[Rudeofus]

Mark, Sodium metaborate 4 mol == NaBO2·4H2O ?

I'll answer instead of Mark: Photo Formulary sells sodium metaborate which according to their MSDS is sodium metaborate 4 mol. This MSDS lists the formula NaBO₂·2H₂O [Na₂B₂O₄·4H₂O]

Likewise there is a reference on http://www.borax.com which lists both 4 mol (NaBO₂·2H₂O) and 8 mol (NaBO₂·4H₂O) sodium metaborate. So for all practical purposes I would assume that Mark means the 4 mol compounds as defined by these references: NaBO₂·2H₂O

The confusing names seem to come from the double compounds Na₂B₂O₄·4H₂O and Na₂B₂O₄·8H₂O