I got a bottle of formic acid recently, but there's no sign on the label about the purity/concentration of it.
How can I tell more or less accurately with a simple method? And if it happends to be too dilluted, can I just boil it to get to the 85% needed for the performic oxidation of isosafrole?
Get yourself an aerometer and mesure the density of the formic acid. That's the easiest and fasted method to measure the concentration of most solvents.
> How can I tell more or less accurately with a simple method?
titration of a diluted sample - get a burette and a graduated flask.
formic acid is usually titrated against KMnO4, but if you can't get
that, then titration against a strong base will work too.
> can I just boil it to get to the 85%
no - bp of formic acid is 100.7°C! you could have found that out yourself,
lazy bastard!