John Burgess wrote: > anhydrous OA has a molecular weight of 45 and the dihydrate 63. My handbook of Chemistry and Physics list OA's molecular weight as 90.04. It is ethanedoic acid, HO2CCO2H or 2 carbon (24), 2 Hydrogen (2) and 4 Oxygen (64) which gives you 90. Formic acid is about 45, so maybe you are thinking about it instead? Plus, if you add 2 water molecules you would get a MW of 45+36=71 for OA dihydrate (but the dihydrate is listed as 126, which makes sense 90+36). Bill Truesdell Bath, Maine -- Visit www.honeybeeworld.com/bee-l for rules, FAQ and other info ---