Formaldehyde solution: the strength of the commercially available solution should be checked as follows: mix 3 ml formaldehyde solution with 50 ml 1N sodium hydroxide solution and 25 ml hydrogen peroxide solution (20 volumes). Heat on a steam bath until effervescence stops. Cool, and titrate with 1N hydrochloric acid using phenolphthalein indicator. Carry out a blank titration using 3 ml water in place of the formaldehyde.
1 ml of 1N sodium hydroxide ≡ 0.0300 g formaldehyde
strength of formaldehyde solution ≡
No math image to display
where:
B = blank titre; and
T = sample titre.