Local Milk O'Magnesia

Tomorrow morning, bright and early, my first year chemists are going to measure the amount of magnesium in Milk of Magnesia (MoM).  The technician who sets things up came yesterday to tell me that the students will have to double up because they had almost run out of MoM.  Something similar happened earlier in the week when I had to leg it to the canteen to buy the last banana after lunch so that a different class could assay that for Potassium.  The banana was a local cock-up but the MoM shortage appears to be systemic.  Can’t be had in any of the pharmacies in town and it is "Sorry currently out of stock" at Boots.  My pharmacist room-mate confirmed the poor supply and thought it was due to the low profit margin on something that was so “appropriate technology”, when proprietary products like Gaviscon are available for sale.  Apparently it is banned in Australia – perhaps because chronic (constipated) users with renal dysfunction are unable to clear the excess Mg from the system.  Although Magnesium is a minority element in the body (about 25g each per adult), it is crucial for the regulation of calcium and potassium flux.  So muscle cramps are a common enough side-effect of excess MoM consumption.   And the ‘flux’ that relieves the constipation seems to preferentially strip out potassium ions, and this can have severe medical effects. More on line at the NCBI's DietaryReference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride. If the Irish gumment is going to ban the stuff, however, then let’s have it out in the open and not let my paranoia come to believe that MoM is being banned by stealth to boost the sales of Gaviscon.

A ban here would be a little ironic because MoM was invented in Ireland almost exactly 200 years ago by Sir James Murray who floated a successful business on the insight that notoriously insoluble Mg salts could be dissolved if he bubbled CO₂ through the mix.  I share this tit-bit from the wholly wonderful book Ingenious Ireland by Mary Mulvihill.
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