Allen Dick wrote:

> ... what exactly is the dihydrate form [of oxaclic acid]?

For the purpose of treating against Varroa, you may use
both, either oxalic acid or oxalic acid dihydrate.
However, be sure to correct for the 'dihydrate' when
weighting the amount of acid you want to use:

 90,04 g  oxalic acid (HOOC-COOH)

       corresponds to

126,07 g  oxalic acid dihydrate (H00C-C00H * 2 H2O)

or: 100.00 g OA  - 140.02 g OA*2H2O
     71.42 g OA  - 100.00 g OA*2H2O

The OA*2H2O should be cheaper and reduces the risk of
hydration (due to air humidity) of pure OA.

Warning Sign    : Xn     Harmful
Risk            : 21/22  Harmful in contact with skin and if swallowed.
Safety          : 2      Keep out of reach of children.
Safety          : 24/25  Avoid contact with skin and eyes.

For more information you may want to consult e.g.
http://ecdin.etomep.net/

THIS IS NO RECOMMENDATION TO USE OXALIC ACID AS A
TREATMENT AGAINST VARROA.

--
Michael Haberl
[log in to unmask]
http://staff-www.uni-marburg.de/~haberl/
http://staff-www.uni-marburg.de/~ag-biene/