Quote Originally Posted by heterolysis View Post
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%.
Given that Formaldehyde is a gas, a v/v number is unlikely, so we can safely assume wt%. I do agree that it's extremely unlikely that anyone dilutes a 37% Formaldehyde in water solution down to precisely 37% another time.

Quote Originally Posted by heterolysis View Post
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.
You may be correct. Here it says "0.1g / ml" which means that the scbt web page likely contains a typo. Given that Phenidone dissolves in water and in Propylene Glycol, I tend to trust the 0.1 g/l number more than the 0.1 mg/l number. I stand corrected.