Abstract: A resinous polymeric substance for use as an aid in froth flotation characterized by its mean molecular weight, elemental analysis, viscosity and infra-red spectrum. A method of making the substance by reacting a carbonyl compound with an amine or ammonia followed by heating; and a method of froth flotation in which the substance is used as an aid. The substance has a mean molecular weight in the range 250-10 000; it includes carbon, hydrogen, nitrogen and oxygen; it has a viscosity of 10 000 to 100 000 centipoise at 20.degree. C. and 100 to 1 000 centipoise at 70.degree. C.; and it has an infra-red spectrum including bands characteristic of the groups --C.dbd.N--, >N--H and >C.dbd.C<.