As Baeyer said long ago: "It seems that all the
aldehydes will, under suitable circumstances, unite with the aromatic
hydrocarbons to form resins." So instead of phenol, other coal tar
products such as cresol, naphthol or benzene itself may be used. The
carbon links (-CH_{2}-, methylene) necessary to hook these carbon rings
together may be obtained from other substances than the aldehydes,
for instance from the amines, or ammonia derivatives. Three chemists,
L.V. Kedman, A.J. Weith and F.P. Broek, working in 1910 on the
Industrial Fellowships of the late Robert Kennedy Duncan at the
University of Kansas, developed a process using formin instead
of formaldehyde. Formin--or, if you insist upon its full name,
hexa-methylene-tetramine--is a sugar-like substance with a fish-like
smell. This mixed with crystallized carbolic acid and slightly warmed
melts to a golden liquid that sets on pouring into molds. It is still
plastic and can be bent into any desired shape, but on further heating
it becomes hard without the need of pressure.
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