Solids are precipitated from colloidal systems by mixing therewith one part to about 5000 parts per million based on the colloidal system of water-soluble polymers formed under non-acid conditions comprising groups capable of substantial ionization and having ions carrying a charge opposed to the charge of the dispersed phase of the colloidal systems. Colloidal systems specified are latices of butadieneacrylonitrile copolymers, polymethyl methacrylate, butadiene-styrene copolymer, polystyrene, and vinyl chlor-vinylidene chloride, dispersions of SiO2 and tap water containing T : O2 and detergents. Precipitating agents specified are (a) cationic for use with anionic disperse systems.-(1) quaternary ammonium salts resulting from the reaction between polyvinyl pyridine (or its copolymers) and butyl bromide; (2) salts of the reaction product of resorcinol or homologue thereof with formaldehyde as described in Specification 572,232, e.g. the hydrochloric salts of such reaction products; (3) the water-soluble quaternary ammonium salts obtained by reacting a primary diamine, an alkyl halide and a halogenated alkyl compound, e.g. by reacting propylene diamine 1,4-dichlorobutane and butyl bromide; (4) salts of polyvinylamine, e.g. the acetate; (5) the water soluble formaldehyde reaction product of guanidine carbonate or substituted guanidine carbonate; (6) salts of polyethyleneimine, e.g. acetate or sulphate; (7) salts of condensed polymeric secondary amine, e.g. as formed by reacting 1-, 4-dibromobutane and 1,6-hexamethylendiamine; (8) salts of condensed mixed primary and secondary amines, e.g. tetraethylene pentamine. (b) Ionic for use with cationic disperse systems.-(1) water-soluble copolymers of maleic anhydride and styrene; (2) acrylic and methacrylic acid polymers; (3) copolymers of itaconic or crotonic acid with styrene and/or vinyl acetate, acrylic or methacrylic acid, e.g. acrylic acid-vinyl acetate polymers as described in U.S.A. Specification 2,326,078. The following examples describe the preparation of precipitants: (16) 121 gs. guanidine carbonate and 100 gs. 37 per cent formaldehyde were mixed while heated on an electric plate; after heating for more than 4 hours with addition of water to facilitate expulsion of CO2 a colourless solution having a pH of 7.2 was obtained which dried to a transparent solid; urea, thiourea, phenol, cresols may be added during the condensation; (19) the guanidine carbonate is replaced by biuret; (21) aminoguanidine carbonate is similarly condensed; (23) cellulose methyl ether amide is prepared by heating the ammonium salt of carboxymethyl cellulose in air at 120 DEG C. to obtain a light brown powder which is then suspended in aqueous NaOH and treated with bromine. Specification 723,869, [Group VIII], is referred to.ALSO:Solids are precipitated from colloidal systems by mixing therewith one part to 5000 parts per million, based on the colloidal system of water-soluble polymers formed under non-acid conditions comprising groups capable of substantial ionization and having ions carrying a charge opposed to the charge of the dispersed phase of the colloidal systems. Colloidal systems specified are latices of butadiene-acrylonitrile copolymers; poly methyl methacrylate, butadiene-styrene copolymers, polystyrene, and vinyl chlor-vinylidene chloride; dispersions of SiO2 and tap water containing TiO2. Precipitating agents specified are (A) cationic for use with anionic disperse systems -(1) quaternary ammonium salts resulting from the reaction between polyvinyl pyridine (or its copolymers) and butyl bromide (2) salts of the reaction of resorcinol or homologue thereof with formaldehyde as described in Specification 572,232, [Group IV], e.g. the hydrochloric acid salts of such reaction products (3) the water soluble quaternary ammonium salts obtained by reacting a primary diamine, an alkyl halide and a halogenated alkyl compound e.g. by reacting propylene diamine, 1.4 dichlorbutane and butyl bromide (4) salts of polyvinylamine e.g. the acetate (5) the water soluble reaction products of formaldehyde and guanidine carbonate (6) salts of polyethylenimine (7) salts of condensed polymeric secondary amines e.g. as formed by reacting 1.4 dibromobutane and 1.6 hexamethylendiamine (8) salts of condensed mixed primary and