> Taking the accepted formulation of 1 litre of water/1 kilo of sugar and
> 35 grammes of Oxalic di-hydrate to prepare a varroa controlling mixture,

Peter, this is an erroneous formula, but a common mistake.
The proper formula for winter treatment is 35g per liter of syrup.
You need 56g OA if you mix a liter of water and 1 kilo of sugar.
Both formulas will give you a 2.7%w:w or 3.4%w:v mixture--appropriate for
winter treatment.

For summer use, some recommend 70g OA in 1 L water plus 1kg sugar (3.4%w:w
or 4.2%w:v)

Europeans tend to express the percentage as w:v, Americans as w:w.  This
leads to much confusion.
In all cases, 5ml per seam of bees, measured accurately.

If your water is "hard," the oxalate will precipitate out as calcium
oxalate.  I suggest using soft water.
For more info, my oxalic article from ABJ (minus photos to date) is free for
viewing at www.randyoliver.com
Randy Oliver

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