Formalin is another common name for formaldehyde when dissolved in water. It can be used regardless of concentration. If you checked the MSDS listed for that specific product you would see it was consisting of 30.0-50.0 wt% formaldehyde, so to me at least it's clear that it is not 14 wt%. As for what the recipe calls for, I'm not sure. It wasn't specified in the original post whether we were talking v/v or wt%, but I made the assumption we were talking about a 37 wt%, 40% v/v, or "100% formalin" solution. It seems unlikely we would be diluting a 37 wt% solution to 37%.
Originally Posted by Tony-S
And I don't know anything about using phenidone first hand, I just read that in an archive somewhere when I was googling the topic. It is capable of forming 10 wt% solutions in methanol if its MSDS is to be believed, though higher concentrations are probably used. Phenidone salts however are unlikely to be soluble in methanol.