This link was posted by a chemist who said he did gas chromatography on several solid fuel tablets to determine their composition.

http://66.39.74.171/cgi-bin/archives/2000/geartalk-20/config.pl?read=8233

Also, my esbit box has a caution on it stating
CAUTION: Harmful
If swallowed call doctor.
Contains methenamine.
Keep out of reach of children.

The chemical name for methenamine is HEXAMETHYLENETETRAMINE (HEXAMINE)