secondary amines e.g. tetraethylene pentamine. (B) anionic for use with cationic disperse systems-(1) water soluble copolymers of maleic anhydride and styrene (2) acrylic and methacrylic acid polymers (3) copolymers of itaconic or crotonic acid with styrene and/or vinyl acetate, acrylic or methacrylic acid e.g. acrylic acid vinyl acetate polymers as described in U.S.A. Specification 2,326,078. Examples are given of pairs of colloidal dispersion and their precipitating agents e.g. (Ex. 10) an aqueous dispersion of polystyrene is precipitated by addition of guanidine carbonate-formaldehyde condensate or (Ex. 11) by addition of polyvinyl N-butyl pyridinium bromide.ALSO:Solids are precipated from colloidal systems by mixing therewith one part to about 5,000 parts per million based on the colloidal system of water-soluble polymers formed under non-acid conditions comprising groups capable of substantial ionisation and having ions carrying a charge opposed to the charge of the dispersed phase of the colloidal systems. Colloidal systems specified are latices of butadiene-acry lonitrile copolymers; polymethyl methacrylate, butadiene-styrene copolymer, polystyrene, and vinyl chlor-vinylidene chloride; dispersions of SiO2 and tap water containing TiO2. Precipitating agents specified are (a) cationic for use with anionic disperse systems-(1) quaternary ammonium salts resulting from the reaction between polyvinyl pyridine (or its copolymers and butyl bromide (2) salts of the reaction product of resorcinol or homologue thereof with formaldehyde as described in Specification 572,232, [Group IV], e.g. the hydrochloric salts of such reaction products (3) the water soluble quarternary ammonium salts obtained by reacting a primary diamine, an alkyl halide and a halogenated alkyl compound e.g. by reacting propylene diamine 1.4-dichlorbutane and butyl bromide (4) salts of polyvinylamine e.g. the acetate (5) the water soluble formaldehyde reaction product of guanidine carbonate or substituted guanidine carbonate (6) salts of polyethyleneimine e.g. acetate or sulphate (7) salts of condensed polymeric secondary amines e.g. as formed by reacting 1.4-dibromobutane and 1.6 hexamethylendiamine (8) salts of condensed mixed primary and secondary amines e.g. tetraethylene pentamine (b) an ionic for use with cationic disperse systems (1) water soluble copolymers of maleic anhydride and styrene (2) acrylic and methacrylic acid polymers (3) copolymers of itaconic or crotonic acid with styrene and/or vinyl acetate, acrylic or methacrylic acid e.g. acrylic acidvinyl acetate polymers as described in U.S.A. Specification 2,326,078. Examples are given of the following pairs of colloidal dispersions and precipating agents: (1) butadiene acrylonitrile polymer dispersed by soap and phenyl guanidine stearateformaldehyde condensate (2) polymethyl methacrylate latices precipated by the hydrochloride of the condensate of resorcinol and formaldehyde condensed in presence of propylene diamine (3) polymerised ethyl acrylate polymer and guanidine carbonate-formaldehyde condensate (4) butadiene-styrene copolymer and phenyl guanidine stearate-formaldehyde condensate (6) butadiene-acrylonitrile copolymer and partly neutralised polyacrylic acid (7) as in (6) employing polyethyleneimine hydrochloride as precipitant (8) butadiene-styrene copolymer and guanidine carbonate-formaldehyde condensate (9) as in (8) employing polyethyleneiminehydrochloride as precipitant (10) an aqueous dispersion of polystyrene is precipitated by addition of guanidine carbonate-formaldehyde condensate (11) as in (10) employing polyvinyl N-butyl pyridinium bromide as precipitant (12) the polystyrene latex of (10) is precipitated by addition of polyethylene imine hydrochloride (13) vinyl chloride-vinylidene chloride latex is precipated by guanidine carbonate-formaldehyde condensate (15) the dispersion of Ex(8) is precipitated by addition of a solution of polyethyleneimine Hydrochloride (20) the latex of Ex(1) is precipitated by addition of a biuretformaldehyde condensate (22) the latex of Ex(4) is precipitated by addition of a polymeric aminoguanidine-formaldehyde condensate (24) the latex of Ex(4) is precipitated by addition of a carboxymethyl cellulose product. Specification 723,869, [Group VIII], is referred to.