This method is for the analysis of the formaldehyde content of aqueous solutions of the gas. With the precautions given, it can also be used to determine the free (unreacted) formaldehyde content of resins used in paper treatment. Experience has indicated the method is adaptable to determination of free or unreacted formaldehyde in urea formalde-hyde resins. Most aldehydes and certain ketones will undergo the same reaction as formalde-hyde. Thus the presence of other aldehydes will give erroneous results. Acids and alkalis interfere in the titration, but this can be overcome by neutralization prior to reaction. There are known instances where the formaldehyde is bound so loosely that it is very difficult not to hydrolyze the resin. Conducting the reaction at 0-5C minimizes the hydrolysis.