDD Magnesium dose at
nearly 2X strength because their "Epsom salt" is really the monohydrate,
at only 56% the expected molecular weight?
-- Sherman Lovell

The arithmetic:
1 dGH = 7.143 mg per liter of Ca
7.143 mg Ca x 24 mg Mg / 40 mg Ca = 4.29 mg Mg per dGH (Right?)

219 mg MgSO4.7H20 x 24 mg Mg / 246 mg MgSO4.7H2O x 1 dGH/4.29 mg Mg
	= 5 dGH for the heptahydrate
219 mg MgSO4.H20 x 24 mg Mg / 138 mg MgSO4.H2O x dGH/4.29 mg Mg
	= 9 dGH for the monohydrate