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Narrative
A solution of aqueous formaldehyde is poured into a beaker. The formaldehyde is mixed with a solution of aniline hydrochloride. In a few seconds the mixture turns red and a solid, red rubbery polymer forms.

Discussion
A solution of aqueous formaldehyde is poured into a beaker. The formaldehyde is mixed with a solution of aniline hydrochloride. In a few seconds the mixture turns red and a solid, red rubbery polymer forms. The reaction involves electrophilic addition of protonated formaldehyde to the ortho or para position of aniline. Further condensation produces a cross-linked polymer connected by methylene bridges analogous to the formation of the phenol-formaldehyde polymer.