Determining the solubility of a compound can be a time demanding procedure, I'm not sure you're ready for this. Try dissolving 359 g/l Sodium Chloride if you don't believe me
If you get the stuff from a reputable source, they should be able to tell you exactly what they have, possibly even a CAS number which would completely eliminate any ambiguity. It's their business after all. The biggest problems come from published formulas which carelessly state "Sodium Metaborate" instead of the exact compound to be used, and no solubility test is going to help you with these.