You may also have lots of trioxymethylene in that flask.
Formaldehyde solution, Formalin, Formol, Morbicid, Veracur (Typharm). A soln of about 37% by wt of formaldehyde gas in water, usually with 10-15%
methanol added to prevent polymerization. This soln is the full strength and also known as Formalin 100% or Formalin 40 which signifies that it contains 40 grams of
formaldehyde within 100 ml of the soln. Colorless liq; pungent odor. On standing, esp in the cold, may become cloudy and on exposure to very low temp a ppt of
trioxymethylene is formed. When evaporated, some formaldehyde escapes, but most of it is changed to trioxymethylene. It is a powerful reducing agent especially in
presence of alkali. In the air it slowly oxidizes to formic acid. d2525 1.081-1.085. One gallon weighs 9.1 lbs. bp760 96 deg. nD20 1.3746. Flash pt 60 deg (140 degF). pH 2.8-4.0.
Misc with water, alcohol, acetone. Keep well closed in a moderately warm place. LD50 orally in rats: 0.80 g/kg (Smyth).