1. A WATER INSOLUBLE, GRANULAR, ANION ACTIVE SYNTHETIC RESINOUS MATERIAL OBAINED BY A PROCESS INCLUDING THE STEP OF BRINGING ABOUT REACTION BETWEEN THE INGREDIENTS OF A MIXTURE COMPRISING FURFURAL AND A MONOMERIC HEAT CONDENSATION PRODUCT OF A MEMBER OF THE GROUP CONSISTING OF GUANIDINE, MONO- AND DI- MONOVALENT HYDROCARBON AND FURFURYL-SUBSTITUTED GUANIDINES, BIGUANIDE, MONO- AND DI-MONOVALENT HYDROCARBON AND FURFURYL- SUBSTITUTED BIGUANIDES AND THEIR SALTS WITH A CARBONYL COMPOUND SELECTED FROM THE GROUP CONSISTING OF ALDEHYDES HAVING FROM 2-10 CARBON ATOMS AND KETONES HAVING FROM 3-13 CARBON ATOMS, THE MOLAR PROPORTION OF SAID MEMBER TO SAID CARBONYL COMPOUND BEING FROM 1:1 TO 1:2, RESPECTIVELY, AND SAID REACTION BEING BROUGHT ABOUT IN THE PRESENCE OF FROM 1-6 MOLES OF MINERAL ACID PER MOL OF MONOMERIC HEAT CONDENSATION PRODUCT.